某电厂二级再热器T91钢管焊接接头裂纹分析

为了避免T91钢管焊缝断裂事故的发生，以某电厂二级再热器T91钢管焊接接头渗漏现象为例，通过化学成分分析、宏观及微观组织分析、显微硬度试验对焊缝开裂原因进行了研究。结果显示:母材及熔敷金属化学成分满足相关标准要求，焊缝组织为粗大的马氏体，焊接热影响区的硬度明显高于焊缝的硬度，裂纹起源于焊接接头热影响区外壁的粗晶区，符合冷裂纹特征。研究结果表明，T91钢管焊接接头的环向开裂是由于焊接线能量太大或现场焊后热处理温度不符合标准要求造成的，除严格执行焊接工艺、控制线能量外，应合理布置加热带及控温热电偶的位置来保证热处理温度。

Crack Analysis of T91 Steel Pipe Welded Joint in a Power Plant Secondary Reheater

In order to avoid the T91 steel pipe weld fracture accident，the leakage phenomenon of welding joint of T91 steel pipe in a secondary reheater of a power plant was taken as an example，the reason of weld cracking was studied by means of chemical composition analysis，microstructure analysis and microhardness test. The results showed that the chemical composition
of base metal and deposited metal could satisfy the requirements of relevant standards，the weld microstructure was the coarse martensite，the hardness of heat affected zone(HAZ) was obviously higher than that of weld，and the crack originated from thecoarse crystal zone of the outer wall of the welded joint HAZ，which conformed to the characteristics of cold crack. The study indicated that the circumferential cracking of the welded joints of T91 steel pipe was caused by the excessive welding line energy or the heat treatment temperature which did not meet the standard after on-site welding，besides strictly enforce welding process and control line energy，the position of heating tape and temperature controlling thermocouple should be arranged reasonably to ensure the heat treatment temperature.