Page 1

OCTOBER 1988 JOURNAL OF THE AUSTRALIAN WATER AND WASTEWATER ASSOCIATION


EXECUTIVE DIRECTOR P. Hu ghes P.O. Box A232 Sydney South 2000 (02) 269 68 14

FEDERAL PRESIDENT M. Dureau , P.O. Box 152, Nort h Ryde 2113 (02) 887 2555.

water

ISSN 0310 - 0367

Offi c ial Jo urnal

AUSTRALIAN WATER AND WAST EWATER ASSOCIAT ION

Vol. 15, No. 4, October 1988

FEDERAL SECRETAR Y G. Cawston Box A232 P.O. Sydney Sth ., 2000. (02) 522 1148

CONTENTS

FEDERAL TREASURER J. D. Molloy, Cl· M.M.B.W. G. P.O. Box 4342, Melbo urne 3001, (03) 615 5991

BRANCH SECRETAR IES Canberra, A.C.T. M. Sharpin, Wi l lin g & Part. , P.O. Box 170, Curtin , A.C.T. 2605. (062) 815 811

New So uth Wales Mrs S. Tonkin-Hill , Sinclair Knight & Part. 1 Chandos St. , St. Leonards, 2065, (02) 436 7166

Vi cto ri a J . Park, Wate r Training Cen tre, P.O. Box 409, Werri bee, 3030. (03) 74 1 584 4

Que ensland D. Mac kay, P.O. Box 41 2, West End 4102. (07) 84 4 3766)

South Au stralia

My Point of View- Trevor Richards

5

Association News and Comments ... . .... .. .. ... . . .. .... . .. .... .

6

Domestic Wastewater Treatment and Disposal .. . .... .. . . . ....... .

15

IA WPRC News ..... . ............ ..... . . . ... .. ... ... .... ... .. .

16

Industry News and Personalities

17, 18

Sydney's Aqueous Waste Treatment Plant -E. Samuel . . . .. .. ..... . .. . .. . .. ... . . .................. .

20

PIPES AND SEWERS FEATURE: Selection of Materials for use in Water Distribution -T. J. Richards ...... . .......... ... . . ... . . .. ..... , .... . . .

24

Determining the Most Economical In-ground Pipe Material -D. J. Murphy . . . .. . . . ..... ... . ........... . .1.

. . . . . . .. ... .

28

Corrosion Protection Systems for Grey and Ductile Iron Pipes and Fittings -D. M. F. Nicholas . . . . .. ... . .. . . ...... ... . .......... . . . . .

32

Large Flexible Plastic Pipes Installation Procedures in Sydney -F. Tapia . .... .......... . . .. . ..... . ... . .. . . . . . ......... .

34

Sewer Condition Evaluation - The U.K. Experience -D. Fiddes ..... .. .... ... ............... .. ... ... .. . .... .

36

Reticulation Sewer Rehabilitation in Melbourne -M. J. Anderson, W. Page, J. C. Parnell, M. J. Poulter, R. J. Vass ... . . ..... . .... .. .. . ....... .. .... .

40

Plant • Products • Equipment . .. . . .... ....... ... ......... ... . .. .

45

Conferences, Exhibitions ..... . . . .. ...... . ... . .... . .......... . .

48

Calendar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

49

R. Townsend ,

State Wa ter Laboratories, E. & W.S. Private Mai l Bag , Salisbury, 5108. (08) 259 0244

West ern Au st ralia A. Gale, Binn ie & Part P/L, P.O. Box 7050, Cloisters Square , Perth 6000 (09) 322 7700

Tasmania A. B. Denne P.O. Box 78A , Hobart 700 1 (002) 30 5562 Northern Territory P. Abbey , P.O. Box 37283 Winnel lie , N.T. 5789. (089) 89 7290

EDITORIAL & SUBSCRIPTION CORRESPONDENCE G. R. Goffin , 7 Mossman Dr., Eag lemont 3084 03 459 4346

ADVERTIS ING Ann Sykes Appita 191 Royal Parade, Parkville 3052 03 347 2377

COVER PICTURE The recently commissioned liquid waste disposal facility of the Sydney Metropolitan Waste Disposa l Authority. The operation of the facility is described in a paper in this edition. As constructed, the p lant has a peak capacity of 72 000 tonnes /year on a five day week, 24 hour day basis. The p lant will treat the wastes rece ived so that they can be discharged to sewer and any residues can be safe ly landfilled or recycled. Fron t cover donated by th e Metropoli tan Waste Disposal Auth ority, Sydney. The statemen ts made or opinions expressed in 'Wa ter' do not necessarily reflect the views of the Aus tralian Water and Wastewater Ass ociation, its Council or committees.

WATER October, 1988 . I


Domestic Wastewater Treatment and Disposal - Options for Dnsewered Areas A one-day seminar held o n 24 J une 1988 by th e South Austra lian Branches of th e Australi an In stitute of Health Surveyo rs and th e Australian Water and Wastewater Associati on at th e State Gove rnment Conventio n Centre, aroused considerable interest. T he semin ar was well attended by about 185 delegates fr om a vari ety of engineering, scientific, health surveying and master plumbing backgro unds.

OPENING T he Semina r was o ffi cially opened by th e Ho n . Don H opgood, Deputy P remier of South Australia, Minister of Wate r Reso urces and Minister for Environment and P lanning. H e stated tha t the semin ar was a timely and necessary exercise in view of the Governm ent 's two-year Mo un t Ldfty Ranges Review stu dy which ·examines land use and all aspects of pollution in th e Mount Lo fty Ranges. He stated that Adelaide itself was well served by a sewerage scheme with treatment of the sewage at fo ur maj or treat ment wo rks. Major co un try towns we re also serviced by sewerage, with some of the smaller towns havi ng comm on efflu ent drainage schemes (CEDS). In the remaining areas, th e use o f septic ta nks with soakage trench was th e predominant method of wastewater disposal. Ge nerall y these worked we ll , but in certa in a reas such septic tank systems had fa iled res ul ting in efflu ent fl owing over pro pert ies and in to adj ace nt streets, creating a n aes th eti c nuisance and a public health hazard.

DOM ESTIC WASTEWATER - THEORY, LEG ISLATION AN D PRACTICE Dr Ian Law of the consulting engineering firm of Camp Scott Furphy, Sydney, was the first speaker and prese nted an in formative talk on septic tank systems, their princip les and pro blems. He pointed out that the septi c tan k/ soil abso rptio n system for onsite domesti c wastewater treatment will be around for a good number of years still. P ro blems assoc iated with such systems were often associated with the efflu ent disposal system and not the septic tank . Further development and interest should therefore foc us on efflu ent treatment and disposal with some of that development now evident in the number of septi c tan k aeration systems which are available in A ustralia. Neil James of th e South Australian H ealth Commission then presented comprehensive details of the new septic tank guidelines for South Australia, which were introduced by th e Commission on 1 June, 1988. T he main changes were an increase in the size of septic tank for a dwelling of up to three bedrooms and a maximum number of six persons, fr om 1620 litres to 3000 litre and for a length of 45 metres o f soakage uni ts. Considerations in evaluating th e sui ta bility of septic tank systems were soil class ification , land slope, fl ooding, seasonal wate r table, and depth to bedrock . H e also presented a number of suggestions in th e use of septic tank/ soakage systems on a variety of housing blocks, as well as drawings of vari ous system components. Trevo r Teakle, Senior Building Inspector and H ealth Surveyor from the Onkaparinga Distri ct Council presented a provocati ve talk entitled 'A view from Local Government ' in which he outlined certain defi ciencies in the current system of appro val, installation , operation a nd maintenance of septic ta nk systems and expressed th e view that Local Governm ent should deal with all aspects of septi c tank install ati on and wastewater disposal, as a total environmental health pac kage ad ministered by qu ali fie d health surveyors. 'Segregated Waste Systems' was th e title of the las t paper of th e morning session by Phillip Geary o f Cro ft and Associates of Newcastle. H e discussed the possibility of segregati on of household was tes into ' blac k ' and 'grey' wa ters with the appropriate disposal meth od fo r each type of was te . ' Blac k' wa ters or toilet wastes co uld be treated in composting, incineratin g or chemical toilets and th e advantages a nd disadvantages of th ese uni ts were also discussed .

Dr Scott Cameron, SA Branch President , A WWA, Mr Kev in Hayley, SA Division President , AIHS, and Dr Don Hopgood , SA Deputy Premier and Minister of Wa ter Resources viewing proceedings of the Seminar.

TREATMENT AND DISPOSAL ALTERNATIVES Douglas H awk ins outlined th e use of sand filt ers as a treatment medium for septic tank efflu ent. H e presented details of the design , performance, supervision and maintenance of these systems based on his extensive experi ence in his job as Manager, Health and Regulatory Services at the City of Doncaster and Templestowe, Victoria. T he use of artificially created above-ground mounds as a soluti on fo r on-site septic ta nk efflu ent treatment and disposal in areas with slowly permeable sub-soils and S€asonally high ground water tables was th e topic of the next paper, presented jointly by Dr Joost Brouwer and Dr Rob ert van de Graaff, both fro m Victoria . T hey emphasized th e need for proper design, construction and maintenance of these systems if th ey are to give satisfactory operati on . Mr Leen va n Lien , Regional H ealth Sur veyor , Department o f Health , NSW , presented a paper on th e use of aerobic treatment systems fo r treating th e efflu ent fr om septic tanks and its disposal by irrigation on site. H e described the various stages o f these units, th eir operation and th e problems ass ociated with their perfo rmance and maintenance, as well as some suggesti ons for improvement. T he first system was installed in NS W in 1983 and it is estimated th at th ere are now 2000 installations in that state, with up to eight manu fact urers and more th an 20 approved designs. T he last speaker for the seminar , Dr Gordon Sewards o f Binnie and P artners in Melbo urne, reviewed a number of low-cost sani tation options such as vacuum sewers, variable grade gravity sewers, se ptic tank efflu ent pumping and the use of grinder pumps for a pressure sewer system. H e discussed the advantages and disadv antages o f each option as well as giving indicative construction and operating costs. In closing th e seminar, Kevin H ayley, President of th e Australian Institute o f H ealth Surveyors, expressed apprec_iation to all th e speakers, to the session chairmen, T rent Caust and Neil P almer, and to the O rganising Committee (Michael Makestas and Lee Morgan) fo r th eir efforts in arra nging th e Seminar. H e also thanked th e 10 companies which had mounted comprehensive trade displays o f aerobi c treatment systems, various compositing toilets, septic tanks, pumping and UV disin fection equip ment.

PROCEEDI NGS In summari zing, th e seminar provided a much needed and timely fo rum for discussio n on the current practices and an up-date on new developments fo r those interested in solutions to domesti c wastewater disposal in unsewered areas. A com plete set of semin ar papers is available and can be obtained fo r $25 (postage included) fr om th e Secretary A W W A (SA Branch) , State Water La boratory, Private Bag, Salisbury 5108, Telephone (08) 259 0211 · Michael Makestc;>s • WAT E R October, 1988- 15


SYDNEY'S AQUEOUS WASTE TREATMENT PLANT Errol Samuel INTRODUCTION Sydney produces about 700Jo of the secondary industrial output of New South Wales. In manufact uring processes, ind ustry produces a relatively small quantity of liquid wastes that are not suitab le for discharge into the sewerage system. For example, in Sydney in 1986, alt hough industry discharged 153 000 ML of effl uent in to the sewerage system it also prod uced 62 ML of industrial liq ui d waste whic h requ ired off-site disposal. Liquid wastes may not be perm itted to be discharged into the sewerage system for a variety of reasons, including potential damage to the system or to treatment plants at the end of the system, risk to maintenance workers, and deleterious impact on the environment. Examples of such wastes are spent acids and alkalis, in terceptor pit wastes, spent degreasing baths, water was hings contaminated wit h oils, solvents , solids, or heavy metals, etc. Where these wastes cannot be economically treated at the generators premises they are removed in road tankers for off-site disposal. T he majority of these wastes are currently disposed of in the Metropolitan Waste D isposal Aut hority's (MWDA) secure landfill operation in Sydney's northwest, known as the Castlereagh Depot. While more than 1000 d ifferent companies use the Castlereagh Depot each year, 850Jo of the waste is produced by some 200 major manufacturing companies. The main producers of industrial liquid wastes are the light-metal processing ind ustries (27%), the chemical and pharmaceutical ind ustri es (1 7.5%) and the paint industry (80Jo).

LIQUID WASTE MANAGEMENT PLAN The MWDA's strategy with regard to the disposal of industrial liquid wastes is: • to encourage recycli ng of selected wastes and waste exchange between companies to the maximum extent possible; • to ensure that all industrial liquid wastes which cannot be reclaimed and re-used will be converted to a chemical form which presents no hazards to the environment when disposed of in a lan dfill or discha rged to th e sewerage system . With regard to its second objective, the MWDA considered that a plant that wou ld collectively treat the wastes prod uced by industry wou ld be the most cost-effective solut ion.

Errol Samuel is Liquid Waste Manager with the Metropo litan Waste Disposal Authority. He is also a Federal Councillor of the A WWA, representing the NSW Branch.

The second phase res ul ted from the need to find an a lternative to incineration for disposal of hydrocarbon-co ntaining sludges. This investigation ultimately res ul ted in the deve lopment of a process for recovering hydrocarbons from sludge. The processes referred to above have been patented. (Australian Patent No. 546677, 1985) .

THE AQUEOUS WASTE PLANT Wastes produced in Sydney fa ll into four broad categories: acids, alkalis, aqueous and combustib le. The quantity of waste produced fluctuates markedly from day to day and year to year. For example a weekly receival rate can exceed the annua l average by 400Jo and da ily variations are far higher. During the des ign and constru ction phase of the plant annual waste generatio n rates increased from 46 000 tonnes/year to about 62 000 tonnes/ year, a 33 OJo increase . Taking the above fluctuations into account it was decided to build a plant wit h a peak design capacity of 12 000 tonnes/ year on a 5 day/ week, 24 hour/ day basis . Should waste generation increase significantly with time, plant capacity co ul d be sign ifica ntly increased by operating on a 7 day/ week basis, with some 1 ampli fication of certain parts of the plant. Fluctuations in the daily waste receival rates are evened out by the provision of two weeks of waste storage capacity (2300 tonnes).

