余热锅炉高压过热器取样管开裂原因

Cracking Causes of Sampling Pipe of High Pressure Superheater for Waste Heat Boiler

某电厂254 MW燃气机组在运行过程中发现,其材料为07Cr19Ni10不锈钢的高压过热器取样管弯头处发生开裂。通过宏观观察、化学成分分析、金相检验、硬度测试、微观分析及金相检验等方法,对取样管的开裂原因进行了分析。结果表明:由于高压过热器取样管安装不当,取样管弯头处受到斜向上的拉应力。同时,取样管原始质量存在缺陷,其在高温高压工况下长期服役,随着第二相逐渐向晶界偏聚,当晶界强度低于所受拉应力时,晶界被拉裂从而形成裂纹。裂纹沿壁厚方向扩展,最终导致取样管开裂失效。

During the operation of 254 MW gas-fired unit in a power plant,it was found that the elbow of sampling pipe of high pressure superheater made of 07 cr19 Ni10 stainless steel cracked.The cracking causes of the sampling pipe were analyzed by means of macroscopic observation,chemical composition analysis,metallographic examination,hardness test,microscopic analysis and metallographic examination.The results show that due to improper installation of the sampling pipe of high pressure superheater,the elbow of the sampling pipe was subject to oblique upward tensile stress.At the same time,the original quality of the sampling pipe had defects.It has been used for a long time under high temperature and high pressure.As the second phase gradually segregated to the grain boundary,when the strength of the grain boundary was lower than the stress,the grain boundary be pulled to crack and formed cracks.The cracks propagated along the wall thickness direction,which eventually led to the cracking failure of the sampling pipe.