Design of crack arrestors for ultra high grade gas transmission pipelines: material selection, testing and modelling

Abstract

One of the major challenges in the design of ultra high grade (X100) gas pipelines is the identification of areliable crack propagation strategy. Recent research results have shown that the newly developed highstrength and large diameter gas pipelines, when operated at severe conditions, may not be able to arrest arunning ductile crack through pipe material properties. Hence, the use of crack arrestors is required in thedesign of safe and reliable pipeline systems.A conventional crack arrestor can be a high toughness pipe insert, or a local joint with higher wall thickness.According to experimental results of full-scale burst tests, composite crack arrestors are one of the mostpromising technologies. Such crack arrestors are made of fibre reinforced plastics which provide the pipewith an additional hoop constraint. In this paper, the material selection, testing and modelling for the designof composite crack arrestors is presented.First, an overview of the most commonly used (integral and non-integral) crack arrestors is given, indicatingthat fibre reinforced devices are one the most promising solutions to arrest running fractures. Then, materialcharacterization of unidirectional fibre glass reinforced epoxy is addressed to measure the orthotropicproperties of this composite material. Traditional mechanical characterization is compared with a nondestructive testing method to measure the elastic constants of the composite material. In the end,micromechanics of fibre reinforced plastics is applied to predict the material properties. The theoreticalpredictions are compared with experimental values.In an accompanying paper, numerical tools to simulate crack initiation, propagation and arrest for this typeof crack arrestors are introduced. The combination of numerical simulation and experimental researchallows deriving design guidelines for composite crack arrestors.

Crack Arrest Toughness of High Grade Gas Pipeline

“…In view of the some above-mentioned weak points, steel rope crack arrestor is replaced by cast iron clamps as crack arrestor [16]. Cast iron clamps as crack arrestor use bolt to fix the fixture in the path of the director to the main pipeline to achieve purpose of ductility and crack arrest.…”