Abstract
Worldwide, a significant proportion of the large diameter (trunk) mains within water networks are still made of aging cast iron material. With corrosion seeming to be the most significant cause of deterioration in cast iron trunk mains, the traditional structural view of the residual strength of the pipe has been based on the strength of the remaining wall thickness, i.e. a loss-of-section approach. In some situations this may lead to an over-estimate of the residual strength and better predictions can be made using an approach based on fracture mechanics. The present research has shown how loss-of-section models of residual strength can be used alongside fracture mechanics models in a twin approach to provide boundaries to the failure envelope for a “ring element” subjected to combined bending and direct (tensile or compressive) forces. When the application of such a failure envelope to a ring from a pipe under combined vertical loading and internal pressure is considered, it was found that in addition to its size, the angular position of a corrosion defect can have a significant effect on the residual strength of the pipe.
Highlights
In the developed world, the water industry tends to operate in a context of large scale infrastructure for the delivery of potable water and the removal of sewage
Recent experimental work [13] on samples sourced from failed large diameter cast iron trunk mains suggested that a fracture mechanics approach to strength analysis is more appropriate in such cases than methods relying solely on loss-of-section
The final section of this paper presents combined loading curves of vertical loading against internal pressure for a ring of a cast iron pipe, following a similar methodology to that suggested by Rajani and Abdel-Akher [10], but with the addition of a fracture mechanics based failure criterion
Summary
The water industry tends to operate in a context of large scale infrastructure for the delivery of potable water and the removal of sewage. Recent experimental work [13] on samples sourced from failed large diameter cast iron trunk mains suggested that a fracture mechanics approach to strength analysis is more appropriate in such cases than methods relying solely on loss-of-section. This suggests a link between the conformation of corrosion defects and the residual strength of samples. The aim of the present work is to show how a fracture mechanics approach could be implemented to estimate the residual strength of pipes and be used alongside loss-of-section models to provide boundaries to the failure envelope In both cases, geometrical and operational conditions are taken into account. The final section of this paper presents combined loading curves of vertical loading against internal pressure for a ring of a cast iron pipe, following a similar methodology to that suggested by Rajani and Abdel-Akher [10], but with the addition of a fracture mechanics based failure criterion
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