协调形变法消除小直径管道焊接应力方法的研究

由焊接残余应力带来的焊接接头应力腐蚀开裂问题，是石油化工行业广泛使用的输送管道的主要失效形式。很多情况下，改变接头的应力分布状态，是解决这一问题的有效方法。结合小直径管道的特点，文中提出一种新的消除应力方法——协调变形法，即在管道焊缝两侧压应力区制造温差，使该区产生一定的与焊缝区相协调的收缩变形。对比协调形变法消除小直径管道焊接残余应力的数值模拟结果和实验结果，分析协调形变法消除残余应力的机理。结果显示，数值模拟结果与实际情况一般都符合得较好，可以达到100％的消除应力效果(内表面轴向应力)。该方法使用简单、效果好，表明协调形变法是消除残余应力的有效方法，可以解决小直径管道由于消除应力难而产生的应力腐蚀问题。

RELIEVING WELDING STRESSES OF GIRTH-WELD PIPES WITH SMALL DIAMETERS BY COMPATIBILITY DEFORMATION METHOD

Stress corrosion cracking (SCC) caused by welding residual stresses is the main sort of failure for the welded joint of pipelines widely used in petrochemical industry. In most cases, changing the stress distributions in the welded joint is an effective method to solve this problem. A new method for relieving residual stresses, compatibility deformation method, was presented. That is, it utilizes a temperature difference in the compressive stress regions on the both sides of weld, and which would make shrinkage compatible with the weld in these areas. The results from numerical analysis and the experiments were obtained and compared for relieving the welding stress of girth-weld pipes with small diameters by compatibility deformation method. Moreover, the mechanism of compatibility deformation method was analyzed. It shows that the numerical analysis results are quite compatible with the experimental results, and the relieving effective can reach to 100% (mainly for the axial stress in the inner surface). This method could be easily applied. Thus, it's assumed that the compatibility deformation method is an effective way to relieve welding stresses of girth-weld pipes with small diameters, and it is completely possible to avoid SCC of pipes with small diameter by this method.