Issuu on Google+

Volume 9 issue 2 September 2010


1

from the Chief Editor

The last issue of 2010 brings forth three new sections that will add to the value of the Journal. The HORIZONS section, coordinated by Dr. C.V. Krishnamurthy, will bring forth some of the technologies that shows promise for a paradigm change in the field of NDT. In this edition of HORIZONS, the focus is of a new concept in X-rays. The BASICS section, coordinated by Dr. O. Prabhakar, will henceforth discuss the fundamental concepts relating to a selected NDT technique or concept. In this issue, he covers the basic concepts of Radiography with excellent illustrations and thorough coverage of the physics behind the technique. The PRODUCTS & PATENTS section, coordinated by Dr. M.T. Shyamsunder, will discuss the new products that have been recently introduced in the NDT market as well new patents in the field of NDE. This volume of the Journal has 4 technical articles. The article from BHEL, Tiruchy on Digital Radiography and Computed Tomography discusses the application of these advanced NDT technologies for improving the inspection of weldments. The HOMC Guided Wave technique is a patented technology that promises the inspection of hidden and difficult to access regions in pipes, tank floors, etc. and has been covered by the authors. The inspection of adhesively bonded structures and the application of mode selection in guided wave based inspection of repair patches have been covered in the technical paper from Pennsylvania State University. Finally, the ASTM standards on digital radiography detectors have been reviewed by the authors from General Electric Company. As we look forward to the NDE2010 in Kolkatta and we wish ISNT Kokatta Chapter all the best for a grand and informative NDE2010. The Editorial Board joins me in congratulating all the ISNT Award Winners for the 2010 and look forward to a great 2011.

Dr. Krishnan Balasubramaniam Professor Centre for Non Destructive Evaluation IITMadras, Chennai balas@iitm.ac.in

URL: http://www.cnde-iitm.net/balas

vol 9 issue 3 December 2010


2

I S N T - National Governing Council Chapter - Chairman & Secretary President Shri K. Thambithurai President-Elect Shri P. Kalyanasundaram Vice-Presidents Shri V. Pari Swapan Chakraborty Shri D.J.Varde Hon.General Secretary Shri R.J.Pardikar Hon. Treasurer Shri T.V.K.Kidao Hon. Joint Secretaries Shri Rajul R. Parikh Immediate Past President Shri Dilip P. Takbhate Past President Shri S.I.Sanklecha Members Shri Anil V. Jain Shri Dara E. Rupa Shri D.K.Gautam Shri Diwakar D. Joshi Dr. Krishnan Balasubramaniam Shri Mandar A. Vinze Shri B.B.Mate Shri G.V.Prabhugaunkar Shri B.K.Pangare Shri M.V.Rajamani Shri P.V. Sai Suryanarayana Shri Samir K. Choksi Shri B.K.Shah Shri S.V.Subba Rao Shri Sudipta Dasgupta Shri N.V.Wagle Shri R.K.Singh Shri A.K.Singh (Kota) Shri S. Subramanian Shri C. Awasthi Brig. P. Ganesham Shri Prabhat Kumar Shri P. Mohan Shri R. Sampath Ex-officio Members Managing Editor, JNDT&E Shri V. Pari Chairman, NCB & Secretary, QUNEST Dr. Baldev Raj Controller of Examination, NCB Dr. B. Venkatraman President, QUNEST Prof. Arcot Ramachandran All Chapter Chairmen/Secretaries Permanent Invitees Shri V.A.Chandramouli Prof. S. Rajagopal Shri G. Ramachandran & All Past Presidents of ISNT

Ahmedabad

Kota

Shri D.S. Kushwah, Chairman, NDT Services, 1st Floor, Motilal Estate, Bhairavnath Road, Maninagar, Ahmedabad 380 028. dskushwah@icenet.net Shri Rajeev Vaghmare, Hon. Secretary C/o Modsonic Instruments Mfg. Co. Pvt. Ltd. Plot No.33, Phase-III, GIDC Industrial Estate Naroda, Ahmedabad-382 330 modsonic@modsonic.com

Shri R.C. Sharma, Associate Director (QA), Rawatbhata 323 307 rlsharma@npcilraps.com Shri S.V.Lele, Hon. Secretary, T/IV – 5/F, Anu Kiran Colony, PO Bhabha Nagar, Rawatbhata 323 307. svlele@npcilraps.com

Bangalore Dr. M.T. Shyamsunder, Chairman, NDE Modelling & Imaging Lab., Cassini Building, GE Global Research, John F. Welch Technology Center EPIP Phase 2, Whitefield Road, Bangalore-560066. Mt.shyamsunder@ge.com Shri S. Kalyana Sundaram, Hon. Secretary Scientist, STDivision,National Aerospace Laboratories, Bangalore-560017.isntblr@gmail.com

Chennai Shri T.V.K. Kidao, Chairman Madras Metallurgical Services Pvt. Ltd. 14, Lalithapuram Street, Royapettah Chennai – 600 014 mmspl@vsnl.net Shri R. Balakrishnan, Hon. Secretary, No.13, 4th Cross Street, Indira Nagar, Adyar, Chennai 600 020. rbalkrishin@yahoo.co.in

Delhi Shri B.S.Chhonkar, Chairman, 90A, Pocket-1, Mayur Vihar - 1 New Delhi 110 091 chhonkar@gmail.com Shri Dinesh Gupta, Hon.Secretary, isntdelhi@gmail.com

Hyderabad Shri G. Narayanrao, Chairman, Chairman & Managing Director, MIDHANI, Kanchanbagh, Hyderabad 500 058. cmd.midhani@ap.nic.in Shri J.R. Doshi, Hon.Secretary, Scientist, Project LRSAM DRDL, Hyderabad 500 058. joshidrdl@in.com

Jamshedpur Mr J. C. Pandey, Chairman, Researcher, R&D, TATA Steel, P. O. Burmamines, Jamshedpur - 831 007 jcpandey@tatasteel.com Mr. M K Verma, Hon. Secretary, Manager, SNTI, TATA Steel N-Road, Bistupur, Jamshedpur - 831 001 mk.verma@tatasteel.com

Kalpakkam Shri YC Manjunatha, Chairman Director ESG, IGCAR, Kalpakkam – 603 102 ycm@igcar.gov.in Shri BK Nashine, Hon.Secretary Head, ED &SS, C&IDD, FRTG IGCAR, Kalpakkam – 603 102 bknash@igcar.gov.in

Kochi Shri John Minu Mathew, Chairman, General Manager (Technical), Bharat Petroleum Corporation Ltd. (Kochi Refinery), PO Ambalamugal 682 302. Kochi johnminumathew@bharatpetroleum.in Shri K.D.Damien Gracious, Hon. Secretary, CM (Advisory Services), Bharat Petroleum Corporation Ltd. (Kochi Refinery), PO Ambalamugal-682 302. Kochi damiengraciousk@bharatpetroleum.in

Kolkata Shri Swapan Chakraborty, Chairman Perfect Metal Testing & Inspection Agency, 46, Incinerator Road, Dum Dum Cantonment, Kolkata 700 028. permeta@hotmail.com Shri Dipankar Gautam, Hon. Secretary, 4D, Eddis Place, Kolkata-700 019. eib1956@gmail.com

vol 9 issue 3 December 2010

Mumbai Shri N.V. Wagle, Chairman, A-601, CASCADE-3, Kulupwadi, Borivali East, Mumbai 400 066. offc@isnt.org Shri Samir K. Choksi, Hon. Secretary, Director, Choksi Brothers Pvt. Ltd., 4 & 5, Western India House, Sir P.M.Road, Fort, Mumbai 400 001. Choksiindia@yahoo.co.in

Nagpur Shri K.R.V.S.Mehar, Chairman Manager – SGS India Pvt. Ltd. 218 Bajaj Nagar, Nagpur-440 010 kuchimanchi.mehar@sgs.com Dr. D.R.Peshwe, Hon. Secretary, Professor, Dept. of Metall. & Materials Engineering, Visveswaraya National Institute of Technology, Nagpur 440 011. drpeshwe@vnitnagpur.ac.in

Pune Shri PV Dhole, Chairman NDT House, 45 Dr Ambedkar Road, Sangam Bridge, Pune- 411 001 info@technofour.com Shri VB Kavishwar, Hon Secretary, NDT House, 45 Dr Ambedkar Road, Sangam Bridge, Pune- 411 001 eddysonic@gmail.com

Sriharikota Shri S.V. Subba Rao, Chairman, General Manager, Range Operations SDSL, SHAR Centre Sriharikota 524124. svsrao@shar.gov.in Shri G. Suryanarayana, Hon. Secretary, Dy. Manager, VAB, VAST, Satish Dhawan Space Centre, Sriharikota-524 124. gsurya@shar.gov.in

Tarapur Shri D.K.Sisodia, Chairman, CS, R&D, TMS, NPCIL 3 & 4, Tarapur 401 502. dksisodia@npcil.co.in Shri D. Mukherjee, Hon.Secretary, Superintendent, QC & NDE, AFFF, BARC, Tarapur-401 502. sorwadip@yahoo.co.in

Tiruchirapalli Shri V Thyagarajan, Chairman General Manager (WRI & Labs) BHEL Tiruchirapalli 620014 isnt_try@sancharnet.in Shri A.K.Janardhanan, Hon. Secretary, C/o NDTL Building 1, H.P.B.P., BHEL, Tiruchirapalli 620 014. akjn@bheltry.co.in

Vadodara Shri P M Shah, Chairman, Head-(QA) Nuclear Power Corporation Ltd. NBCC Plaza,Opp. Utkarsh petrol pump, Kareli Baug, Vadodara-390018. npcil.bar@gmail.com M S Hemal Mehta, Hon.Secretary, P-MET, Hi Tech Pvt. Ltd. 1/5-6, Baroda Indl. Estate, Gorwa Vadodara-390016. pmetco@gmail.com

Thiruvananthapuram Dr. V.R. Ravindran, Chairman Division Head, Rocket Propellant Plant, VSSC, ISRO, Thiruvananthapuram - 695 022 drvrravi@yahoo.co.in Shri. Imtiaz Ali Khan Hon.Secretary, Engineer, Rocket propellant Plant, VSSC, Thiruvananthapuram 695 013 imtiaz_ali@vssc.gov.in

Visakhapatnam Shri Om Prakash, Chairman, MD, Bharat Heavy Plate & Vessels Ltd. Visakhapatnam 530 012. Shri Appa Rao, Hon. Secretary, DGM (Quality), BHPV Ltd., Visakhapatnam 530 012


3

Journal of Non-Destructive Testing & Evaluation

Volume 9

issue 3

Contents

Chief Editor Prof. Krishnan Balasubramaniam e-mail: balas@iitm.ac.in

Co-Editor Dr. BPC Rao bpcrao@igcar.gov.in Managing Editor Sri V Pari

5

Chapter News

8

Basics

13

Horizon

17

Producs & Patents

25

Digital radiography and Computed radiography for Enhancing the Quality and Productivity of Weldments in Boiler components

e-mail: scaanray@vsnl.com

Topical Editors Dr D K Bhattacharya, Electromagnetic Methods

Dr T Jayakumar,

December 2010

Ultrasonic & Acoustic Emission Methods

R.J. Pardikar

Sri P Kalyanasundaram, Advanced NDE Methods

Sri K Viswanathan, Radiation Methods

31

G.K. Padmashree, Debasish Mishra, Clifford Bueno and Joe Portaz

Editorial Board Dr N N Kishore, Sri Ramesh B Parikh, Dr M V M S Rao, Dr J Lahri, Dr K R Y Simha, Sri K Sreenivasa Rao, Sri S Vaidyanathan, Dr K Rajagopal, Sri G Ramachandran, Sri B Ram Prakash

ASTM standards on digital detector arrays for industrial digital radiography – a bird’s eye view

34

Inspection of Adhesively Bonded Aircraft Repair Patches using Ultrasonic Guided Waves Padmakumar Puthillath, Cliff J. Lissenden and Joseph L. Rose

Advisory Panel Prof P Rama Rao, Dr Baldev Raj, Dr K N Raju, Sri K Balaramamoorthy, Sri V R Deenadayalu, Prof S Ramaseshan, Sri A Sreenivasulu, Lt Gen Dr V J Sundaram, Prof N Venkatraman

39

HOMC Guided Wave Ultrasonic Technique – A new paradigm for corrosion detection Krishnan Balasubramaniam, K.S. Venkataraman and Issac Anto

Objectives The Journal of Non-Destructive Testing & Evaluation is published quarterly by the Indian Society for NonDestructive Testing for promoting NDT Science and Technology. The objective of the Journal is to provide a forum for dissemination of knowledge in NDE and related fields. Papers will be accepted on the basis of their contribution to the growth of NDE Science and Technology.

The Journal is for private circulation to members only. All rights reserved throughout the world. Reproduction in any manner is prohibited. Views expressed in the Journal are those of the authors' alone.

Published by RJ Pardikar, General Secretary on behalf of Indian Society for Non Destructive Testing (ISNT)

NDE 2010 December 9-11, 2010 @ Science City Convention Centre, Kolkata

www.nde2010.com

Modules 60 & 61, Readymade Garment Complex, Guindy, Chennai 600032 Phone: (044) 2250 0412 Email: isntheadoffice@gmail.com and

Printed at VRK Printing House 3, Potters Street, Saidapet, Chennai 600 015 vrkonline@gmail.com Ph: 09381004771

About the cover page: The cover page shows the Ultrasonic C-Scan Image of a graphite epoxy composite laminate with a resin starved region shown in red/pink color and fiber orientations in the background (Courtesy: Advanced Composites Division, National Aerospace Laboratory, Bangalore, India)

vol 9 issue 3 December 2010


4

Classifieds Scaanray Metallurgical Services

Transatlantic Systems

(An ISO 9001-2000 Certified Company)

NDE Service Provider Process and Power Industry, Engineering and Fabrication Industries, Concrete Structures, Nuclear Industries, Stress Relieving Call M. Nakkeeran, Chief Operations, Lab: C-12, Industrial Estate, Mogappair (West), Chennai 600037 Phone 044-2625 0651 Email: scaanray@vsnl.com ; www.scaanray.com

Electro-Magfield Controls & Services & LG Inspection Services We manafucture : Magnetic Crack Detectors, Demagnetizers, Magnetic Particles & Accessories, Dye Penetrant Systems etc Super Stockist & Distributors: M/s Spectonics Corporation, USA for their complete NDT range of productrs, Black Lights, Intensity Meters, etc. Plot 165, SIDCO Industrial Estate, (Kattur) Thirumullaivoil, Vellanur Village, Ambattur Taluk Chennai 600062 Phone 044-6515 4664 Email: emcs@vsnl.net

Madras Metallurgical Services (P) Ltd Metallurgists & Engineers

Metallography Strength of Materials Non Destructive Testing Foundry Lab

Serving Industries & Educational Institutes for the past 35 years

24, Lalithapuram street, Royapettah, Chennai 600014 Ph: 044-28133093 / 28133903 Email: mmspl@vsnl.com

OP TECH ASNT Level III Intensive Taining Educational CDs PT, UT, RT, MT, ET, Basic Metallurgy and Mechanical Testing Call 93828 12624 Land 044 - 2446 1159

B Ram Prakash A 114, Deccan Enclave, 72, T M Maistry Street, Thiruvanmiyur, Chennai 600 041

Southern Inspection Ser vices Services NDT Training & Level III Services in all the following ten NDT Methods

Shri. K. Ravindran, Level III RT, VT, MT, PT, NR, LT, UT, ET, IR, AE

vol 9 issue 3 December 2010

Support for NDT Services NDT Equipments, Chemicals and Accessories Call DN Shankar, Manager 14, Kanniah Street, Anna Colony, Saligramam, Chennai 600093 Phone 044-26250651 Email: scaanray@vsnl.com

