Failure analysis of ruptured pipe connected to natural gas pre-heater

Failure Analysis was made on a ruptured low carbon steel pipe that was connected to a natural gas pre-heater in a chemical plant. The pipe has been in service for about 30 years. The analysis indicated that failure of the pipe was due to thin-lip rupture, resulting from high temperature sulphidation. The rate of sulphidation was much faster at the bend areas where turbulent flow was occurring. The pipe also suffered from graphitization due to decomposition of the pearlite phase as a result of long service time at moderately high temperature. It was recommended to replace the pipe with a new one and to regularly monitor the pipe thickness with special emphasis on bend areas. The plant was also advised to minimize the ingress of humidity and oxygen into the piping system during shutdowns.