Abstract： Cracking and leakage of 20 steel superheat tube in a waste heat boiler occurred after service for less than one month. The reason for cracking was determined by macroscopic analysis, chemical composition test, mechanical property test, microstructure observation, microscopic analysis, and fracture analysis. The results show that the cracking of superheat tube belongs to brittle fracture. There are precipitated tertiary cementite and dispersed oxide inclusions along ferrite the grain boundaries of ferrite in microstructure, leading to grain boundary embrittlement and insufficient toughness of the material. During the process of cold bending, some cracks were initiated on the elbow surface. When the superheat tube with crack defects was used, the cracks expanded gradually with time under the action of high temperature and internal pressure of steam in the furnace, which finally resulted in cracking and leakage of the superheat tube.
2022, Vol. 40 
