Guided waves methodology application final paper

GUIDED WAVES METHODOLOGY APPLICATION IN THE ANALYSIS OF PIPELINE INTEGRITY OF PEMEX DOCKS ALONG PACIFIC COAST AND MEXICO GULF Hernan Rivera, Carlos Mares, Jorge Canto, Corrosion y Proteccion Ingeneria, S.C. Rio Nazas 6. Cuernavaca, Morelos.

Mexico. 62290.

Carlos G. López, Cecil H. Knight, Jose H. Jimenez Gonzalez, Guadalupe Corrales Gonzalez, PEMEX Refinacion. Torre Ejecutiva, Marina Nacional 329, Col. Huasteca, México, Distrito Federal, C.P. 11311.

Jorge A. Ascencio, and Lorenzo Martínez * Instituto de Ciencias Físicas, Universidad Nacional Autonoma de Mexico, Ave Universidad 1001, Col. Chamilpa, Cuernavaca, Morelos. CP 62210. *

Also at Corrosion y Proteccion Ingenieria SC

Abstract As a part of the Direct Assessment goals the knowledge of the problems allows a better decision process. In this way, the use of novel methodologies for the evaluation metal corrosion phenomena increases de possibilities of pipeline integrity analysis; one of these new techniques is the guided waves application. Particularly, PEMEX has been making efforts in order to get more information about the pipeline integrity of its network, and several cases have been studied with this methodology. Our group has participated as corrosion evaluation specialist and the experiences have shown the necessity of extra information about the technique and the involved variables, so we have improved laboratory exercises to get that kind of data.

The evaluation of pipeline integrity with the guided waves technology has become in a very useful tool for non ILI susceptible pipelines. The success of this technique is based on the capability of a continuous surface evaluation. This technique is based in the induction of mechanical vibration on the pipeline, and the evaluation of the reflections generated by the defects in both internal and external surfaces. Because the guided waves are mechanical vibrations propagated trough the pipeline, there are many factors involved in its attenuation, such as the pipeline geometry, coatings, the product inside the pipeline and the physical characteristics of the soil or the water if the pipeline is buried or submerged.

Field experiences and laboratory tests performed using the Magnetoestrictive technology developed by the Southwest Research Institute, have been analyzed to determinate the effect of attenuation caused by some specific conditions of the pipeline, the environment and the operation parameters of the guided waves equipment. The application of the guided waves in PEMEX operation docks in Northwest Pacific coast (Mazatlan), south Pacific coast (Acapulco) and southeast Gulf of Mexico (Lerma) where cases as generalized corrosion in external surfaces and pitting or certain coating types have represented a difficult for the technique application. These conditions have been reproduced in the laboratory to characterize the effect of this condition in the attenuation of the guided waves signal.

In this work, we present evidences of the mentioned corrosion cases, which are determined by using the guided waves methodology; however we are focused to determine the effect of the different involved variables in the laboratory analysis, it means the consideration of parameters associated to the pipeline and to operational conditions. This combined analysis of both laboratory studies and site evaluations allow a complete reference about the capabilities of guided waves methodology and the perspectives for application in PEMEX pipeline network.

Introduction.Hydrocarbons transportation by means of pipelines is sustained in the confidence of their operation, which is based on the consideration of systems integrity. Consequently the maintenance and prevision of incidents requires an in-field pipeline continuous evaluation in order to prevent complications derived from corrosion related problems.

In this way the risk reduction in function of the corrosion evidences analysis on the exposed pipelines (internally and externally) is really important and consequently

multiple methodologies have been proposed, from the visual inspection to the use of electromagnetic and acoustic non-destructive sources (mainly internally); as the ultrasonic one, which allow detecting zones with corrosion and also can be obtained corrosion profiles. The necessities of the pipeline industry and own evolution of the technologies have derived in the application of a new methodology that has gained attention in the recent years, because its versatility, functionality and efficiency, which is known as Guided Waves.

In the continuous effort by PEMEX Refinacion to inspect periodically the pipelines integrity, using mainly the line inspection and when is required, it use to employ alternative technologies for the analysis. In the particular case of external pipelines, metal structures are exposed to very complex environmental conditions and consequently it is convenient to find precise mechanisms that allow having the confidence in the inspections to support the operation and safeguarding of the pipelines.