Betz Engineering & Technology Zone An ISO 9001 : 2008 Company 49, Vellalar Street, near Mount Rail Station, Chennai 600088 Mobile 98401 75179, Phone 044 65364123 Email: betzzone@vsnl.net / rg_ganesan@yahoo.com

International Training Division 21, Dharakeswari Nagar, Tambaram to Velachery Main Road, Sembakkam, Chennai 600073 www.betzinternational.com / www.welding-certification.com

KIDAO Laboratories NABL Accredited Laboratory carrying out Ultrasonic test, MPL and DP tests, Coating Thickness and Roughness test. We also do Chemical and Mechnical tests

A-3, Mogappair Indl. Area (East) JJ Nagar, Chennai 600037 Phone 044-26564255, 26563370 Email: kidaolab@giasmd01.vsnl.net.in; kidaolabs@vsnl.net www.kidaolabs.com

Dhvani R&D Solutions Pvt. Ltd 01J, First Floor, IITM Research Park, Kanagam Road, Taramani, Chennai 600113 India Phone : +91 44 6646 9880

• Inspection Solutions • Software Products • Training • Services & Consultancy

-

CUPS, TAPS, CRISP, TASS SIMUT, SIMDR Guided Waves, PAUT, TOFD Advanced NDE, Signal Processing C-scans, On-line Monitoring

E-mail: info@dhvani-research.com

www.dhvani-research.com

No.2, 2nd Floor, Govindappa Naicker Complex, Janaki Nagar, Arcot Road, Valasaravakkam, Chennai-600 087 Tamil Nadu, India Phone : 044-2486 8785, 2486 4481 E-mail: sisins@gmail.com and sisins@hotmail.com Website: www.sisndt.com


5

CHAPTER NEWS

participants were 10. Mr.M.V.Rajamani was the course Director and Mr.Sathya Srinivasan was the examiner ASNT LEVEL-III HELD FROM 02.10.2010 TO 29.10.2010

Chennai Course, Exams & Technical Talk: UT Level-II (ASNT) course was conducted from 20.08.2010 to 29.08.2010. No. of participants were 18 and for examination 21. Mr.R.Balakrishnan was the course Director and Mr.Sathya Srinivasan was the examiner 19.09.2010 Dr. VAIDEHI GANESAN, NDED, Metallurgy & Materials Group, Indira Gandhi Centre for Atomic Research, Dept of Atomic Energy Kalpakkam-603 102 delivered a technical talk on “FAILURE ANALYSIS AND STRUCTURAL INTEGRITY ASSESSMENT OF SOME ENGINEERING COMPONENTS USING VARIOUS NDE TECHNIQUES”. 60 members attended the meeting. MT & PT Level-II (ASNT) course was conducted from 17.09.2010 to 23.09.2010. No. of participants were 7 and exam 8. Mr.M.V.Rajamani was the course Director and Mr.P.N.Udayasankar was the examiner In-house training on MT Level-I & II held from 27.09.2010 to 01.10.2010 at M/s.Sundram Fastners Limited, Autolec Division, Chennai. No. of participants for Level-I is 11 and Level-II is 8. Mr.M.S.Ramachanran was the course director and Mr.P.N.Uhayasankar was the examiner. PT Level-II (ISNT) course was conducted from 04.10.2010 to 10.10.2010. No. of participants were 7. Mr.R.Sreedharan was the course Director and Mr.P.N.Udayasankar was the examiner ; EC Meeting 04.08.2010 ; EC Meeting 19.09.2010 ; EC Meeting 09.10.2010 One day workshop on “Positive Material Identification Using HandHeld XRF with Special Reference to API RP 578 and API RP 938” held on 11.11.2010. No. of participants attended 90. R T Level-II (ASNT) course was conducted from 22.10.2010 to 31.10.2010. No. of participants were 18 for course and 20 for examination. Mr.S.Subramanian was the course Director and Mr.P.N.Udayasankar was the examiner UT Level-II (ASNT) course was conducted from 12.11.2010 to 21.11.2010. No. of participants were 21 for course and 25 for examination. Mr.R.Balakrishnan was the course Director and Mr.Sathya Srinivasan was the examiner One day workshop on “Helium Leak Testing” was held on 30.11.2010. No. of Participants attended were 60 MT & PT Level-II (ASNT) course was conducted from 26.11.2010 to 05.12.2010. No. of

Method

Date

Visual

02.10.10 04.10.10 05.10.10 08.10.10 09.10.10 11.10.10 12.10.10 14.10.10 18.10.10 21.10.10 22.10.10 25.10.10 26.10.10 29.10.10 01.10.10 04.10.10 Total

Basic Penetrant Magnetic Particle Ultrasonic Basic Radiographic Eddy Current

No of participants

Method Director

4

Mr.R.Ramakrishnan

20

Dr.O.Prabhakar

10

Mr.G.Jothinathan

17

Mr.R.Ramakrishnan

20

Dr.O.Prabhakar

24

Mr.G.Jothinathan

25

Mr.R.Subburathinam

0 120

Kalpakkam Course & Exams: Kalpakkam Chapter has been quite active under the able guidance of Shri Y.C.Manjunatha Chairman ISNT Kalpakkam, Shri P.Kalyanasundaram, Past Chairman and the support and patronage of Dr Baldev Raj, Distinguished Scientist and Director IGCAR and Shri Prabhat Kumar Project Director, BHAVINI. The Executive committee meetings were held and the chapter had also organised about four technical talks. More than 25 members were enrolled during the last one year. The thrust of Kalpakkam Chapter has been in fostering NDE Science and Technology in Education and Research. As part of this objective, the Chapter had actively collaborated with educational institutions in organising the following events at Kalpakkam and Chennai. 1.

Orientation program for Engineers, St. Josephs College of Engineering, April 2010. About 50 students and faculty in the field of mechanical engineering participated in this event.

2.

Training Course on Non-Destructive Testing for Aeronautical Engineers in Collaboration with Aeronautical Society of India (Chennai), July 1-3, 2010. About 80 students belonging to Aeronautical Engineering from the various colleges in Chennai participated.

3.

Course on Interpretation of Radiographs, Satyabama University, NCB and Scanray, Oct. 28-30, 2010. 24 candidates from all over India participated. vol 9 issue 3 December 2010


6

4.

One Day workshop on NDT organised by TIFAC – Core Hindustan Institute of Technology and Science, Dec. 03, 2010. About 100 students, researchers and faculty will be participating in this event. Apart from the above, members of Kalpakkam chapter actively participated as faculty in the ASNT refresher courses at Chennai and have been contributing for the activities at a national level. A matter of pride for ISNT Kalpakkam chapter is that the Standard on Thermal Imaging in Electrical Installations has been accepted by the International Standard Organisation (ISO) for publication during the ISO SC 135 meeting in Moscow. This is the first standard from India in NDT to be considered and accepted by ISO. Members from Kalpakkam Chapter have also actively contributed to national and international journals. During this year more than 15 international journal publications have resulted. Many of the members have also been honoured by other national and international bodies.

Mumbai Course & Exams: Welding Inspector examination on 13.12.09 Interpretation of weld Radiogrpah examination on 20.12.09 UT Level II For ONGC 15.02.10-20.02.10 RT level II for ONGC from 22-02-10 to 27.02.10. General Orientation on NDT for Naval Officers from 08-03-10 to 12.03.10 PT Level I for Naval Officers from 13-03.10 to 16.03.10 MT Level I for Naval Officers from 17.03.10 to 20.03.10 PT Level II for ISNT, Tarapur Chapter on 24- 07- 2010 at Tarapur, RT Level I for Ammunition Factory Khadki on 24- 072010 at Pune Welding Inspector at ITT, Mahim on 15.08.10 Technical Lecture: On 13.01.10 by Dr.Garri Passi on Advanced Instruments & Technologies in UT Mr. Mr Greg Pupchek and Mr. Silvano Succetti, U.S.A, on Computer Radiography & Digital Imaging on 1808-2010

vol 9 issue 3 December 2010

Ultrasonic Testing Practices in the Nuclear Power Industry by Mr. Peter Schmitt, Germany on 07- 09-2010 Conducted One day Workshop on Positive Material Identification using Handheld XRF with special Reference to API RP 578 and API RP 938 on 9th Nov. 2010 at Hotel Atithi, Mumbai Activities: EC meeting on 15.01.2010 ASNT Level III Course Directors & Coordinators meet on 16th Feb 2010 EC meeting on 26th Feb 2010 EC meeting on 7th April 2010 EC meeting on 25th June 2010 EC meeting was held on 11thAugust, 2010 NCB and NGC Meeting held on 29thAugust AGM was held on 25th Sept. 2010 Participants were around 175 members. APCNDT 2013 committee Meeting was held on 2nd October 2010 EC Meeting was held on 19thOctober 2010 APCNDT 2013 Meeting was held on 15th November 2010

Pune National “ International Certification and Career Opportunities in NDE and Inspection 1.

API Certification - by Shri:D.D. Joshi

2.

NDE Certification - by Shri.J.R. Hiremath (ASNT, EN etc.)

3.

Welding and Painting

An industrial /field Visit to facilities of industrial X-Ray and allied Radiographers and UT Quality India 9th Executive Committee meeting, Technofour, Pune Dt. 05/09/2010 Annual General Meeting, Hotel Ambassador, Model Colony, Shivajinagar, Pune, Dt. 20/10/2010 10th Executive Committee meeting, Technofour, Pune, Dt. 27/10/2010


7

BASICS

Industrial Radiography Dr. O. Prabhakar, OP-TECH, Chennai INTRODUCTION From the time Roentgen discovered X-rays and used it to radiograph his rifle, X-rays are being used in the industry to reveal internal flaws in manufactured components. In many industries like thermal and nuclear power generation, aircraft, chemical industries etc., this method plays a key role. THE METHOD

In addition gamma radiography is extremely portable and does not need electrical power for its operation. LIMITATIONS Compared to other methods the initial costs are high. Large spaces are needed particularly if one is employing powerful isotopes like Cobalt 60. Inspection times are high. It is difficult to reveal cracks particularly tight cracks. Radiation safety and protection are major issues.

The industrial radiographic method is based on the principle of “Differential Absorption” of Electromagnetic radiation in matter.

ELECTROMAGNETIC RADIATION (EM) All the radiant energies like radio waves, heat radiation, visible or light rays, X-rays, gamma rays and cosmic

Fig. 1 : Basic arrangement for radiographic inspection

Fig. 2 : Electromagnetic (em) spectrum

X- or gamma rays are passed through a component and the transmitted rays are recorded on a photographic film, fluoroscopic screen or a detector. The basic arrangement to take a radiograph is shown in figure 1. The most common recording medium employed is the photographic film. The exposed film is further developed, fixed and washed just like an ordinary photo film in a dark room. The developed film called “Radiograph” is viewed under proper lighting arrangement for interpretation and evaluation.

rays belong to the same spectrum. The EM spectrum is shown in Fig. 2. They all can travel in vacuum and possess the same velocity in vacuum. They differ in their wavelength or energy values. One single ray is also known as “Photon” and does not possess any electric charge or magnetic moment. The straight line propagation of these waves is utilized in Industrial radiography (RT). These rays can also diffract but this is not of interest in RT but used in metallurgy.

ADVANTAGES A direct view of the internal discontinuities is obtained making it relatively easier to interpret the radiographs. Discontinuities that are volume based like porosity, shrinkage etc. are easily detected. The method is readily accepted by various manufacturers because of the easy interpretation and extensive codes and standards available.

IONIZING ABILITY X- or gamma rays are not seen by the human eye directly. Fortunately these rays ionize matter, that is it splits them into positive ions and negative charge. There are four major ionization types of interest to RT and they are: 1.

Photographic effect

2.

Fluorescence effect

3.

Electrical conductivity

4.

Biological effect vol 9 issue 3 December 2010


8

BASICS

Of these four, the first two are used to take radiograph and the third is used to detect and quantify radiation levels. In RT one has to take safety precautions against the biological effects. A doubt one may have is whether the component becomes radioactive after being exposed to X- or gamma rays. Under the conditions RT used in the industry this danger does not exist as most of the interactions between the X- and gamma rays and the matter involve shell electrons and not the nucleus. However care must be taken while exposing the modern digital detector panels to X- or gamma rays. Above a certain kilovoltage they may damage the detector panels. X-RAY GENERATION If an electrical source is used to generate the electromagnetic waves of the required wavelength, then

1.

Thickness of the sample.

2.

Kilovoltage to be employed.

3.

Tube current

4.

Time of exposure

These four variables are plotted in a graph called exposure charts that are used by radiographers to take an acceptable quality radiograph. These charts are dependent on the film to focus distance, film type used, material being radiographed and the darkness of the film desired. Equations are available for taking into account all these factors and arrive at the final exposure conditions. One should try to employ the lowest kilovoltage for any given job that gives adequate transmitted X-rays for a satisfactory radiograph. Increasing the kilovoltage would increase the penetrating power of the X-rays but the radiograph will be of poor contrast. GAMMA RAY PRODUCTION

Fig. 3 : Scheme of x-ray generation with an x-ray tube

it is known as X-rays. A basic X-ray tube is shown in Fig. 3. The tube is essentially a vacuum tube (diode) with an anode and cathode. Electrons are emitted by a heated filament and they are further accelerated by employing a very high electrical voltage between the cathode and the anode. The accelerated electrons are made to strike a target like tungsten and suddenly decelerated. The kinetic energy of the electrons is converted into heat and X-rays.

The type of element in the periodic table is determined by the number of electrons or protons in the nucleus. If the number of neutrons in the nucleus is altered the element type is not altered and is known as “isotope”. Some of these isotopes decay giving out radiation and particles and such isotopes are known as “Radioactive isotopes”. These radioactive isotopes may occur naturally or may be produced artificially in a nuclear reactor. Some of these radioactive isotopes give out electromagnetic waves that can be used to take radiograph of components. Just to distinguish the source employed to produce the EM waves, the term “Gamma Rays” is used to denote the EM rays given out by radioactive isotopes. The most commonly used radioactive isotopes are Iridium – 192 and Cobalt – 60. How the unstable Co60 decays producing gamma rays is described in Fig. 4.

So the production of X-Rays consists of three steps: 1.

Thermionic emission of electrons from a heated filament.

2.

Accelerating the electrons by employing a high voltage of the order of 50 to 400 keV.

3.

Suddenly decelerating these accelerated electrons by striking them against a target made of high melting point metal.

The variables that one needs to consider while taking a radiograph are: vol 9 issue 3 December 2010

Fig. 4 : Disintegration of cobalt -60.


9

BASICS

Fig. 5 : Gamma ray source container

Fig. 6 : Characteristics of industrial radiographic film

The parameters that one needs to consider while selecting a source are:

The characteristic curve, sometimes referred to as the H and D curve (after Hurter and Driffield), expresses the relationship between the exposure applied to a photographic material and the resulting photographic density. The characteristic curves of a fast and slow film are shown in Figure 6. The characteristic curve can be used to solve quantitative problems arising in radiography and in the preparation of technique charts. The simple logic we use is that “Pairs of exposures having the same ratio will be separated by the same interval on the log relative exposure scale, no matter what their absolute value may be.� (Ref: RT in Modern Industry-Kodak)

1.

Energy of the gamma rays

2.

Half life of the isotope

3.

Size of the isotope

4.

Cost of the isotope

Figure 5 shows a typical manually operated gamma ray source container. Exposure charts for gamma radiography are different from that of X-rays. In this case we need to consider the source strength instead of kilovoltage and tube current. The gamma rays from cobalt 60 have relatively good penetrating ability as the wavelength is smaller. Co 60 can be used to radiograph sections of steel 9 inches thick, or the equivalent. Radiations from iridium 192 have lower energy. Ir-192 emits radiations equivalent to the x-rays emitted by a conventional x-ray tube operating at about 600 kV. The intensity of gamma radiation depends on the strength of the particular source used specifically, on the number of radioactive atoms in the source that disintegrate in one second. This is measured as curies (1 Ci = 3.7 x 10 s-1). PHOTOGRAPHIC DENSITY Photographic density is the measure of blackness of the fully developed and fixed radiograph. This determines the viewing facility one needs to interpret and evaluate radiographs. FILM RADIOGRAPHY In film radiography one employs a film to record the information carried by the transmitted X- or gamma rays. Films used in RT consist of a flexible and transparent base coated with a radiation sensitive silver compound. The coating is applied on both sides of the base.

