在检修期间对某电厂高温过热器出口集箱管座焊接接头进行磁粉探伤时,发现存在裂纹缺陷,采用应力分布模拟、显微组织观察、硬度测试等方法,对该管座焊接接头进行了失效分析。结果表明:在长期高温服役过程中,高温过热器出口集箱管座焊接接头热影响区粗晶区组织老化严重,老化等级达到4.5级,高温力学性能明显下降;同时现场安装强力对口等施工不当造成管屏附加二次应力集中,在附加二次应力的作用下,裂纹在管座焊接接头上半圈热影响区粗晶区应力集中处萌生;随着服役时间的延长,裂纹内基体组织脱碳,焊接接头发生高温蠕变开裂。

During the maintenance period, the crack defect was detected during the magnetic particle inspection of the welded joint of the outlet header of a high temperature superheater in a power plant. The failure analysis of the pipe socket welded joint was carried out by stress distribution simulation, microstructure observation and hardness test. The results show that during the long-term high-temperature service, the coarse-grained area of the heat affected zone of the welded joint of the high temperature superheater outlet header was seriously aging, and the aging grade reached level of 4.5; the high-temperature mechanical properties significantly decreased. At the same time, the improper on-site installation of strong counterpart caused the additional secondary stress concentration of the tube panel. Under the additional secondary stress, the cracks initiated at the coarse-grained area of the heat affected zone on the upper half circle of the welded joint of the pipe socket. With the extension of service time, the substrate structure in the crack was decarbonized, and high temperature creep cracking occurred in the welded joint.