600MW机组锅炉末级过热器爆管原因分析

Burst Cause Analysis on Final-stage Superheater Tube for 600MW Boiler

针对某电厂2210 t/h锅炉末级过热器TP347H奥氏体不锈钢爆管试样进行爆口宏观检验、材质成分分析和金相组织检验。综合测试分析认为,在短时超温运行后,晶界析出大量碳化物,使晶界附近形成贫铬区,晶界严重弱化;管外壁的浅表折叠形成残余应力和粗大晶粒形成了应力集中脆性区域。在高温运行工况下,内壁的晶间腐蚀,外壁应力集中脆性区域承载能力的下降和残余应力三者共同作用下,其韧性、强度和有效承载截面逐步减小,最终在介质内压周向应力作用下导致断裂。

For the burst fracture of final stage superheater of 2210 t/h boiler made with TP347H austenitic stainless steel, the burst fracture macroscopic examination, the material composition analysis and microstructure examination were carried out. It can be obtained that after short time over temperature operation, large amounts of carbide precipitate near the grain boundary, which can form the chromium depleted zone, severely weaken the grain boundary. The light folding of outer wall of the tube forms residual stress and coarse grain produces the stress concentration brittle region. In high temperature operating conditions, under the effect of the intergranular corrosion of inner wall, the decline of carrying capacity of stress concentration brittle region of outer wall and residual stress, the toughness, strength and effective bearing section reduce gradually, and finally, the steel tube fractures under internal compressive stress.