engleski

Identifying the causes of pipe cracking at the gas pipeline pressure test

A part of the pipe from the main gas pipeline Pula – Karlovac DN 500/75 was delivered to a laboratory at the Faculty of Mechanical Engineering and Naval Architecture (FSB). The pipe was longitudinally welded, the material specification was API 5L grade X70. The delivered pipe cracked at the factory-made weld, and then deformed. The pipe is passed factory hydrostatic at 101 bar for 20 s min., and should withstand the field pressure test of 94 bar for 24 hours. However, the cracking occurred at hydrostatic pressure test of 72 bar only. It is therefore necessary to detect the cause of the material fracture, i.e. why the pipe deformed and burst. Laboratory tests were carried out on the fractured pipe material. The tests included visual control of pipe material, weld and fractured areas, non-destructive testing methods, testing of mechanical characteristics of the base material and weld, hardness testing and microstructure analysis of the base material and weld joint cut out from the pipe of the main gas pipeline. The results were compared with the specified gas pipeline material characteristics, and the conclusions were made about the possible causes of the pipe butrst.

Gas pipeline; material testing; microstructure

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