AQUEOUS WASTE PLANT

PLANT SITING Although there is general pu blic acceptance of the necessity for a faci li ty for the treatment of industrial liquid waste, obtaining development approval is a major task because of the NIMBY (Not In My Back Yard) syndrome. The MWDA lodged its first development application in March 1982 and only in its third attempt, and after a Commission of Inq ui ry, was approval obtai ned in October 1985 for construction of a plant at Hill Road, Lidcombe . During the siting process the MWDA recognised that there was significant public opposition to incineration because of the possibility of it dealing with intractable wastes. It was therefore decided that the treatment plant would not include incineration an d this led to research into alternative processes.

RESEARCH INTO TREATMENT METHODS The wide variations in the nature of the waste requiring disposal made extensive testing of the proposed treatment processes essential. Therefore, in 1977 the MWDA established a pilot plant at its Castlereagh Depot. The first phase of the research work concentrated on the treatment of aqueo us waste with the objective of prod ucing a liquid effluent that was suitable for discharge to sewer, and hydrocarboncontaining sludges (from centrifuging and disso lved air flotation) that could be incinerated . 20

WATER October, 1988

1. 2. 3. 4.

Entrance Weighbridge Car parking Administration Building /including Laboratory & Offices) 5. Covered Tanker Discharge Area 6. Receival Area /including Degritting, Screenings & Storage). 7. Aqueous Waste Storage Area 8. Combustible Waste

10

0

Storage Area

9a. Acid Storage Area 9b. Alkaline Waste Storage Area 10. Firewater Storage Tank 11. Cooling Tower 12. Effluent to Sewer Storage 13. Workshop 14. Aqueous Waste Processing Building (including Centrifuges, Filter Press, Polyelectrolyte Tanks and Recovery Plant) 15. Lime Silo & Slaker 16. Acid Neutralisation

Io'ii'o) 17. Acidification & OAF 18. Thickener (Hydroxide Sludge) 19. Filter Cake & Recovery Plant Residue Storage 20. Electricity Substation 21. Thermal Oil Area 22. Float Storage


The plant will treat the wastes received so that they can be discharged to sewer and so that any residues produced during the treatment process can be safely landfilled or recycled. A combina-. tion of conventional unit processes and unit operations are used to break down the waste feed stocks into : • Clear, oil-free water which wi ll be discharged to sewer; • Metal hydroxide filter cake which will be landfilled; • Recovered hydrocarbons which will be recycled as a fuel ; • Char (solid) wh ich wi ll be landfi lled. The processes used to treat wastes are described below and reference should be made to the process schematic and plan of the plant.

such that a high BOD discharge was perlillissible into a trunk sewer rather than construct an on-site biological treatment plant for reduction of BOD. This was mainly because pilot plant studies indicated that the varied nature of the waste would result in operational problems for such a treatment plant. The underflow from the thickener (mainly iron and zinc hydroxide) contains about 40Jo solids and is dewatered in an automatic filter press at a pressure of 14 atmospheres. Preliminary filtration tests indicate that the cake will have a dry solids content of between 35-400Jo and its discharge properties are excellent. The filter cake is transported by conveyor to a filter cake silo, from where it is discharged into trucks for removal to landfi ll .

Waste Receival All tankers delivering waste to the plant are sampled. The samples are examined in the laboratory to ensure that the waste is compatib le with the plant's treatment processes and to determine into whic h storage tank the waste should be discharged. The tankers then proceed to the plant's elevated discharge area where they couple up to hoses provided by the plant and discharge their waste by gravity. Removal of gross solids is achieved by processing aqueous wastes through trammel screens and acid and alkali wastes through sieve bend wedge-wire screens. The screens selected have a lready successfully processed over 200 tonnes of waste. Screened aqueous waste is settled to remove grit and is then pumped to above-ground steel storage tanks. Acid and alkali wastes are pumped directly to storage. The storage tanks, in addition to providing essential buffer capacity, also average out the properties of the waste thereby facilitating treatment.

Treatment When an aqueous waste storage tank is full its contents are examined in the laboratory to determine the chemicals needed to ensure optimum treatment. After dosing, the aqueous waste is pumped at a controlled rate to a decanter centrifuge for separation of solids. Flocculation with a polyelectrolyte is essential for the effective operation of the centrifuge which separates the waste into a centrate (consisting of oi1, water and a small percentage of solids) and an oily sludge that, on average, consists of 550Jo water, lOOJo solids and 350Jo oily material. The sludge has a paste-like consistency and is pumped to the recovery plant to recover its hydrocarbon content. The centrate overflows to an acidification reactor where it is dosed with waste acid to reduce the pH to between 3 and 5 so as to break down any oily emulsions which may exist. Hydrocarbons and solids remaining in the centrate are then removed by dissolved air flotation (DAF). The float produced by the DAF plant is pumped to the recovery plant for processing. The clear liquid leaving the DAF plant is free of oil and solids but contains dissolved heavy metals (mainly iron and zinc) . These metals are precipitated as their hydroxides by adjusting the pH to between 8.5 to 9 with lime or waste alkali. Precipitated metal hydroxides are separated by settling in an 18 m diameter thickener, the overflow from which is discharged to the sewer. An emergency control system can adj ust the pH of the thickener overflow to ensure it remains within the Water Board's limits. The water discharged from the plant will meet all the Water Board's standards with the exception of BOD. The latter is a negotiable stand ard and the MWDA preferred to locate its plant Treatment Processes

Neutr9liu11on

Preclpitallon

>---,,-...,~.Ellluerd

Sedimen1a1lon

Fillratlon

Filler Ceke 1ol.M"Clllll Recovered Fuel

Res idues to lendUH

Screening1 1ol.ardllll

Hydrocarbon Sludge Treatment The sludge produced by the centrifuge and float from the dissolved air flotation plant will be fed continuously to the recovery plant. In this plant the water and low boiling hydrocarbons in the feed are evaporated in five scraped surface heat exchangers which are heated by heat transfer oil at a temperature of 300°C. The vapours produced in the evaporation process are condensed and the condensate separates into its water and hydrocarboncontaining components on standing. The water thus produced is returned to the acidification reactor and the hydrocarbons are available as a lo w viscosity, clean, high calo rific value fuel. Inert material in the centrifuge sludge, together with some high boiling hydrocarbons and carbon-containing materials produced during the heating process are produced as a light brown to black solid residue or 'char' which can be safely landfilled. The heat transfer oil referred to earlier is heated by either natural gas or recovered hydrocarbons. Because the recovered hydrocarbons may contain chlorinated hydrocarbons such as trichloro-ethylene and some inert material the flue gas leaving the hot oil heater is scrubbed for removal of hydrochloric acid and particulate material.

NOVEL FEATURES ' Wherever possible, off-the-shelf, proven technology or equipment has been used in the plant. There are, however, a number of items of plant that (to the best knowl<,dge of the author) have not been used in a similar duty or have been used in Australia for the first time. These are as follows: • a bin transport system utilising the dinosaur hydraulic roll on/ roll off container system; • an automated, high pressure, cloth washer on an automatic filter press; • scraped-surface heat exchangers of the hollow screw type; • a silo for storage of filter cake.

PLANT MAINTENANCE The maintenance philosophy of the plant reflects the overall objective of the plant, i.e. to provide an uninterrupted service to industry at minimum capital and operating costs consistent with meeting specified treatment standards. The main features of the philosophy adopted were: • those items of plant that were likely to require a high level of maintenance (e.g. pumps) or have extended repair times (e.g. centrifuges) would be duplicated. Major items of plant would not be duplicated . • in selecting equipment, capital and operating cost and proven history on a similar duty were all taken into account. • maintenance of the plant, and in particular all specialised maintenance, would be contracted out as far as possible. During the tender-evaluation period maintenance contracts for equipment being offered was discussed with tenderers. • the amount of breakdown maintenance would be minimised by installation of a computerised maintenance system for planning and control of preventative maintenance. The system installed is Mainpac. It is micro-computer based and uses the Xenix operating system. The cost of hardware, software and data base preparation was about $110 000. • on ly very limited maintenance capability is maintained within plant staff and is used primarily for undertaking relatively small tasks and emergency breakdown work. CONTINUED ON PAGE 30 WATER October, 1988

21


SELECTION OF MATERIALS FOR USE IN WATER DISTRIBUTION T. J. Richards SUMMARY Selection of materials for use in water di s tribution requires a t h oro u g h knowled ge of both the system requirements an d the properties of the vario us materials. Examples are used to demonstrate the importance of these poihts. The logical approach to pipe materials selection developed by WRc Engineering is outlined.

INTRODUCTION This paper looks at some of the factors that should be considered when selecting materials for use in wate r supply distribution systems. Most of the examples considered relate to pipe materials, because they are of particular interest and they represent the major part of the cost of a new system, but the general principles apply to all materials used. A designer selecting a material is faced with a number of seemingly simple questions, such as: â&#x20AC;˘ Will the material do the job? â&#x20AC;˘ How long will the material last? â&#x20AC;˘ How much will the material cost? While the qu estions are simple, the answers are often very complex. This paper looks at some of the answers and outlines an approach to materials selection developed by WRc Engineering, U .K ., which is based on a know ledge of the limitations of the availab le materials.

WILL THE MATERIAL DO THE JOB? Th is question immediately leads to "What is the job? ". In the simplest sense the function of a pipe material is to convey water from one place to another; however, the pipe has to withstand the particular stresses imposed on it and, in the case of pipes used for drinking water, must not contaminate the conveyed water. The job needs to be specified carefully. Materials suitable for use in certain applications may be totally unsuitable fo r use in others. To illustrate the need to define the requ irements carefully two examples are considered - the use of uP VC pipe where cyclic pressure surges are expected and the effect that pipe materials may have on the conveyed water.

Pressure Surges and uPVC Pipes The method used to calcu late the wall thickness o f uPVC pressure pipes is outlined in the standards for these pipes (AS 1477.1 - 1988). A design or safety factor of 2.1 is app lied to the extrapolated 50-year burst stress and the wall thickness is selected to ensure that the hoop stress in the pipe at the nominal working pressure does not exceed this hydrostatic design 24

WATER October, 1988

stress. On this basis uPVC pipelines should have an indefinite life when operated at pressures below the nominal wo rking pressure. Yet there are uPVC pipelines wh ich have fai led within 20 years of installation . One factor that can lead to premature failure is neglecting to consider the effect of surge pressures, resu lti ng from the operation of valves and pumps, on the material. Many designers underestimate the effect of surge pressures in pipelines, particular ly in uPVC pipelines where the low stiffness of the materia l is usually thought to mean that the maximum stress caused by water hammer will be low (James Hardie & Coy, 1978) . One common approach in selecting the class of pipe has been to estimate the maximum possible static head and to allow an add itiona l amo un t, say 20 m, for water hammer. Field measurements (Creasy and Sanderson, 1977; Kirby, 1980) on uPVC rising mains have shown that the peak ma xi mum and minimum press ure s associated with switching on and off pumps can be much higher than 20 m in some cases the peak pressure was nearly twice the static pressure. In a material whic h can fai l by fat igue as a result of repeated cyclic pressure surges, such as uPVC, it is important to define the expected operating conditions carefully. The correct class of pipe can then be selected after taking into consideration the likely range of pressures and the number of pressure cycles expected during the estimated li fe of the pipe (B .S. I., 1977). By ensuring that the service conditions are carefu lly defined, i.e. that the " job" has been specified correctly, it is possible to select an appropriate class of uPVC pipe which should give satisfactory service for the design li fe.

Pipe Materials and Effect on Water Standards for plastics pipe materials ge nerally include an "Effect on Water" clause. In many cases this is worded in general terms, e.g. the pipe material must not cause the conveyed water to have any objectionable taste, odo ur or colour and toxic constituents should not be leached from the pipe material by the conveyed water . Other pipe materials are not normall y subject to "Effect on Water" requirements. There appears to be no good reason why all pipe materials should not meet similar requirements. The Standards Association of Australia has recently set up a new Technical Committee, CH/ 34, 'Materials in Contact with Drinking Water'. This Committee has been established to develop a standard test method for leaching potentially toxic components from manufactured materials in contact with drinking water. It was seen to be important that a uniform approach

Trevor Richards

Trevor Richards is a Materials Engineer with the Rural Water Commission of Victoria . He represents the Co111m ission on a number of Standards Australia committees and is chairman of the technical committees dealing with polyethylene p ipes and fittings and uPVC pipes and fittings. shoul d apply to the testing of all pipe materials and to other materials such as paints and rubber rings. This method has been used overseas, for example in the U.K. (WRc, 1984, WRc, 1984b ; WRc, 1985), and internationally there is considerab le interest in t he deve lopment of standard test methods. A second problem that needs to be considered is how to assess whether the substances leached from a pipe material are present at a concentration that could be considered dangerous. T he tendency in the past has been to use the WHO G uideline Values (WHO, 1984) as the limiting concentration of the various species in the test water . There are two problems with th is approach the Guideline Values were developed as criteria for assessing the suitability of a supply water and represent allowab le concentrations for life- long expos ure, and many of the potential contaminants which could be extracted from pipe materials are simply not listed. Tests for organoleptic parameters, such as taste and smell , are more difficult to define but need to be forma lised. At this stage it is virtually impossible to decide whether any pipe material can do the job of conveying water without contamination because there is no clear picture of what constitutes contamination.

HOW LONG WILL THE MATERIAL LAST? With the growing awareness of the asset value of water distri bution systems the tendency in recent years has been to expect or demand longer service li ves from pipe materials. Many authorities are now designing systems on the basis of a minimum useful life of 100 years and are requiring manufacturers to demonstrate that their products can last that long . There is certainly nothing wrong with the concept but it is only possible to predict when failure will occur if the way in which failure will occur is known. No


amount of accelerated testing or mathematical prediction will work if the failure mechanism that occurs in practice is different from the method that is observed in the test. An example that demonstrates this is the interpretation of pressure tests on uPVC pipes.