RADIOGRAPHIC CONTRAST Radiographic contrast between two areas of a radiograph is the difference between the photographic densities of those areas. It depends on both subject contrast and film contrast. Subject contrast is the ratio of x-ray or gamma-ray intensities transmitted by two selected portions of a specimen. Subject contrast depends on the nature of the specimen, the energy of the radiation used, and the scattered radiation, but is independent of time, milliamperage or source strength, and distance, and of the film characteristics or film processing. Film contrast refers to the slope (steepness) of the characteristic curve of the film. It depends on the type of film, the film processing, and the density and is independent of subject contrast. GEOMETRIC UNSHARPNESS The area over which the electrons strike the anode determines the size of the focal spot. In order to obtain a good radiograph one would prefer to have as small a focus size as possible. However as the focal spot size vol 9 issue 3 December 2010


10

BASICS

in the film. This is termed as ‘inherent unsharpness’. This depends on the energy of the photon striking the film.

Fig. 7 : Geometric unsharpness

decreases the intensity of the EM radiation obtained is also less. The focal spot should be as small as conditions permit, in order to secure the sharpest possible definition in the radiographic image. The degree of sharpness of any shadow depends on the size of the source of X-rays and on the position of the object between the X-ray source and the film—whether nearer to or farther from one or the other. When the source of X-rays is not a point but a small area, the shadows cast are not perfectly sharp (in Figure 7) because each point in the source of X-rays casts its own shadow of the object, and each of these overlapping shadows is slightly displaced from the others, producing an ill-defined image. From simple geometry one can derive an expression for the geometric unsharpness as: Ug = F (b/a)

PENETRAMETERS Penetrameters are used while taking every radiograph to check whether the radiograph is satisfactory or not. The test piece is commonly referred to as a penetrameter in North America and an Image Quality Indicator (IQl) in Europe. Examples are shown in Figure 8. It contains some small features (holes, wires, etc.), the dimensions of which bear some numerical relation to the thickness of the part being tested. The image of the penetrameter on the radiograph is permanent evidence that the radiographic examination was conducted under proper conditions. A penetrameter is used to indicate the quality of the radiographic technique and not to measure the size of cavity that can be shown. (Ref: RT in Modern Industry-Kodak) DISCONTINUTIES In castings shrinkage, pipes, gas porosity, lack of fusion of the chills, hot tears and core shift are revealed. However thin cracks are difficult to be revealed. Weld defects like gas porosity, lack of penetration, slag inclusions and tungsten inclusions can be revealed. However, laminations in the base plate can not be revealed by RT. When dealing with castings, it may be better to use penetrameters based on finished rather on rough-wall thickness and this way penetrameter sensitivity is not compromised. Individual casting that are more prone to non-systematic flaws (random) require more radiography.

Even without any geometric unsharpness blurring of the sharp edge may occur due to movement of electrons

Contrary to common misconception, there is no such thing as 100 % radiographic coverage for all castings. To make sure that no coverage problem occurs between the foundryman and the user, it is essential to follow proper and early planning of the radiography.

Fig. 8 : Penetrameters

Fig. 9 : A typical illuminator to view radiograph

INHERENT UNSHARPNESS

vol 9 issue 3 December 2010


11

BASICS CODES & STANDARDS

The American Society for Testing and Materials has committee on Non-Destructive Tests. This committee has prepared reference materials concerning recommended practices for radiographic testing, and radiographic references for various industrial processes and materials. For example, it has comparison radiographs for steel castings, aluminium and magnesium castings, steel welds and castings for aerospace applications. All the alloys are not represented. Hence a mutually acceptable document between the foundryman and the user may be adopted. As an example, titanium alloy castings can be judged by aluminium and steel reference radiographs.

Fig. 10 : A typical radiograph (schematic).

RADIOGRAPHS Figure 9 shows a typical illuminator to view a radiograph. A typical radiograph of a weld showing Porosity is shown in Figure 10. Weld bead is thicker than the base metal. So it appears white. Defects like porosity are of low density material and hence appear as dark spots in the radiograph as shown in Fig. 10.

AWS D1.1/D1.1M:2004 code contains the requirements for fabricating and erecting welded steel structures. In this code, section 6 on inspection section contains criteria for the qualifications and responsibilities of inspectors, acceptance criteria for production welds, and standard procedures for performing visual inspection and NDT (Nondestructive testing) including RT.

“WCAE-2011” World Conference on Acoustic Emission–2011 Beijing (WCAE-2011) is organized by the Chinese Society for Nondestructive Testing (ChSNDT) and undertaken by Technical Committee on Acoustic Emission of ChSNDT (TCAE). Conference Date Venue

August 24 to 26, 2011 Beijing International Convention Center and Beijing Continental Grand Hotel No.8 Beichen Dong Road, Chaoyang District, Beijing 100101, P.R. China Room Reservations: Tel: ++86-10-84980105 ; Fax: ++86-10-84970106 E-mail: bcgh@bcghotel.com Website: www.bcghotel.com ; www.bicc.com.cn

Call for Papers

The papers are sought in all areas related to acoustic emission such as follows: AE signal detection and processing AE behavior of materials AE in pressure equipment AE in structures AE in civil engineering and geology AE in transportation engineering AE in condition monitoring and diagnosis for mechanics AE in medical science AE standardization AE instrument and new developments AE and applications in other fields

Key Dates

Abstract submission April 30, 2011 Notification of acceptance May 15, 2011 Submission of full papers June 30, 2011 Registrationf and payment of registration fee July 15, 2011 Registration Fees (including: Welcome Party, Welcome Dinner and three Lunches) General: 450 US$ ; Student: 300 US$

Contact

Conference-secretariat and Mailing Address Mr. Zhanwen Wu, WCAE-2011 Secretariat China Special Equipment Inspection and Research Institute Building 2, Xiyuan, Hepingjie, Chaoyang District, Beijing 100013, China Email:wcae2011@vip.csei.org.cn Phone: +86-10-59068313 ; Fax: +86-10-59068666 vol 9 issue 3 December 2010


12

Can

x-rays

HORIZON

be

refracted, focused and collimated? C.V. Krishnamurthy Department of Physics Indian Institute of Technology, Madras Chennai 600036, Tamilnadu, India e-mail: cvkm@iitm.ac.in

The (surprising?) answer to all the three characteristics is yes! But then, it should not be surprising, for X-rays are electromagnetic waves just like visible light are and they must exhibit such wave-like characteristics. We are very familiar with “optical elements” such as lenses that produce focused beams or collimated beams of light. We also know that focused beams improve signal to noise ratio, and enhance image resolution.

Let’s take a closer look at how it happens in optics. The refractive index of the materials (n), such as glass, used to make lenses for visible light (wavelength is about 530 nm for green) is about 1.5 typically. The refractive index of a medium, we recall, scales the path length of a plane wave in that medium by a factor n. The changed path length within the medium changes the phase of the plane wave. The change is with respect to vacuum or air and so proportional to n – 1. The material is shaped in the form of a “lens” to produce refracted rays with corresponding phase delays such that an incident parallel beam is changed to a transmitted beam converging at a focal plane. The refraction and focusing phenomenon is described with the help of rays by invoking Snell’s law at the curved interfaces using local tangents and local normals at various points on the curved interface. We are aware that in the focal plane, there is a finite beam spot size arising out of wavefronts not all adding up with the same phase at every point of the focal plane. In fact, the wave nature prevents the spot width to be reduced beyond a fundamental limit that is based on the wavelength. Even when the incident beam is highly vol 9 issue 3 December 2010

monochromatic and naturally narrow as from lasers, the focal spot sizes cannot reduce beyond a diameter of the order of the wavelength. The beam spot quality at the focal plane depends on (a) how parallel the incident beam is, (b) how well the lens is shaped, and (c) how absorptive is the lens material. When the incident beam is diverging, it is possible to collimate the beam to be parallel by using the same refraction and phase shifting processes of a lens in a ‘reverse’ manner. Imperfections, such as surface roughness and curvature errors, arise during lens fabrication. When the corresponding phase errors are less than π/4, the degradation due to imperfections would be negligible. Noting that different parts of the incident beam travel different path lengths, any attenuation due to absorption would lead to unequal amplitudes adding up to form a poor beam at the focal plane. It is thus desirable either to have a material with insignificant absorption or to work with a very thin lens. The creation of refractive lenses and prisms, which are direct and immediate analogs of devices working in the visible range, had long been thought of as being impossible because of the extremely small deviation of the refractive index from unity, for the X-ray range - the small deviation of the refractive index from unity (δ=1–n≈10 –5–10–6), and a relatively high radiation absorption. Only a relatively small set of materials wherein refraction prevails over absorption (chemical elements, inorganic and organic compounds with Zeff << 12–14) are suited for the implementation of refractive optical elements. When use is made of these materials, owing to the extremely low magnitude of the refractive index decrement it is required to form refractive profiles with radii of curvature of the order of several micrometers. We note that the refractive index can be wavelength dependent or, in other words, energy dependent. Let’s consider the refractive profile shape required to focus rays on a point lying on the central ray (optical


13

HORIZON

Refractive profile for an X-ray lens. Optical paths to the focal point are Re n = 1– δ < 1.

and OP = y + F, with n = 1 – δ + iβ, and

axis). The condition to be satisfied by such a profile is that equal optical paths result for points equidistant from the optical axis. The change of wave-vector directions in individual portions of the transmitted wave is assumed to be negligible owing to the smallness of the refractive index decrement. Then, the refractive profile is equivalent to a thin lens. When a plane wave is incident on the input plane of a focusing element, according to the Huygens - Fresnel principle the secondary sources excited by the incident wave are located on the curved profile. It turns out that the perfect shape of refractive surfaces for X-ray lenses is close to the parabolic one in the approximation of paraxial optics. A focal distance of 10cm < F < 1m is attainable for a radius of curvature of a single refractive profile equal to 1 μm < R < 10 μm for typical values of the refractive index decrement δ given above. Fabricating such refractive profiles of X-ray lenses calls for the development of an adequate technology. Errors in the profile due to fabrication must be such that the associated phase errors are within π/4. The precision of lens formation is determined by the quantity λ/π(n-1) which lies in the range between several micrometers to tenths of a micrometer in the visible light optics. For a glass lens with for n = 1.5 for λ = 0.5 μm, for instance, an accuracy of 0.3 μm may be considered sufficient. In the X-ray band, the admissible departures of the refractive profile under fabrication from the ideal one are substantially greater. In particular, typical values of the phase-shifting path for materials which may be employed in the fabrication of X-ray lenses amount to 10–100 μm. Therefore, the requirements on the accuracy of refractive profile fabrication are, in view of the possible departures ranging into the fractions of a micrometer, attainable for present-day technologies. To form single lenses with a radius of curvature R < 1μm, use is presently made primarily of silicon and polymer materials, which is due to the possibility of resorting to a wide range of technologies exploited in

Planar parabolic lenses: (a)SEM image; (b) photograph of the focal spots, obtained on the BM05 beamline at an energy of 17 keV. From V V Aristov, L G Shabel’nikov, Physics - Uspekhi 51 (1) 57 - 77 (2008)

microelectronics. Silicon refractive elements are practically void of intrinsic imperfections and, hence, do not give rise to their associated intensity losses. Single and compound planar lenses have been fabricated and tested extensively. Compound lenses were found to follow the additivity property for the lens power. A property of the parabolic profiles (Figure a) is that the optical path of a ray and, accordingly, the total phase shift in traversing several lenses remain constant. The retention of the focal distance is ensured for all lens rows, which is confirmed by direct experimental measurements (Figure b). The increase in the number of lenses in a row for a constant aperture is compensated for by a corresponding change in the radius of curvature. Accordingly, the lens power of a row is the superposition of the successive action of single lenses and is the same for all rows. The lens-power additivity of the refractive profiles follows directly from summation of the phase shifts produced by single lenses in the total phase shift acquired by the ray in transit through the set of profiles. The additivity of the lens power of a set manifests itself only for refractive lenses and is not inherent in other types of X-ray focusers such as Fresnel zone plates. Kinoform lenses have also been fabricated and tested using beam lines from the European Synchrotron

x = λ/δ

Cross-sectional schematic of the kinoform lens. The Brookhaven kinoform single lens made of Silicon shown below has the following parameters: Energy at 13 keV; focal length = 15 cm; aperure was 100 μm (V) x 10 μm (H); focal size achieved ~ 1 μm FWHM (theoretical limit was 0.2 μm FWHM). From: Ken Evans-Lutterodt et al.: “Single-element elliptical hard x-ray micro-optics”, Optics Express (2003) 11, 919-926. vol 9 issue 3 December 2010


14

HORIZON

Top panel: Schematic and the SEM image. Bottom panel: Intensity in focal plane measured with knife-edge scan. E = 13.4 keV, F =55 cm, intensity gain = 39, FWHM = 1.4 mm, the fraction of power in the central peak is 41%. Björn Cederström et al.:”Generalized prism-array lenses forhard X-rays”, J. Synchrotron Rad. (2005). 12, 340–344

Radiation Facility (ESRF). By removing the redundant 2π phase-shifting from the refractive counterpart (top left in the Figure), one arrives at the kinoform (bottom left in the Figure). This is the analog to the Fresnel lenses used in lighthouses. The removal of the unnecessary material greatly reduces losses and increases the focusing efficiency.

Many other compound element configurations, such as the prism-array lenses shown below, have been conceived, fabricated successfully and tested. The classic manifestation of the wave nature of the electromagnetic radiation is the interference effect. Here we see a demonstration of the interference effect with X-rays!

(a) Schematic view of the x-ray bilens interferometer. (b) Scanning electron microscope micrograph of a single silicon bilens consisting of 6 individual parabolic lenses. (c) General view with five bilens systems fabricated on the same substrate. A. Snigirev et al., Phys Rev Lett., 103, 064801 (2009) vol 9 issue 3 December 2010


15

HORIZON

The planar parabolic bilenses were manufactured using a process involving electron beam lithography and deep etching into silicon. The length and aperture of each single, double concave individual lens are 102 and 50 μm, respectively. Structures are 70 μm deep. The radius of the parabola apex is R=6.25 μm, and the minimum thickness between the parabola apexes is 2 μm. The split distance between lenses is d = 60 μm. The Si bilens system was mounted at a distance z0 = 54.16 m from the source. Interference patterns were recorded by means of the high resolution x-ray CCD camera with a spatial resolution about 1.3 μm (0.645 μm pixel size). The experimental tests of the bilenses were carried out at the ESRF beam line ID06 for an x-ray energy in the range 10–20 keV. The advent of compound refractive lenses, which attracted considerable attention of researchers throughout the world, significantly broadened both the possibilities for making X-ray optical devices and the spectral range

of their applications. In recent years, refractive optics has turned into a branch of X-ray optics in its own right, which has seen the realization of novel and uncommon approaches to lens development, pertaining to both design solutions and fabrication technologies. New approaches have been formulated and their elaboration would allow bringing the spatial resolution to magnitudes characteristic of modern techniques of scanning microscopy. ADDITIONAL REFERENCES FOR FURTHER READING: 1. A. Snigirev, V. Kohn, I. Snigireva, B. Leneler, A compound refractive lens for focusing high-energy X-ray, Nature, v.384, n.7, p.49-51 (1996). 2. H. Bradaczek, G. Hildebrandt, Real X-Ray Optics - A Challenge For Crystal Growers, Journal of Optoelectronics and Advanced Materials Vol. 1, No. 2, p. 3 – 8 (1999) 3. V. G. Kohn, On the Theory of X-ray Refractive Optics: Exact Solution for a Parabolic Medium, JETP Letters, v.76, n.10, pp. 600-603 (2002).

