Unearthing the Past to Chart the Future

INTRODUCTION• Logan City Council provides water and wastewater services to 300,000

people living and working across 957km2 of urban, semi-rural and emergingneighbourhoods.

• The City of Logan water supply network features 2,200km of mains,of which nearly 900km are asbestos cement (AC) pipes.

• Historically, Council’s water mains renewals programs were reactive andaddressed frequently failing AC mains (mainly DN100 reticulation mains).These mains are between 30 and 55 years old, as shown in Figure 1. Failuredata collected by Council indicates that the likely service life of AC mains is60 to 70 years, which means that the risk of pipe breaks and bursts in thecoming years is high.

• Pipefittingsinstalledacrossthecitybefore1980weremadeofunlinedcast iron, and they are now showing signs of severe tuberculation.

Troy Kasper, Priyanthi Samarakoon, Sandamali Weerakoon and Matt ThomsonLogan Water Infrastructure Alliance - Logan City Council, Downer, Cardno and WSP

Testing of AC pipes in the field

Testing of this 1980s AC pipe shows that the magenta areas are sound; the lighter coloured areas are not

Tuberculation in an unlined fitting

Replacement of fittings and mains presented opportunities to collect data on AC mains

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AC PVC DICL CICL PE MSCL UK

AC Mains

Unlined Fittings

Figure 1: COMPOSITION AND QUANTITY OF WATER MAINS INSTALLED OVER TIME

RESULTS• Opportunistic condition assessments in one of the City of Logan’s older

water supply zones (Eagleby DMA 55) showed that:- while age was a factor in the deterioration of AC pipes, there was no direct

correlation between age and pipe failure rates- there was internal and external deterioration of the pipes (see Figure 2)- internal deterioration was not uniform, suggesting that pipe wall

composition during manufacture may have been inconsistent- there was evidence of possible periods of aggressive water in the pipes- results were inconsistent, with deterioration levels varying on each side offittings–possiblytheresultofvaryingqualityofACmainsorconstruction methods.

Percentage of pipe samples with external degradation

Percentage of pipe samples with internal degradation

Percentage of pipe samples with eff ective thickness > 60% (remaining life > 10 years)

Percentage of pipe samples with eff ective thickness > 40% and <–60%

Percentage of pipe samples with eff ective thickness <–40% of original wall thickness

Percentage of pipe samples estimated to fail within 10 years

100%0% 10% 20% 30% 40% 50% 60% 70% 80% 90%

65%

29%

36%

35%

74%

91%

Figure 2: PERCENTAGE OF PIPE SAMPLES WITH DEGRADATION AND ESTIMATED REMAINING LIFE

CONCLUSIONOpportunistic condition assessments and failure analyses of AC water mains have increased Logan City Council’s knowledge of the variable condition of its water supply network. Gaining this knowledge by ‘unearthing the past’ is helping Council to make informed decisions about how to best manage ageing AC mains.

CONDITION ASSESSMENT APPROACH• A risk based approach was used to determine the priority of water mains

renewals in DMAs. This considered:- likelihood of water main failure based on criteria such as age, material,

pressure, environmental conditions (such as reactive clay) and historical performance

- assessment of the consequence of failure based on criteria such as diameter, location and critical customers serviced

- analysis of historical failures and failure modes to determine trends and hotspots.

Akeyfindingwasthatwaterpressureondeterioratedpipewallscontributedto nearly 50% of AC main failures.

• A practical, safe method was developed for opportunistic conditionassessment of AC mains on site, using a phenolphthalein indicator.Test results informed decisions on whether to renew the whole main orjustunlinedfittings.Theonsiteassessmentcouldbesupplementedbytesting of rubber rings and pressure testing of mains as desired.

CHALLENGES AND OPPORTUNITIES• Council recognised that the performance of AC water mains cannot bejudgedonfailurehistoryalone.Historicaldatadoesnotofferaforwardviewof likely pipe failures, or indicate where investment in water main renewalsis a priority. A better approach was required.

• Replacementofunlinedpipefittingsofferedanopportunitytocollectdata on AC mains. This was because replacement of the mains required aclean cut of the pipe. The cut section, particularly at a tee junction wherea hydrant and valve are located, was considered the ideal place for acondition assessment.

• Replacingwatermainsandfittingscanbehighlydisruptiveforcommunitymembers. A challenge was to plan a renewals program which minimised thefrequency and duration of impacts. A way to achieve this was to conduct allrenewals on a district metered area (DMA) basis, replacing all assets whichwere unlikely to provide an additional ten years of service.