再生加热器不锈钢筒体开裂原因分析

Cause Analysis of Cracking of Austenitic Steel Shell of Regenerator Heater

介绍了某炼油厂再生加热器奥氏体不锈钢筒体在工艺调节过程中发生开裂并导致泄漏自燃的情况。通过宏观观察、材质分析、金相检验、扫描电镜及能谱、拉伸测试等方法对筒体进行了检测分析。结果表明,筒体的母材中铬、镍含量低于标准,焊材中不含钛元素;其次,加热器筒体的焊缝及母材靠近内表面的区域均出现明显的晶间贫铬;微观断口形貌可观察到韧窝及撕裂岭形貌;金相可观察到晶界空洞。通过分析证实焊缝及母材断裂具有沿晶蠕变断裂特征,加热器筒体的开裂归因于晶间贫铬和蠕变的综合作用,产生蠕变的原因是高温及低应力的长期作用;贫铬的原因主要是焊缝不锈钢缺乏Ti,故容易在晶界析出碳化铬,造成晶间贫铬。母材虽然为含钛不锈钢,但由于铬镍含量低,加之长时间在敏化温度区间内工作,使得不锈钢发生了晶间贫铬现象。晶间贫铬及蠕变造成焊缝及母材的强度降低,导致筒体的断裂失效。

The regenerator heater shell cracked during the process adjustment, leading to leaking auto - ignition. The failed sample was tested by macroscopic observation, material analysis, metallographic examination, scanning electron microscopy （SEM） , energy spectrum and tensile test, etc. The results show that chromium and nickel in the internal surface area of weld and parent metal are lower than the standard specifications, and there is no Cr in welding material. In addition, the analysis has proven that the fractures of welds and materials have the characteristics of intergranular creeps. The cracking of heater shell is contributed to combination effect of intergranular poor Cr and creeps. The creeps are caused by the long - term high temperature and low stress. The poor Cr is mainly because that there is little Cr in stainless steel welds. Although the base metal is Ti - containing stainless steel, the stainless steel is subject to intcrgranular poor Cr due to the long - term lower Cr and Ni and sensitive temperature conditions. Intergranular poor Cr and creep will result in the reduction of base metal strength and cracking failure of heater shell.