Advt. tariff & Journal subscription ( India & SAARC countries ) Classified advt (Business card)

: Rs

600/-

BackCover (Multi Colour)

: Rs 12,000/-

Inside Cover - Front (Multi colour)

: Rs 11,000/-

Gate fold - Front (Multi colour)

: Rs 10,000/-

Inside Cover - Back (Multi Colour)

: Rs 11,000/-

Gate fold - Back (Multi colour)

: Rs 10,000/-

US $ 350

Inner Pages Full (Multi Colour)

: Rs

8,000/-

US $ 300

Inner Pages Full (Black & White)

: Rs

6,000/-

US $ 200

Inner Pages Half (Black & White)

: Rs

3,000/-

US $ 125

Panel Display (6 cm X 4 cm)

: Rs

1,200/-

US $ 50

US $ 350

Journal subscription rates : Rs. 700 per annum and US $ 60 (R & D establishment and educational institutions)

Payments should be made by means of a Demand Draft, drawn favoring “JNDE – ISNT”, payable at Chennai. Mr. V. Pari

Managing Editor Journal of Non Destructive Testing & Evaluation Modules 60 & 61, Readymade Garment Complex, Guindy, Chennai 600032 Phone: (044) 2250 0412

vol 9 issue 3 December 2010


16

NDE P A T E N T S

A new feature in the Journal of NDE

Compiled by Dr. M.T. Shyamsunder General Electric, Bangalore

Starting from this issue, we are introducing a new section, which will discuss different aspects of Intellectual property in the area of Inspection and Nondestructive Evaluation and would list some of the recently granted patents in this area. To start with we are covering United States Patents and Trademark Office (USPTO) and hope to add the others including the Indian, European, Japanese and the World Patent organizations in the coming issues. We hope you will find this section useful and interesting. Please send your feedback, comments and suggestions on this section to mandayam.shyamsunder@gmail.com

In today’s growing and competitive world, any progressive and growth oriented individual or organization cannot undermine the role of Intellectual Property (IP). Intellectual Property takes a number of different forms such as, Patents, Trademarks, Copyrights, Trade Secrets, etc. Patents form one of the critical forms of IP from a perspective of a researcher, scientist, engineer or technologist working for academia, R&D organizations, product manufacturer, service provider and others. Technically, a patent is “a set of exclusive rights granted by a state or national government to an inventor or their assignee for a limited period of time in exchange for a public disclosure of an invention.” Some form of the patent exists in most countries but the laws vary greatly. The USPTO defines a patent as “an intellectual property right granted by the Government of the United States of America to an inventor “to exclude others from making, using, offering for sale, or selling the invention throughout the United States or importing the invention into the United States” for a limited time in exchange for public disclosure of the invention when the patent is granted”. Some of the principal objectives of patenting one’s inventions include; Revenue from licenses or sale, Keep others out of the market, Restrict competitors, etc. Patenting can be a lifeline for a company; not only can it be used to keep competitors at a safe distance, it can also provide a firm with a competitive advantage that can lead to expansion and increased profits. There are different perspectives of patenting; one of them states the social objectives of patenting as primary and the commercial objectives as secondary. Of course with the process of patenting comes issues such as costs, liability, infringements, etc and they have to be dealt with suitably. Given below are links to a few websites from different countries, which will provide you with a lot of information on the patent process, database, statistics vol 9 issue 3 December 2010

and other relevant details of interest to the budding inventors http://www.patentoffice.nic.in/ http://patinfo.nic.in/ http://www.uspto.gov/ http://ep.espacenet.com/ http://www.epo.org http://www.jpo.go.jp/ http://www.wipo.int In the forthcoming issue of the Journal of NDE, we will dwell in detail on some of the essential aspects of patents, the philosophy behind it, and the patenting process and the challenges thereof. Listed below are a few selected patents in the area of eddy current testing which were issued in 2010. If any of the patents are of interest to you, a complete copy of the patent including claims and drawings may be accessed at some of the websites mentioned earlier. UNITED STATES PATENT 7,830,140 Eddy current system and method for estimating material properties of parts Inventors: Tralshawala; Nilesh , Plotnikov; Yuri Alexeyevich Assignee: General Electric Company (Niskayuna, NY) Abstract : A method of inspecting a test part is provided. The method includes positioning an eddy current probe on a surface of the test part and scanning the test part using the eddy current probe to generate a first signal corresponding to a no lift-off condition of the test part. The method further includes positioning the eddy current probe at a pre-determined distance from the surface of the test part and scanning the test part using the eddy current probe positioned at the pre-determined distance from the test part to generate a second signal corresponding to a lift-off condition of the test part. The method also includes processing the first and second


Products & Patents signals to estimate an electrical conductivity of the test part. UNITED STATES PATENT 7,812,601 Material condition assessment with eddy current sensors Inventors: Goldfine; Neil J, Washabaugh; Andrew P., Sheiretov; Yanko K, Schlicker; Darrell E., Lyons; Robert J, Windoloski; Mark D, Craven; Christopher A, Tsukernik; Vladimir B, Grundy; David C. Assignee: JENTEK Sensors, Inc. (Waltham, MA) Abstract : Eddy current sensors and sensor arrays are used for process quality and material condition assessment of conducting materials. In an embodiment, changes in spatially registered high resolution images taken before and after cold work processing reflect the quality of the process, such as intensity and coverage. These images also permit the suppression or removal of local outlier variations. Anisotropy in a material property, such as magnetic permeability or electrical conductivity, can be intentionally introduced and used to assess material condition resulting from an operation, such as a cold work or heat treatment. The anisotropy is determined by sensors that provide directional property measurements. The sensor directionality arises from constructs that use a linear conducting drive segment to impose the magnetic field in a test material. Maintaining the orientation of this drive segment, and associated sense elements, relative to a material edge provides enhanced sensitivity for crack detection at edges. UNITED STATES PATENT 7,768,259 Device for non-destructive eddy current inspection of a hole formed in a conductive part Inventors: Cabanis; Patrick, Cheynet; Sandra Carole Angele, Gaisnon; Patrick, Le Corre; Christian. Assignee: SNECMA (Paris, FR) Abstract : Using eddy currents to inspect a hole that is possibly not rectilinear and/or of section that is not circular. The inspection device comprises a stick shaped and dimensioned to be capable of being engaged in said hole, at least one arm hinged to a support fastened to one end of the stick, an eddy current sensor being embedded in said arm, and resilient means for urging the arm outwards against the inside surface of the hole. UNITED STATES PATENT 7,705,589 Sensor for detecting surface defects of metal tube using eddy current method Inventors: Kim; Young Joo, Ahn; Bong Young, Lee; Seung Seok, Kim; Young Gil, Yoon; Dong Jin. Assignee: Korea Research Institute of Standards and Science (Daejeon, KR) Abstract : A sensor for detecting surface defects of a metal tube solves a problem of a conventional eddy current probe in that it is difficult to detect a crack in the circumferential direction of a metal tube. The sensor

17

includes a plurality of coils wound at a predetermined inclined angle. The plurality of coils is inserted into the inside of a metal tube. Alternating current is applied to the coils to measure a change in impedance of the coils due to a change in an eddy current generated in the metal tube, thus detecting a surface defect of the metal tube. UNITED STATES PATENT 7,657,389 Method of aligning probe for eddy current inspection Inventors: Suh; Ui W, Knepfle; Richard C. Assignee: General Electric Company (Schenectady, NY) Abstract : A system and method using a touch probe device for eddy current inspection. The touch probe provides a simple approach for coming within close contact of the specimen while maintaining a normal angle and pressure at the right positions. The use of the touch probe further reduces the total time for the eddy current inspection. The touch probe aligns the probe to a specimen to be inspected, for the purpose of reducing measurement errors and increasing productivity. UNITED STATES PATENT 7,782,048 Eddy current testing method, eddy current testing differential coil and eddy current testing probe for internal finned pipe or tube Inventors: Sawawatari; Naoki Assignee: Sumitomo Metal Industries, Ltd. (Osaka, JP) Abstract : The invention provides an eddy current testing method for an internal finned pipe or tube which can securely detect a micro defect generated in a trough portion in an inner surface of the pipe or tube, even in the case that an inner surface shape of the internal finned pipe or tube is non uniform in a circumferential direction of the pipe or tube. The eddy current testing method in accordance with the invention detects a defect existing in a trough portion of the pipe or tube (P) by arranging a differential coil (2) constructed by a pair of coils (21, 22) having such a dimension as to be arranged within the trough portion of the pipe or tube (P) and coming away from each other in an axial direction (X) of the coil, within the trough portion of the pipe or tube (P) along a direction in which the trough portion of the pipe or tube (P) extends, and relatively moving the differential coil (2) in the direction in which the trough portion of the pipe or tube (P) extends. UNITED STATES PATENT 7,750,626 Method and apparatus for eddy current detection of material discontinuities Inventors: Lefebvre; J. H. Vivier, Mandache; Catalin V. Assignee: Her Majesty the Queen in right of Canada, as represented by the Minister of National Defence of Her Majestyâ&#x20AC;&#x2122;s Canadian Government National Research Council of Canada vol 9 issue 3 December 2010


18

Products & Patents

Abstract : A method of eddy current testing without the need for lift-off compensation. Signal response features similar to those used in pulsed eddy current techniques are applied to conventional (harmonic) eddy current methods. The described method provides advantages in terms of data storage, since only two response parameters, the amplitude and phase, are sufficient to reconstruct any sinusoidal signal, therefore allowing for scanning of large surfaces. UNITED STATES PATENT 7,711,499 Eddy current data interpolation/extrapolation Inventors: Junker; Warren R, Nenno; Thomas W, Yaklich; Daniel J, Pocratsky; Ronald J. Assignee: Westinghouse Electric Co LLC (Cranberry Township, PA) Abstract: A method of synthesizing nondestructive examination data of a component that combines data sets acquired at least two different frequencies. At least one of the data sets is interpolated or extrapolated to the equivalent of data acquired at one of the other frequencies employing a third, reference set of eddy current inspection data that is acquired at each of the inspection frequencies being combined.

UNITED STATES PATENT 7,683,611 Pipeline inspection using variable-diameter remote-field eddy current technology Inventors: Burkhardt; Gary Lane, Crouch; Alfred Eugene, Parvin, Jr.; Albert Joseph, Peterson; Ronald Herbert, Goyen; Todd Hegert , Tennis; Richard Franklin Assignee: Southwest Research Institute (San Antonio, TX) Abstract : The present disclosure relates to a device and method for pipeline inspection, The inspection device may include an exciter coil capable of providing an alternating current magnetic field and producing eddy currents. A plurality of sensors may then be provided which are capable of sensing a magnetic field produced by the eddy currents and the sensors may be engaged with a sensor shoe. The sensors may then be capable of being positioned at a first distance D1 with respect to an inner pipe wall surface and capable of providing coupling to the magnetic field produced by the eddy currents. The sensor shoe may also be capable of retracting to a second distance D2, wherein D1<D2. The sensor shoe may be connected to a sensor support arm wherein the support arm may be pivotably attached to a fixed hub and to a control arm which control arm may then be pivotably attached to a driven hub.

National NDT Awards

No.

Award Name

Sponsored by

1.

ISNT - EEC National NDT Award (R&D)

M/s. Electronic & Engineering Co., Mumbai

2.

ISNT - Modsonic National NDT Award (Industry)

M/s. Modsonic Instruments Mfg. Co. (P) Ltd., Ahmedabad

3.

ISNT - Sievert National NDT Award (NDT Systems)

M/s. Sievert India Pvt. Ltd., Navi Mumbai

4.

ISNT - IXAR Best Paper Award in JNDE (R & D)

M/s. Industrial X-Ray & Allied Radiographers Mumbai

5.

ISNT - Eastwest Best Paper Award in JNDE (Industry)

M/s. Eastwest Engineering & Electronics Co., Mumbai

6.

ISNT - Pulsecho Best Chapter Award for the Best Chapter of ISNT

M/s. Pulsecho Systems (Bombay) Pvt. Ltd. Mumbai

7.

ISNT - Ferroflux National NDT Award

M/s. Ferroflux Products Pune

(International recognition)

8.

ISNT - TECHNOFOUR National NDT Award for Young NDT Scientist / Engineer

9.

ISNT - Lifetime Achievement Award

M/s. Technofour Pune

Note-1: The above National awards by ISNT are as a part of its efforts to recognise and motivate excellence in NDT professional enterpreneurs. Nomination form for the above awards can be obtained from ISNT head office at Chennai, or from the chapters. The filled application are to be sent to Chairman, Awards Committee, Indian Society for Non-destructive Testing, Module No. 60 & 61, Readymade Garment Complex, SIDCO Ind. Estate, Guindy, Chennai-600 032. Telefax : 044-2250 0412 Email: isntheadoffice@gmail.com

vol 9 issue 3 December 2010


19

vol 9 issue 3 December 2010


20

EPOCH 600

ULTRASONIC FLAW DETECTOR

Economical Size, Quality Performance The EPOCH 600 Digital Ultrasonic Flaw Detector combines Olympus’ industry leading conventional flaw detection capabilities with the efficiency of a highly portable, intuitive instrument. The EPOCH 600 is an exciting new addition to the Olympus flaw detector product line, incorporating quality flaw detection features for any level of user. • • • • • • • •

Compact and rugged, weighs only 1.68 kg (3.72 lb.) Vibrant full VGA sunlight viewable display PerfectSquare™ tunable square wave pulser Intuitive user interface EN12668-1 compliant Digital high dynamic range receiver Digital filtering enhances signal-to-noise ratio Two hardware configurations: - Adjustment Knob (designed for IP66 rating) - Navigation Pad (designed for IP67 rating)

EPOCH 600 and EPOCH 1000 Series

Exclusive Distributor in India: Blue Star Limited Tel: +91 444-244-4000 • ndtenquiry@bluestarindia.com For worldwide representation visit www.olympus-ims.com • info@olympusNDT.com

vol 9 issue 3 December 2010


21

Contact Mr. D. Simon Amallaraja |

0 9866343309,9848043309|amallraja@fourvector.com

Ms.Gomathi Ramasamy |

0 7702733309 | gomathi@fourvector.com

Mr. Frank Edwin Vedam |

0 8978517118 | frankedwinz@fourvector.com

vol 9 issue 3 December 2010


22

vol 9 issue 3 December 2010


23

vol 9 issue 3 December 2010


24

vol 9 issue 3 December 2010


25

Technical Paper

Digital radiography and Computed radiography for Enhancing the Quality and Productivity of Weldments in Boiler components R.J. Pardikar AGM / NDT, BHEL, Tiruchirappalli,Tamilnadu-620014. E-mail:rjp@bheltry.co.in

ABSTRACT: This paper presents a detailed performance analysis and comparison of Conventional film radiography, Real Time Radioscopy with Digital Radiography (DR) using Digital Detector Array and Computed Radiography (CR) using Flexible Phosphor Imaging Plates, in the case of Quality evaluation of weldments in Boiler Components. Conventional Film Radiography is a slow, expensive and hazardous method, particularly for mass production. Eventhough Real Time Radioscopy (RTR) with Image Intensifiers is an alternative to film radiography, conventional RTR systems are compared unfavorably with film radiography in two aspects viz.low contrast sensitivity and limited resolution. The new digital detector arrays have the potential to substitute the X-Ray films as they have considerably higher image quality than the conventional Image Intensifiers. They allow fast acquisition of radiography images with high dynamic range, and high signal to noise ratio. Computed Radiography is one of the Digital Radiographic Techniques used in lieu of conventional film radiography. The Phosphor Imaging plates (IP) are used as digital detectors in place of photographic X-Ray films. The experimental results revealed that DR can successfully replace Real Time Radioscopy with X-Rays and Image Intensifier, for Tubular Steel welds up to Single wall thickness 12mm. Using the Digital Detector Arrays with 200 microns pixel pitch, it was possible to achieve more than 3 line pairs / mm, at an MTF of over 20%. On the other hand CR has been found to be suitable for Radiography of thick wall welds (Steel thickness up to 140 mm) in Boiler components using Gamma Ray Isotopic Sources like Ir-192, Co-60 and X-Ray sources including Linear Accelerators (up to 6 MeV) with high spatial resolution, meeting the 2 % Radiographic sensitivity requirements as per ASME code. Key words: Real Time Radioscopy (RTR), Digital Radiography (DR), Computed Radiography (CR), Weldments in Boiler Components, Quality evaluation

1.

