某电厂低压加热器管板与壳体T型焊接接头开裂失效分析

Failure Analysis of Cracking in T-Type Welded Joints between Tube Sheet and Shell of Low-Pressure Heaters in a Power Plant

某电厂低压加热器服役5年后,管板和壳体的T型焊缝部位发生严重开裂;通过宏观检查、断口形貌分析、金相组织分析、能谱分析(EDS)、化学成分分析和硬度检测等检验检测,对焊缝开裂原因进行了分析。分析表明:由于焊接热影响区(HAZ)存在对碱应力腐蚀开裂敏感的淬硬马氏体组织,且焊接接头未进行消应力热处理,在碱性环境中,管板焊接热影响区发生了碱脆,支裂纹在焊缝中扩展穿透造成设备失效。对T型焊接接头失效的原因进行分析,对类似场合换热器设计、制造和使用具有借鉴意义。

After 5 a of service,severe cracking occurred at the T-type weld seam between the tube sheet and shell of a low-pressure heater in a certain power plant.The causes of the weld cracking were analyzed by macroscopic inspection,fracture morphology analysis,metallographic structure analysis,energy-dispersive spectroscopy(EDS),chemical composition analysis and hardness testing.Results showed that due to the existence of a hardened martensite structure in the heat-affected zone(HAZ)of the welding,which was sensitive to alkali stress corrosion cracking,and the lack of stress reduction heat treatment of the welded joint,alkali embrittlement occurred in the welding heat affected zone of tube plate,and crack branches propagated and penetrated through the weld,causing equipment failure.The analysis of the failure causes of T-type welded joints is of great significance for the design,manufacture,operation of heat exchangers in similar situations under the same working conditions.