High cycle fatigue strength and the fatigue strength reduction factor of socket welded pipe joint

摘要

Based on a vast amount of data (about 600) acquired over the past several years on small diameter socket welded joints of various design by the four point bending fatigue tests and the rotating bending fatigue tests, the fatigue strength reduction factor (FSRF) was determined for high cycle fatigue, while the effects of various parameters, such as the steel species, nominal pipe diameter, practice of post-weld heat treatment (PWHT), pass sequence and bead shape, and root defect, were evaluated inquantitative terms.As it was shown that the fatigue strength depended greatly on the welding pass sequence, probably because the distribution of the residual stress at the root and toe was altered, test pieces were prepared in pairs of the as-welded ones and the ones withtheir residual stress relieved by PWHT so as to assess the effects of the residual stress. Then, with a band in which the S-N data of typical socket joint should fall having been established, the FSRF was deduced based on the lower limit curve of thisband. The adverse effects of pipe nominal diameter and root defect size on the fatigue strength were successfully quantified.