局部焊后热处理加热宽度的直接评定方法

A Direct Assessing Method of Heated Widths During Local PWHT

局部焊后热处理通常用来改善焊接接头的性能和消除焊接残余应力。影响局部焊后热处理的因素很多 ,其中加热宽度是最重要的一个控制参数。然而对于加热宽度的确定 ,各国标准规定就很不一致。本文采用粘弹塑性有限元分析 ,提出一个基于残余应力消除效果的局部焊后热处理的直接评定方法。该方法可清楚地显示整个热处理过程中的应力变化并可找到临界的加热宽度。对存在原始焊接残余应力的管接头在不同的热处理条件下进行分析。研究表明 ,局部热处理后的最大残余应力随加热宽度的增加而降低 ,当加热宽度达到一定值时 ,残余应力变化十分缓慢 ,可找到一临界加热宽度 ,其残余应力值与均匀热处理时十分接近。采用此方法可评价各种因素对局部焊后热处理的影响 ,并寻求最佳加热条件。通过系列的分析计算表明 ,5rq的加热宽度准则是合理的。

Local postweld heat treatment (local PWHT) is usually performed for tempering and relaxation of residual stresses. Many factors have an influence on PWHT procedures and the heated width is the most important parameter controlling the effectiveness of local PWHT. However,the determination rules of this parameter are very different in the different codes. In this study,a direct method to assess the effectiveness of local PWHT was used based on the thermal visco elastic plastic FEM with the consideration of creep phenomena. This method clearly shows the whole history of stress relief during PWHT and a critical heated width can be obtained. The pipe with original welding residual stresses is analyzed under different conditions of PWHT. Investigations show that the maximum residual stress after PWHT decreases when the heated width increases. When the heated width becomes large enough,the residual stress after PWHT changes very slowly and a critical heated width can be found which gives a residual stress close to the value obtained from th uniform PWHT. A series of different PWHT conditions are studied to find the critical heated width by using this method. It is found that a heated area of 5 rq centered on weld seems resonable from the view of stress relief.