Nowadays most of the newly installed pipe for water and gas distribution systems
is extruded from PE. Once a PE grade has been selected for pipe production,
processing conditions control the properties and performance of the finished pipe.
The aim of this study is to investigate the development of residual stresses during
post-extrusion cooling, and the effect they have on the pipe performance.
A comprehensive simulation of the cooling process considering temperature dependent
thermal properties is presented. The development of crystallinity is predicted
by coupling the heat transfer analysis to a kinetic model of crystallisation. Using
the residual temperature field concept, the residual stress distribution through the
pipe wall is found. Different techniques to measure residual stresses such as ring
slitting and layer removal are compared experimentally, and a method is proposed
to resolve a very localised region of high compressive stresses at the outer surface
of the pipe. Shell theory is used to predict barreling: the tapering of the
pipe wall near the cut ends due to the release of residual stresses. It was found
that these variations in diameter could increase the gap between the pipe and the
electrofusion fitting, which could in turn reduce the strength of the joint and the
integrity of the pipeline. The effect of residual stresses on Rapid Crack Propagation
(RCP) is also investigated. Because thermal history determines not only
residual stresses but also crystallinity, two experimental techniques were used to
heat treat the pipes to modify one variable at a time and investigate its effect on
RCP separately. It was found that the effect of crystallinity is not as signi cant
as that of residual stresses. Lower critical temperatures were found for pipes with
lower residual stresses. A qualitative explanation for this transition is offered in
terms of crack shape.