INTRODUCTION

Radiography is very well established as an NDT technique, using both film and electronic X-Ray detection systems. However there are still many inspection problems, where existing Radiographic inspection techniques are inadequate in determining the presence of critical defects in steel weldments. How ever, Film Radiography is a slow and expensive and hazardous method, particularly for mass production where thousands of weld joints are to be inspected everyday. Real Time Radioscopy (RTR) with Image Intensifiers is an alternative to film radiography with considerable saving in running cost and processing time. However conventional RTR systems are compared unfavorably with film based systems of radiography in two aspects viz.low contrast sensitivity and limited resolution. Focal spot size and limited spatial resolution in the Image Intensifiers will cause noisy image compared with film radiography. In order to meet the sensitivity requirements as per code it is necessary to interface the RTR system with an image processing system for suitably enhancing the images. The new digital detector arrays have the potential to substitute the X-Ray films. Digital Detector Arrays are Vol. 9, Issue 3 December 2010

imaging plates, are claimed to provide Radiographic inspection with considerably higher image quality than the conventional Image Intensifiers. They allow fast acquisition of radiography images with high dynamic ranges. These detectors should enable new computer-based applications with new intelligent computer based methods. However, the overall performance of radiographic systems with digital imaging plates mainly depends upon the quality of these imaging devices, which converts the radiation profile into electronic images. The parameters to the image quality like Linearity, Signal to Noise ratio, Dynamic Range, homogeneity of the images etc, can be influenced by the producer and user of the system.

2. REAL TIME RADIOSCOPY (RTR) OF WELDS IN TUBULAR PRODUCTS [1] Real time Radioscopy inspection systems using 320-kV X-Ray system and Image Intensifier (in lieu of Film) as the Imaging device has been installed at BHEL Trichy for online inspection of Straight Tube circumferential butt welds in boiler components. The feedback regarding the quality of the weld is given to the welder immediately, and the welding parameters are adjusted accordingly to control the process. The joints are made by MIG welding between Journal of Non destructive Testing & Evaluation


26 tubes having outside diameter ranging from 38 to 76 mm and thickness ranging from 4 to 12mm . The major defects, which occur during this welding process, are Porosity, Gas Hole, Crack, Lack of fusion, Incomplete Penetration, Excess penetration, Burn through etc. To meet the sensitivity requirements it is required that planar flaws such as crack, lack of fusion, lack of penetration in welds, etc, the criteria of satisfactory image quality should be more than a conventional IQI sensitivity value. An additional measure of image quality is required. This can be provided by the image of a duplex wire IQI, such as the type III A in BS 3971: 1985. The major limitations of Image Intensifiers are Limited Resolution, Poor Signal –Noise Ratio, Low Contrast, Non linearity, Limited Dynamic Range, etc. However using image processing techniques ,image quality is considerably improved and brought in par with the film radiography. But due to the degradation of Image Intensifiers over a period of time the image quality, even after image processing does not meet the sensitivity requirements as per code. Hence the image intensifiers have limited useful life and need to be replaced once in 3 to 4 years.

3. NEED FOR DIGITAL RADIOGRAPHY Therefore to meet the quality requirement consistently as per the code, BHEL decided to replace the Image Intensifiers with new generation Imaging devices such as Digital Detector Arrays .The radiographic process using digital detectors is termed as “Digital Radiography”[2]. It offers several advantages such as defect recognition software, advance analysis tools, shorter exposure times, and good response at lower energies. Since these panels are directly connected to a PC for power and control, this enables the system to be used in Real time mode.

4. DIGITAL RADIOGRAPHY WITH DIGITAL DETECTOR ARRAY[3] Digital Radiography is the State of art technology based on Digital Detector Array systems in which the X-ray image is displayed directly on a computer without intermediate imaging optics or mechanical scanning. The incident X-Rays are converted in to electric charge and then to digital image through a large area panel sensor. Compared to other imaging devices Digital Detector Arrays provides high quality digital images even better than film radiography with better signal to noise ratio and dynamic range of 12 to 16 bit [4], which provides high sensitivity for radiographic application. Two distinct technologies are available for Digital Detector Array: “indirect conversion” and “direct conversion “. The first design is based on a photo diode matrix, which is read out by thin film transistors (TFT). These components are manufactured of Amorphous Silicon and they are resistant against highenergy radiation. Incoming X-rays first strike a Cesium Iodide scintilator that converts the X-Rays into light. The Journal of Non destructive Testing & Evaluation

Technical Paper

photo diodes are charged by this light photons. The primary benefit of Cesium Iodide technology is the excellent DQE [5]. The light then passes through a photodiode matrix of amorphous silicon, which is converted into electrical signals, which are amplified and digitized. The light is directed onto the silicon without lateral diffusion, which ensures image sharpness. The digital data is then processed into images via a corresponding gray value table, and is displayed, printed or sent to computer as required. The system offers the additional advantages of image postprocessing and archiving. The second type of Digital Detector Arrays is based on a photo conductor like Amorphous Selenium or Cd-Te on a multi-micro electrode plate, which is read out by TFTs again. This type provides the highest sharpness and has the potential for high-resolution systems, which could compete with NDT-film. Here the photons when impact over the photo conductor like amorphous Selenium, they are directly converted to electronic signals which are amplified and digitized. As there is no scintillator (or Phosphor), lateral spread of light is absent here. This is an important difference between direct and indirect construction. A-Se has higher work function and hence less number of charge pairs are produced for a given energy; but it directly receives x-rays and hence overall conversion efficiency is better than indirect type. This compensates to an extent for lesser charge pairs [6]. In the case of Real Time radioscopy examination of welds it is essential to have a continuous series of images (30 frames per second), to enable online inspection with Automatic Defect Recognition. [7]

5.

PERFORMANCE COMPARISON OF IMAGE INTENSIFIER WITH DIGITAL DETECTOR ARRAY EXPERIMENTAL RESULTS

In order to make the decision with regard to the replacement of Image Intensifier with Digital Detector Array for RTR of tubular welds, a series of experiments were carried out to assess the performance characteristics of the Digital Detector Array and Image Intensifier and their comparison. A scrupulous account of all the tests done on both Image Intensifier and Digital Detector Arrays is given in the following sections. A variety of detailed performance characterization measurements have been performed under a set of typical Industrial Radiography conditions. These include spatial resolution (MTF), Contrast Sensitivity, Linearity, and Signal–Noise Ratio. Based on these the performance of the detectors can be compared. 5.1 Resolution

The Modulation Transfer Function (MTF) test results of Digital Detector Arrays are compared with that of Image Intensifiers. The test results reveal that the Nyquist Vol. 9, Issue 3 December 2010


Technical Paper

Fig. 1 : MTF comparison between Digital Detector A rray (left),with 200micron pixel pitch and Image Intensifiers(right)

27

Fig. 2 : Linearity Comparison between Digital Detector Array and Image Intensifier

frequency of the Image Intensifier is 3.5 lp/mm, and for imaging small features at 3.5 lp /mm, the MTF is 20%. For the Flat Panels, the Nyquist frequency is 5.0 lp /mm. The resulting MTF indicates excellent resolution for imaging of small features, with significant MTF(over 20%) at 5.0 lp /mm, which makes the spatial resolution superior to Image Intensifier. 5.2 Linearity

Linearity [3. of detector response is a key factor in producing high-quality digital radiographic images. In order for the normalization procedure to work over a wide range of exposure conditions, the detectorâ&#x20AC;&#x2122;s basic response needs to be extremely linear over the detectorâ&#x20AC;&#x2122;s useful dynamic range. Linearity is characterized by illuminating the detector with an industrial X-ray source. A series of images are acquired at each dose level, and the mean signal (which is characterized by the mean Gray level of the image) is calculated over a small region in the center of the detector. The images are collected at a source-detector distance of 70 cm, using a 320kV X-Ray system. The operating voltage is maintained at 45 kV. The variation of the signal value with increasing the dosage value is plotted. By using the results of the linearity test conducted on Individual detectors, the comparison is obtained here. The test results show that, the flat panels show linear behavior over a wide range of exposure conditions, where as Image Intensifier is nonlinear. Vol. 9, Issue 3 December 2010

Fig. 3 : Contrast Sensitivity Comparison between Image Intensifiers and Digital Detector Arrays Journal of Non destructive Testing & Evaluation


28

Technical Paper

5.3 Contrast Sensitivity

6.

The measurement of contrast sensitivity (CS)of the Digital Detector Array and Image Intensifier is carried out by using three step wedges, which are having thickness 5mm, 10mm and 20mm respectively. In the experiment conducted, in order to have better accuracy of the test results, the CS value for each step in comparison with base thickness was taken and the mean value was taken as the Contrast Sensitivity of the particular Step wedge. The procedure is repeated for each step wedge at dosage values (mA minutes) 2,2.5,3 and 3.5 respectively. The values of contrast sensitivity obtained as a result of these calculations are given below. The given below comparison shows that in the case of Digital Detector Arrays the Contrast Sensitivity is better.

Computed Radiography is one of the Digital Radiographic Techniques used in lieu of conventional film radiography. The Phosphor Imaging plates (IP) are used as digital detectors in place of photographic X-Ray films. These detectors enable new computer based applications with intelligent computer based methods. They can substitute film applications with several advantages like Image Enhancement, Automated Defect Recognition, shorter exposure times (70% of film), greater Linearity and Range, sharing information, Digital Archiving and Reporting. The CR also provides considerable saving in cost of consumables (Film) and totally eliminates hazardous chemical processing of films. The High Definition Computed Radiography systems (HD-CR) can produce high image quality, meeting the Radiographic sensitivity requirements as per international codes.

5.4 Signal to Noise Ratio (SNR)

The SNR experiments were conducted in the case of Digital Detector Array and Image Intensifier by using the contrast sensitivity gauges and exposing, at different X-Ray dosage level conditions. The images of the step wedge were captured at different mA minute values of the X-Ray equipment keeping the voltage fixed. Three step wedges (thickness 5mm, 10mm and 20 mm respectively) were used for conducting the test. Each of these was exposed to X-Ray radiation at dose values 2, 2.5,3 and 3.5 mA min conditions. The signal gray value was measured from each of these images. Also the standard deviation in these images, which is the measure of noise were noted. For comparison of detectors in terms of signal to noise variation, we use a parameter called normalized SNR or SNR

norm

, which is given by

Where ,BSR is

Basic Spatial Resolution of the Detector.

COMPUTED RADIOGRAPHY (CR) [8]

The Imaging Plate is a Flexible Polymer support coated with sensitive layer (BaFBr doped with Eu2+), used in much the same way as X-Ray film and wrapped around the job for exposure to ionizing radiation (X-Ray / Gamma Ray) during Radiographic Testing. The latent invisible image is created by Photo Stimulated Luminescence process, when the IP is exposed to ionizing radiation .The conversion of latent image to digital image is obtained by scanning of IP by LASER, during which the release of electrons emit energy in the form of blue light that is detected by a Photo multiplier tube and then converted to a digital image. The amount of blue light is linear measure of Radiographic Density at this point. The typical pixel pitch of such scanner is 50 to 150 micrometer. A LASER beam with extremely fine resolution of 12.5-micrometer spot size, together with highly efficient light bunching system can attain 20 lp/mm of resolution, revealing extremely small defects. 6.1 Computed Radiography of thick wall Boiler components

Fig. 4 : SNR comparison between Digital Detector Array and Image Intensifier. Journal of Non destructive Testing & Evaluation

In order to meet the code of construction (ASME, section I), and the Indian Boiler regulations at present 100% radiography is carried out on butt welds of Boiler pressure parts such as Headers, Pipes, Drums etc. Since Radiography is time consuming, hazardous and expensive, BHEL has decided to go in for Computed Radiography of these welds. Initially it is proposed to use the computed radiography system for evaluation of welds of thickness ranging from 10-70 mm using X-Ray source up to 400 kV and Ir-192 source. However the feasibility study for assessing the performance of Computed Radiography has been carried out up to 140mm using the isotopic sources like Co-60 and Linear Accelerator. The experimental study was carried out to evaluate the quality of radiographs achieved with imaging plates (GE IT Imaging plates, IPCII-High speed, and IPS-III High Contrast) and Laser processing using scanner GE IT-CR 100, and comparison was made with the performance of Agfa D7 and D4 Vol. 9, Issue 3 December 2010


29

Technical Paper

films. Both ASTM strip hole IQI and wire type IQI were used for assessing the contrast sensitivity and duplex wire IQI as per EN 462 for the spatial resolution. The selection of IQI was done based on the thickness of the job. The thickness of the Image Intensifying screens and the exposure time to achieve the required optical density and sensitivity for the specific Phosphor imaging plates, were arrived on trial and error basis as there are no exposure charts available for Imaging plates.

Table 5 : Wire type IQI Sensitivity with 4 MeV Linac Steel weld thickness, mm Relative exposure w.r.t Agfa D7

Required High Agfa wire contrast D 7 dia in IP mm

Agfa D 4

80

1.27

-

0.8

0.5

90

1.27

1.25

-

0.4

110

1.6

1.25

-

1.25

160

2.5

-

2.5

1.25

6.2 Experimental results Table 6 : Hole type IQI Sensitivity with X-Rays

Comparative Penetrameter sensitivity achieved with Phosphor Imaging plates and X-Ray films for weldments in Steel thickness ranging from 30mm to 160mm,using various radiation sources.

Steel weld thickness,mm Relative exposure w.r.t Agfa D7

High speed IP (0.25)

High contrast IP (1.0)

30

30-2T

30-1T

40

35-2T

35-1T

50

35-2T

35-1T

Table 1 : Hole type IQI Sensitivity with Ir-192 Steel weld thickness, mm Relative exposure w.r.t Agfa D7

High speed IP (0.25)

High Agfa contrast D 7 IP

Agfa D 4

30

30-1T

30-1T 30-1T 30-1T

40

35-2T

35-1T 35-2T 35-1T

50

35-2T

35-1T 35-4T 35-2T

Table 7 : Wire type IQI Sensitivity with X-Rays Steel weld thickness,mm Relative exposure w.r.t Agfa D7

Required wire dia in mm

High Speed IP

High Contrast IP

30

0.6

0.5

0.5

40

0.8

0.6

0.5

50

0.8

0.6

0.6

Table 2 : Hole type IQI sensitivity with Co-60 Steel weld thickness,mm Relative exposure w.r.t Agfa D7

High contrast IP

Agfa D 7

Agfa D 4

40

35-1T

35-2T

35-1T

60

40-2T

-

40-2T

80

50-2T

50-2T

50-2T

90

50-2T

50-2T

50-1T

110

-

50-2T

50-1T

Table 3 : Wire type IQI Sensitivity with Co-60 Steel weld thickness, mm Relative exposure w.r.t Agfa D7

Required wire dia in mm

High contrast IP

Agfa D 7

Agfa D 4

80

1.27

-

0.63

0.6

90

1.27

0.8

1.25

0.8

110

1.6

1.25

1.25

1.25

Table 4 : Hole type IQI Sensitivity with 4 MeV Linac Steel weld thickness,mm Relative exposure w.r.t Agfa D7

High contrast IP

Agfa D 7

Agfa D 4

80

50-2T

50-2T

50-1T

90

50-2T

50-1T

50-1T

110

50-2T

50-2T

50-1T

160

80-2T

80-1T

80-1T

Vol. 9, Issue 3 December 2010

Table 8 : Duplex Wire sensitivity achieved with various sources (As per EN 14784-2, Duplex wire Separation (EN 472-5)) Ir-192

Co-60

4 MeV Linac

Class A

Class B

Required

6

7.00

Achieved

8

8.00

Required

6

6.00

Achieved

7

6.00

Required

6

7.00

Achieved

7

7.00

NOTE:The relative exposure values for CR with IPs were approximately 70% as that of D7 films.