Start

Yes

Yes

Pressure Tests on uPVC Pipes The properties of mo st plastics materials depend on the time scale of the experiment used to measure the property. This needs to be taken into account when designing plastics pipes with expected useful lives of 50 or 100 years . The pressure which, if app lied continuously for 100 years, will cause failure at 100 years is considerably less than the pressure which is required to cause failure in five minutes in the laboratory. To establish the relationship between the burst strength of plastics pipes and the time to failure it is usual to carry out a series of pressure tests and to plot the results to give a stress regression time which can be extrapolated to predict the burst strength at the required future time, usually 50 years. As indicated above, a safety factor is then applied to the 50-year burst stress to give the hydrostatic design stress, which forms the basis of calculation of pipe wall thickness (AS 1477-1973). There has been some concern in recent years about premature failure of uPVC pipe. The field failures were invariably brittle wh ile fa ilures in the laboratory were always ductile, with extensive swelling of the pipe prior to final bur.st. It was clear that different mechanisms were involved. A considerable amount of work in the U.K. (Marshall and Birch, 1982) demonstrated that the toughness of the pipe material (which is related to the processing conditions) has a considerable effect on the way the pipe performs in service. Brittle fracture is associated with low toughness pipe. Pressure tests cannot be used to determine whether a pipe sample has adequate toughness because the stress state introduced into the material by the internal pressure does not favour brittle fracture. A test to measure toughness of uPVC pipe has been included in BS 3505 (BSI, 1986) and some British manufacturers have promoted their product on the basis of the improved toughness shown up by this test (Lyall, 1987). Tests on a locally produced pipe which failed after 10 years service (Truss, 1985) showed that the premature failure could be explained by the lo w toughness of the pipe material.

Failure of Ductile Iron Pipe In contrast to those of uPVC, the mechanical properties of ductile iron are usually considered to be independent of the time of measurement. A rapid hydrostatic pressure test on each pipe durin g manufacture is sufficient to demonstrate that there are no hidden defects in the cast pipe which could cause premature failure .

Yes

Yes

No

Yes

Yes

Addkional fimkafions for A.C.

No

Figure 1. Pressure pipe selection procedure (example). De Rosa, 1987.

Once installed, ductile iron pipes could be expected to have an infinite life because the operating pressures in a reticulation system are well below the pressure required to burst a pipe. Yet authorities which have used ductile iron pipes report occasional failures in their pipes (Nicholas, 1988) . The failures are invariably the consequence of corrosion and, as Nicholas points out, this corrosion can be avoided by careful attention to installation, including the use of protective polyethylene sleeving, and reinstatement of the sleeving after service connections are made. Without careful specification and supervision of installation, failure as a result of corrosion damage will always be a possibility. Because the rate of corrosion is affected by so many variables, even knowing how the pipe will fail is not enough to determine when it will fail und(;r these circumstances.

HOW MUCH WILL THE MATERIAL COST? In recent years the introduction of programmable calculators and computer software has enabled every designer to carry out detailed analysis of the costs of various alternative materials using Net Present Value or some similar financial appraisal technique which takes into account the likely service lives of the different options. Unfortunately, the precision of the mathematical procedures is not matched by the accuracy of the two basic estimates that need to be made before any such calculation can be made. As indicated above it is very difficult to determine precisely when a material will fail in service and it is probably even more difficult to predict future economic trends which may have a significant effect on the discount rate used in the calculations. WATER October, /988

25


The cost of installation, which is usually a significant part of the total cost, depends on the material but is strongly influenced by local conditions, e.g. a contractor trying to build up business in a 路 new area (Murphy, 1987). Future costs associated with maintenance of a particular material are also difficult to estimate but may be much higher than the future component of initial cost derived from the financial appraisal. The wisdom of selecting a pipe material for a particular project on the basis of a I or 2% difference in net present value, when the calculations are based on rather shaky assumptions, must be questioned.

THE WRc ENGINEERING PIPE MATERIALS SELECTION MANUAL APPROACH WRc Engineering has recently published a Pipe Materials Selection Manual for water mains (De Rosa, Hoffmann and Olliff, 1988). Wh ile many designers concentrate on the 路 advantages of the various pipe materials, the approach used in the Pipe "Materials Selection Manual has been to identify the limitations of the different materials. Once the limitations are known and the general requirements of a project are established, it is relatively easy to decide whether a particular material is a candidate for the projects. By providing strong technical and scientific support for the U.K. Water Industry, WRc Engineering has been able to encourage improvements in both materials and manufacturers' quality systems. This has given the industry more confidence in the various products and, by reducing the variability of quality, the limitations have been defined more precisely. The procedure for selection of a pressure pipe then becomes a simple, logical process, as shown in Figure I. The approach to the question of asset lives is interesting . "Provided pipe materials are selected, designed, insta lled and operated with in their limitations of use, their effective lives are indeterminate, and there is no technical justification for ascribing different asset lives to different material", (De Rosa, 1987). On this basis, the onl y cost that matters is the initial cost - 路 use the cheapest material that will do the job . Non-U.K. purchasers of the Pipe Materials Selection Manual are warned that the manual has been developed specifically for U .K. water mains applications and is based on U .K . practice and materials. Whil st the underlying philosophy suggested in the Man ual for the- development of cost-effective pipe materials usage policies is generally applicable, it should NOT be assumed that the pipe materials performance inferred in the Manual will apply in non-UK situations, where different pipe materials specifications, quality levels, installation practices and practical experience obtain. The Water Technology Committee of the Australian Water Resources Council has set up a working group on pipeline

materials, which has among its aims the investigation of ways to collaborate with WRc En g in eer-in g t o produ ce a n Austra lian version of th e Manual.

CONCLUSIO NS Proper selection o f ma terials fo r water supply applications can only be made when the performance requirements of the system are known and the relevant properties of the materials are defin ed. The use of financial appraisal techniques based on predicted life times to " select" between materials is questioned. The approach used by W Rc Engineering in development of the Pipe Materials Selection Manual, where the limitations of pipe materials are identified , rather than the ad va ntages, is reco mme nded .

REFERENCES AS 1477. 1 - 1988 . Unplasticized PVC (uPVC) pipes a nd fi tt ings fo r pressure applicat ion s. Part I uPVC Pipes fo r pressure ap plicati ons. SAA (1 988). BSI, ( 1987), A md 2377 , Amend ment Slip No. I to BS C P31 2: Part 2: 1973, Code of Practice fo r Plasrics Pipework (thermop/asrics mareria/s), Pa rt 2 Uplasticized PVC pi pewor k fo r th e co nveya nce o f liquids under pressure. BSI, ( 1986) . BS 3505 : 1986 Bri tish standa rd specificatio n for Unplasticized po lyvinyl chloride ( P VC-U) pressure pipes for cold potable wate r. Londo n , British Stand ards Institu tion. C REA SY, J . D. and SAN DE RSON, P. R. ( 1977). Surge in Wa ter a nd Sewerage P ipelines. WRc

Technical Report TR 5 I. DE ROSA , P . J. (! 987) . Selecti on o f Pipe Materia ls fo r Wate r Supp ly. A WRC WTC Workshop on

Pipe Materials Options, Melbourne. DE ROSA , P . J. , HOFFMAN, J . M., a nd O LLIFF, J . L. (1988). Pipe Material Selection Man ual, Warer Mains, U.K. Edirion. Swind o n, Wate r Research Centre/ Water A uthorities Associati on . J AM ES H A RDI E & CO Y PTY LT D ( 1978). Hardie 's Texrbook of Pipeline Design, 1978. p. 4-70. KIR BY, P . C., (1 980) . Surge a nd fatigue in unplasticized PVC sewer ri sing mains. Plasr. Rubb. Marer. Appl., 5(2) , 78-82. LY ALL , R. (I 987). Frac ture to ughn ess techn o logy brin gs new dimension to press ure pipes decisio n. Pipes and Pipelines, Dec. 1987, 495. MARS HALL, G . P . and BIRC H , M . W ., (1982). Design fo r to ughness in polymers. 3 - Criteria fo r high toughn ess in uP VC pressure pipes. Plasr. Rubb . Process. A ppl. , 2(4) , 369-379. MURPHY , D. J . ( 1987). Determining th e most economical in-gro und pipe materia l: the d iffic ulties , a suggested solu tion and some results. A R WC WTC

Workshop on Pipe Marerials Oprions, Melbourne. and Warer (this editi o n) . NI C HOLAS , D. M . F . (1988). Corros io n P ro tectio n Systems for G rey a nd Ducti le Iro n Pi pes a nd Fittings. Warer (this editio n). TRUSS, R. W . (1 985). Un de rsta nd in g britt le fa ilure of uPVC (unplas ticized po lyvin yl chloride) pipe. Pure & A ppl. Chem., 57(7), 993- 1000. WHO, (1984). Guidelines for drinking warer qualiry, Vol. I Recommendations. Ge neva, World Health Organisation. WRc (1984a). The United Kin gdom Water Fitt ings Bye-laws Sche me . WR c IGN 5-01-01. WRc (1984b). Req uirements fo r the testin g of no nmeta llic materi a ls for use of co nt ac t with pota ble water. WR c IGN 5-01 -02. WRc (1985). Requirements fo r the tes ting of Metallic Materi als for use in co ntact wit h potab le water.

WRc IGN 5-01-03.

HAZWASTE UPDATE In all future issues of the journal it is intended to include an update on news items relevant to the management and disposal of hazardous waste . Federal Councillor Errol Samuel, acting in the role of an associate editor, will coordinate this activity and should you have an y material for inclusion please do not hesitate to contact him on (02) 412 1388 or c/ o Metropolitan Waste Disposal Authority, P.O. Box 699, Chalswood 2057 , Sydney , Australia.

CHANGING STANDARDS FOR SYDNEY WASTE TANKERS Liquid wastes produced by industry and not suitable for discharge to sewer are often remo ved by road tanker fo r off-site disposal. The standards required for these tank ers are to a large exten t dependent on what the tankers carry , what systems they use for transferring wastes and whether they propose to use the Metropolitan Waste Disposal Authority's (MWDA) aqueous waste plant. At the same time it has been necessary to develop standards for sampling and discharge of tankers at the plant. These standards will ensure that odour is minimised and discharge can be achieved with maximum safety. Industrial liquid wastes vary considerably in composition and may range from a mixture of oil, water and solids to dangerous goods such as acids, a lkalis and solvents. The Department of Industrial Relations and Employment (DIRE) has indicated that, as most tankers carrying li quid wastes will at some time carry wastes that are dangerous goods they must comply with the NSW Dangerous Goods Regulations 1978 particularly with regard to carriage of potentially fl ammab le materials. Th e industry has been given unti l 1st November, 1988 to meet certain minimum requirements and at a later date, to be agreed with the industry, to meet all the requirements of Australian Standard 2809. As a large percentage of tankers use vacuum or pressure in the tank to transfer liquid into and out of the tanker the question arises as to 路 whether the tank is regarded as a pressure vessel under the Factories Shop & Industries Act , 1962. The DIRE has advised that although the tanks are considered pressure vessels an exemption would be granted provided th ey were not subj ected to an internal pressure (positive) exceeding 35 kPa when discharging contents. The MWA has required the industry to provide standardised samp li ng points at both the bottom and middle level of the tank , and standardised discharge outlets . These standards will progressively res ult in liquid waste tankers complying with the Australia n Standard for Road Tank Vehicles for Dangerous Goods. This will ensure a higher standard of safety for transport of liquid wastes from factory to the plant , which is an integral part of the total disposal system. Errol Samuel

26

W AT ER October, / 988


DETERMINING THE MOST ECONOMICAL IN-GROUND PIPE MATERIAL: A SUGGESTED SOLUTION D. J. Murphy ABSTRACT A computer program developed by the Public Works Department of NSW produces average costs of pipeline constru ction by contract (excluding pipe supp ly costs) which are to be used to estimate the cost of future works. Because of the variable factors in pipeline construction and particularly in the tendering practices of some contractors, the cheapest pipe material cannot always be predicted in specific contracts with confidence using the computer program. However, trends of prices for pipeline construction for different pipe materials can certainly be determined. The program relies upon a data base of previous tender prices and the accuracy of the results increases with the size of the data base.

INTRODUCTION The Public Works Department is the constructing authority in New South Wales and carries out water supply and sewerage construction in country towns by contract. Approximately $100 mis expended annually on these works, of which pipeline construction is a significant proportion. The problems of estimating the in-ground cost of pipelines of different materials are many and varied. The department, in developing a computer program that analysed the rates submitted by firms tendering for contract work and produced graphs of pipeline construction costs, has created a data base that can be used to compare in-ground costs of pipelines of various materials. The difference in cost of different pipe materials is fai rly clear cut. However, the cost of excavating, then laying and joining pipes of different materials is difficult to assess because of several variab le factors. This latter cost only has been considered in this paper. Also, only costs of construction by contract have been considered, as no data was available from day labour construction.

CHOOSING THE PIPE MATERIAL Several factors affect the choice of pipe material. The commonly available materials are vitrified clay (VC), unplasticised polyvinyl chloride (uPVC), concrete, ductile iron (DI), steel (MS), and until recently, asbestos cement (AC). Other materials being used increasingly include glass-fibre reinforced plastic and polyethylene. All pipe manufacturers supply pipes in different strength classifications. Pipes must be strong enough to cope with handling forces, external loads when buried and internal loads from the operating system and temperature chan ges . Pipelines must be capable of resisting corrosion. External corrosion depends on the chem ical constitution and the ph ysical properties of the soil, the soil moisture content and groundwater movement. Internal attack must be particularly considered in the transport of liquids such as sewage and untreated raw water. Pipe materials can be protected where necessary by internal or external lining, although of course, this adds to the cost. Other factors to be considered include size (most manufacturers fabr icate pipes in a relatively limited range of diameters), availability, compatability with existing pipe systems and in some cases, specific client wishes. However, subject to all the above, the most important criterion for pipe material is cost - not simply the supply cost, but the overall in-ground cost of the comp leted pipeline.

FACTORS AFFECTING IN-GROUND PIPE COSTS As stated earlier, pipe supply costs are not considered here. The in-ground cost of pipelines is dependent on pipe weight, length of pipe, depth of trench, ease of handling, joint type, special backfill requirements and ease of testing. Some pipes such 28

WATER October, 1988

Don Murphy is a graduate in Civil Engineering from the University of NSW and an Inspecting Engineer in the Construction Division of the Public Works Department of NSW. He has been associated with estimating practices in the Department for many years and has encouraged the development and use of computer-based estimating programs to estimate the cost of work carried out by private contractors.

