长期服役后TP304H/T22型异种钢焊缝失效原因分析

Failure Reason Analysis of TP304H/T22 Type Dissimilar Steel Weld after Serving for Long Time

某电厂进口亚临界锅炉在检修中,发现高温过热器出口管段TP304H/T22型异种钢焊缝从内壁开裂。通过对失效异种钢管样的宏观形貌、规格尺寸、化学成分、显微硬度、显微组织等方面的分析,得出结论:裂纹从内壁的焊接内衬环与母材的未熔合位置起裂,并向焊缝内部扩展;焊缝及两侧母材的规格尺寸、化学成分、显微硬度和显微组织均符合要求;焊接衬环与母材的未熔合界面具有应力集中效应,是异种钢焊缝在设计寿命前开裂的主因。检测试验发现,射线检测和超声相控阵检测均无法有效检出此类裂纹。

During the maintenance of an imported sub-critical boiler in a power plant, it was found that TP304H/T22 type dissimilar steel weld seam in the outlet pipe section of high temperature superheater cracked from the inner wall.Based on the analysis of the macroscopic morphology, specification size, chemical composition, microhardness, microstructure and other aspects of failed dissimilar steel tube samples, it is concluded that the crack starts from the the unfused interface between the inner welding ring and the base metal, and propagates towards the inner of the weld seam.The size, chemical composition, hardness and microstructure of the weld seam and base metal at both sides are consistent with the requirements.The unfused interface between the inner welding ring and the base metal has the effect of stress concentration, which is the main reason for the cracking of the weld of dissimilar steel before the designed life.The detection tests show that the crack can not be detected effectively by either X-ray detection or ultrasonic phased array detection.