In this work we resume the experience of the work Group in the inspection of pipelines of PEMEX docks in Mazatlan, Acapulco, (localized at the pacific coast) and Lerma (at the Gulf of Mexico). With help of the variety of cases, the advantages, weakness and ideal conditions for the use of this methodology in equivalent systems are evaluated. In order to understand the technique as a plausible solution for inspection complex cases, we show the basis for the methodology, field measurement examples and a resume of the identified elements that made more difficult (or impossible) the application of the Guided Waves methodology.

Studied sites.

The inspection of docks has common elements as their exposition to environment with saline conditions and equivalent temperatures, focusing the analysis in the pipelines of each one of the installations listed in table 1, for the docks of Mazatlan, Acapulco and Lerma, which have singularities that allowed to identify the advantages and limitations and particular requirements to use the guided wave technique in the pipelines, mainly for aerial ones, but with extra possibilities.

Maritime Terminal at Mazatlan 1 Universal 1 Diesel 1 Gasoline (Magna) 1 Gasoline (Premium) 2 COPE

Evaluated Installations “Port Operation Residence (POR)” y “Storage and Deliver Terminal (SDT)” at Acapulco POR 1 Diesel 2 Gasoline (Magna) 1 Gasoline (Premium) 1 Against-fire SDT 1 Diesel 2 Gasoline (Magna) 1 Gasoline (Premium) 1 Against-fire

Maritime Terminal at Lerma 1 Diesel 2 Gasoline (Magna) 1 Gasoline (Premium) 2 COPE 1 Against-fire

Table 1. Inspected pipelines in Mazatlan, Acapulco and Lerma facilities

For the different cases, because the changes in the pipes direction become a guided wave attenuation parameter, only the data obtained after one direction change are

considered, so then it is required to make a new inspection after the second direction change. In this way, the selection of inspection sites was made considering how to cover the full pipeline path without considering more than one elbow each inspection.

Another parameter that affects the capability of this technique is the condition of the pipeline surface, because in several segments along the maritime terminal the pipelines were highly wrinkled avoiding getting a good signal during the evaluation.

Guided Waves Methodology The used methodology is schematized in figure 1, which involves a field procedure with the next steps: Site selection (SS) –based on the viable conditions to the operation of the technique and the information necessities-, a visual characterization (VC) –that generates the first approach to identify substantive elements of corrosion evidences-, the equipment installation (EI) –including accessories and under required conditions-, and the analysis run (AR) –where conditions are selected in function of frequencies and adequate wave types; this field study is followed by the laboratory process, where it is considered: the value reading (VR) –from the field analysis-, a system calibration (SC) –by means of value parameterization-, the signals analysis (SA) –from the study of curves-, a data confrontation (DC) –based on the multiple wave shots-, the simplified discrimination (SD) –to exclude noise and no important signals (for our analysis) effects-, and a verification against alternative data (VD) –that allow establishing the best interpretation of data and a identification of the corrosion effects, all these together derive in the determination of evidences and corrosion profiles with high precision.

Figure 2. Guided Waves inspection methodology flow chart. SS – Site Selection, VC – Visual Characterization, EI – Equipment Installation, AR – Analysis Run, VR – Value Reading, SC – System Calibration, SA – Signal Analysis, DC - Data Confrontation, SD – Simplified Discrimination, VD – Verification against alternative Data

The main used sensor involves the Magnetoestrictive (MsS) technology, developed and patented by the Southwest Research Institute. This sensor generates and detects electromagnetic guided waves that are transmitted over the tested material. In order to generate the waves, it is considered the magnetoestrictive principle (or Joule effect) that involves a small change in the physical dimensions of ferromagnetic materials (in the order of part per million in case of carbon steels) caused by the application of a external magnetic field. The inverse effect (Villari effect) is considered, which is referred to a modification in the magnetic induction of ferromagnetic materials derived from a mechanical strain.

The equipment setup consists in the collocation of a 2� wide and 0.006� thickness metallic (iron cobalt alloy) tape (Figure 2a). The main characteristic of this material is that it can be inducted a magnetic field in any direction. The metallic tape must be adhered over the exterior pipeline surface as a ring around it. The tape must have an enough longitude to surround totally the pipe avoiding it overlap or leaving empty spaces bigger that 2mm between its ends. The tape must be in an axis perpendicular to the pipeline, and it must be placed directly over the pipeline metallic surface, so then, if this has any mechanical coating, this must be removed during the operation of the technique. In case the applied paint has a good adhesion and a low thickness, it is possible to fix the tape over the paint. The metallic tape must be perfectly adhered in its entire surface to the pipe and it is used fast dry epoxy glue, which acts as interface between both surfaces and consequently any bubble must be avoided to reduce complications in the transmission of waves to the pipeline. When the tape has been placed over the pipeline, a magnetic field is induced using a magnet, with a longitudinal sense orientation respect the tape. The reading process is based on the installation over the tape of a coil with a current that induce the magnetic field and generates the guided waves. This coil works also as a sensor for the reception of the reflected signal.

