屏式过热器爆管原因分析

Explosion Causes Analysis of a Platen Superheater Tube

某燃煤电厂屏式过热器发生爆管,在上部焊缝附近和下部弯管背弧面各产生一个爆口。为分析原因,取样进行了宏观形貌检查、化学成分分析、金相检验、能谱分析、硬度检测、常温力学性能试验。分析结果表明,下部弯管的失效原因是管子本身强度不够和外壁结焦严重共同导致的长时超温爆管。下部爆口产生后介质的流失导致管壁温度进一步升高。上部焊缝焊接工艺不当导致附近管段周向热膨胀不均。同时,新更换的管子强度偏低。在以上三方面因素综合作用下,最终在上部焊缝热影响区附近发生二次爆管。

A platen superheater of a coal-fired power plant was broken,and two blast holes were generated near the welding seam and on the back arc of the lower bend tube.In order to find out the cause of the failure,macroscopic morphology examination,chemical composition analysis,metallographic examination,energy spectrum analysis,hardness test and mechanical properties test at room temperature were carried out.The results showed that the failure of the lower bend was subjected to long-time overtemperature explosion caused by the insufficient strength of the tube and the serious coking outside.The loss of medium at the lower blast hole caused the wall temperature to rise higher.Improper welding process of upper welding seam leaded to uneven circumferential thermal expansion of the tube near the heat-affected zone.In addition,the strength of the newly replaced tube was not sufficient.As a result of the above three reasons,a subsequent failure occurred near the heat affected zone of the upper welding seam.