Calgary is a city of almost 900,000 people and one of the ...



Water Pipe Materials in Calgary, 1970-2000

Roy Brander, P.Eng

Sr. Infrastructure Engineer

Calgary Waterworks

Calgary is a city of almost 900,000 people and one of the fastest-growing in North America ; we expect to reach 1 million before 2005. We have 4000km of water mains, the majority of them relatively young, since half our growth has been since 1970. An unusual feature is the proportion that is PVC, now the single largest component of our system. Another is that the majority of our ductile iron pipe is YDI, yellow-jacket pipe that is especially well protected against corrosion, both with coating and cathodic protection.

In consequence, our break-rate has now been stable for some years at only 500 breaks/year, 400 of them main breaks. Roughly 60-70% of them are related to external corrosion. We have reduced our replacement program repeatedly in recent years, and now feel that we have come through the other side of a 25-year problem that started in the early 70's when our main break rate started to climb alarmingly. After a few years of it, we started to increase our replacement program, indicated in kilometres by the bars in the chart at left. We continued those increases until just a few years ago, with cumulative costs (compared to the 1986 and 1999 levels) over this period in the high tens of millions of dollars. We were concerned that the break rate would spiral out of control as we had a great deal of pipe all installed during short "boom" periods that could have reached the end of its life all at once. One “boom” had occurred in the 1950’s with CI, the other was Calgary’s “1970’s oil boom” in which various DI pipes were used during the growth period.

It would require considerable historical research to depict what pipe was installed originally, but we have a good database of what is still in the system. In the case of the PVC and YDI data-series, it's the same thing, because almost none has ever been replaced. CI has been left out of this picture because it pre-dates our decisions in the 1970's that caused our evolution through different pipe materials. The installation histogram of PDI, poly-wrapped ductile iron (in green), would have originally been twice as tall; we've pulled out a couple of hundred kilometres of the original 700 or more that went in. Most of our DI it is PDI, the “bare” DI is the much smaller black curve. We started off installing PDI and DI in about equal amounts, but shifted entirely to PDI in the early 70's as corrosion became a concern, while also trying out AC, asbestos cement, which gave us a lot of trouble with "workmanship-related" breaks, and various other DI coatings, like Taped-Urethane DI, and YUDI, yellow-jacketed urethane DI. But the coating we switched to aggressively in 1975 was, “Yellow-Jacket” on the ductile iron, a heavy polyethylene. The great surge in main break rates in the early 70's was largely due to corrosion problems, and Calgary was expanding into areas that had much more corrosive soil. We still use YDI, in any location where there is a concern about hydrocarbons ever having been in the soil. But after just 5 years of YDI, we switched again to PVC as the material of choice, and that continues today.

This is a map of Calgary showing just the water mains, and colour-coded by material type. It shows the “growth rings” of our city very plainly, with the dark blue as the thick-wall (pit) cast iron from 1900 to 1955, thin-wall (spun) cast in magenta from 55-68, and the light blue of DI from 68 to 78. The various DI wrappings are lumped together in light blue except the YDI, which is orange, and then the PVC is the green in the outermost ring. The Grey is the colour for "other" much of which is concrete feedermains, and our brief flirtation with AC down in the south end in the early 1970's.

The major growth area in the 1970's was in the flat plains area in the northeast, indicated by the dotted rectangle on the previous map. A lot of it had formerly been ponds and sloughs and the soil was far more corrosive than anything we'd encountered previously.

The northeast is a good showcase for the colour-code system because it has a little of everything, from the thick and thin-wall cast of the previous growth ring to all the materials we went through in the 70's. The blue DI and the green PVC are intermingled in this area, but because so much of the DI and PDI had to be replaced. Where there are blocks of blue DI colour in the centre area, those blocks are the survivors of when it was all DI. Some of it even had to be replaced during our YDI years in the late 70's, when the DI was just 7 to 10 years old. The problem was mainbreaks, superimposed on the pipes as red dots. All of the dots on the green PVC happened to the CI or DI pipe that the PVC replaced.