It is convenient to establish that because the waves are determined by the media, the geometry plays an important role in the behavior of the waves. In opposite to the conventional inspection systems, by ultrasonic, where the waves are propagated always in constant velocities, the propagation velocity of the guided waves varies significantly against the frequency and the media geometry. Also, for a similar frequency these can be propagated in different ways. There are three different types of waves; longitudinal, torsional and flexural ones (Figure 2b). However it is important to establish that just for the torsional waves the velocity is constant for any frequency value, so this is the preferred mode to inspect pipelines, and consequently the used by us.

Field results The capabilities of this technique to inspect the pipelines of the mentioned docks were recognized from the generated results, with the experience of very illustrative typecases, as the determination of effects of the exterior corrosion shown in figure 3 and the interior as it is illustrated in figure 4, however to understand more the capabilities of this technique, we will show a resume for the different docks.

Mazatlan.

From all the detected defects, some of them are discarded because they are signals generated by any other element as weld points, supports, etc. The rest of the defects were verified directly in the site by using a scanning ultrasonic device, capable of

detecting coating thickness and metal without needing to remove the paint. In the table 2, the resume of defects is shown that were verified and the result of such inspection.

Pipeline COPE 5 S2 COPE 5 S3 COPE 6 S2 COPE 6 S2 DIESEL S1 DIESEL S1

Symbol S1 S2 S1 S1 S1 S2

Distance (m)

Reflection (%)

Phase (%)

−4.7 6,9 −0.4 −4.3 2,1 3

1,1 2,2 9,1 2,7 1,3 4,2

−36 −78 3 −7 9 −54

Anomaly determination alter inspection External welding point Strain on support Internal metal excess Pipeline strain Thickness loss (17 %) Thickness loss (10.8 %)

Table 2. Detected defects by the guided waves inspection in Maritime Terminal of Mazatlan.

From the six verified defects of the site, it was determined that the corresponding to section 2 of COPE 5 must be an excess of material. Besides the detected defect at the section 3 of the same pipeline corresponds to a signal generated by a slight deformation induced by the pipe support. In the COPE 6 pipeline were also detected two anomalies, the first is about a metal excess on its internal surface, while the second one is associated to a metal fabrication defect, which induce a small deformation detected by the instrument; however none of them represents risk to the pipe integrity. In the Diesel pipeline of 20’’ a couple of defects associated to thickness loss were found; the first correspond to 17% of the wall total thickness and is identified in the external surface – observed as a prick and illustrated in figure 3a, with its corresponding device lecture and a detailed selected area; besides the second defect that shows a 10.8% loss and it is in the internal pipeline surface. In none of the cases the loss is significant to require corrective actions.

A

B

Figure 4. a) Localized corrosion as pitting in a diesel pipeline of Mazatlรกn; and b) generalized corrosion example in a pipeline of Acapulco. Both show their corresponding data plots.

Acapulco.

From the obtained signals we identified multiple defects, and we could establish that some of them can be discarded because they are really effects of some other elements as welding points, supports, etc. The rest of the defects were verified directly on site by using a scanning ultrasonic system, which can detect coating and metal thickness without necessity of removing the paint.

Based on the obtained analysis of the guided waves study several defects were found, mainly in the Gasoline Magna 2 and Magna 3, showing localized corrosion up to 120 thousandths of inch, that involves a thickness loss of 33%. Table 3 shows the thickness in different points of the detected zones that are associated to defects.

Nominal Thickness (inches) 0.365

MAGNA 2 Prick deepness Thickness (inches) loss (%) 0.05 14% 0.05 14% 0.06 16% 0.06 16% 0.05 14%

MAGNA 3 Prick deepness Thickness (inches) loss (%) 0.120 33% 0.090 25% 0.080 22% 0.050 14% 0.040 11%

Table 3. Average thickness along the defects of Gasoline Magna 2 and Magna 3 pipelines.

