Washington Gas has been researching a number of innovative methods for the repair and
replacement of older large diameter cast iron mains. We considered direct burial, rolldown,
U Lining, PIM, and guided boring. The ideal replacement technique would allow for a fully
rated (64 psi or 5 bar) system which would have a low installation cost, a minimum 50 year
life, rapid and easy installation, and provide a safe, secure, all- fused system. Trenchless
technology is very attractive due to the low cost and minimal disruption to our customers.
We wanted to replace an older 24" cast iron pipe operating at 20 psi (1.4 bar) with an
inserted 16" IPS plastic main rated for 64 psi.
Washington Gas would require the following performance criteria :
1. The polyethylene (PE) pipe must be rated at 64 psi and yet have the maximum internal
diameter. Thus high density Standard Dimension Ratio (SDR) 17 was chosen.
2. The PE pipe must have a very high resistance to slow crack growth because of the
potential stresses and damage that would be inherent in insertion.
3. The pipe must have the highest resistance to rapid crack propagation since it would be
unrestricted inside several sections of a 24" cast main. Furthermore, it would be possible
to have dramatic swings in pipe temperature, and if the pipe were to be impacted with
enough force to break through the casing rapid crack propagation (RCP) could, in theory,
4. Controlling the gas flow is also critical, therefore a 16" squeeze off tool was developed
and tested by Mustang Manufacturing. Ideally, the PE pipe would have to be able to be
squeezed to 100% shutoff with no damage or reduction in usable life.
5. Joining the PE pipe was also an important consideration. It was imperative to develop
and test plastic-to-steel transition fittings as well as complying with the requirements
of the Plastic Pipe Institute (PPI) universal procedure (PPI TR - 33/99).
We selected a material that would meet all of these criteria and that is PE-100. It is impervious
to RCP because it has a critical temperature of zero degrees Fahrenheit (-18 degrees Celsius),
and has a slow crack growth resistance of over 2000 hours in the PENT test. PE-100 can
withstand substantial backhoe hits and mechanically induced damage that would cause
failures in other piping systems. The PE-100 material we chose was Phillips 8300 pipe
made from Solvay TUB 121 resin.
On August 21, 2000 Washington Gas installed the first 16" IPS PE-100 material in the
United States. We will monitor its performance closely over the next 10 years.
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The market for high performance polypropylene (PP) piping systems in North America continues to
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Author(s) : Steve Sandstrum, Stefan Dreckoetter, Zak Schultz
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The market for high density polyethylene (HDPE) pipe continues to expand across a
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Plastic Pipe - A Critical Tool for Water Resource Management