The second version, below, highlights where the replacement has been by turning from red to white any break that was on pipe now replaced. Some of the YDI is replacements, but most is original. As shown at left, YDI does have some breaks, and a few blocks out in the far east end are becoming a concern. A program to repair faults in the cathodic protection systems is being stepped up.

But note also, the blocks of DI that not only survive, but to this day, have very few breaks. We've recently run a Hydroscope through some of those mains, and a few barely even have pits, though they are just a few hundred metres from blocks that had to be replaced very young. Corrosion is highly dependent on local soils. The very worst locality is the south end of this area, indicated in the dotted rectangle on the previous map, is about six square miles of the system that was a mixture of CI and DI, is shown below with all main breaks restored to red:

This area will be used to show a time-series that may explain why Calgary became so concerned with corrosion problems in the 1970’s and began aggressively researching cathodic protection, and switched the preferred mains material twice in one decade: first to YDI, then to PVC.

The impetus for this is only partly explained by the sharp increase in overall breaks shown on the history graph on the first page. The situation was exacerbated by geographic concentration.

The time-series on the next page will remove the visual distraction of the pipes, and show only coloured dots for the main-breaks. The time-series will only show the historical period in question, the 1970’s, as opposed to all breaks that have occured in the six sections from 1960-2000.

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In 1970 and 1971, there were a few more breaks in this area than the city average, shown here by the white dots. Their pattern was not especially unusual for the city norm. There were a few blocks that had a couple of breaks per block per year.

Adding in the 1972-73 breaks in orange, there is already a trend of increase visible, and a concentration of much of the increase onto a few blocks that were getting too many complaints to be left in the ground. We also started to see some repeat breaks in the DI blocks further north, mains that were just four and five years old – only a few breaks per year to pipes of this age, but it escalated to dozens per year by the end of the decade – and PDI mains had as many as DI.

The colours are changed at random with each two-year period, to highlight the added breaks. 1974-75 was the turning point for us. The trend continued to worsen. It wasn't just that our break rate had gone up 50% in five years, it was that much of the increase was concentrated in one area where the public was understandably up in arms - and that a lot of the main affected was very young. We did understand it was the corrosive soil and not anything different about the DI from CI, but still it was plain that “Something Had To Be Done”. The Chief Engineer of the time, Jim Bouck, was presented with considerable pressure from the public and their aldermen. His first judgment was that they were having about as much trouble with PDI as with bare DI, and though they continued to use polywrap, he was very concerned to find a better protection. The PVC industry and the developers were already pushing for PVC, but there was no AWWA spec for it at the time, and Jim wanted to wait for that blessing before committing to it. In 1973, that was still five years away, so we turned to YDI as a stopgap while the status of PVC with AWWA standards was resolved.

This last display of the time-series adds the 1976-1977 breaks in magenta, and 1978-1979 in red.

By 1976, we had started installing YDI and begun a cathodic protection program requiring an anode install at every repair site. The break rate overall held about even, but it continued to concentrate in this area, with new breaks appearing in the DI at the north end of it that were only a few years old.

And 1978-79 were the worst years of all, as the break rate, helped along by some cold winters, skyrocketed from 800 to 1200 per year. It was around this time that we pulled out a few pipes that were less than 10 years old. There was no longer any doubt that we had been correct to change pipe materials and create a full-time corrosion control group, which has since increased to six positions.

It was also at this time that the AWWA C900 spec was approved and we began the switchover from YDI to PVC that offered the hope of an end to metallic corrosion altogether. We were tentative with PVC at first, gradually ramping up its use after a few years of experiments and some lessons learned about installation technique. YDI was installed in at least equal amounts for four more years.

Yellow-Jacketed Ductile Iron pipe is not well-known in the water utility industry outside Canada, and some explanation of it may be needed. In contrast to PDI, which is wrapped in an 8-mil poly sheet out in the field and not bonded, The Yellow-Jacket of YDI is a 40-mil high-density polyethylene that is strongly bonded to the pipe.

