Failure investigation of a fractured vent line

• Published in: Engineering failure analysis Vol. 124; p. 105331
• Main Authors: Brewitt, N.P., Spowage, A.C., Mustapha, K.B.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-06-2021
• Subjects: Failure Analysis; Failure Investigation; Fatigue; Gate Valve; Vent line; Fatigue; Failure Investigation; Failure Analysis; Gate Valve; Vent line
• ISSN: 1350-6307; 1873-1961
• DOI: 10.1016/j.engfailanal.2021.105331

•The paper investigates the cause of a fracture in a vent line of a main gas process line.•The failure investigation details the methodology , research and analysis used.•The fractographic features observed have been explained.•FEA was used to identify the position of the maximum stress intensity.•It was concluded that the vent line failed due to a fatigue cracking mode.
During a routine inspection, the sound of venting gas was heard in the area of the compression module on board a five-year-old natural gas platform in the South China Sea. The sound was traced to a fractured 25 mm vent line pipe on a main process gas line. Analysis of the failure showed that a fracture occurred due to a fatigue failure mode. The fracture was initiated under high stress concentration at the weld toe influenced by a small amount of undercut typically found in such welds. This paper provides a summary of the investigation, methods used, key results and analysis which led to the identification of the root cause of failure.