Girth welded joints of pipelines may possibly contain defects which could reduce the fatigue strength of the joints under earthquake conditions. Hence it is necessary to identify the fatigue properties of the joints containing various defects and clarify the acceptable size of weld defects.
In this study, very low cycle fatigue tests and fatigue life estimation by fracture mechanics analysis of butt welded joints containing defects were carried out. The influence of plate thickness ranging from 9mm to 19mm on fatigue properties and the acceptable defect size in the welded joints were investigated. It was recognized that the fatigue life for the thickness of 19mm is shorter than that for the thickness of 9mm when the ratio of defect size to thickness is constant. The acceptable defect size in the welds under the earthquake conditions prescribed by the Japan Gas Association, namely, the strain amplitude of 0.5% for 50cycles of cyclic displacement, is proposed as a result of the analysis.