The corrosion active zones in the pipelines PEMEX Gasoline Magna 2 and Magna 3 are localized in the inferior section of the pipelines at 18.62 m. and 25.72 m. from the

discharge nucleus of the POR respectively. In figure 3b is illustrated the case of the second pipeline (Magna 3), where are also included the obtained signal. In this case, the recommendation was to follow a continuous evaluation of the dimensions along the section by using ultrasonic method for the internal defects or pit gauge for the external ones; besides to remark the requirement of corrective procedures (as section substitutions or wrapping pieces installation) in case of loss bigger than the fixed by the limits established in the valid norms.

It is clear in both cases that the contribution of the technique is important, because it allows the evaluation of corrosion effects for relatively long sections over the pipeline; however the goal is bigger the analysis of possible internal defects and consequently we are using examples of data from the Lerma (in Campeche) dock to illustrate its capability.

Lerma.

Based on the analysis of results from the guided waves inspection several defects were detected, which were verified and dimensioned with additional tools. In fact, the characteristics and dimension of the pipelines in the Lerma dock derived in the identification of a big amount of different corrosion evidences.

In order to understand these elements we must consider that in is arriving to the storage and deliver terminal, pipelines initiate an originally bury segment that allows crossing under the Campeche-Merida highway. This section has been dig up and actually the pipelines are exposed up to the limit of the highway.

The evaluation of the pipeline conditions in the highway cased cross results fundamental because this is the only point where pipes are not accessible to the direct inspection, for that very reason it generates important results by means of the guided waves technique.

In the case of beach pipelines of Lerma, we could identify that the pipeline external surface show generalized corrosion in the entire zone of the highway cross, which does not allow an adequate adhesion of the metallic tape on none place. In order to solve this, several tests were realized filling the surface, mainly with epoxy materials, that use to generate a uniform contact but they did not transmit the signals adequately, and then was impossible to reach that these were broadcasted along the pipeline.

Additionally and again in the sites where were successfully installed the test stations, the problems remain when the pipeline shows generalized corrosion, because the constant changes of the transversal section generate a big quantity of reflections that are added and cause an interference in the signal limiting the right interpretation.

The case of the COPE L1 and L2 pipelines is different, these have a FBE coating that has kept the metallic surface in good conditions, so the surfaces does not show generalized corrosion. In these pipelines were installed the guided waves monitoring stations, however the results were not satisfactory, maybe because the signal could be emitted but the attenuation does not allowed enough reaching because there are two important attenuation elements: the own product that is transported in the pipeline,

which has a high viscosity and it can absorb the energy of the induced mechanic waves in the pipeline, besides the seal used between the casing and the carrier pipeline In table 4 a resume of the defects that require more attention is shown, and consequently the most complex distinguished problems are illustrated, but without doubt the most impacting one is related to the plausible determination of internal corrosion in several sections and pipelines.

Pipeline

Diámeter

Pipeline ID section

Frecuency Hz

Distance from inspection station

Comments

COPE L1

12"

2

32

−5.8

Internal corrosion 48.33 % wall thickness loss

COPE L2

12"

1

128

−1.1

Internal corrosion 15.00 % and external corrosion 25.00% wall thickness loss. Sever generalized corrosion in bottom of pipeline

8”

1

32

−0.9

Internal corrosion 24.30 % and external corrosion 15.00% Wall thickness loss

DIESEL

Table 4. Significative detected defects in Lerma Pipelines.

In figure 5 an identified site with internal corrosion is shown, which had not been previously identified by any inspection and it was confirmed later by the ultrasonic method application; the derived signal of the study is added to the photography of the affected element A

B

Figure 5. Internal corrosion identified in the pipeline of the Lerma dock by using the guided waves technique and its local confirmation.

In the case of the different inspections, the results are evident and can be distinguished the advantages associated to the technique, which will be listed below; however it is convenient also to establish the complexities for its implementation, which are basically related to: •

The necessity of having an accessible pipeline; because when the sections inundate –as it is shown in figure 6a- is impossible to analyze the structure. The experience with pipelines that use to be inundated demonstrated the impossibility the application of the technique.

•

•

•

The pipeline geometry and surface regularity for the metallic tape setup becomes really relevant, so in cases as the illustrated in figure 6b the application of the technique is restricted, and epoxy resins allow adapting the Fe-Co tapes for certain cases and it is possible to obtain results, under limited conditions.

The existence of straight sections, without accessories, because when these are present as in figure 6c, the capability of the technique is restricted and the necessity of multiple shots is increased elevating the required time and resources to use.

The presence and homogeneity of coatings becomes important too, because similarly than for the geometry problems, these induce complications for the device installation as in cases as shown in figure 6d; these problems derive into a limited production of results and the implementation of the technique requires an extra of skills for the fitting as in the mentioned cases for irregular surfaces.

