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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.
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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, “YellowJacket” 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, thinwall (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.
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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
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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 19761977 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.
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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
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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 corrosionrelated 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.
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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.
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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. Strongarmed 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 pipelengths 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.
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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.