Don Murphy

as uPV C are light a nd easy to handle and are 6 m long, whereas VC pipes are more than five times the weight and are supplied in 1.5 m lengths and thus have four times the number of joints. Against this, the bedding and backfill requirements for VC pipes are not nearly as stringent as those for uPVC pipes. In addition to the above factors, costs of different locations vary depending on soil types, topography, groundwater, rock, etc. In addition, the remoteness of the site and the availabili ty of labour, plant and materials are all items that cause variations in the cost of constructing pipelines. Costs over time also vary and these costs depend on rises in costs of materials, wage variations and interest rates, but are also very dependent on market factors, such as the competitiveness of the industry , the amount of work available, discounts being given for materials, etc. Finally, perhaps the most important factor affecting in-ground pipe costs is the attitude of the contractor. A review was carried out of 1everal contracts where the tenderers were given the opportunity to tender on laying pipes of different materials. In each contract, there was ge neral consistency in tenderers choosing one pipe material to be more economical than another. However, there were instances where the lowest tenderer preferred to use a pipe material different from that of the other tenderers. Very often, some tenderers put all pipe materials on par. Obviously, different contractors place different emphasis on the various factors that affect the cost of laying pipes of di fferent materials.

ESTIMATING PROGRAM FOR IN-GROUND PIPELINE COSTS Because the Public Works Department carri es out such a large amount of pipeline construction by contract, it was seen to be very beneficial to produce reasonably accurate estimates of tender prices of pipeline construction easily and consistently. The obvious solution was a computer appl ication using the vast amount of data ava ilab le from all the unit rates submitted by tenderers on previous works.

Computer unit rates A program was devised that finds the mean of all unit rate tenderers for a particular pipeline construction for each item of work in the contract. It then determines the standard deviation for each item, and disregards all tendered rates that are outside the mean, plus-or-minus two standard deviations. A new mean and standard deviation are calculated and again, any rates beyond twice the standard deviation from the mean are disregarded . A final mean of the remaining unit rates is determined and this becomes the 'comp uter unit rate' for that item. This process is repeated for every item in the pipeline contract. Thus, computerised unit rates become avai lable for every contract and may be used to estimate unit rates for future contracts.


These calculated 'computer unit rates' are believed to be a better representation of the likely costs of items of work in future contracts than the actual unit rat<;:s submitted by the winning tenderer of the past contract. Rates from winning tenders can be mislead ing. Generally (but not always), the lowest tenderer is awarded the contract. Quite often, particularly in work such as pipeline construction, the lowest tenderer may be a small firm that owns its own excavating equipment, and does not charge plant depreciation in the contract price . Then again, the tenderer may be a family company that does not have to consider full award wages, etc. for the labour involved. These factors tend to result in ' unreasonable' unit rates. In addition, the use of 'computer unit rates' to some extent smooths out the unbalancing of rates to which some tenderers resort, i.e.: it minimises the loading of particular rates that a tenderer may hope will increase in quantity or rates which the tenderer has loaded so that he receives large initial progress payments for lesser value work. Thus, these computer unit rates can be used to build up detailed estimates for future works when quantities of individ ual items are known . They can also be accumulated to produce a total construction cost per metre length of pipeline, i. e. to produce ' feasi bility' estimates.

Feasibility estimates Feasibility estimates for each contract are obtained from the unit rate data by determining an average depth for the pipelines in the contract - for water supply contracts, one average depth is calculated for all the pipelines in each job , whereas for sewerage contracts, an average depth for each pipe diameter is calculated. Using this average depth, the cost of excavation and backfilling can be converted from a cubic metre basis to a linear metre of pipeline basis. Added to the earthworks cost is the lay-and-join cost of the pipeline per linear metre. To this figure is added a cost which represents all those items that are common to pipeline construction, e.g., in sewerage work this includes restoration of surfaces, concrete for manholes, etc . Thus, a 'feasibility' rate per linear metre for each pipe diameter in the project is produced. The remaining items are those that are specific to individual pipeline projects. These include rock excavation , dewatering, sheetpiling, ballast, etc. These items can be very critical, of course, to the final estimate of the cost of the contract. However , at the time of carrying out a feasibility estimate , it is unlikely that these items can be quantified with any accuracy. Hence, the costs of these items are estimated using simple rules, such as: close timbering - add 750Jo of the feasibility pipeline rate; I0OJo rock in the excavation - add 200Jo of the pipeline rates, etc.

The computer program allows the estimiuor to enter the conditions pertaining to the job being estimated, such as terrain, soil and rock types, depth of pipeline , quantity of excavation, etc. and the program chooses jobs out of the database that have similar conditions. Use of the data from these jobs should ensure that the most relevant estimating information is accessed.

The software The program is written in 'Revelation ', a data-based management and business-oriented development tool for microcomputers. The program is suitable for IBM personal computers or compatibles of IBM PCs. The estimator can update the data base to any month of any year for the past seven (7) years and the future seven (7) years. If the estimator is interested in any particular contract, he can call up all the details of that contract. The program will give him some general information for each job on the data base such as the location, the tender date, average depth of pipeline, amount of excavation, percentages of rock, dewatering, etc. Also the estimator may request a graph to be displayed for the costs of pressure pipeline construction against diameter for individual pipe materials or he may request a grap h for gravity pipelines for specific diameters over a range of depths. These graphs can be dumped to a plotter or a printer.

RESULTS FROM THE PROGRAM Using 135 separate contracts, a line of best fit of the costs of installing pressure pipelines has been plotted on Figure I for unplasticised polyvinyl chloride, ductile iron , mild steel and asbestos cement pipes. T he graph shows for each pipe material , the cost per linear metre of various diameters of pipes . !Ur/Cl/LAT/ON ANO r.41/NK MA INS

"' .---.-----,----,---,-- -- ---- -

l-----+----+---1------i---¡ - -

80

Ii. PIPE

VlLOEO

70

GO

~

Time indices To be useful, however, the feas ibility rates must be able to be expressed in common dollars. There is no point in having data two years old if you cannot update it to today's value or indeed, a value two yea rs in the future. To provide this facility, the Department produces indices which are a combination of cost indices and market condition indices. The cost indices record all increases in labour costs, material costs and plant hire costs from sources such as wage awards, Australian Bureau of Statistics data on material costs and annual plant contracts called by Government and semi-Government bodies. They are combined together in the ratio that is normally experienced in engineering type construction , i.e., 400Jo labour, 400Jo materials and 200Jo plant. The cost indices are used in association with market condition indices. Market condition indices measure those areas of change in costs that are not directly measurable - costs such as competitiveness, amount of work available, profit margins, etc. They are a measure of the movement in tender prices if inflation were zero. In practice, they are determined by updating a previous contract price to that of a recent contract for the same type of work using the cost indices and conve rting the difference in price to a market conditions index. The combination of cost/ market condition indi ces is applied to each feasibility rate so that the estimator can update all proj ects to a common date.

Locality variations The problem of changes in price due to changes in locality and other conditions is a more difficult problem to apdress directly .

~" l:\t

so

~ ~ __,

~ ~

"'

'--

JO

a

to

:4 ,C. r.euNK

0

-t---+---

"

'A IN.5

- - + - -- t - --+----+---+----+---+- - - 1

/~

PIP!

0/AM!TtR S {mm)

Figure 1. Preliminary rates for w/s pipelaying (excl. supply).

The results should be treated with some care as there is a fairly large divergence from the line of best fit for some of the points, which emphasises the difficulties in being able to assess accurately the true cost of constructing pipelines of different materials (the points obtained from each of 135 contracts have been omitted for clarity) . WATER Oclober, / 988

29


In order to obtain some idea of the program's validity, the feas ibility estimate obtained by the computer for each contract was compared to the actual rates .tendered by the winning tenderer. Over all the contracts considered, the computer feasibi li ty estimates were, on average, just under 13% higher than the winning tenderer's rates. This is considered a reasonable result, since one wo uld expect, and wish, that the accepted tender wo uld be lower generally th an the estimated rate . However, the standard deviation was just over 9%, indicating that there were several accepted tenders that differed considerably from the computed 'average' feasib ility estimates. It is interesting to compare these results with a similar exercise carried out for the constru ction of reservoirs . For reservoirs, the computer feasibility estimates were on average, just on 9% higher than the winning tenderer's rates and the standard deviation was just over 7%. The probable explanation of the different results between pipelines and reservoirs is that reservoir work is above gro und , there are fewer unknowns, the spread of tenders is much less than that for pipelines and (perhaps) the competence of reservoir contractors is higher, generall y, than pipeline contractors .

CONCLUSION T he costs of constru cti ng pipelines of different materials can be estimated using tende red rates of previous contracts. Using a large data base, average trends in pipeline construction can be determined. However, because there are so many variable factors involved in pipeline construction, the results cannot be considered definitive for individual contracts. Certainly, it is not possible to predict the outcome of a specific contract. The diversification of tenderers and thei r particular preferences, will ensure that the peculiarities of an individual tende rer will determine the cheapest pipe material, not logical, well reasoned economic judgement.

E. Samuel Continued f rom Page 21

WASTE NOT ACCEPT ABLE AT THE PLANT The aqueo us waste plant has been designed to only treat industrial liquid wastes that are delivered to the plant by tanker. There are a variety of other wastes, e.g. 200 litre drums, spadeable sludges, packaged wastes, etc. that are predominantl y solid and which the plant will not be capable of treating. These wastes will continue to be deposited in the MWDA's secure landfill depot at Castlereagh. In tractable wastes such as PCB's will also not be accepted at the plant and will need to be stored until an environmentally satisfactory method of disposal is available. T he problem of disposal of these wastes is presently being addressed by the Intractable Waste Task Force.

PLANT COSTS At the time of writing this paper the water treatment plant or cold part of the plant had been commi ssioned and appeared to perform as designed . The sludge processing or hot part of the plant had been precommissioned an d sludge processed for a total of abo ut 10 hours. The results obtained so far are extremely encouraging and it is p lanned to divert all of Sydney's industrial liquid waste to the plant fro m 18th October, 1988 . With plant construction work complete together with the bulk of the commissioning costs it is estimated that the fina l capital cost of the plant will be $23.6 million. The MWDA has decided to charge a fixed fee of $1 14/ tonne for treatment of waste. This cost compares favo urab ly with that being charged by other treatment plants such as in Melbourne.

CONCLUSION Syd ney now has a state-of-the-art treatment facility that will result in a significant upgrading in the standard of liquid waste disposal. The plant will provide its users with a disposal service at a very competitive cost.

1

13TH AWWA CONVENTION CANBERRA, 6-10 MARCH, 1989 • • •

Our biggest convention yet Over 130 synopses accepted Theme 'Investing in Water Features: The Australian Water Industry in the 1990s

• • • •

A new program format Less Technical Sessions More Specialised Workshops and Seminars Come and participate

ENJOY A UNIQUE CANBERRA PROFESSIONAL AND SOCIAL EXPERIENCE

30

WATER Oc1ober, 1988


CORROSION PROTECTION SYSTEMS FOR GREY AND DUCTILE IRON PIPES AND FITTINGS D. M. F. Nicholas

ABSTRACT The general corrosion performance of buried grey cast iron is reviewed and compared with that of the newer ductile iron. The effectiveness of loose polyethylene sleeving in protecting both materials is shown and an argument is presented to show the benefit of protecting all buried iron regardless of so il type. The mechanism of some recently observed failures in sleeved ductile iron is presented, and the need for proper ed ucation of all those personnel involved in pipeline systems is emphasised. Finally, the need for high quality internal linings on previously uncoated valves and hydrants is shown and some effective coating systems described.

CORROSION PERFORMANCE OF UNPROTECTED BURIED CAST IRON Grey Cast Iron Cast (grey) iron has an extensive history of use both overseas and in Australia, which has been reviewed elsewhere (Ferguson, Nicholas 1983). Many pipelines buried over a century ago continue to be operational. However, like all metals, cast iron is subject to corrosion and in a few highly aggressive environments life is often quite short. The ge neral durability of cast iron is mainly attributed to the formation of a silica-rich graphite residue which results from the initial corrosion of the pipe sur face. This 'graph itised' layer slows but does not prevent further corrosion, which in cast iron then takes the form of pitting attack. Occasionally, the graphitised layer can in fact mask extensive attack of a pipe which seems vis ua lly unimpaired. The rate of piiting attack which directly effects the useful life of the pipe is largely determined by the corrosivity of the soil. This is briefly outlined in a later section and has been discussed by many authors in relation to both grey and ductile iron, Fuller (I 972), Scholes, Fuller (1973).

Ductile Iron For pipes, this material was commerciall y introduced to Australia in 1976 and has now supplanted grey iron entirely. Whilst fittings continue to be made of both materials, it is likely that ductile iron will predominate in the near future. The corrosion performance of ductile iron has been extensively researched, not least because ductile pipes are thinner walled than their grey iron counterparts. A sign ificant fee ling has grown in the water 32

WATER October, /988

David Nicholas graduated with an honours degree in metallurgy from Sheffield Polytechnic (UK) in 1970. He worked as a metallurgist at BHP, Newcastle before spending a brief period as a computer salesman for Burroughs Ltd in the mid seventies. He joined the Hunter District Water Board (HD WB) as that organisation 'sfirst materials/ corrosion engineer in 1978. Active in the Australasian Corrosion Association, he is also Marketing Manager of Hunter Watertech, the marketing division of the HDWB. David Nicholas

industry that the 'life-to-failure' of ductile iron will be less than that of grey iron: the facts, however, do not support these dire predictions. Performance of these two materials in an identical corrosive environment will be greatly affected by the morphology and distribution of the graphite particles, which is itself the main factor behind the quite different mechanical behaviour between the irons (summarised in Table 1). TABLE 1. MECHANICAL PROPERTIES OF GREY AND DUCTILE IRON PIPE MATERIAL Tensile Strength Elongation 0.20/o proof stress Hardness

Grey fron

Ductile fron

180-300 MPa Ni l Nil BHN 175-2 10

420-500 MPa 10-25 0/o 300-350 MPa BHN 165-230

A clear indication of the difference in performance between the materials is given by the vast overall improvement of all properties of ductile iron. Experience has shown that nearly all failures of grey iron pipes occur as a result of a combination of loading (particularly pressure surges) and corrosion. Grey cast iron is a brittle material, notch sensitive, and consequently failure can occur at a much lower load than would be expected given the residual thickness of the material. Ductile iron , where the stress of a corrosion pit is more evenly distributed, rarely fails from other than pure corrosioninduced pitting. Thus, a greater degree of penetration from pitting can be tolerated in ductile than in grey iron before failure becomes likely. A lthough it is likely that other factors are involved in the actual corrosion process, such as the lower corrosion current generated in ductile iron as a result of the smaller surface area of the cathodic graph ite, even the most pessimistic analysis shows that the actual corrosion rates, i.e. the amount of metal lost per unit current, is very simi lar. The

Melbourne Board of Works (1980) has shown that even so, the pits on ductile iron are less deep than for grey iron under id entica l conditions. Thus, under analysis, all evidence points to ductile iron being a far superior material in all aspects to the grey iron it replaces.

