Page 25 - Gi September2020

corrosion is not that it occurs, but that such as that achieved using polyethylene have three time-dependent failure
its occurrence is very hard to predict. (PE) materials, for example, are modes. These are variously referred to
Many variables affecting what will predictable. And they are predictable as ductile rupture, stress crack rupture,
happen need to be measured on a from knowledge of the polymer used, the or oxidation breakdown.
job-by-job basis, which makes transported fluid in the application, and For ductile rupture, independent of
predicting failure in corroding pipes the pressure regime used for a pipe time, a very high internal pressure can
very difficult. And predicting failure is network. With that knowledge, a exceed the strength of the pipe causing
important when you are managing well-constructed pipeline can have it to stretch and fail in a ductile way.
critical long-term investments. predictable performance measured in With stress cracks, at lower pressures
hundreds of years. but much longer timescales, the reliable
Predicting failure A science example can clearly lifetime limit could be a brittle crack
The failure modes of a plastic pipe illustrate the pipe classification system. grown through the material. With
system, particularly a welded system Polyethylene pipes (in our example) oxidation, largely independent of

25

12/08/2020 17:34
BFPPipes.indd 2 12/08/2020 17:34
BFPPipes.indd 2