Cracking Reason Analysis of High Temperature Superheater Coiled Pipes in a Thermal Power Plant

In a thermal power plant, 60% high temperature superheater colied pipes cracked after 10 h running. To find out the cracking reasons, means methods such as magnetic powder inspection, chemical compositions analysis, hardness test, metallographic examination and tensile test were applied. The results show that there was serious uneven distribution of Mo element which led to microstructure segregation in the material of the pipes. Thereafter it caused the plastic property and corrosion resistance of some regions decreased. Because of the combined effects of high temperature and high pressure vapor and high residual stress of the coiled piped, stress corrosion cracking occurred with cracks extending from inside wall to outside wall.