From the test results shown in the above tables, the following conclusions can be drawn. In the case of Ir192 source, for 50mm Steel thickness, the High Speed IP gives a hole type IQI sensitivity of ASTM 35,2-2T (1.75 %) which is better than, the corresposing value (ASTM 35, 2-4T) achieved by Agfa D7 film (High Speed film). Similarly, the High contrast IP gives a sensitivity of ASTM 35,2-1T, which is superior to the corresponding value (ASTM 35,2-2T) given by a fine grain film Agfa D4.In the case of the Co-60 source even at 90 mm thickness, a High Contrast IP gives sensitivity on par with Film. Table (2) shows the performance results with Hole type IQI, which shows the sensitivity ASTM 50, 2-2T, achieved by both IP and Film, Where as the Table (3) shows the same test conducted with Wire type IQI, which Journal of Non destructive Testing & Evaluation


30

Technical Paper

clearly tells that IP has achieved a sensitivity of 1.25 % on par with Films. Table 4 and Table 5 show the Sensitivity values achieved, when 4 MeV Linac is used, with Hole type IQI and Wire IQIs respectively .The sensitivity is on par with Agfa D7 film. In the case of X-Rays upto 300kV, both the High Speed IP and High Contrast IP are able to achieve better than 2 % sensitivity. Table 8 shows that spatial resolution achieved by IPs, with duplex wire IQI in the case of various Radiation sources are better than the required values, as per standards.

associated with Film processing ,thereby increasing the speed and efficiency of Radiographic Testing. Other significant advantages of CR include the electronic archiving of Radiographic images and online transmission of images for away center evaluation.

7. CONCLUSION

2. Bruce Blakeley, ‘Digital Radiography- is it for you?’ Insight, 46(7) (2004) 403-407

The feasibility study and the experimental results clearly revealed that the transition from Film Radiography to Digital/ Computed Radiography of the welded components is practicable and can meet the National and International Radiography Code requirements. Digital Radiography can successfully replace Real Time Radioscopy with X-Rays and Image Intensifier, for Tubular Steel welds up to Single wall thickness 12mm. Using Digital Detector Arrays with 200 microns pixel pitch, it was possible to achieve more than 3 line pairs / mm,at an MTF of over 20%.The implementation of DR will facilitate the Automatic Defect Recognition during online inspection of welded joints, avoiding the subjectivity in humane evaluation .On the other hand Computed Radiography using High Contrast Phosphor Imaging Plates has been found to be suitable for Radiography of thick wall welds (Steel thickness up to 160 mm) in Boiler components such as Headers, Pipes, Drums etc using Gamma Ray Isotopic Sources like Ir192, Co-60 and X-Ray sources including Linear Accelerators (up to 4 MeV) with high spatial resolution, meeting the 2 % Radiographic sensitivity requirements as per ASME code.CR will considerably reduce the exposure time and also completely eliminate the chemical hazards

Journal of Non destructive Testing & Evaluation

REFERENCES 1. R.J.Pardikar, ‘Real Time Radioscopy and Digital Image Processing Techniques for on-line Inspection of Welds in boiler Tubes’ Journal of Non-Destructive Evaluation, 20(3) (2000) 68-72

3. G.A.Mohr and C.Beuno, GE A-Si Digital Detector Array detector in industrial digital radiography’, BINDT Insight, 44(10) (2002). 4. V.R.Ravindran, ‘Digital Radiography Using Digital Flat Panel for Non-Destructive Evaluation of Space Vehicle Components’, Journal of Non-Destructive Testing & Evaluation , Vol.4, Issue 2, September 2005. 5. Giakos, G.C.; Suryanarayanan, S.; Guntupalli, R.; Odogba, J.; Shah, N.; Vedantham, S.; Chowdhury, S.; Mehta, K.; Sumrain, S.; Patnekar, N.; Moholkar, A.; Kumar, V.; Endorf, R.E., ‘Detective quantum efficiency [DQE(0). of CZT semiconductor detectors for digital radiography’, Instrumentation and Measurement, IEEE Transactions, 53(6) (2004) P 1479 – 1484 6. P.R.Vaidya, “Digital Flat Panel Detectors in Industrial Radiography”, International Workshop on Imaging NDE- 2007, April 25-28, 2007, Kalpakkam, Chennai, India. 7. Rajashekar Venkatachalam , Manoharan V , Raghu C , Venumadhav Vedula , Debasish Mishra , 12 th A-PCNDT 2006 – Asia-Pacific Conference on NDT, 5th – 10 th Nov 2006, Auckland, New Zealand 8. P.R.Vaidya andA.V.S.S.Narayana Rao, “Performance Evaluation of the Imaging Plates for Industrial Radiography Application”, Journal of Non-Destructive Evaluation, 20(3) (2000) 53-56.

Vol. 9, Issue 3 December 2010


31

Technical Paper

ASTM standards on digital detector arrays for industrial digital radiography – a bird’s eye view Padmashree G K1, Debasish Mishra1, Clifford Bueno2 and Joe Portaz3 1 2

GE Global Research Bangalore, India GE Global Research Niskayuna, USA 3 GE Aviation, Cincinnati, USA

ABSTRACT Digital detector array technology is becoming increasingly important, as industrial radiography is transitioning from film to digital. Standards for industrial digital radiography are vital to the introduction and widespread use of this technology for inspection, sustenance of digital conversion and accelerated digital-to-shop floor transition. In this paper, we highlight the importance of standards and present an overview of the recently published ASTM standards on digital detector arrays for industrial digital radiography.

1.

INTRODUCTION

Digital radiography, in recent times, is gaining momentum in industrial inspection as it stands to offer a multitude of advantages over conventional film radiography. The crux of this technology lies in employing a digital detector array for x-ray imaging of industrial components, as opposed to using a silver-halide film as the x-ray recording medium. This therefore gives industrial radiography the advantages of high-throughput inspection together with significantly reduced cost of repetitive inspections. It also eliminates chemical processing involved in film radiography, allows for data archival and improves defect detection. Alongside these advantages, rapid advances in digital technology have made industrial digital radiography fascinating from a technology standpoint. Such advances cater to current challenges in the application-space, while newer applications propel further advancement of this technology. Such interplay between technology and applications has resulted in a wide variety of digital x-ray systems coming into existence and making their way to the marketplace. The plethora of applications makes it almost impossible to have a single standard digital radiography system to address all applications, the design of a digital x-ray detection device being a major consideration in its own right. As a result, there are almost as many choices of detectors as there are ways to configure the overall test system, leaving the user overwhelmed. In the absence of any standardization, the choice of detectors becomes difficult. This warrants the development of guidelines on ‘minimum requirements and deployment of digital x-ray detectors for industrial inspection’. Needless to say, absence of such guidelines will result in a slow standardization process that could hamper the application of this technology. Introduction of industrial digital radiography into the marketplace will be slow without effective standards, as manufacturers of digital detectors find resistance to the Vol. 9, Issue 3 December 2010

introduction of this new technology while end-users seek these standards for guidelines on usage. Therefore, standards in digital radiography are vital to the introduction of this technology for industrial inspection. To this end, several joint committees have worked towards the development of standards for industrial digital radiography in the last decade. These standards include guidelines on the measurement of instrumental parameters, as well as minimum requirements for instruments, practice and evaluation. Standards like the ISO standards and European standards have come into existence with mutual recognition, and they serve to bring about an international harmonization of rules across the globe for non-destructive evaluation (NDT) in general and industrial radiography in particular. ASTM (American Society for Testing and Materials) standards have also been under development in this time frame. The emerging standards from these organizations provide guidance in evaluating different xray digital systems, methods of calibrating systems, and practices for use and implementation of radiography for industrial applications. An overview of the ASTM standards on digital detector arrays (DDA) is presented here.

2. ASTM STANDARDS FOR DIGITAL DETECTOR ARRAYS ASTM has developed and recently published four standards for DDAs targeting industrial applications. Each of the four standards addresses an aspect of DDA manufacture and use, while they collectively address all the aspects pertaining to DDAs in general. Thereby, these standards serve as a complete and comprehensive source of information to the manufacturers and users by assisting them in standardization of measurements, reporting DDA properties that help users make informed decisions on DDA purchase, guidelines on introduction of DDA technology into operations for almost any inspection application, providing tests and guidelines on methods to Journal of Non destructive Testing & Evaluation


32

Technical Paper

Fig. 1 : Chart showing the various DDA Standards developed by ASTM.

establish and track baseline performance of DDAs over time. The four ASTM Standards for DDAs are:

specific DDA to meet the NDT requirements. The metrics, for which each DDA will be evaluated, are listed here.

(a) Basic Spatial Resolution (SRb) is the smallest geometrical detail that can be resolved using the DDA. (b) Efficiency of the DDA is the signal-to-noise ratio normalized for basic spatial resolution (detector normalized signal-to-noise ratio dSNRn) at 1 mGy, for different energies and beam qualities. (c) Achievable Contrast Sensitivity (CSa) is the optimum contrast sensitivity obtainable using a standard phantom, with an x-ray technique that has minimal contribution from scatter. (d) Specific Material Thickness Range (SMTR) is the material thickness range within which a given image quality is achieved. (e) Image lag is the residual signal in the DDA that occurs shortly after the exposure is completed. (f) Burn-in is the change in scintillator gain that persists beyond the exposure. (g) Bad pixel is a pixel whose performance is outside the specification range for a DDA pixel. (h) Internal scatter radiation (ISR) is the scatter radiation within the detector.

路 路 路

ASTM E2597: Standard Practice for Manufacturing Characterization of Digital Detector Arrays. ASTM E2698: Standard Practice for Radiological Examination Using Digital Detector Arrays. ASTM E2737: Standard Practice for Digital Detector Array Performance Evaluation and Long-Term Stability. ASTM E2736: Standard Guide for Digital Detector Array Radiology.

A chart with all the four ASTM DDA standards and their highlights is shown in Fig. 1.

3. OVERVIEW OF THE ASTM STANDARDS FOR DIGITAL DETECTOR ARRAYS This section gives an overview of the scope and significance of the four ASTM standard for DDAs. The reader is encouraged to refer to the original standards for a detailed and extensive read. 3.1 ASTM E2597 Standard Practice for Manufacturing Characterization of Digital Detector Arrays

ASTM E2597 serves as a starting point for the end user to select a DDA for a specific application, based on the DDA system performance data provided by the DDA manufacturers and suppliers. This standard describes the evaluation of a DDA in terms of a common standard for quantitative comparison of DDAs, based on a set of technical measurements. DDA manufacturers and integrators are the intended users of this standard. It serves to assist them in providing the end user with quantitative results of DDA characteristics and metrics, which would in turn help the user to select an appropriate applicationJournal of Non destructive Testing & Evaluation

An explanation for all the metrics and a detailed procedure to carry out tests for quantifying each of these metrics is described in this standard [1]. Quantitative results for these metrics may be presented in the form of a diagram, which describes the DDA performance comprehensively and serves as a user-guidance for appropriate choice of DDA. 3.2 ASTM E2698 Standard Practice for Radiological Examination Using Digital Detector Arrays:

ASTM E2698 standard serves to assist the end users in establishing the minimum requirements for radiological Vol. 9, Issue 3 December 2010


33

Technical Paper

inspection using the purchased DDA, and is intended to control the quality of x-ray images. It establishes the basic parameters for the application, for various components of the x-ray inspection chain, namely, system configuration, data acquisition software, DDA, image display station, image quality indicators, and radiation sources. The procedure for qualification exposure with image quality indicators (IQI) includes details on x-ray tube potentials, tube current, integration time, source-to-detector distance (SDD), object-to-detector distance (ODD), collimators and filters, DDA settings. The aspects related to geometrical considerations for establishing image quality, geometric magnification, evaluating IQI visibility using contrast-to-noise ratio (CNR), window-level and image zoom settings are documented in this standard. It helps the user to get the required signalto-noise ratio (SNR) to set up the required magnification and provides guidance for viewing and storage of radiographs. It also assists the user with marking and identification of parts during radiological examinations. The equipment monitoring requirements, procedural requirements and examination details are provided in detail in this document [2]. 3.3 ASTM E2737 Standard Practice for Digital Detector Array Performance Evaluation and Long-term Stability

ASTM E2737 is intended to help the end user in confirming that the DDA system performs as required, and is stable in its performance over its lifetime. This practice describes the evaluation of DDA systems for industrial radiology. It serves to ensure that the evaluation of image quality meets the needs of the users and their customers, and enables process control and long-term stability of the DDA system. DDA system performance tests specified in this practice need to be completed upon purchase of the detector from a manufacturer, and at intervals specified, so as to monitor its long term stability. Although many of the details listed in this standard have similar metrics to those listed in ASTM E2597, data collection methods are not identical. This document establishes standard techniques for assuring repeatability throughout the lifecycle testing of the DDA. The general testing procedure includes phantom specifications, calibration method and bad pixel standardization for DDAs. Core image quality tests for spatial resolution, contrast sensitivity, signal-to-noise ratio, signal levels and bad pixel distribution, material thickness range image lag and burn-in, offset value, are described. A detailed description of the test procedures is documented in this standard [3].

and performance parameters of DDAs, while additionally serving as an in-detail reference and guide for Standards E2597, E2698 and E2737. It guides the user to make an informed decision on the purchase and use of a DDA for a given target application. It is an extensive document designed to assist the end user to set up the DDA with minimum requirements for radiological examinations. It also describes DDA architecture, various digitization methods, and the overall signal chain in a DDA system. Other topics include DDA properties, factors that influence the image quality in DDAs, various calibration and correction procedures, potential sources of radiation damage to a DDA, general guidelines for DDA selection, imaging considerations with a given DDA, display storage and retrieval methods [4]. 3.5 ASTM E2699

In addition to the four Standards summarized above, ASTM E2699 Standard on Practice for Digital Imaging and Communication in Nondestructive Evaluation (DICONDE) for Digital Radiographic Test Methods facilitates uniformity across operators and digital radiography equipment, by specifying image data transfer and archival methods in commonly accepted terms. This standard has been developed to overcome the issues that could come up while analyzing and archiving data captured with DDAs. This standard defines a method where all the digital x-ray technique parameters and test results are stored and communicated in a standard manner, regardless of changes in digital technology [5].

4. CONCLUSION Digital radiography for industrial inspection is a technology that offers a huge advantage in terms of throughput and cost. Standards play a vital role in the introduction of this technology to the marketplace. ASTM has developed standards for digital detectors arrays targeting industrial applications. All of these four Standards are now published. They are consistent, cross-referenced, and would certainly expedite film-to-digital transition and digital sustenance.

REFERENCES 1. ASTM E2597 Standard Practice for Manufacturing Characterization of Digital Detector Arrays. 2. ASTM E2698 Standard Practice for Radiological Examination Using Digital Detector Arrays. 3. ASTM E2737 Standard Practice for Digital Detector Array Performance Evaluation and Long-Term Stability.

3.4 ASTM E2736 Standard Guide for Digital Detector Array Radiology

4. ASTM E2736 Standard Guide for Digital Detector Array Radiology.

ASTM E2736 standard is a generic guide on DDAs, which serves as a tutorial for selection and use of various DDA systems. It assists the user to understand the definitions

5. ASTM E2699 Standard on Practice for Digital Imaging and Communication in Nondestructive Evaluation (DICONDE) for Digital Radiographic Test Methods.

