1000 MW超超临界发电机组过热器管T91/HR3C钢焊接接头开裂原因分析

Analysis on Cracking of T91/HR3C Steel Welded Joint of Superheater Tube in a 1000 MW Ultra-supercritical Power Generation Unit

某1000 MW超超临界发电机组运行了约7万小时后其过热器管T91/HR3C钢焊接接头开裂。对开裂的过热器管进行了宏观分析、硬度检验、金相检验和力学性能试验。结果表明:过热器管异种钢焊接时焊缝金属溢流至T91钢侧母材形成扇形异常区,且未焊后热处理,导致接头T91钢侧熔合线部位组织和性能极不均匀,长时间高温运行过程中产生氧化缺口。在内应力、交变应力和拘束应力等的共同作用下,氧化缺口根部产生裂纹,裂纹沿熔合线扩展导致接头开裂。

After a 1000 MW ultra-supercritical power generation unit operated for about seventy thousand hours T91/HR3C steel welded joint of superheater tube in it cracked.The macroscopic analysis,hardness test,metallographic examination,mechanical property test for the cracked superheater tube were carried out.The results showed that the weld metal overflowed into the T91 steel side base metal during welding of dissimilar steel of the superheater tube to form an abnormal fan-shaped area,the post-weld heat treatment was not performed,and,as a result,the microstructue and performances in T91 steel side fusion line were extremely uneven,thereby oxidation notches formed during long-term high-temperature operation.Under the common action of internal stress,alternating stress and restraint stress,cracks originated from the root of oxidation notch and propagated along the fusion line,thus resulting in the joint cracking.