The purpose of this study is to develop a simulation method to predict tensile strain limit for leakage from flaws in girth welds of high-pressure pipe. The material properties of each area in welds are measured by experiments using small size specimen. Ductile crack growth simulation is conducted using FE-model of girth welded joint of pipe to which the measured material properties are assigned, and the predicted ductile crack growth behavior and tensile strain limit are compared to experimental results. The effect of the material properties of weld metal and shape of welds on tensile strain limit is discussed.
High-pressure gas pipelines are required to prevent leakage by ductile crack growth from flaws in girth welds under large ground movement associated with earthquake. Thus, a strain-based design concept is efficient for pipelines installed in a seismic region (Barbas and Weir, 2007; Kan et al., 2008).
It is important for engineering critical assessment to clarify not only tensile strain limit for leakage or allowable weld flaw size but also the most concerned flaw location for leakage. The tensile strain limit for leakage has been determined based on a fracture mechanics approach (Sakimoto et al., 2009; Fairchild et al., 2011). However, resistance of ductile crack initiation and growth from the weld flaws is influenced by heterogeneity of strength and ductility in the multi-pass welds with various configurations (Gioielli et al., 2007; Motohashi et al., 2007). In some cases, a ductile crack deviates from initial flaw plane (Fairchild et al., 2008; Fairchild et al., 2011). Thus, it is difficult to evaluate the effect of the properties of welds on tensile strain limit for leakage by conventional fracture mechanics approach. On the other hand, there is a potential that tensile strain limit for leakage can be improved by appropriately controlling welds. However, a guideline for controlling the welds to improve tensile strain limit for leakage has not been presented.