CORROSION PROTECTION OF BURIED CAST IRON Loose Polyethylene Sleeving is an admittedly highly inelegant form of protection ~ut its effectiveness was initially reported by Wagner (1964) as a result of trials started in the early fifties in highly corrosive tidal muck in Florida, USA. The good results demonstrated were followed by extensive trials being undertaken e lsew h ere, in c ludin g Australia. The Hunter District Water Board (HDWB) which commenced using polyethylene sleeving on grey iron in 1966, has regu larly exhumed these early trials and reported excellent results (Ferguson, Nicholas, 1983). The protective mechanism is not completely understood, but is likely to be a combination of the following factors: • providing a uniform environment between the pipe surface and the soil, eliminating, in particular, differentialaeration corrosion cells. • reducing the diffusion rate of substances, particularly oxygen, to the pipe surface, thus slowing corrosion rates. Any water trapped will tend to be relatively deaerated with a subsequent reduction in the cathodic reaction rate. • reducing the rate of diffusion of corrosi_on products away from the metal surface. As a result, there will be an increase in hydroxyl ion content of any trapped moisture to a point where the iron becomes passive. Any rise of pH above a value of nine will also inhibit the activity of any sulph ate-red ucing bacteria present. All these mechanisms probably play some part, depending on precise soil conditions. It is important to realise that the


sleeving does not stop the ingress of often quite large quantities of water, as our exhumations showed. This water had had little effect on the corrosion of the iron. Sleeving was made mandatory for all pipes buried in the HDWB area of operations from 1976 onwards. In all sleeving operations since 1966, only five failures have been reported (on both types of iron). Four of these were cases of corrosion occurring as a result of sleeving being removed to make an uninsulated service connection with copper tube. The bare iron area, together with the galvanic couple produced between the iron and the copper, led to pipe fa ilure in soi ls of lo w resi stivity. Thi s phenomenon was recognised in 1980 and shortly afterwards all service connections were insulated and standard practice altered to ensure that the sleeving was repaired at service connections. More recentl y, the Sydney Water Board has had an 'outbreak' of "these types of failure on ductile iron which had an identical cause. It is interesting to note that little work has been published on this galvanic couple problem, although it has been recognised elsewhere and remedial measures taken (MMBW, 1980). Future field-work is planned to measure the relationship between soil resistivity and corrosion current using zero resistance ammeters coupled with data loggers. Initial work comparing such techniques with the simplistic ' instant' measurements using standard multimeters shows that the latter technique gives neithe r accurate results nor shows the variation of current with time due to various environmental factors such as stray currents and moisture content. Other types of failures have been reported elsewhere, including failures due to entrapped clay within the sleeving and mechanical damage to the sleeving itself, sometimes due to penetration of the polyethylene by the peening pattern of the ductile iron surface. These failures have occasionally prompted interest in other coatings. However, these failures are relati vely few and the costs of some alternative factory-applied coat systems are prohibitive, with equally no guarantee of I OOOJo success. Typical costs for loose sleeving rarely exceed 3% of total job cost, whilst costs in volved with (say) a fusion bonded epoxy system might add over 30% to job cost. The experience of HDWB with loose sleeving has shown the prime importance of correct installation practice, in common with all coating systems. Accordingly, within the HDWB, all personnel involved with handling ductile iron pipes are trained in both the need for wrapping and the correct app lication methods to be used.

SOIL CORROSIVITY This is a complex and incompletely und erstood subject which depends on a la rge number of variables. Whilst a full discussion of these factors is beyond the scope of this paper, several categories of corrosive environments can be summarised: acidic soils, neutral and alkaline soils, anaerobic soils, stray electric currents, galvanic couplings.

The problems associated with galvanic couplings have been briefly discussed above, and the other conditions obviously a lso require careful consideration. Various systems of measuring chemical and physical parameters and assembling them into coherent corrosivity assessment systems have been proposed, and are used by some water authorities to determine when protection is req ui red. In our view, these systems suffer from severe practical disadvantages: • The high cost of sampling and analys is compares unfavourably with the relatively low cost of sleeving . • Uncerta in ty of various protection criteria. • Very wide range of soil corrosivity over relatively short distances, particularly in an urban environment. Trenching itself can act as a carrier of corrosive material for considerable distances from its initial position. • Changing soil conditions with. respect to time and land usage. • Desire to protect pipes from stray current effects. • Need to guarantee a minimum pipe life of 100 years under all conditions. Our ran ge of exhumations under varying soil types have given us confidence that polyethylene sleeving will protect pipes under the most adverse corrosive conditions: consequently our rationale, with which most other major water utilities agree, is to sleeve all pipes and ignore soil testing. We find little justification for the use of the more expensive tape wrapping systems u se d by some authorities. However, the continued use of soil testing for research purposes, particularly in conjunction with some current efforts to develop reliable electrochemical tests to predict corrosion rates on installed unprotected pipe, is both necessary and indeed vital to the industry .

INTERNAL LININGS ON SPRING HYDRANTS AND VALVES For man y decades it has been common for these items to be supplied with the standard cosmetic tar coating as a ' lining' material. By the early eighties, HDWB operations staff were becoming alarmed at the number of spring hydrants becoming prematurely blocked, and thus inoperative, due to the grow th of tuberculation inside the hydrant. This corrosion phenomenon is large ly caused by the presence of iron-fixing bacteria present in relatively stagnant conditions, which readily attach to the rough as-cast surface and produce the voluminous corrosion product. ' Ordinary' electrochemical attack also contributes to the phenomenon. The need for a substantial lining to combat this condition has frequently been demonstrated. Requirements for high quality internal coatings have restricted themselves, so far, to two effective systems: (i) Fluidised bed applied Nylon 11 over suitably grit blasted and epoxy primed substrate. More recently , the manufacturer has introduced a complex chemical cleaning method, incorporating ultrasonic

baths, which has i.nproved coating adhesion. (ii) F usion Bonded Epoxy (FBE) applied in a similar manner to (i). The initial application of this FBE using electrostatic spray was not successful, largely due to the difficulty of spraying complex shapes and achieving a pinhole-free coating. A change to fluidised bed practice has immeasurably improved coating integrity . Several years experience with both coatings, particularly the more resilient Nylon 11 system, has demonstrated the effectiveness of a coating both on hydrants and other valves and fittings. The initial cost premium of coating such items ($15-$20 for a spring hydrant) is more than covered by an expected doubling of effective life. It is difficult to support any argument which suggests that such items should not be lined . The requirements for coatings on spring hydrants alone has demanded a much improved casting practice from foundries as well as partial redes ign of the hydrants themselves, basically to remove sharp edges which cause 'pull-back' of the coating. The improved foundry practice was required as surface porosity, blowholes and other casting defects must be eliminated before a pinhole-free coating can be achieved . Merely requiring a coating has led to an improvement in the quality control of the castings themselves. These requirements have not always been popular with manufacturers, as at present not all authorities, by any means, see the need for such coatings. Similarly, smaller ,valves have for some years been specified and supplied with either nylon or an FBE coating. Larger gate valves, too massive for fluidised bed application, pave been a considerable problem. Several have been coated with ultra high build vinyl ester systems, but problems have been encountered with this a·pplication, because so far neither manufacturer nor coating app licator have much experience with coating such large valves.

CONCLUSIONS Ductile iron has greater durability than grey iron, notwithstanding the greater wall th ickness of the latter. Polyethylene sleeving is the most costeffective protection currently available for cast irons, and its use on all buried mains in urban areas is strongly recommended. This philosophy is to be preferred to a decision system based on the current status of soil corrosivity assessments. Failures of sleeved ductile iron are mostly due to previous poor practice in making service connections. As with any corrosion protection system, the correct application of sleeving requires proper training and understanding. Proper linings for hydrants, valves, and other water supply fittings, are mandatory to achieve a minimum service life without fai lure. Both Nylon 11 and FBE, applied by the fluidised bed technique, are proven systems for this application.

CONTINUED ON PAGE 35 WATER October, 1988

33


LARGE FLEXIBLE PLASTIC PIPE-S: INSTALLATION PROCEDURES IN SYDNEY F. Tapia ABSTRACT Glass Fibre Reinforced Plastic (GRP) Pipes were introduced into the Sydney Water Board approximately five years ago as an alternative to concrete pipes in order to counter the increasing cost of maintaining concrete sewer pipes which were deteriorating due to gas attack. The increasing use of GRP pipes. particularly in large sewer mains (i.e. DN 600 to 900 mm) has necessitated the introduction of a uniformly high standard of bedding and backfilling. This paper describes the Water Board's procedures for installation of GRP and profiled-wall HOPE pipes, both for gravity (sewer) purposes and for pressure (water) applications. Measured deflections of installed pipes indicate that the adopted method satisfies the design and installation conditions necessary t.o achieve long term service .

INTRODUCTION GRP pipes were first introduced by the Board in early 1984. Being aware of the increasing cost of maintaining deteriorating concrete sewers, the Board selected large sewer carriers for an evaluation of GRP pipes. In the first installations , filament-wound GRP pipes with a stiffness of 1250 N/ m 2 were used. Later , centrifugally cast GRP pipes (Hobas)* with a stiffness of 5000 N/ m 2 and profiled wall HOPE pipes (i .e. Black Brute)t were tried for gravity sewer installations. In addition, two experimental water installations were made of centrifugally cast GRP pipes (DN 450 mm and DN 600750 mm) with a stiffness of 5000 N/ m 2 for pressure applications. The installation procedures described in this paper aim to minimise initial and long-term deflection or distortion caused both by soil placement and compaction, and subsequent consolidation of the soil surround. It is important to note that this paper is intended to bring to notice some of those aspects of construction where the use of GRP pipes may call for special attention. It does not provide a general description of pipeline construction, which is already covered by documents such as the draft document 'Underground Installation of Glass Fibre Reinforced Thermosetting Plastics (GRP) Pipes' (SAA, 1987) and the UK Water Research Centre Guidelines (WRC, 1981). At the end of the paper values are given of measured deflections in installed GRP and profiled wall HOPE pipes (Table 1). Where practicable, monitoring of pipe deflections will continue for at least five years from date of installation to determine the effects of creep of both pipe and soil.

Fernando Tapia is a Civil Engineer with the Sydney Water Board and is currently employed as Engineer Technical Standards in the Materials and Standards Section of Design Branch. His duties include preparing the Board 's standards, specifications and guidelines for the selection and use of engineering products and standards. Fernando Tapia

Bedding The granular material which has been preferred in the past for bedding consisted of single-size 20 mm rounded gravel. More recently, single-size 14 mm gravel complying with AS2758 - Part 1 has been adopted since it is more readily available and is more economical to use. Generally the single size gravels are preferred for bedding and pipe zone backfill, as gravels achieve the best results for the minimum compactive effort. A 150 mm minimum thickness of granular bedding material should be maintained under the barrel of the pipe in order to provide uniform support. Care should be taken to ensure that the bedding material under the pipe is compacted to at least 600'/o Density Index.

Backfilling Pipe zone backfill should be the same granular materials as used for bedding, (i.e., single-size 14 mm gravel complying with AS2758 - Part I). Backfill should be carefully placed and compacted in layers of between 150 and 300 rnm at the sides of the pipe, to a consolidated height of at least 300 mm above the top of the pipe . Refilling shou ld be carried out simultaneously on both sides of the pipe with adequate precautions taken to ensure that neither the pipe nor external protec~on is displaced, deformed or damaged during refilling. SELECTED FILL OR ROADBASE DEPENDING ON LOCATION

* BACKFIL L LAYERS TO I eg

CONSISTING OF AND COMPACTED

LIMIT 9Sž

SU B SIDENC E STANDARD

EXCAVAT ED SOIL PLAC ED IN TO A STA OARD SUF F ICI ENT TO

AN

PROCTOR

ACCEPTABLE

L E VEL .

DENSITY . )

4'

GENERAL REQUIREMENTS Since the design of GRP and HOPE buried pipes is based on the principle of flexible conduit technology (in that the response to imposed loading involves an interaction between the buried pipe and the surrounding soil) it is essential that soil conditions that relate to trench construction, and to pipe installation, be determined prior to construction of the pipeline. Proper bedding and backfill procedures are essential to the performance of the pipe and must be thorough ly understood and carefully observed during installation.

Trench Construction The size of GRP and profiled wall HOPE pipes used in sewer carrier mains, together with other requirements (e.g., pipeline gradients) normally results in the pipeline being laid in relatively deep trenches, between 4 to 6 m deep. In the western suburbs of Sydney these are generally in firm clay soils and in close proximity to natural water courses. For pressure (water) app lication , the GRP pipes are laid at standard trench depth, which provides at least 1 m of cover above the top of the pipe. â&#x20AC;˘ Hardie 's Pipeline Systems.

t Hardie lplex Pipeline Systems 34

WATER October, 1988

Pty ltd.

Figure 1. Typical installation.

Proper compaction is achieved by thoroughly rodding the granular material by spearing into the gravel layers with forks or tamping bars. A density index of at least 60070 is thereby achieved. Mechanical vibrating equipment is therefore not required alongside the pipe. Pipe zone backfill must also be compacted against the undisturbed trench side. Any temporary trench shoring or moveable shields should be raised or removed progressively to ensure that placing and compaction of backfill occurs below such trench protection and to ensure that removal of the trench protection does not disturb already compacted backfill. The use of the geotextile fabric, 'TERRAM IO00A't or similar material, differs according to the installation condition. In very i !Cl Operations Ltd.


sand y, sil ty or soft clay soils, particularly where gro und water is present , the geotextile fabric mu st be la id in the excavated trench such that it full y encases the pipe bedding (i nclud ing any overexcavation) , surround and cover. This is to prevent the in trustion of an y adjacent fine soil and consequ ent loss of the necessary foundation or side sup port fo r the pipe, or both (see Figure 1). In stiff clays, rocks or shales above water tab le level (see Figure 2) a hori zo ntal layer of geotextile fabric must be laid in the trench above the pipe zo ne backfi ll .

