Full Description

Calgary, Alberta is a city of almost 900,000 people and one of thefastest-growing in North America. We have 4000 km of water mains, the majority ofthem relatively young, since half our growth has occurred since 1970. An unusualfeature is the proportion that is polyvinyl chloride (PVC) pipe, now the singlelargest component of our system. Another is that the majority of our ductile ironpipe is YDI, yellow-jacket pipe that is especially well protected againstcorrosion, both with coating and cathodic protection. In consequence, ourbreak-rate has now been stable for some years at only 500 breaks/year, 400 ofthem main breaks. Roughly 60-70% of them are related to external corrosion. Wehave reduced our replacement program repeatedly in recent years, and now feelthat we have come through the other side of a 25-year problem that started in theearly 1970s when our main break rate started to climb alarmingly. After a fewyears of it, we started to increase our replacement program. We continued thoseincreases until just a few years ago, with cumulative costs (compared to the 1986and 1999 levels) over this period in the high tens of millions of dollars. Wewere concerned that the break rate would spiral out of control as we had a greatdeal of pipe all installed during short "boom" periods that could have reachedthe end of its life all at once. Calgary's changes in preferred pipe materials,first to YDI, and then PVC, came about during a time of very heightened concernabout external corrosion, a concern that may not affect every utility. Thesubsequent cost and work-time advantages of PVC have, however, been pursuasive,and we would certainly continue to use it even if a perfect and free cure foriron corrosion appeared. The primary concern with PVC is that it is wise - evenessential - to handle it and work it with great care, and bed it in "soft"non-damaging materials such as sand, pea gravel and granulite. The obviousrecommendation for further study is that utilities from warmer climates thanCalgary share with the industry their total construction costs with the fullvariety of pipe materials that utility construction engineers now can choosefrom. Includes figures.

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Edition: Vol. - No. Published: 06/01/2001 Number of Pages: 10File Size: 1 file , 1.1 MB