螺旋缝埋弧焊弯管残余应力及使用安全性研究

Investigation on residual stress of SSAW bent pipe and safety assessment

为探明感应加热控轧钢螺旋缝埋弧焊管弯制后残余应力对使用安全性的影响 ,采用机械切割应力释放法 ,选取外径为 711mm、壁厚为 9 5mm的X60钢级的直管、弯管和热处理后弯管 ,进行内外表面残余应力的测试和力学性能试验。结果表明 ,感应加热控轧钢推制弯管的残余应力较直管明显增加 ,经回火热处理后 ,虽然残余应力状态得到明显改善 ,但强度指标进一步降低。还采用失效评定图技术和PREFIS软件分析了弯管热处理前后的使用安全性 ,指出残余应力对弯管的脆断倾向有较大的影响。据此建议对弯管的推制工艺和热处理去应力工艺展开研究 。

To make clear the influence of the residual stress on the SSAW (spiral-seam submerged-arc welded) induction bent pipes, tests of residual stress on both the inner and outer surfaces of the pipes and a mechanical properties test are made by the stress release method. The test pipes include X60 steel SSAW straight pipe, bent pipe and heat-treated bent pipe, all with 711mm OD and 9.5mm thickness. The test results show that the residual stress of the induction bent pipe increases at a larger degree compared with that of the straight pipe, and if it is heat-treated, its intensity index will decrease though its residual stress is released greatly. The safety of the bent pipes before and after heat-treatment is also analyzed by adopting the FAD (failure assessment diagram) technique and PREFIS software, and it is indicated that the residual stress has an obvious effect on the brittle-fracture trend of the bent pipes. To ensure the reliability of the bent pipes, measures should be taken to reduce the residual stress in the course of pipe bending and heat-treatment.