SELECTED DEPENDING

BACKFILL

* REFER

FIGURE

NOTE 1

TERRAM 10 00A

DEFLECTION MEASUREMENTS

GEOTEXTILE

By meas uring deflection , pipelaying work can be checked, particu la rl y with rega rd to co mpactio n and th e use of the correct bedding material. A fter back fillin g has been completed de flections should be meas ured as specified below . Vertical and hori zo ntal diameter (D v, DH) m easurements shou ld be taken at th e midpoint of each of the first three laid pipes and th ereafter every fourth pipe and at selected joints at the followin g times: (a) Immediately after pipes are laid in the trench (D v, , DH ,). (b) On completion of placeme nt and compaction of the pipe zone ·backfi ll material (Dv2, D H2 ). (c) T we nty-fo ur hours followin g completion of the backfi lling of the trench to the gro un d level (D vJ, DHJ). Deflection is calcul ated using the fo rmul a: . Dv, - Dv, De fl ect1on (OJo) = - - - x 100

Dv,

Further deflection measurements should be made prior to commission ing the pipeline to ensure that th e pipe zone backfill has stab ilised and that short term deflections are within specified limits (i .e. 40Jo max.). The depth of cover of th e pipe, location (chainage) and in-situ soil shou ld be recorded at each joint and midpoint of pipe where defl ection measurements are taken. Defl ections in th e pipelines laid by the Sydney Water Board since 1984 are being monitored . T he results of th e la test measurements are summa rised in Tab le 1.

FABRIC

_ _J 300 mm Min SINGLE SIZE

GRAVEL

Figure 2 . Installation details for go od ground cond iti ons. (Stiff clays, rocks/ shales abo ve watertable)

CONCLUSIONS The installation o f the G RP and profi led wall HDPE Pipes by the Sydn ey Water Board shows: • Full-time supervision of th e compaction operation and proper moni to ring are both essential if consistent results are to be obtained. • The use of single-sized gravel eliminates the need for special co mpaction techniq ues and associated quali ty control field tests. The Water Board no w accepts that large diameter GRP and HDPE Pipes (i. e., 450 mm and above) are viable opti ons for sewer carri ers. Care is needed to ens ure that all aspects of design and installation are full y considered.

REFER ENCES

TABLE 1. DATA OF SEWER CARRIER MAI NS Location Length, Date

Pipelin e Type

Max. Cover m

Deflecrion % Date

Rive rsto ne 11 85m ' 84

Fil. Wou nd Di a. 900 mm

GRP

5. 0

Not available

Bou nd C reek 375 m '84

Fil. Wound Dia . 900 mm

GRP

4 .0

0.6-4.3 Jul '84

Bound Creek 438 m '84

Fil. Wound Dia. 900 mm

GRP

3.8

0. 5-3 .2 Mar ' 87

Ropes C reek. 900 m '84

Fil. Wo und Dia. 900 mm

G RP

4.4

0.4-2.2 Ja n '85

Albio n Park 413 m '84

Fil. Wo und Dia. 900 mm

GRP

4.3

0.4-4 . 1 Jan '85

Bunga rribee Cree k 1023 m '85

Fil. Wo und Di a. 900 mm

GRP

4. 1

1.1 -4 .4 May '87

Bungarr ibee Creek 772 m '86

Centr. Cast Dia. 900 mm

G RP

5.3

1.1 -4.2 Sep '86

Bungarr ibee C reek 566 m '86

P ro f. Wa ll - HOP E Dia. 900 mm

5. 3

1.0-7.2* Feb 88

Bungarr ibee C reek 390 m '86

Prof. Wall - HOP E Dia. 600 mm

5.3

0 .3-8 .8* Feb 88

Hay Street 196 m ' 87

Centr. Cast Dia. 750 mm

GRP

5.4

0.4-3.8 J an 87

P yes Cree k 260 m ' 87

Centr . Cast Dia. 525 mm

G RP

5. 0

Not ava ilable

Pyes C reek 260 m ' 87

Centr. Cast Dia. 450 mm

GRP

3.3

Not availab le

Ban k Street 46 m '87

Prof. Wall - HOPE Dia . 750 mm

6 .6

0. 7-2 .0

• Large defl ecti o ns occurred on ly in local sections, a nd are prese ntl y being evalua ted . Possibl y they we re caused by extreme condi tio ns duri ng insta llatio n.

I . SAA ( I 987). 'Undergrou nd In sta llat ion of G lass Fibre Rein forced Th erm osetting P lastic (GRP) P ipes' , Standards Association o f A ustra lia . Draft Document: P6B057FB I . 2. WRC ( I 98 I). 'G uidelin es to the Water Industry for the Insta llation of G lass Fibre Rein forced Plastic Pipes', Wat er Research Centre, Wilt shire, UK. Report No .: E R 31E.

CHANGED YOUR ADDRESS? - Please inform your Branch Secretary to assure your copy of 'Water'.

D. M. F. Nicholas Continued from Page 33

REFERENCES FERGUSON, P. a nd N IC H OLAS , D. M. F. (1983). Corrosion protection o f buried cast iron wa ter ma ins . Co rrosion Australasia Vo l. 9 , No. 2. FU LLE R, A . G. ( 1972). The soil corrosion resistance of grey a nd ductile iro n pipe: a review o f available informat ion . BCIRA Report I.R . 206. MELBOURNE AN D METROPOLITAN BOARD OF WORKS (1980). Cast iron pressure pipes - co rrosio n c haracteristics of grey and ductile iro n pipes, sleeved a nd unsleeved. Report s MMBW -W-0105 and 0106 . SC H OLES, J . P. and FULLER , A.G . (1973). Propert ies of ductile iron pipe a nd their re levance to modern water sup ply practice. BCIRA Report 11 3 1. WAGNER , E. F. (1 964). Loose plastic film wrap as cast iron pipe protection. Journal AmWWA, March. WATER October, 1988

35


SEWER CONDITION EVALUATION THE U .K. EXPERIENCE David Fiddes (A report by Bob Swinton) INTRODUCTION The Workshop on 27th to 29th June , organised by th e Water Board (Sydney) and atte nded by re presentatives of Water Auth o rities and consultants from all over A ustralia and New Zealand , was convened to address the mounting problem of management of sewer assets, and in particular, to estab lish a consistent system for reporting of defects, leading to a computerised assessment of priorities for rehabilitation or ren ewal. The guest speaker , Dav id Fiddes, reported that th is same subject had been addressed in the U .K. and valuab le lessons had been learnt.

U.K. CONCERN -

INITIAL SURVEY

Concern abo ut deterioration of sewers was first ex pressed in U.K . in th e early 1970s, but it was only when the Regional Water Authorities were esta blished in 1974 that a more complete overview of the situatio n was made possible. A National Assess ment was published in 1977 which showed that the rate of curre nt spending seemed to ass ume an average life of 200 years, and th e main rehabilitation strategy was 'crisis maintenance', with little logical assessment of priorities , mainly because of a lack of reliab le consistent information. A project was commenced at WRc E ngineering to establish a register of sewer failur es, but after two years this was abandoned because both th e hu ge variation in year-to- year data and the interaction between structural an d hydraulic defi ciencies made it unlikely that any obvious corre lation could res ult within a reasona ble time scale. T he survey made it clear that th ere was a wide spectrum of failures - I 0% of fa ilures acco unted for 80% of all costs. The pre liminary results from th e survey showed up districts where the incidence of sewer fa ilures was twi ce the national average. T he ' hot spots' were the old industrial towns of the No rth of England (dating back to the start of th e Industrial Revolution), coastal towns (built on allu vial soils), and towns built on erodible soils. The North -West Water A uthority covered the wo rst area, the Severn Trent A uthority had the lo west number of problems. Further analysis showed that in N. W . W .A., of a total of 546 fa ilures, 108 occurred in sewers buried more than 3 metres, a much higher proportion than anyw here else. In Severn Trent , an attempt was made to correlate percentage of unso und length witli age. Whilst the overall unsound percentage was 2%, only 13% of sewers over 96 years old were classified as un sound , hard ly a clear condemnation on the basis of age alone . From an a nalysis of current capita l spending it was fo und th at wh ile 80% of ex penditure was on rehabilitation, most of this was for hydraulic reasons with stru ctural repairs respons ible for less than one third of the rehabilitation costs. T he inferences drawn from analys is of the sur vey res ults were: • structural problems were not as bad as had been feared • hydraulic problems were worse than structural • older sewers may still have a long life (some sewers over 150 years old were still so und, and some of the 2000 year old Roman sewers were in good co ndition).

STRATEGY OPTIONS Three strategies for sewer maintenance we re considered reactive or crisis main tenance, renewal on age, a nd pre-emptive maintenance . Renewal on age was clearly not a solutio n; the surveys had sho wn that age was not a good way of predicting residual life and that a program of plan ned replacement simply on the basis of age wo uld require large amo unts of money in the future . For example, it was estimated that if all sewers were to be replaced as soon as th ey attai n I 00 years of age, the annual cost 36

WATER October, 1988

David Fiddes is the General Manager, Projects, of WRc Engineering in th e U.K. H e was invited to Australia to participate in th e Wo rkshop on Sewer Condition Evaluation held in Coogee, Sydney on 27-29 June, 1988. H e gave a number of presentations during his brief stay in A ustralia, covering not only sewer assessm ent and rehabilitation, but also hydraulic performance. This report is a summary of the talk David presented in the MMBW theatre/le to MMBW officers and members of the Victorian Branch on July 5, in itself a summary of his presentation to the Workshop.

David Fiddes

throu gho ut U.K. wo uld have been £M200 in 1985, escalating to £M450 in 2035. Ass uming 130 yea rs as the criterion , the annual cost wou ld be only slightly red uced, to £M l 30 in 1985, an d £M3 60 in 2035. These hu ge sums can be compared with th e current rate of spend ing of £M60 per annum, whic h in itself does not all ow for catch-up of back-logs. A ttention th en shi fted to ' pre-empti ve maintenance' in volving a survey of existin g sewer conditions. A ro ugh estimate of th e cost of CCTV scanning of th e whole of the U.K. system gave a fi gure of £M250 . However, this estimate led to th e belief that CCTV scann ing co uld be cost effecti ve in about 20% of'critical sewers'. The definiti on of 'criti cal sewer ' then became a vital part of th e projects, and was based on the follow ing criteria: Depth : Brick masonry : Ground condition : Diameter: Traffic: Access Whether under buildings , railways, etc., aitd whether the sewer was a Main . It was found that whereas clay sewers comprised 80% of the U.K. system , only 14% we re critical , mainly du e to their smaller di ameter. T he critical sewers comprised 60% of the large concrete sewers and 25% of the brick sewers. An estimate of futur e spending over the next 20 years, based on crisis maintenance, was then made : £M over 20 years Back-log 1000 Short-li fe sewers 1500 Flooding/ surcha rging 2000 Correcting overfl ow 1500 Total

6000 ie an average spending rate of £M300 per annum. It was also possible that pre-empti ve maintenance prompted by assessment of condition could increase this expendit ure by 15%.

WRc SEWER REHABILITATION MANUAL In 1984 WRc Engineering published the Sewer Reha bilitation Man ual which presented a basic framework fo r sewerage rehabilitation and allowed th e most cost-effecti ve solutions to be achieved. The Man ual provides a detailed method of carr ying out a program of Sewer rehabilitation. The Manual explained CCTV Inspectio n procedures, laid out a systematic data recording method and spelt out a decision matrix based on degree of integri ty, incidence of surchargi ng and pollution by overfl ows, leading to a decision on rehabilitation or reinforcement, with replacement as a last resort. T his was integrated into software as the WALRUS package. In recent yea rs, more attention has been given to flow atten ua tion techniques to extend the hydra ulic capacity in ra in fa ll events. Decisions on rep lacement or rehabilitation are constantly being revised as new techno logies become app lied to in-situ rehabilitation .


PILOT STUDIES

STRUCTURAL ASSESSMENT IN U .K.

After the Manual was published, pilot studies were commenced in each R. W .A. to prove the effectiveness of the procedu res, to establish centres of expertise, to refine and tune the methodology, and to quantify implications in resources and management. These pilot areas were selected on the bases of reasonable records being already available, the presence of majo r perceived problems, the availability of tradi tional solutions and reasonable size (a population of 30 000 to 100 000 was considered managable) . The NWWA was an obvious place to sta rt. It had been estimated that to clean up pollution from the rivers in the area would require of the order of £M3000, including £M2000 for sewers alone. A contract was let to WRc E ngineering for a two year, £M3 stud y based on the Sewer Rehabilitation Manual. Sewers were grouped into strata corresponding to different levels of 'criticality' and the costs of applying the pre-emptive approach were estimated (Table I) .

David Fiddes then described the process causing structural deterioration of sewers, from an initial defect, leading to exfiltration, followed by infiltration, which results in formation of voids in the soil surrounding the sewer, and consequent distortion and eventual collapse. He outlined the current methods used in the U .K. for assessment of structural performance: (i) Identify critical sewers, a once-only decision, and mark them on the maps. Base this decision on high cost of repair, community (eg traffic delays), and hydraulic significance. (ii) Collect data on traffic, ground conditions, social cost etc by an obj ective procedure and screen this information into priorities. Take off the details onto sheets, then onto a fin al plan. Sewer condition is assessed by CCTV inspection after cleaning. This wor k is carried out by contractors who are required to use trained operators. The operators must have attended a course based on the WRc Man ual of Sewer Condition Classification which contains tabular photographs of standard defects, to enable consistent coding. For quality control about 507o of the length must be cross-checked by an independent engineer . It is vital that the contractors do not form a judgement, their function is to record data . T he Engineer the scores the data for severity; he can display it on a pictogram if desired and eliminate non-critical zo nes. At the same time as CCTV survey is conducted, photographs are taken through the TV system, say every 10 m, and these are stored in card index files. They are much easier to access than video tapes, and allow comparisons to be made in the future. T he photographs can be compared with standard-defect photographs, which have been published as wall-charts. The Engi neer thus has a visual grading, and can add to the assessment his knowledge of soil type and freq uency of surcharge to finish up with a priority listing. WRc has, to date, not been able to develop a better method of assessing condition than CCTV, photographs and walk-through , though other techniques are still being explored . It was emphasised that the danger lies in collecting TOO MUCH data, which can overwhelm the decision-making process. Inspection should only be instituted for critical sewers, when judged to be needed, and the minimum amount of good data collected. If the sewer is in bad condition, there will be an immediate decision as to when to repair , and 1 data need only be stored for statistical purposes. When a sewer is borderline, a collection of photographs, in colour, with good definition, graded according to the standard defect analysis, is easily stored for futur e reference and readily reviewed.

