Modified Equation To Predict Leak/Rupture Criteria For Axially Through-Wall Notched X80 and X100 Linepipes Having a Higher Charpy Energy

Abstract

A method of predicting the leak/rupture criteria for API 5L X80 and X100 line pipes was evaluated based on the results of hydrostatic full-scale tests for X60, X65, X80, and X100 line pipes with an axially through-wall (TW) notch. The TW notch test results defined the leak/rupture criteria, that is, the relationship between the initial notch lengths and the maximum hoop stresses during the TW notch tests. The defined leak/rupture criteria were then compared to the prediction of the Charpy V-notch (CVN) absorbed energy-based equation, which has been proposed by Kiefner, Maxey et al. This comparison revealed that the CVN-based equation was not applicable to the pipes having both a CVN energy greater than 120 or 130 J and flow stress greater than the level of X65. In order to predict the leak/rupture criteria for these line pipes, the static absorbed energy for ductile cracking, (Cvs)i, was introduced as representing the fracture toughness of a pipe material. The (Cvs)i value was determined from the microscopic observation of the cut and polished Charpy V-notch specimens after static three-point bending tests. The CVN energy in the original CVN-based equation was replaced by an equivalent CVN energy, (Cv)eq, which was defined as follows: (Cv)eq=4.5(Cvs)i. The leak/rupture criteria for the X80 and X100 line pipes with higher CVN energies were reasonably predicted by the modified equation using the (Cvs)i value.