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

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 07cr19Ni10 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.