Failure Analysis of a Threaded Pipe Ruptured During Hydraulic Testing

摘要

In the present case study, failure analysis of a piping system that ruptured during hydraulic testing has been carried out to find the root cause and determine the mode and mechanism of failure. Chemical composition of the pipe was found to be in compliance with the standard composition of AISI4130. The failure cause of the pipe has been investigated through visual examination, microstructural observation, hardenability analysis, and fractography. Threaded grooves were produced through machining after heat treatment. Variation in hardness and strength through thickness (from case to core) was evaluated using standard hardenability graph. Hardenability analysis showed that the strength of the pipe after machining was still well above the calculated maximum stress at any point of piping system. This finding was further supported by the microstructural study. The actual cause of pipe failure during hydraulic test was found to be due to the stress concentration factor being developed by some notch from improper thread machining which lead brittle failure and was also revealed by fractography analysis.