TABLE 1. COMPARISON OF CRISIS VER SUS PRE-EMPTIVE MAINTENANCE (N.W.W.A.) Stratum

N o. Units

6

7 16 10 17 30

4 3 2

Cost estimates, £M Initial Revised 31 5 480 240 128 90

207 266 2 19 216 198

For the more critical sewers, the pre-emptive method wo uld show considerable savings. However, for the less critical sewers. INCREASES in costs were shown up . These, in fact, highlighted that there was a need fo r additional sewerage schemes. At the other end of the spectrum, in the Severn-Trent Authority, there were no major 'hot spots', so a more leisurely view could be taken. It was decided to update all records and perform hydraulic assessment by 1994 and either CCTV or walk-through inspection of all critical sewers by 1997. The systematic inspection started on the worst sewers, and immediately showed up lots of uns uspected problems. The total of unsound lengths was about the same as recorded for NWW A, but work could afford to concentrate wherever the consequences would be the most severe. These were nearly always in the core of the system, usually the oldest areas of the cities.

ACCOUNTING SYSTEMS Allied to the proposals for privatization of the water authorities in the U .K. there has been detailed discussion on the most appropriate accounting practices to deal with assets such as sewers . Current-cost accou nting, which is based on the estimated asset li fe, was considered to be unsuitable for work with sewers which are ass umed to have an infinite life; if the residual life of the asset cannot be estimated then it is not possible to determine the cost of owning the asset. Renewals acco unting, which is based on the cost of maintaining an asset (eg a sewerage system) to a required standard, and involves an ass umption of infinite life with an allowance for maintenance of the asset over a defined period, eg 25 years, was considered to be more appropriate. Renewals Accou nting allowed authorities to establish a framework for estimating and recording costs of system maintenance. This then became an Asset Management Plan, and costs were allocated between capital and revenue. The approach had immediate relevance, since, in theory, a privatized Autho rity could allow its assets to run down in favour of dividend distribution, therefore some form of control was required. T he Drainage Plan provided a basis. This could be updated, say, every five years, and audited fo r its engineering content by an independent engineering company or consultant, and would define what financial reserves had to be put aside to cover the required maintenance. T he end result would be the no vel situation where the acco untants would be instructing the engineers to spend the allocated money. As a result of the incentive provided by privatization there has been more progress towards development of a suitable asset management plan in the last two years than there was in the previous 20 years.

ADAPTATION TO AUSTRALIA In conclusion, David Fiddes recommended the WRc Manuals, but cautioned that they could not be expected to apply directly to Australian conditions. A sub-committee was formed at the Works hop to tackle the necessary adaptions. For example, some of the technical terms do no t translate accurately from E nglish to Australian! It was notable that the incidence of corrosion of concrete sewers in U .K. is minimal compared to Australian experience. This may be attributable to our higher temperatures, allied to longer residence times. Consequently, the adaptations must be performed with due caution . In his address to the meeting, David Fiddes referred to the 1986 edition of the WRc's Sewerage Rehabilitation Manual. The first edition of this manual , which was produced and compiled under his project management, was published in 1983 and promoted by the UK Water Authorities Association Advisory Committee on Sewers and Water Mains. Feedback on use of the manual and results of ongoing research have been incorporated in the second edition, which from now on will be progressively updated with replacement loose leaf sections. Volume I outlines recommended procedures and implementation issues. Volume II sets out how to choose the critical sewers for examination, describes survey and analysis methods, and advises on when and how to consider hydraulic upgrading and/or renovation . Volume III enables engineers to decide whether the renovation option is suitable to meet identified needs and if it does, to prepare detailed schemes. Published by Water Research Centre, PO Box, Frankland · Road, Blagrove, Swindon, Wiltshire, UK SN58YR. • WATER October, 1988

37


RETICULATION SEWER REHABILITATION IN MELBOURNE M. J. Anderson, W. Page, J.C. Parnell, M. J. Poulter, R. J. Vass ABSTRACT This paper reviews the progress m~de, principally over th 7 past decade, in rehabilitation of the agemg cement-concrete reticulation sewers which comprise at least 1300 km, or IOOJo, of all sewers in the Melbourne sewerage system . Sewer system condition and trends are reported. An outline of the inspection and ass~ssn:ient methods and the criteria used to select sewers for renewal 1s given together with a comment on the deve!~pm_ent of a? overall rehabilitation strategy. Numerous rehab1htat1on techniques are available and still emerging. The selection of appropriate methods is discussed, together with a brief review of design and construction management issues. .. . The information is considered useful for other authont1es m similar situations and the paper concludes with a discussion on issues related to effective pipeline rehabilitation management in Australia.

Max Anderson

W. (Bill) Page

Mal Poulter

Roger Vass

INTRODUCTION Any large urbanised and sewered city like Melbourne has many thousands of kilometres of underground long-life sewers. Longevity of the asset is essential as the city becomes more and more developed and opportunities for relatively low cost replacement become less. While extensive and regu lar condition monitoring, rehabilitation and maintenance are undertaken on the _larger diameter strategic sewers, these only comprise a small fraction of the total asset. The majority of sewers are small diameter and non-strategic. Rehabilitation strategies and programs must be developed for all these assets to ensure service standards are maintained and to minimize the extent of emergency renewal. In Melbourne, although parts of the sewer system are approaching 80-90 years of age, some 600Jo of sewers were constructed less than 25-30 years ago. However, 900Jo of the 14,500 km of sewers are small diameter (375 mm or less) and this fact caused the Melbourne and Metropolitan Board of Works to begin, in the late 70s, to look closely at the condition, future performance and rehabilitation needs of this asset category. At least 1300 km ( or about 1OOJo) of all reticulation and branch sewers were constructed using concrete pipe. Present records do not allow an accurate estimate, another estimate indicates there may be some 2100 km of concrete pipe. Many of the pipes are now approaching 80 years of age with the oldest laid in 1905. In the late 70s-early 80s it became noticeable that these sewers were collapsing at an increasing rate . The demand on manpower was rising and the cost to repair a collapsed and blocked sewer was high. The MMBW began a program of sewer investigation and renewal of these sewers. This program has evolved as more knowledge has been gained . . This paper details some of the Board's experience and approach to the problem in the hope that others may contribute their views and experiences.

HISTORY OF RETICULATION SEWER CONSTRUCTION About 400Jo of the 1300 km of concrete reticulation and branch sewers have been co nstructed in the Board's Southern Region which covers much of the older inner Bayside suburbs located on sand or clay-sand belts. Of a total of approximately 850 km of 100, 150, 225 and 300 mm diameter reticulation sewers constructed in the region up to the year 1940, 523 km, or 610Jo, was constructed using concrete pipe. One third of the concrete pipe (169 km) was laid in the period 1905 to 1910. Althoug~ the rate of construction varied betwee n years the average expans10n over 36 years was 14.5 kilometres per year.

COLLAPSE OF CONCRETE SEWERS Studies have concentrated on collapses which cause blockage and loss of service (other stoppages due to siltation a nd root 40

WATER October, 1988

The authors are all civil engineers employed by the Melbourne and Metropolitan Board of Works in various aspects of the management of sewer assets. Max Anderson, B.E., is Pipeline Asset Life Project Officer, Regional Operations Group (Southern Region) and is involved in assessment of sewer condition and performance. . W. (Bill) Page, Dip. C.E., is Engineer, Renewals Section, Sewerage Urban Development Branch, System Planning Division and is responsible for the planning of inspection programs and renewals. 1 John Parnell, B.E., is Direct Management Engineer, Engineering Services Section (Southern Region) R egional Operations Group and is responsible for the design and construct/On of rehabilitation works. Mal Poulter, Dip. C.E., M.I.E.Aust., is Materials Coordination Engineer, Research and Investigations Branch, Systems Planning Division and is responsible in part for the approval of appropriate materials (and methods) for sewer rehabilitation. Roger Vass, B.E., M.Eng.Sci., Ph.D., M.I.E.Aust., is Engineer for Renewals, Offers and Backlog, Sewerage Urban Development Branch, Systems Planning Division and is responsible for the overall strategic planning of reticulation sewer rehabilitation .

penetration may occur but these have been excluded). There has been a total of 676 concrete sewer collapses recorded to date in Southern Region. Figure 1 shows the trend of these collapses. Prior to 1982 collapses were increasing exponentially but have decreased since 1982; it is believed that the programmed rehabilitation of sewers over the past five years has restored many sewers which had been in imminent danger of collapsing. The average rehabilitation rate over the past six years has been 3.2 kilometres per year with a maximum of 6.2 kilometres in 1985 as shown in Figure 2. The number of sewer collapses per kilometre for a particular diameter sewer is one quantifiable measure of performance. It has been observed, by ranking sewer reticulation areas in descending order of collapse rate, that the performance is linked to location, pipe size, pipe age and pi'pe material. This list is now being used to target photographic inspection and rehabilitation programs. Previous collapses on manhole lengths that subsequently have been rehabilitated are excluded from the calculation of the collapsed rate used in the ranking of areas.


OBSERVATIONS OF SEWER PIPE LIFE

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Analysis is currently under way to determine the probabilities of collapse for particular categories of sewer with time . Conclusions from this work are difficult because of the limited amount of data. However , it is known that 83% of pre-1911 150 mm diameter concrete pipe manhole lengths have had at least one collapse. The distribution of these collapses is shown in Figure 3. The mean of the record is 71 years and standard deviation is 13 .5 years. It is clear that there is a long 'lead-in' period when there are very few, if any, failures per year. The bulk of first collapses have occurred over a period of 25 years from a pipe age of 55 years to 80 years. Therefore the average life of the pre-191 I 150 mm concrete pipes is estimated to be approximately 70 years. Similar conclusions for pre-I 91 I 225 mm diameter pipes cannot be drawn because only 9%, or 161 mannole lengths out of a total of 1828, have experienced a first collapse. However, it does appear that the mean life of this category of sewer pipe is longer than that of its smaller counterpart. The percentage of the system to have experienced a second collapse is only small at th is stage, but the mean times to the second, third and subseqent collapses are approximately 7, 5 and 3 years respectively. The number of repeat collapses will increase at a faster rate t han the first collapses as more and more manhole lengths reach the end of their useful lives.

Figure 1. Total sewer collapses by year, southern region.

SEWER REHABILITATION STRATEGY

7

The Board' s overall sewer rehabilitation strategy has four aims. These are : - to avoid a crisis maintenance program for the overall sewer system - to avoid wholesale renewal as a solution - to reduce the risk of costly and disruptive loss of service on the most strategic sewers - to use the most cost-effective rehabilitation method.

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Rectification of da mage to the fa bric a nd the emergency recon struction of short lengths to overcome a local per forman ce fa ilure .

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Meth ods of rein stating the existing sewer perfor mance lo original design intent o r margina ll y beller which incorporates the origina l sewer fabri c.

Renewal

A s fo r 'Renovatio n' except the pipe is replaced off- line (o r if replaced o n-line t he origina l pipe plays no pa rt in ac hieving performan ce)

Replacement

As fo r ' Renewa l' except a substa ntia l improvement in perfo rmance over that o f the original design intent. On-line or o ff- li ne replacement is possible.

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A s for ' Stru ctural ' but the methods differ eg reduced frictio n losses.

As for Structural but is called an Augmentatio n because of increased hydra ulic demands.

Intercep tio n (Attenua tio n n o w reductio n)

Original line rema ins but has reduced performance requireme nt s compa red with original design. O ther existing or new lines carr y the load removed .

Reliev ing (sometimes called - Reinforcement Duplication)

Origina l line continues to perform a t design intent. Excess load s a re di verted to a new line which in conjunctio n with ex isting sewer increases ove ra ll now performance.

80

SEWER AGE (years)

Sta ndard or no n sta ndard, irregula r or regula r, intermillcnt or continuous act ivit y designed to ma inta in perform a nce a l design level.

WATER October, 1988

41


While the reticulation sewers cannot be considered strategic they are, by far, the majority of sewers and any escalation of deterioration may impose a substantial maintenance bill. Hence the first aim has been given some priority to these without limiting the_ attention given to the far less numerous but more strategic maJor sewers. These latter are addressed more on an individual basis rather than on the group basis approach reserved for the smaller sewers . The objective of the strategy is clearly to provide a level of service to the customer at least cost. Maintenance of a required performance is thus the goal. In all cases rehabilitation recovers performance. 'Performance' is the efficient conveyance of sewage remote from the environment at defined reliability. Reliability should be defined in terms of allowable infiltration, frequency of blockage, surcharging and cleaning over the design life. The reliability would be expected to change with time. There are several rehabilitation options availab le as shown in Table I . All are, by definition, performance based. In practice it is usually cheaper to use the bore created in the ground by the existing pipe for as long as possible. Rehabilitation for structural reasons indicates that the sewer .has deteriorated and a decision is needed to determine whether the rehabilitation category will allow established or required performance for less than, equal to, or greater than remaining design life, or will reinstate original design life . Hydraulic considerations must be applied and again these are expressed in terms of performance reliability viz. 'Will the sewer convey sewage flows, at acceptable surcharge frequency, less than, equal to, or greater than the nominal design capacity?' Rehabilitation for hydraulic reasons alone need not involve structural rehabilitation analysis beyond assessment of remaining life. In fact structural life may be increased by undertaking interception or relieving works. Deciding whether to repair, renovate or replace is a complex issue and requires the following details: - benefit-cost of repair versus the other options - funding policy for works - service policy (reactive versus pro-active) - available rehabilitation techniques and costs - knowledge of the disadvantages/ advantages of these techniques - assessed pipe physical conditions and future performance - assessed hydraulic requirements - assessed ground conditions - accessibility of sewer - site constraints and conditions - works scheduling - service provision during rehabilitation - emergency service recovery after failture - disruption costs during rehabilitation - consequences of failure (pollution, numbers affected, duration)

For a p~rticular manhole length to b~ placed on a 'programmed renewals' :-vorks program (ie fa lling into the Type 3 category), it is generally mspected via a Closed Circuit TV or 3D camera. The condition of the line is assessed from the resulting film and ~rioritised along with other manhole lengths. From this prioritisat10n, a three year program of works is produced. In order to determine whether a manhole length is to be inspected, the following criteria are taken into account: - Pipe material - Local knowledge of Operations personnel - The number of dig-outs in the area - The known conditions of other areas in the general vicinity - Age of pipes in the area - Consequence of collapse - Catchment performance By taking these factors into account it is anticipated that lines which a re expected to be in good condition and lines which are expected to be in very poor condition will not be inspected. Those lines which are anticipated to be in very poor condition (ie Type 2 sewers) are immediately placed on the 'programmed renewals' works program. Those sewers for which inspection is warranted become Type 3 sewers and are placed on an inspection program. Once an inspection has been completed the film is examined to assess the condition of the sewer lines. The pipe condition is rated on a scale of 0-100 which takes into account the internal corrosion, infiltration, cracking and tree root penetration. The pipe condition rating is only one of the factors used in assessing if a line should be placed on the program of works. The complete assessment criteria for selection onto the works program is as follows - Pipe condition - The number of dig-outs on the particular manhole length - The number of dig-outs in the area - The age of the pipes - Performance of lines immediately upstream and downstream - Consequence of collapse - The known condition of other areas in the general vicinity - Performance of the area as a whole - Catchment performance When all the assessment criteria have been considered it becomes obvious if certain manhole lengths are in immi;ent danger of fai lu re. These 'at risk' manhole lengths are then placed on the rolling three year works program for design and construction. Priorities on this program are assigned to those lines which are considered the most urgent, ie those lines with the most points on the assessment criteria list.