Vol. 9, Issue 3 December 2010

Journal of Non destructive Testing & Evaluation


34

Technical Paper

Inspection of Adhesively Bonded Aircraft Repair Patches using Ultrasonic Guided Waves Padmakumar Puthillath, Cliff J. Lissenden and Joseph L. Rose Engineering Science and Mechanics Department 212, EES Bldg., Pennsylvania State University, PA 16802, U.S.A Email: ppkumar@psu.edu

ABSTRACT Aircraft structures subject to service loads and chemical environments develop structural weaknesses like cracks, corrosion etc. In order to mitigate the resulting reduction in the useful service life of aircrafts, repairs are done in the form of adhesive bonding of plates such as a titanium plate to aluminum fuselage. Typical of adhesive joints, these bonded repair patches also have interfacial (adhesive) or bulk (cohesive) weaknesses in the joint. Nondestructive inspection of these structures is required to ensure the quality of the repair patches. Conventional inspection approaches using normal or oblique incidence of ultrasonic waves has limited capability in detecting both the adhesive and the cohesive weaknesses present in the adhesive joints. A systematic approach for the inspection of adhesive repair patches using ultrasonic guided waves is demonstrated in this work. Among the multiple modes and frequency combinations possible in a structure, defect sensitive guided wave modes were selected from theoretical studies. The selected mode-frequency combination is ensured to work over a range of bondline thicknesses that can occur in real joints. An angle beam wedge arrangement to generate defect sensitive modes was used to successfully inspect epoxy bonded titanium - aluminum samples prepared with simulated adhesive and cohesive weaknesses. Keywords: Adhesively Bonded Repair Patch, Ultrasonic Guided Waves, Dispersion, Adhesive and Cohesive Weakness

1. INTRODUCTION Aircraft structures are subject to in-service loading like fatigue, thermal and chemical environments that can initiate points of weakness within the structure, such as fatigue cracks, corrosion, and delamination, thus leading to a reduction in their service life. In the military, aging induced structural weaknesses in aircrafts are mitigated using appropriate repairs because replacement is prohibitive in terms of time and cost [Pyles 2003]. Repairs can be performed using mechanically fastened or adhesively bonded patches. In comparison to mechanical fastened repairs, a bonded repair produces minimal alteration to the aerodynamic contours, results in weight savings in addition to avoiding the stress raisers associated with bolt/rivet holes. Adhesively bonding metal or composite patches to the damaged surface of aircraft, after appropriate surface treatment, can improve the stiffness of the weakened part [Pyles 2003]. The adhesive bonding used is susceptible to interfacial (or adhesive) and bulk (or cohesive) defects, making nondestructive inspection essential in order to ascertain the quality of repairs. Practical cases of adhesive repairs can be found in the literature [Baker 2009, tâ&#x20AC;&#x2122;Hart and Boogers 2002]. Recently, researchers have demonstrated a method for health monitoring of repairs using strain gages bonded to the aircraft skin and repair patch [Baker 2009]. The ratio of strains was used to detect debonding between the skin and the repair patch. This is a good approach for local inspection, but requires either an extensive coverage of the repair patch using strain gages or optical fibers to obtain a global inspection. The use of commercial bond Journal of Non destructive Testing & Evaluation

testing equipment like Bondascope [Baker 2009] and the Fokker Bondtester [tâ&#x20AC;&#x2122;Hart and Boogers 2002] in successfully detecting cohesive defects is also shown in the literature. This is again a local inspection approach, and similar to an ultrasonic C-scan, is not successful in detecting adhesive weakness in bonding. Ultrasonic wave propagation through structures is dependent on the material elastic properties. Ultrasound provides a nondestructive means of adhesive bond quality assessment. Pilarski and Rose [1988] have shown the importance of generating shear at the interface between the adhesive and adherend. This was an improvement of the bulk wave approach that needed very high frequencies (> 10 MHz). Ultrasonic guided waves are special kinds of waves propagating primarily under the influence of the geometry and boundary conditions of a waveguide. They are characterized by dispersion which is captured in the form of phase and group velocity variation with frequency [Rose and Pilarski 1988]. Rose and co-workers [1996] have successfully demonstrated mode selection principles by employing modes from the overlap between dispersion curves of the individual plate that form the adhesive bond. This study comprehends the progress made in mode selection for inspection of defects in an adhesive joint titanium patch bonded to aluminum aircraft skin using epoxy. In this paper, a theoretical study is carried out where the guided wave phase velocity dispersion curves are used in conjunction with wave structures to determine optimal conditions for inspection of adhesive and cohesive Vol. 9, Issue 3 December 2010


Technical Paper

weakness in continuous waveguides. Epoxy bonded aluminum - titanium repair patches were prepared with interfacial weakness conditions simulated by using teflon inserts and other surface variation techniques. The inspection technique presented here is applicable to the inspection of bonded repair patches under the condition that both the transmitter and the receiving transducers rest on the bonded joint. The optimal guided wave mode was generated in the bonded sample using an ultrasonic transducer mounted on an acrylic angle beam wedge. The difference in transmission in terms of the signal content was successfully analyzed and used to discriminate between the defective and non-defective regions in the structure. This work has been recently reported by Puthillath and Rose [2010].

2.

GUIDED WAVE MODE SELECTION

Ultrasonic guided wave dispersion curves provide the theoretically possible phase velocity and frequency combinations that can exist in a structure having free

35 boundaries. Each point on a dispersion curve has a unique wavestructure and it holds the potential to solve different inspection problems. In the literature there have been instances [Rose and Pilarski 1992] where the guided wave mode selection has been carried out to address different defect detection scenarios. The Lamb wave phase velocity dispersion curves for a typical adhesive repair patch - epoxy (0.66 mm thick) bonded titanium (1.6 mm), aluminum (3.175 mm) joint â&#x20AC;&#x201C; is shown in Fig. 1. Since the repair patch geometry under study is not mid-plane symmetric, the modes are referred by numbers rather than the conventional Antisymmetric (A) or Symmetric (S) notation. In this work, both the adhesive and the cohesive weakness in the epoxy layer are studied. The adhesive weakness is assumed to be located between the aluminum and the epoxy layer. This assumption comes from the fact that repairs are performed on field and hence the possibility that the surface of aluminum does not meet the cleanliness condition required for bonding is high.

Fig. 1 : Lamb wave dispersion curves for aluminum-epoxy-titanium adhesive repair patch and two wave structures or cross-sectional displacement profiles (at locations 1 and 2 on the dispersion curves). The dotted lines demarcate the aluminum, epoxy and the titanium regions, with aluminum being at the bottom. A larger in-plane displacement (ux) at the aluminum-epoxy interface can be noticed at location 2. Vol. 9, Issue 3 December 2010

Journal of Non destructive Testing & Evaluation


36 In order to inspect the interfacial weaknesses at the aluminum-epoxy interface in the bonded repair patch, the in-plane displacement at that interface was used as the criterion. The normalized displacement wavestructures for two neighboring modes (modes 17 and 18) on the dispersion curves at the same phase velocity value (14.37 km/s) and frequency 2.5 MHz is also shown in Fig. 1. The interfacial in-plane displacement profile across the frequency-phase velocity space of choice is shown superimposed on the guided wave modes on Fig. 2 as an easy reference tool. In addition to the interfacial in-plane displacement feature, in order to simplify the interpretation of the experimentally measurements waveform, it is mostly preferred to have minimum number of modes excited within the structure. The guided wave mode selected should also have a smaller wavelength to improve sensitivity to smaller defects. The mode 18 (from Fig. 1), identified with an arrow in Fig. 2, at a higher phase velocity range (14-16 km/s) was thus selected for inspection of the bonded joint. A big challenge in practical adhesive bond inspection problems is the change in the bond-line thickness. Despite attempts made to control the thickness of the bond line namely the use of cured epoxy strips, glass beads, shimstocks etc., local variation in adhesive thickness is possible. In the guided wave based inspection scenario, a change in bond line thickness implies a change in the thickness of just one layer of the layered waveguide – implying a new problem to be solved. The effect of 100 % variation in the thickness of the bond-line on the Lamb wave phase velocity dispersion curves was studied by varying the thickness from 0.4318 mm to 0.8636 mm. Though not shown here, it was noted that the selection of ~15 km/s and 2.5 MHz was found to result in a high interfacial in-plane displacement throughout the range of the thickness considered.

Technical Paper

3.

PREPARATION OF SAMPLES WITH SIMULATED DEFECTS

In order to verify the theoretical work, small repair patch samples – i.e. epoxy bonded titanium-aluminum joint were created. Aerospace grade sheet epoxy – EA9696 was used as the adhesive. Defects were introduced at controlled depths in order to study the wave propagation across cohesive and adhesive weaknesses. aluminum (3.175 mm) and titanium (1.6 mm) plate samples were degreased using a solvent, polished using abrasive disc pads, cleaned with acetone followed by coating with sol-gel and water based primer. The use of the sol-gel is to improve the adhesion for bonding metals. The primer provides better mechanical properties and corrosion resistance. For each repair patch, two epoxy layers were stacked between the prepared faces of the aluminum and titanium plates and cured under vacuum conditions with the application of appropriate pressure and temperature inside an autoclave. Square defects with 0.5" sides were introduced at the aluminum-epoxy interface for creating adhesive weakness and between the layers of epoxy to create cohesive weakness. A folded strip of teflon was also suitably placed for creating both adhesive and cohesive weaknesses in the repair patch. A bubble wrap was used to create another instance of adhesive weakness. The repair patches prepared were cut to form samples for testing shear strength using ASTM 3165. From the test results, it was observed that the good bond region in the repair patch sample was stronger than any simulated weaknesses. The results from the ASTM 3165 tests thus point to the reliability of the fabrication procedure implemented and also provide support to the methods of simulating weaknesses in the bonding.

4.

EXPERIMENTAL WORK AND RESULTS

There are various techniques for exciting guided waves in structures for experimental work viz. acrylic wedge, oblique incidence in a water immersion mode, or a comb transducer with or without time delays. A variable angle acrylic wedge arrangement was adopted due to its ease of implementation and flexibility to generate guided wave modes at different phase velocities.

Fig. 2 : Normalized in-plane displacement value is shown superimposed over the dispersion curves for titaniumepoxy-aluminum joint. The arrow on top of the figure indicates the mode 18 – that has one of the highest inplane displacements at the aluminum-epoxy interface. Journal of Non destructive Testing & Evaluation

The mode identified in Fig. 2 (mode 18) was generated using a variable angle beam acrylic wedge set to an incidence angle of 10°. Experiments were performed by arranging the wedge mounted transducers (2.25 MHz, and 12.7 mm in diameter) in pitch-catch configuration and varying the excitation frequency from 1 MHz to 3 MHz in steps of 50 kHz. The RF signals collected were squared and summed to obtain an energy quantity for each excitation signal in the range of frequencies 1 MHz and 3 MHz at 50 kHz intervals. A comparison of the variation in the transmitted energy quantity obtained from the frequency sweep experiments is shown in Fig. 3. Vol. 9, Issue 3 December 2010


37

Technical Paper

The signals collected in pitch-catch mode across the simulated defects using a pair of 2.25 MHz, 6.7 mm diameter commercial transducers mounted on fixed angle wedges is shown in Fig. 4. The pulse input to the transmitter was a tone burst cosine pulse at 2.5 MHz. The RF signals from Fig. 4 clearly show that the guided wave mode selected from the theoretical study was able to distinguish between the different cases of interface conditions simulated and a good joint among the repair patch samples fabricated. It is interesting to note that the mode selected specifically for sensitivity to adhesive weakness is also sensitive to the cohesive weakness because the displacement at the middle of the epoxy layer is still significantly high. Fig. 3 : Energy transmission from frequency sweep experiments using variable angle acrylic wedges adjusted to 10° incidence and reception angle in pitch-catch mode. Commercially available 2.25 MHz transducers were used as transmitter and receiver and tone burst input was supplied to the transmitter.

It can be observed from the Fig. 3 that the range of excitation frequencies - 2 to 2.5 MHz, with incidence and reception angles of 10°, is sensitive to the adhesive and cohesive defects simulated in the bonded repair patch samples. The transmission is maximum in the case of a good bond and minimum in the case of a cohesively weak bond. The energy transmission in the adhesive weakness cases lies between the two extremes. The variable angle wedges were replaced by small fixed angle wedges having the same incidence angle (10°), thus reducing the number of contacting interfaces between each of the transducers and the bonded plate by one from the initial count of three.

CONCLUSIONS In this work, a theoretically driven systematic approach to selection of guided wave modes for the inspection of adhesive and cohesive weaknesses in an adhesively bonded repair patch, comprised of epoxy bonded aluminum and titanium repair patch, is presented. One of the guided wave modes with large in-plane displacement at the aluminum-epoxy interface in a titaniumepoxy-aluminum bonded joint was selected for the inspection. Several repair patch samples - epoxy bonded aluminum-titanium plates - were fabricated in the lab with simulated interfacial weakness conditions. Acrylic angle beam wedges set to an angle of 10°, with 2.25 MHz transducer mounted on top was found to be able to generate interface sensitive mode in the bonded repair patch. Using a matching receiver, it was possible to distinguish between the good and bad repairs. The applicability of the selected experimental parameters over a very large range of adhesive thickness was ensured in order to keep the selection valid for a real repair patch sample where the bondline thickness can vary. Though the solution presented in this paper is specifically tailored to detection of adhesive weakness at the aluminumepoxy interface in a repair patch sample, the general approach laid here can be applied to the problem of detecting defects in any layered anisotropic media. In such a case, modes can be selected for sensitivity to the different interfaces present there.

REFERENCES 1. Raymond Pyles. Aging Aircraft: USAF workload and material consumption life cycle patterns, RAND Pittsburgh, U.S.A. 2003. 2. Alan Baker, Nik Rajic and Claire Davis. Towards a practical structural health monitoring technology for patched cracks in aircraft structure, Composites: Part A, 40 (2009) 1340-1352. Fig. 4 : The RF signals collected by placing fixed angle wedges (10°) with 2.25 MHz transducers mounted on top, across the defective and non-defective repair patches in a pitchcatch mode. A tone burst excitation source was used to pulse the transmitter. Vol. 9, Issue 3 December 2010

3. W. G. J. t’Hart and J. A. M. Boogers, Patch repair of cracks in the upper longeron of an F-16 aircraft of the Royal Netherlands Air Force. Structures and Materials Division, National Aerospace Laboratory NLR-TP-2002-294. (2002).

Journal of Non destructive Testing & Evaluation


38 4. J.L. Rose, Ultrasonic wave in solid media, Cambridge University Press, Cambridge, (1999). 5. A. Pilarski and J.L. Rose. A transverse wave ultrasonic obliqueincidence technique for interfacial weakness detection in adhesive joints, Journal of Applied Physics, 63 (1988) 300-307. 6. J.L. Rose, K.M. Rajana and J.N. Barshinger, â&#x20AC;&#x153;Guided waves for composite patch repair of aging aircraft,â&#x20AC;? in Review of Progress in QNDE, 15B, eds. D.O. Thompson and D.E. Chimenti, Plenum Press, New York (1996) 1291-1298.

Journal of Non destructive Testing & Evaluation

Technical Paper 7. A. Pilarski and J.L. Rose. Lamb wave mode selection concepts for interfacial weakness analysis, Journal of Nondestructive Evaluation, 11(34) (1992) 237-249. 8. P. Puthillath and J.L. Rose. Ultrasonic guided wave inspection of a titanium repair patch bonded to an aluminum aircraft skin. International Journal of Adhesion and Adhesives, 30 (2010) 566573.