As this photo of some removed jacket beside a pipe sample shows, it is stiff, tough stuff. This pipe coating had been used in the oil industry since the sixties, and it is Calgary’s connection with the oil industry that made us aware of it. The completeness of the coating, and the rarity of scratches causing corrosion “holidays” (if correctly installed) meant that they oil industry could cathodically protect kilometres of pipe with each (impressed current) anode bed. We get about 100m of protection out of each magnesium anode in contrast to 10m with bare DI, because there are so few spots that can leak metallic ions.

As this closeup shows, the pipe is also protected against internal corrosion with a cementitious lining. In 1973, with our corrosion problems just becoming apparent, Jim Bouck began pressing our pipe suppliers about giving us YDI. The problem was that the pipe used by the oil industry had no bells. A way to pull the coating over a bell of water pipe had never been developed.

But pressed directly by our Chief Engineer, developers, and CANRON, the DI supplier, Calgary's Shaw Pipe redeveloped their coating manufacture to pull the yellow jacket over a bell, and to install one of these straps with a bubble of gel coating over the strap weld. These alterations were necessary, as the original product for hydrocarbons is simply welded end-to-end and is not troubled by services.

After manufacture and deployment began in Calgary in 1975, Canron and Shaw also sold a lot of YDI to other Canadian municipalities. However, Jim Bouck actually counselled many smaller towns to not bother with the extra expense of YDI - not if they couldn't install it properly, or couldn't run a consistent cathodic protection maintenance program afterwards. The YDI shown here is ready to go into the trench. It is resting on tires to prevent any coating scratches. Before it goes in, we jeep it again in the field - use a high voltage to check it for any breaks in the coating. We use sand, pea gravel or other clean fills for bedding and the first half-metre of the pipe zone. Then we check the current flow at the anode test points forever, reinstalling the anodes every 20 years. It's a lot of trouble.

We find it, however, well worth it – the YDI break rates are a fraction of those on any other metallic pipe - just over a tenth. So far, of 600 km, we've never replaced any for corrosion-related causes, and only a few hundred metres for any reason. You'll note that I've just lumped together PDI and DI together on one line of this chart. In 1978, Jim Bouck and other Calgary engineers attended the AWWA conference and described their problems and their YDI approach, and said that PDI had no discernably different break rate from bare DI. That got them a lot of hot replies and raised voices.

A quarter century later, I'm prepared to modify that assertion somewhat, on behalf of my predecessors. We not only have data from another 25 years of break rates, but data from sandblasting thousands of metres of recovered mains and measuring pit depths. This graph follows the break rates for the DI and PDI that is still in the system today, so the breaks are all from the same cohort of pipe. Note that the breaks are all normalized to the age of the pipe at the time they happened, rather than by year of break. This is necessary for clear comparison as we started with PDI five years after “bare” DI. The pattern is clarified by smoothing out the yearly ups and downs with a 5-year moving average. The difference can be seen to be reasonably consistent over time. It is in very good agreement with an independent number from a completely different study. We measured corrosion rates on all kinds of our pipe by recovering samples and measuring maximum pit depths per metre. From the two studies, we can say, roughly, that PDI offered us about a 30% average reduction in corrosion rate, and consequently in corrosion break rate, where no (unisolated) copper services are involved.

So the DI series in the breaks graph repeated below, which combines “bare” DI and PDI, could be split into two lines a bit apart. 30% is nice, but the near-90% reduction we get with YDI, is well worth it, even at the expense and trouble. There is no break rate for PVC on this chart. If we're getting about 200 breaks per year on 500km of DI, and 30/yr on 600km of YDI, what's the rate on PVC?

In 1990, we had about a third the PVC we have now; we've gone from 500km then to 1400 now. And we've had 17 breaks on all of it over those ten years. The decade’s average would be under 0.2 breaks/100km on this graph – too small to show. Of the 17, only eight are actual repairs to PVC not near some kind of connection, though construction errors like bending it or placing it on a large rock were usually involved. One was a leak between PVC and PDI where the clamp between them was not on right. The other eight are all related to service taps; either they pulled out, or a crack in the PVC spread out from the tap site. You can never have perfect workmanship.