A

B

C

D

Figure 6. Complications for the application of the guided waves technique. a) sites with limited access, b) irregular surfaces, c) present accessories and d) coating and pipeline damage.

Laboratory results In addition to field experience, a 4” pipeline was installed in a test field to verify the effect of coating and earth in the signal attenuation. The test pipe is an interface air – earth section and some defects were induced to the segment.

Inspections were performed before and after the application of the RAM-100 coating over the external surface of the pipeline section in the interface. For comparative

purposes the location of the test station and all the equipment operation parameters were fixed for all the inspection runs.

Table 5 selected operation parameters for all the inspection runs in the test field

In the firs part of the experiment the test station was installed in the interface region of the pipeline. In figure 7a it is possible to identify several defects and the elbow weld in both upper and lower direction changes conducting the inspection over a bare pipeline.

In figure 7b, after the RAM-100 coating application, the attenuation is very strong so it is not possible to detect any of the defects or elbow welds from the same test station location. In the second case the coating was removed from the pipeline in the area of the test station setup, so the metallic tape was directly attached to the bare metallic surface.

Figure 7 Guided waves inspection results a) with bare pipeline and b) after RAM-100 coating application in the interface

The second experiment consisted in installing a new test station over the aerial pipeline away from the interface coated section. The intention was to determinate if the attenuating coating effect is not related to the test station location but only to the coating in the inspected section.

Opposite to the expected results, figure 8a shows that it is possible to detect reflections from defects and welds present in the coated area if the signal origin is set away from the coated area. In the other side, the attenuation of the signal is higher if the origin of the Guided Waves is set over the RAM-100 coated area (even if the coating is removed in the test station stripe.

Figure 8 Guided waves inspection results a) with test station setup away from coated pipeline area b) with test station setup in the coated area.

Conclusions and perspectives With help of the experience of more than 300 shots over the variety of characteristics for the different docks, we can conclude that this technique is very useful for the inspection of relatively long sections of pipelines, which must be free of accessories and with no more than one direction changes, also with regular surface and it operation is better in presence of well preserved coatings because the importance of a good contact of the metallic tape over the whole circumference of the pipe. However, there are also several correction methods that can be used to solve the original problems of the sites, as the use of epoxy resins on irregular surfaces and multiple shots when there are accessories, between some other that can be designed during the operation.

We can also determine that the main distinguished advantages of the guided waves technique can be associated to: •

Capability to make a continuous inspection along pipeline segments, instead the necessity of punctual analysis for ultrasonic devices. This is particularly important to identify the most of the corrosion problems with a bigger spread, reducing the probability to omit important sites and also to increase details for a study of the evolution and segmental profiles.

•

Capability of identifying bigger thickness losses than 5% of the pipeline transversal section, which could appear with no generalized corrosion on the surface.

•

This can be focused to sites considered as highly critical, where it is possible to install permanent stations for a periodic monitoring procedure or even for a whole section, deriving into real time results and with high confidence. This for remote sites and for critical sites, where the own environment and pipeline conditions are identified.

•

Capability to discriminate signals reflected by welding points or accessories in the pipeline, which reduce the mistake probability and help in the interpretation of corrosion profiles.

After the important information obtained for this technique, and the satisfaction of the PEMEX personal, we can identify multiple perspectives of application, and this motivate or involving in the related parameters to exploit better the capabilities of the technique. In this way we can recognize opportunities to impact in the inspection of •

Aerial and submarine installations, where the tape can be installed and the pipeline is straight as it is required in general for this technique.

•

Partial analysis of bury pipelines, with the limitation of short distances and depending of the own land conditions.

•

Pipelines installed at big height where the operation of other systems becomes complicated and where the installation of the guided waves devices is relatively accessible.

•

Internal analysis of pipelines with casings, where the own geometry and conditions involve the impediment for other thechniques.

•

Evaluation of earth-air interfaces, with an important contribution to the corrosion profiles in the sections where the media difference use to induce significant problems.

The laboratory test show that it is possible to inspect a RAM-100 coated interface (where corrosion is highly expected because of oxygen concentration difference) by seting up the test station away from the RAM-100 coated area (i.e. over the aerial section of the pipeline) In fact, the success of the implementation of the guided waves technique was well established and the perspectives of application are clear, but also the plausible

contribution in the development of the own methodology and the exploiting of it derive in the identification of laboratory task for our group and whom are involved in the application of this relatively new inspection technology.

References.