STANDARDS & TESTING | PROCESSING
Assessing pipe performance – and estimating its likely lifetime – is achieved by a growing number of sophisticated testing procedures. Lou Reade reports
Assessment puts pipes through testing times
Plastic pipes are increasingly replacing their metal equivalents, as they are proved to have high performance and long lifetimes. However, it is vital to assess their performance – both in advance of installation, and as a way of assessing damage and identifying the reasons behind failure. Researchers at the University of Alberta in
Canada have devised a new test method to evaluate the environmental stress cracking resist- ance (ESCR) of polyethylene (PE) pipe. The new method applies transverse loading to
the central area of a plate specimen. This generates local stretch, which results in a truncated cone. Time for crack initiation in the truncated cone, during the exposure to an aggressive agent, was then used to characterise ESCR in the sample. Results from the new method were consistent with those from the ASTM D1693 standard, said the
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researchers, who pointed out that their technique does not require any pre-notch – and takes less than 3% of the time of the traditional test. The test was run on two grades of HDPE and two
of LLDPE, as well as two specific pipe grades – PE2708 and PE3608.
Based on the new test method, the researchers have built a stand-alone device to characterise ESCR, which uses a change in electrical conductiv- ity to measure the time for the crack development. The device is relatively compact and easy to operate – and can determine that time for crack initiation automatically and accurately without the need for a commercial test machine, said the researchers.
“Since the new test method does not require any
pre-notch to accelerate crack formation, it avoids the potential scattering of results that can be
April 2018 | PIPE & PROFILE EXTRUSION 15
Main image: Pipe failure has many causes – and can be identified by a number of analytical methods
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