放空口高颈法兰开裂分析

Failure analysis on cracking of hubbed flange of blow-off vent

某炼油厂加氢装置中的新氢压缩机二级出口缓冲罐高颈法兰运行1年后发生开裂。对开裂法兰进行了宏观检查、光谱分析、力学性能分析、金相分析、断口扫描电镜形貌及能谱分析,找出法兰开裂原因。结果表明：法兰原材料中存在大量的Ⅱ型Mn S夹杂,当其长期运行于氢气和腐蚀环境下,薄弱的圆弧处发生氢致开裂,裂纹沿厚度方向由内壁向外壁扩展。同时,法兰显微组织中的带状组织和环境中的腐蚀性介质,加速了裂纹的扩展,最终导致高颈法兰完全断裂。

The hubbed flange at the secondary of exit buffer tank of make-up hydrogen compressor was found cracking after used only 1 year.The cracking flange was examined by means of macroscopic examination,spectral analysis,mechanical properties analysis,metallographic analysis,fracture scanning electron microscope morphology and energy spectrum analysis in order to find out the cause of cracking. The results show that there are a large number of type Ⅱ of Mn S inclusions in the flange raw materials. When the flange ran in an environment of hydrogen and corrosive media for a long time,cracking first initiates at the arc position with thin wall,and then extends from the inner wall to the outer wall in the thickness direction. At the same time,the banded structure and corrosive medium in environment accelerate the crack propagation,resulting in the completely fracture of the hubbed flange.