APPLICATION OF THE STRATEGY

CONSEQUENCE OF COLLAPSE

The strategy is applied in three ways: Type 1 - at the time of co llapse a decision is made whether to repair locally the collapsed section or renew the complete manhole length . Type 2 - for those sewers with a past history of poor performance a decision is made whether to add these to a "programmed renewals" works program (see Type 3 cases) or to schedule these for construction at next collapse . Type 3 - for those sewers with a reasonable past performance a decision is made to add these to a 'programmed renewals' works program after condition inspection and assessment. The emergency repair on a concrete pipe can be in the form of a short localised replacement of the same size pipe in either vitreous clay or (!P_YC. This method has been extensively used in the past because 1t 1s the fastest way to overcome the immediate problem. The decision -to repair or rehabilitate between manholes was not made until a shaft had been excavated to the pipe and the condition of the pipe assessed. From the computer-recorded performance history of sewers and kn?wn costs to repair or rehabilitate the sewer, the Board is now usmg a net present va lue economic analysis to assist in determining the appropriate time to rehabilitate a sewer manhole length. This analysis can be carried out at the time a sewer collapses ~'.ype 1 situation) or prior to a collapse (Type 2 situation). A sens1tiv1ty a nalys is 1s undertaken by varying the estimated costs and the estimated or predicted years to subsequent collapses. The analysis is computerised for quick evaluation an¡d alteration. 42

WATER October, /988

INSPECTION, ASSESSMENT AAD SELECTION

. ~ 'consequence of collapse' rating system to apply to ind1v1dual manhole lengths is being developed. This rating incorporates the environmental and service impact to the public and the hydraulic system respectively. Factors considered in developing this rating are: - size of the pipe - location of the pipe - zoning of the area - disruption to veh icle and pedestrian traffic - noise disturbance - dirt and dust pollution - potential for property damage - difficulty in providing continued service

SEWER REHABILITATION METHOD SELECTION One of the factors required in deciding on rehabilitation is the availability of suitable construction methods. The technology of underground or trenchless renovation and replacement of pipel_ines is developing rapidly. If a successful long life rehabilitat10n 1s to occur then careful selection of the method is important. A detailed review of the various methods has been given by ".ass (1~88): ~n summary, Table 2 lists the methods and their principal su1tab1hty agamst the rehabilitation requirements. It is argued that a successfu l selection is based on a detailed knowledge of _th e practical ' limitations-of-use', ie to identify where a particular method will not perform satisfactorily


(de Rosa, 1987). Provided any method is selected, designed, installed and operated within its 'limitations-of-use' then the effective life of the rehabilitation works is indeterminate and there is no technical justification for ascribing different asset lives to different methods. Details of these limitations for each method must be obtained from t~chnical reports, specifications, codes of practice, manufacturers' literature , in-service performance and the construction process. This is the ideal case and a set of 'rules' or decision protocol on method selection is not yet available although work is progressing on such a protocol (Parent, 1987). Experience in Australia is so limited, both in terms of the many available methods, their costs and knowledge of our sewerage systems, that such a procedure will be difficult to implement. TABLE 2. APPROPRIATE REHABILITATION TECHNIQUES Ca1egory

Me1hod Repair

Reno vate

Renew

Replace

lnsitu liners Slip liners Wound liners Segmental liners Stabilisation Sealing Dosin g (friction reduction) Micro-t unnelling Augers Im pact Molin g Directional dri lli ng Pipe rammin g Conventional tunnelling Tren ching Shared conduits

MELBOURNE BOARD EXPERIENCE WITH REHABILITATION TECHNIQUES Management of Design and Construction Reticulation lines assessed as requiring rehabilitation are designed to current standards. Main requirements are: - diameter of sewer required, which determines method of renewal - condition of manhole, eg step irons, cover, concrete condition - manhole spacing - location , diameter and material of connection In Southern Region a 19-man construction team is used, usually split into two gro ups of between 7 and 15 on each job. Some work is undertaken by contract.

Rehabilitation Construction Methods Slip-lining with UPVC and Polyethylene Pipe

About 15 km of reticulation sewers have been slip-lined using UPVC, mostly in 225 mm diameter sewers . Polyethylene has been used in a few cases. Slip-lining is used wherever possible as it is generally the cheapest method. A large number of the original concrete sewers were constructed in 225 mm pipe and can thus be slip-lined to 150 mm or 175 mm . Slip-lining is straightforward and usually trouble-free. The sewer is first plugged and the pipe inserted from the upstream end and when necessary the sewer can be released. Problems can be caused by excessive sediment build-up in the line which then requires auger clean-out. Occasionally the leader of the liner pipe can become stuck due to the misalignment of the existing pipe. Size-for-Size/Pipe Bore Replacement

To date size-for-size has been done by open cut, impact moling or reaming. The more powerful 'expander' type impact moling has not been used either for size-for-size or upsizing replacements. Approximately 9 km of reticulation and branch sewers have been replaced using a reaming technique. Size-for-size replacement of 150, 225 and 300 mm diameter sewers and upsizing of sewers from 225 to 324 mm and 305 to 365 mm has generally been successful but with some difficulties. Problems encountered have

been the breakdown in butt-welding equ1ipment and difficulties in boring through concrete-encased pipe, inspection sha ft fittings, repaired sections and poor ground conditions. A boring rate of 8 metres per hour can be achieved. Impact Moling has been used with moderate success on 700 metres of size-for-size replacement of 100, 150, and 225 mm diameter sewers using the 'Grundomat' impact moling machine operated by contractors. Subject to satisfactory set-up preparation , overall laying rates of 80 m per day, including reconnection, have been achieved. Retardation of moling due to friction on the new pipe and suspected loss of air at the head has occurred. Difficulties have been encountered when trying to crack and displace pipe fragments into stiff clay or crushed rock bedding or when cracking concrete-encased pipe and fittings and repaired pipelines. For size-for-size replacement the sewer is usually plugged and bypass-pumped, and the line completed before being re-instated. The advantage of slip-lining and bore replacement methods is that each connection is rebuilt and any concrete pipes in the connection are replaced. Shafts are excavated at all connections and at each manhole for entry and exit of the Impact Mole. The sewer is pressure-tested prior to connections being made. In-situ-lining Processes

These methods are used where surface obstructions or depth make them more practical and economical than other techniques . The in-situ lining process is particularly useful where the old cement concrete sewers are in reasonable condition but suffering invert erosion and bore corrosion causing pocking and exposure of the aggregate. The sewer is cleaned and plugged prior to the contractor being given access. The sewer is usually educted (including connections on the line) due to the short duration of the work . After curing of the lines connections are reopened from inside the pipe and the line reinspected by CCTV. Amatek (formerly Monier) 'Insituform ': Since the original trials in 1979, 4460 m of Insituform have been installed (to July 1987) in 150, 225, 300 and 450 mm sewers. No significant problems have occurred with the installation of this product and lines that have been checked after five years service are giving satisfactory service. Humes ' Duraliner': This process has been used to renovate 70 year old concrete sewers 150, 225 ÂĽ1d 300 mm diameter. Trials in 1985 , 1987, and 1988 have resulted in some satisfactory lining operations but also unsatisfactory linings (Poulter, 1987). The lining process has been, in this time, continually refined and developed. Coatings -

Spray on Cement-Polymer Mortar -

'Supaline'

A trial has been carried out on 120 metres of a 305 mm diameter; 70 year-old cement concrete pipe. Inspection of the sewer indicated invert erosion (5-15 mm), with slight H2S corrosion but a structurally sound pipeline. The cement lining was completed in 50 minutes and cured for five hours. The resulting lining thickness was found to be not within tolerance, with thin sections and major corrugations. Modifications to equipment and technique are required to overcome these problems. The Board has used other techniques but few are suitable for the rehabilitation of the smaller diameter reticulation and branch sewers which are the subject of this paper. Refer to Poulter, 1987 for more details .

REHABILITATION HISTORY AND SUCCESSES IN THE SOUTHERN REGION Figure 2 showed the length of sewer pipe that has been rehabilitated annually from 1966 to 1987. A total of approximately 33 000 metres has been rehabilitated, with 17 125 metres, or 600Jo, of the work occurring since 1983. This work has been carried out as a consequence of the extensive photographic inspection program which started in 1982. Figure 4 highlights the significant reduction in collapses in the municipality of Brighton, Vic, as a consequence of the intensive rehabilitation program. Collapses fell from 19 in 1982 to 1 in 1987 whilst 11 600 metres of concrete sewer was rehabilitated. In 1988/89 the board has budgeted $3. 9 m fo.r rehabilitation of reticulation sewers. Approximately $1.65 m of this will be spent in the Southern Region and 200Jo of this on bore-relining (in-situ lining) methods. WATER October, /988

43


COSTS OF REPAIR AND REHABILITATION

CONCLUSION

The cost of dig-out repairs is primarily dependent on the depth to which a shaft must be excavated. Other factors such as pipe diameter and location provide the variation in cost. The curve shown in Figure 5 plots costs of 108 dig-outs versus depth. Table 3 summarises the costs to rehabilitate 150 mm and 225 mm diameter sewers in the Southern Region. Programmed rehabilitation commenced in April 1982 and all costs have been adjusted to February 1988 figures in accordance with the consumer price index.

The foregoing has outlined one authority's approach to a particular asset management situation. All-similar urban water and sewerage authorities in Australia have very substantial amounts of buried assets which dominate their assets register and valuations. These pipeline assets will not last forever. Responsible asset management strategies must be developed by engineers to ensure cost-effective future investment in rehabilitation work by these authorities. It is believed that any successful application of a strategy needs the following: - awareness of the emerging technology: This involves detailed knowledge of the technique, examples of its successful and unsuccessful use, full cost identification, participation in trials (not necessarily in Australia) and definition of the limitations of use - knowledge of trends in the asset condition, and forecast performance - a procedure for selecting rehabilitation method - establishment of a market With regard to the last point, the rehabilitation market in this country is small and unco-ordinated compared to some overseas countries. The pipeline rehabilitation market is potentially enormous yet to date we have seen only minor experimentation with the newer methods and wide use of only a limited range of methods; this is certainly the case for water mains and sewers. The steps required if a market is to be established are: - prepare a detailed profile of Australian sewers - prepare a national strategy for the rehabilitation program - undertake a nationally co-ordinated series of trials in this country or sponsor overseas trials - prepare a local 'limitations of use' selection protocol for various approved methods - invite registration of interest from various contractors with particular techniques to meet the Nationa l Strategy - commence a series of nationally co-ordinated tenders for particular parts of the rehabilitation strategy - commence to assist the Australian industry to market its expertise and capability to countries in our Regi<;m. The final outcome of this approach is new technology, greater productivity, reduced unit costs, new employment, new markets and exports. Jobs will be undertaken on a straightforward commercial basis and not as special exp,erimental projects.

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REFERENCES

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ANDERSON, M. (1988). 'A Study of the Collapse of Concrete Sewers in Melbourne' s Southern Region' to be published as part of the Pipeline Life Project sponsored by the Urban Water Research Association . DE ROSA , J. ( 1988). 'Selection of Pipe Materials for Water Supply' in Proc. Workshop on ' Pipeline Materials Options' sponsored by Water Tech. Comm. Australian Water Resources Council (Melb., Vic.) Jul y. GIDDINGS, B. D. (1985) . 'Sewer Rehabilitation in Melbourne' proc. Nat. Conf. on Eng. in Australia (Melbourne). PARENT, R. A. (1987) . 'Los Angeles Concrete Sewer Assessment Program' Paper 5. 1, in No-dig '87 Conference, Int. Soc. for T renchless Tech. (U.K.), April. POULTER , M. (1987). 'Sewer Rehabi lit ation - Strategy, Assessment and Materials' in Proc. Workshop o n 'Pipeline Materia ls Options' sponsored by Water Tech. Comm. Aust. Water Res. Council (Melb , Vic), Jul y. VASS, R. J. (1988). 'Sewer and Water Main Rehabilit at ion - a review of methods and their solution', A WWA Summer School ' Optimizing the Use of Water Industry assets', (Hobart, Tas.) 22-26 Feb.

ACKNOWLEDGEMENT

TABLE 3. SUMMARY OF REHABILITATION COSTSt Method

Slip Lining (UPVC)

(1982-88)

Original Pipe Size

Size New Pipe

Total Length Metres

Average Cost Per Metre

225 mm 225 mm 300 mm

150 mm 175 mm 225 mm

12 220 2 391 203

$232 $203 $6 11

150-225 mm

3 570

$159*

150 mm 225 mm

596 3 310

$453 $400

93 1

$480

150 mm 225 mm

705 I 087

$425 $370

150-225 mm

I 196

$398

(1987/ 88) Bore Relin e (In-situ lining)

(1982-88)

150 mm 225 mm

(1987/ 88) Impact Moling (Grundomat)

(1982-88) (1987/ 88)

44

WATER October, /988

150-375 mm 150 mm 225 mm

Cost Range

The authors acknowledge the assistance of many staff involved in the asset management area and are grateful to the Board for permission to publish.

($122-250)

($374-607)

Footnotes, Table 3

t ($214-526)

All costs are total contract plus Board costs as at February 1988. â&#x20AC;˘ Significant reductions in site establishment costs have occurred in recent years.

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Water Journal October 1988  

Water Journal October 1988