Crack arrestor design by finite element analysis for X100 gas transportation pipeline

The interest of gas companies in the use of high grade steel pipes, equivalent to X100 and higher, for the construction of long distance gas pipelines has become a consolidated trend in the world; in response to this market demand, steel makers have successfully developed new classes of high grade steel for large diameter pipelines, but some limitations might occur to their application if important aspects related to their structural reliability, such as the resistance to ductile fracture propagation, are not completely clarified. Recent efforts spent in investigating this aspect, that is the ductile fracture propagation control, have demonstrated that the class of X100 large-diameter steel pipes being considered, when operated under severe operating conditions (high usage factor, rich gas, low temperature), may lie on the fracture propagation/arrest border line. In this case external mechanical devices, i.e. crack arrestors, may be required to ensure arrest of a propagating fracture This paper presents a crack arrestor design approach by finite element analysis for a X100, largediameter gas transportation line operating under severe conditions, such as those mentioned above. A CSM finite element model specifically developed for simulating dynamic ductile fracture propagation (PICPRO) has been used and implemented to consider the effect of crack arrestor constraint on the running fracture. Several types of crack arrestor have been considered, including a steel sleeve with or without grout, thickerwalled pipe and types of composite crack arrestor, and relevant design criteria have been obtained. Numerical predictions were also compared with the results of recent experimental full-scale burst tests carried out on X100 large diameter pipelines, demonstrating the capability of the model developed to correctly predict the crack arrestor performance.