Cracking Reasons of a 0Cr18Ni9 Austenite Stainless Steel Pipeline

0Cr18Ni9 austenite stainless steel has been used for the gas piping project in a certain corporation, the pipes were joined together with welding and the manual arc welding procedure was carried out. The transmission medium in the pipeline was enriched ammonia liquor containing hydrogen sulphide and other corrosive media, the medium pressure was 0.5 MPa and temperature was 35~45℃. Transverse crack was found nearby the welding joint when the production was resumed after one year, including half a year of operation and half a year of suspend production. Cracking causes of 0Cr18Ni9 austenite stainless steel pipe were analyzed by a series of examinations, such as macroscopic test, metallographic test and chemical compositions analysis as well as SEM analysis. The results showed that the crack of 0Cr18Ni9 austenite stainless steel pipe was polythionic acid stress corrosion cracking. By purging 0Cr18Ni9 austenite stainless steel pipe with argon and sealing pipe ports at opposite ends, polythionic acid stress corrosion cracking could be prevented. The possibility of polythionic acid stress corrosion cracking could also be decreased by reducing welding current, increasing welding rate and reduction in scope of heat effective zone during welding.