超超临界机组水冷壁管失效分析

Failure Analysis on Water-cooled Wall Tube of Ultra-supercritical Unit

某1000MW超超临界机组1号锅炉右侧标高75.1m处第58和59根水冷壁管,材料为12Cr1MoVG钢、尺寸为28.6mm×5.8mm,运行了约8个月后发生开裂泄漏。对开裂的第58根管进行了宏观分析、金相检验和硬度检测,以确定其开裂的原因。结果表明:第58管焊缝和热影响区均存在过热组织,且硬度远高于要求值,从而焊缝和热影响区的塑性、韧性及抗疲劳性能急剧下降,在内应力、拘束应力和焊接应力的综合作用下在焊缝熔合线附近开裂。

The 58th and 59th water-cooled wall tubes 28.6 mm in OD by 5.8 m long,made from 12Cr1MoVG steel,at a height of 75.1 m on the right side of the boiler No.1 of a 1000 MW ultra-supercritical unit leaked because of cracking after about 8 months of operating.The cracked 58th tube was tasted for appearance,microstructure and hardness for the purpose of discoering the cause of its cracking.The results demonstrated that the 58th tube exhibited overheated structure in both weld and heat affeted zone and higher-than-desirable hardness,thus resulting in severe reduction in plasticity,toughness and fatigue resistance of the weld and heat affacted zone,and cracking near weld juncrion by the combined action of inner stress,restraint stress and welding stress.