Vol. 9, Issue 3 December 2010


39

Technical Paper

HOMC Guided Wave Ultrasonic Technique â&#x20AC;&#x201C; A new paradigm for corrosion detection Krishnan Balasubramaniam1, K.S. Venkataraman2 and Issac Anto2 1

Centre for Nondestructive Evaluation, Indian Institute of Technology Madras, Chennai-600036, India 2 ESCON Technologies, SINGAPORE 3 Dhvani Research and Development Solutions Pvt. Ltd, Taramani, Chennai INDIA 600113 E-mail : balas@iitm.ac.in ; Venkat@escon-ndt.com ; issac.anto@dhvani-research.com

ABSTRACT The paper describes the application of Higher Order Modes Clusters (HOMC), a new guided ultrasonic waves based technique. HOMC uses relatively very high frequency guided ultrasonic waves, when compared to the long range guided wave techniques, and travel in a relatively non-dispersive manner. However, the range of inspection for HOMC is relatively short, up to 2 m. The HOMC technique can be implemented in several modes, particularly Axial HOMC and Circumferential HOMC techniques. The range of applications includes corrosion detection in hidden pipe support regions, tank floor annular plate in the storage tank floor, hidden regions under flanges in off-shore structures, etc.

1. INTRODUCTION In-service degradation due to mechanisms such as corrosion at pipe supports is one of the leading causes of process piping failure. The support regions in pipes are very vulnerable to accelerated corrosion as these are sites for water logging, stress and contamination. While the long range guided waves, using the fundamental guided wave modes operating in the low frequency regimes, can be employed for the corrosion damage in pipes, the presence of sacrificial weld pads, the co-located flanges, pipe bends, etc., limit the long range techniques. In addition, it is the beam supports and the saddle clamps that have historically caused the majority of the problems.[1].

Higher Order Modes Clusters, called here as HOMC has been developed. Ultrasonic guided waves (circumferential or axial modes), once generated will be reflected from corrosion and other features on the pipe. Inspection can be carried out from the accessible portion of the pipe [6-10]. Circumferential HOMC guided wave modes are used for most pipe sizes, however, in larger diameter pipe where the support pad welded extends over nearly one half of the circumference, the Axial HOMC guided wave mode will be more advantageous to deploy.

2. THE HOMC METHOD

The ultrasonic guided waves, unlike longitudinal and transverse bulk wave modes, are a manifestation of geometrical confinement of acoustical waves between boundaries [2, 3]. In many instances, these waves travel long distances, depending on the frequency and mode characteristics of the wave, and follow the contour of the structure in which they are propagating. Usually, these waves not only propagate along the length of the structure but also cover the entire thickness and circumference (in the case of cylinders and rods). The use of guided wave modes is potentially a very attractive solution to the problem of inspecting the embedded portions of structures because they can be excited at one point on the structure, propagated over considerable distances, and received at a remote point on the structure. Applications to problems like corrosion monitoring, pipeline wall thinning inspection, weld defect detection and such industrial problems are well known [4,5].

To identify the relevant guided waves for specific applications, their dispersion characteristics and excitation modes need to be examined. Three standard ways of representing the steady state solution for guided waves are shown in Fig. 1. This solution is for a mild steel plate with the wave incident through Plexiglas. Fig. 1a shows the phase velocity curves for various modes as a function of frequency-thickness (MHz-mm) product. While the nondispersive regions are indicated by flat portions, the highly dispersive regions of the modes are indicated by steep slopes. Fig. 1(b) shows the group velocity curves for these modes. Figure.1(c) provides a convenient representation in terms of angles of excitation for each of these modes. The plot in Fig. 1c represents the incidence angle in degrees through Perspex. For instance, to generate S0 mode at 1.5 MHz-mm product Fig. 1c indicates that a 300 angled Perspex wedge needs to be used for excitation.

A new concept for the improved inspection of corrosion at the support region of pipelines using a short-range ultrasonic guided wave technique that uses a collection of

Dispersive modes are complex to work with as it involves sophisticated signal processing techniques to handle them. Non-dispersive modes are very useful in many practical NDE applications. Fig. 1b shows the group velocity curves

Vol. 9, Issue 3 December 2010

Journal of Non destructive Testing & Evaluation


40

Technical Paper

work [7,8] as these modes have higher spatial and temporal resolution characteristics than the fundamental modes. However working with HOM-GW involves dealing with complex multimodal and dispersive signals requiring sophisticated techniques for interpretation. The region marked 3, in Fig. 1c, lying between 15 MHzmm product to 35 MHz-mm product is the higher order modes cluster of guided wave (HOMC- GW) regime and forms the subject of the present investigation. Modes in this regime are found to have small differences between their group velocities and small differences in the associated angles of excitation. Table 1, constructed specifically at 16 MHz-mm product presents the various modes and associated angles of excitation through Perspex. Owing to the small differences in group velocities and nearness in angles of excitation between the adjacent modes, excitation at any given frequency â&#x20AC;&#x201C; thickness (MHz-mm) product within this regime is seen to lead to a formation of a multi modal cluster. As the various modes that take part in the cluster move with nearly the same group velocity, with the cluster appearing to move as a distinct non-dispersive envelope. It is worth noting from Table 1 that although the group velocities of the fundamental modes A0 and S0 are close to the higher order modes, their angles of excitation are distinctively different from the higher order modes resulting in their negligible contribution to the HOMC-GW.

3.

ADVANTAGES AND LIMITATIONS

The HOMC techniques have the following characteristics that favor its selection for corrosion detection: 1. The use of high frequencies that allows for improved sensitivity to smaller defects and improved resolution in imaging corrosion defects including pitting type.

Fig 1 : Disperse plot for a Mild steel plate with Plexiglas incidence. (a) Phase velocity plot, (b) Group velocity plot, (c) Angle of incidence through Plexiglas. (1) Conventional guided wave regime. (2) Higher order modes guided wave regime. (3) Higher order modes cluster guided wave regime.

for these modes. When phase velocities are difficult to measure in dispersive regimes, group velocities are measured.

2. The minimal displacement at the pipe surfaces leading to insensitivity to surface conditions. This allows for the inspection on loaded and coated structures and insensitivity to surface welds such as tack welds. 3. Non-dispersive nature of the wave mode cluster that is insensitive to subtle changes in geometry of the structures. The key limitation of the technique is the careful choice of the wedge angle and the distance of inspection being limited to approximately 2 meters.

Fundamental modes like A0 and S0 shown in Fig. 1c as region 1, are relatively easy to generate and work with in practice as these modes are well separated in time owing to their vast difference in velocity.

4. RESULTS AND DISCUSSION

The region marked 2, in Fig. 1c belongs to the higher order mode guided waves (HOM-GW) regime at a higher frequency-thickness (MHz-mm) product (3 MHz-mm to 10 MHz-mm). HOM-GW was recently exploited to look into application involving pipe support corrosion detection

4.1 Corrosion under pipe support (CUPS)

Journal of Non destructive Testing & Evaluation

There are three different techniques in HOMC that will be explained with relevance to specific applications as below.

Pipelines in process industries such as refineries and chemical plants are supported at intermediate distances by pipe supports. Corrosion is more prone to occur at these Vol. 9, Issue 3 December 2010


41

Technical Paper

support regions of pipelines due to the presence of all the key ingredients needed to accelerate corrosion like water, minerals, and the stress concentration in the presence of a crack. The common types of corrosion at the supports include corrosion spread along the circumferential or longitudinal direction of the pipe. In most cases the corrosion defect at the support locations is localized in nature with smaller pitting corrosion. In order to mitigate the corrosion to pipes at these locations, the industry often resorts to providing a sacrificial plate (often called sacrificial welded pad) that is placed in between the pipe and the support. The plate is tack welded around the boundaries of the plate. However, it has been observed that while this sacrificial pad reduces corrosion, it does not completely prevent it. The inspection of the pipe in this region with the welded pad is more difficult in comparison to the scenario without the pad. Among the various techniques used for the detection of corrosion like defect in pipelines, ultrasonic NDE plays a

Fig. 3 : Typical C-HOMC imaging Results for corrosion in pipe support locations.

major role. To perform a conventional ultrasonic inspection in such inaccessible region (i.e. at support locations), the pipes have to be lifted out of the supports, which involves complete shutdown of the flow lines and the risk of stressing a pipe that would have been already weakened by corrosion. Circumferential guided wave modes are used for most pipe sizes, however, in larger diameter pipe where the support pad welded extends over nearly one half of the circumference, the axial guided wave mode will be more advantageous to deploy. Experimental data obtained from the calibration sample with programmed defects and on field tests show that the size and location of the defects correlates well with the time-of flight and amplitude ratio of the reflected signals from the defects. A and B-scan images were used to visualise and classify the defect size and location. A Semi-Automated Scanning system called CUPS (Corrosion Under Pipe-support Scanner) has been developed and tested to ensure high speeds of inspection in line with industry requirements. 4.2 Critical Region Inspection Scanner for Pipes (CRISP) Fig. 2 : (a) The schematic of the C-HOMC technique for corrosion detection under pipe supports using HOMC guided wave technique and (b) a photograph of the pipe support with a sacrificial weld pad. Vol. 9, Issue 3 December 2010

Pipelines systems in the industries have various critical regions where the susceptibility of corrosion is very high and the possibility of inspecting them very low. Journal of Non destructive Testing & Evaluation


42

Technical Paper

These Critical Regions include, but not limited to cases as below: z

z

z

z

Under clamps - Riser Pipes - Plant piping (U bolt clamp corrosion) Soil to Air Interface - Road Crossing Pipes - Partially buried piping including Lamp Posts Protective wrapping covered region - Temporary Repair Locations with clamps or coating. Inspection of Girth Welds especially at Heat Affected Zone (HAZ).

Few of such applications are shown in Fig. 4. Conventional NDT techniques do not help in reliable inspection of these regions and very often requires, clamp removal followed by visual inspection. Techniques that provide some information do not have the sensitivity to find small defects such as localized pitting corrosion

Fig. 5 : A typical A-HOMC scanner along is shown for a tac welded region in a pipe and (b) shows the A-HOMC result showing the detection of corrosion in the pipe above the weld pad region.

Ultrasonic guided waves (axial modes), once generated will be reflected from corrosion and other features (welds, etc.) on the pipe. Inspection can be carried out all around the pipe by moving the probe around the pipe circumference. Inspection can be carried out with the scanner at distances up to 2 m, along the length of the pipe, from the region of interest. An example result and the CRISP scanner used for obtaining this result is shown in Fig. 5. Experimental data obtained from the calibration sample with programmed defects and on field tests show that the size and location of the defects correlates well with the time-of flight and amplitude ratio of the reflected signals from the defects. A and B-scan images were used to visualise and classify the defect size and location. The A-HOMC technique is capable of detecting small pin hole type defects, such as caused by pitting corrosion, as well as large area corrosion damage. Other types of defects such as cracks, weld defects, gouging damage, etc. are also imaged using the method. The presence of surface coatings such as insulation does not affect the wave.

Fig. 4 : Typical applications for the CRISP based HOMC technique. Journal of Non destructive Testing & Evaluation

A Semi-Automated Scanning system called CRISP (Critical Region Inspection Scanner for Pipes) has been developed and tested to ensure high speeds of inspection in situations where hidden regions must be inspected for corrosion detection. Vol. 9, Issue 3 December 2010


43

Technical Paper

Fig. 6 : (a) Schematic of application of HOMC technique for TAPS and (b) a typical tank floor annular plate with thinning in the critical region close to the wall.

Fig. 7 : (a) A typical result using TAPS showing corrosion near wall and (b) robotic scanner with probe holder for scanning the storage tanks.

4.3 Tank Annular Plate Scanner (TAPS)

Standard inspection techniques often involves the emptying the tanks for internal inspections, which implies large periods of operational unavailability, with expensive, time consuming and hazardous cleaning processes, involving safety issues to workers. For safety and environmental reasons, the Magnetic Flux Leakage (MFL) technique is one of the commonly used methods for carrying out this inspection. Alternatively, Acoustic Emission (AE) has also been shown to indicate regions of corrosion activity. . Accessibility to this zone of the annular plate (very close to and/or under the retainer wall) is highly restricted and hence poses difficulties when using the currently available MFL and similar floor scanning NDE methods.

Corrosion detection in the annular plate region of aboveground storage tanks is a critical need for tank farm operators in the oil and gas industry. In the case of storage tanks, since the region of the annular plate near the shellto-bottom fillet weld (both on the top and bottom side) is subjected to metallurgical change due to the irregular heating and cooling arising from the welding process, it makes the region more vulnerable to corrosion when compared to other regions. It is also observed that the maximum stress in a tank bottom exists at the toe of the inside shell-to-bottom fillet weld at the annular plate. These may result in stress corrosion cracks and/or pitting corrosion on the liquid side of the annular plate and subsequently cause leakage. The schematic of the annular plate corrosion is shown along with a typical plate with corrosion is illustrated in Fig. 7. The critical zone between the tank shell wall and the first few inches of the annular plate is difficult to inspect with conventional floor scanning methods due to the presence of coatings, uneven surfaces and a lack of access due to the presence of the weld toe. This region, however, is prone to accelerated corrosion due to the additional stresses caused by the weight of the tank wall and the increased possibility of water entrapment under the annular plate. Repairs in this region demand replacement of the entire annular plate and this leads to long shutdown of the tank, and often failures occur without any warning. Vol. 9, Issue 3 December 2010

A Robotic Scanner called TAPS (Tank Annular Plate Scanner) has been developed and tested to ensure high speeds of inspection in line with industry requirements. Typical result for imaging the detection of corrosion near the wall location in the annular plate is shown in Fig. 7.

6. CONCLUDING REMARKS HOMC-GW appears to have several attractive features for NDE applications. These are (i) tighter envelope that improves the temporal resolution (ii) shorter wavelength that improves the spatial resolution, (iii) The vanishing surface displacements of the out-of-plane component that is insensitive to surface loading, and (iv) sub-surface defect detectability. Using the new HOMC technique new applications for hidden and inaccessible regions can now be made inspectable. Journal of Non destructive Testing & Evaluation


44 REFERENCES 1. Jim Britton, “Corrosion at pipe support, Causes and solutions”, 2003 2. Meeker T.R and A.H. Meitzler, “Guided Wave propagation Elongated Cylinders and Plates,” Physical acoustics, Vol. 1 Part A, 1964, pp. 111-167. 3. Zemmanek J.JR. , “An Experimental and Theoretical Investigation of Elastic Wave Propagation in a Cylinder,” The JASA, Vol. 52, No. 1 (part 2), 1972, pp. 265-283 4. W. D. Wang, “Applications of guided wave technique in the petrochemical industry” in Review of Progress in QNDE, 18A, op. cit. (1998), pp. 277-284. 5. USNRC, “An Approach for Plant Specific, Risk- Informed Decision Making. In- service Inspection of Piping”, U.S. Nuclear Regulatory Commission, Draft Regulatory Guide DG-1063 (1997).

Journal of Non destructive Testing & Evaluation

Technical Paper 6. Wei Luo, Xiaoliang Zhao, and J.L Rose., A Guided Wave Plate Experiment for a Pipe, Journal of Pressure Vessel Technology 2005 by ASME AUGUST 2005, Vol. 127 / 345. 7. K. Shivaraj, K .Balasubramaniam, C.V. Krishnamurthy and R. Wadhwan, ASME Trans. J. Pressure Vessel Technology (2007). 8. L. Satyarnarayan, J. Chandrasekaran, Bruce Maxfield, Krishnan Balasubramaniam, “Circumferential higher order guided wave modes for the detection and sizing of cracks and pinholes in pipe support regions”, NDT&E International 41 (2008) 32–43. 9. C. Jayaraman, C. V. Krishnamurthy, and K. Balasubramaniam , Higher Order Modes Cluster (HOMC) Guided Waves – A New Technique for NDT Inspection AIP Conference Proceedings, Rev. of Prog. QNDE (Ed. D. Thompson and D.E. Chimenti) Vol. 28 1096, 121 (2009) 10. Chandrasekaran. J, I. Anto, K. Balasubramaniam and K.S. Venkatraman, Higher order modes cluster (HOMC) guided waves for online defect detection in annular plate region of above ground storage tanks, INSIGHT, 51(11) (2009).

Vol. 9, Issue 3 December 2010



jnde