At the 2000 AWWA Infrastructure Conference in Baltimore, a couple of American engineers expressed surprise at our success with PVC; they had thought that trouble with taps was very common. But our experience is less than one PVC problem at services per year of 100,000 installed. We believe this to come from a single policy: intensive training. This is a real source of pride for Calgary Waterworks, our pipeman training facility. It occupies two large truck bays. The structure in the background was built for it, to allow simulation of the above ground parts of the system.

On the floor, are the underground parts: examples of virtually every combination of materials and fittings in our system. In an intensive two-week course, every pipeman works repeatedly with all of them, practicing procedures for construction and repair.

The mezzanine floor of the structure, 3m (10’) up, is a steel grating walkway as in a refinery or other plant, which allows us to simulate the top of the trench while being able to see through the grating to the pipes below. When you practice hydrant maintenance, you can see the lead and pipe below it.

Of particular interest are problems involving mixtures of materials, since we have so many.

All pipes shown here are run “wet” and under full pressure.

Training PVC tapping is one of the most important topics within the training course. PVC takes at least five minutes longer to tap than DI, and veteran foreman and trainer John McConnell great care in getting out every thread of plastic from the hole when you remove the coupon.

After the maincock has been inserted a few threads, the whole tapping machine can be removed and the maincock turned home with a torque wrench. It's important for long life of the plastic to not wrench it in too hard.

With use of teflon tape around the maincock threads, however, it rarely comes to that. Strong-armed staff can do the final turns with their bare hands to show off - it takes about 10 foot-pounds.

The trainers are very strict on this matter, however, checking every tap with a ruler to see that the pipe bulges out around the tap by only a few millimetres. A large bulge resulting from too high a torque when turning in the maincock would indicate that a stress-point has been created in the PVC – so the few millimetres allowed in training is well within the C900 specification and industry recommendations.

There is a significant cost in time for tapping PVC, taking over 10 minutes to do a tap. However, the overall cost of PVC main installation or replacement averages about half that of YDI, the only two distribution system materials in significant use in Calgary for some years.

The saving is two-fold. First, the materials cost of a given pipe-length of PVC is about half that of YDI, a saving of about $25/m Canadian. ($5US/ft). The savings for material would undoubtedly be much less compared to “bare” DI, as for us both PVC and YDI are bedded in “clean” materials such as sand or pea gravel around the pipe zone, and bare DI is still bedded in native material by some utilities. Between the cost of pea-gravel and the cost of hauling away some native material, as much as half this saving (at a rough estimate) may be removed.

However, a saving that is little different between YDI or “bare” DI vs. PVC is construction time. Calgary has both its own in-house crews and a variety of contractors for main replacement, and decades of reasonably consistent figures for construction work: and a crew averages about six pipe-lengths of YDI in a day, or twelve pipe-lengths of PVC.

The extra time for tapping PVC is more than made up by the considerably greater ease of handling it. A pipe-length may be easily moved by two workmen, heavy equipment is not required to lower it into the trench or around the site. The importance of this may be much higher in Canada, where trenches 3m deep (10’) are necessitated by our frost depth.

In any climate, however, PVC can be cut far more easily and quickly than DI.

CONCLUSION

Calgary changes in preferred pipe materials, first to YDI, and then PVC, came about during a time of very heightened concern about external corrosion, a concern that may not affect every utility.

The subsequent 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 for iron corrosion appeared. The primary concern with PVC is that it is wise - even essential - to handle it and work it with great care, and bed it in "soft" non-damaging materials such as sand, pea gravel and granulite.

For Calgary, and in the rest of Canada, with 3m-deep water pipe trenches, the added cost to the job of the bottom metre being more expensive fill is not nearly as large as the savings from the quicker work (once the staff is trained in the material). The cost-savings ratio may be significantly smaller in areas where the entire trench is only 1.5m deep, and handling the far heavier metallic pipe is not so difficult.

The obvious recommendation for further study is that utilities from warmer climates than Calgary share with the industry their total construction costs with the full variety of pipe materials that utility construction engineers now can choose from.

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