FPSO典型焊接接头初始表面裂纹对残余应力影响研究

Effect of initial surface crack on residual stress of typical welded joints of FPSO

FPSO目前已成为深水作业的重要设备之一。FPSO为大型焊接结构,焊接过程中不可避免的会有残余应力产生。而焊接接头的焊趾附近容易萌生表面裂纹,裂纹的产生会使残余应力发生重分布,从而影响焊接残余应力对结构疲劳强度的评估。本文首先基于热-弹塑性基本理论和X射线衍射法对FPSO典型焊接接头初始残余应力进行数值模拟和试验研究,结果发现焊趾附近初始横向残余拉应力较大;随后在焊趾附近引入表面初始裂纹,分析含表面初始裂纹的FPSO典型焊接接头残余应力重分布。结果表明引入初始表面裂纹后,裂纹尖端出现了较大的残余拉应力,而远离裂纹区域的残余应力大小和分布几乎不受表面初始裂纹出现后的影响。本文的研究可为FPSO安全性能评估提供参考。

FPSO has become one of the important equipment for deep-water operation. FPSO is a large welded structure, and residual stress would inevitably occur in the welding process. However, surface cracks are easy to occur near the weld toe of welded joints, and the residual stress would be redistributed because of the generation and propagation of cracks,which would affect the evaluation of structural fatigue strength by welding residual stress. Firstly, the initial residual stress of typical FPSO welded joints is numerically simulated and experimentally studied based on the basic theory of thermal elasticplastic and X-ray diffraction. The results show that the initial transverse tensile residual stress near the weld toe is large.Then, the surface initial crack is introduced near the weld toe, and the redistribution of the residual stress of the typical FPSO welded joints with surface initial crack is analyzed. The results show that there is a large residual tensile stress at the crack tip after the introduction of initial surface crack, and the magnitude and distribution of residual stress far away from the crack are almost unchanged with the appearance of initial surface cracks. The research of this paper could provide reference for FPSO safety performance evaluation.