In this article a failure of a diffuser, with vanes, made from material P265GH, in a gas compressor is investigated. The gas compressor was in service for over 10 years. The gas contained both CO2 and H2S. Relative humidity of the gas was 100 %. It was found that the diffuser was fractured in 3 locations. Composition of the material was investigated using spark emission spectroscopy. The fracture surfaces were investigated with optical microscopy and analytical SEM. Elemental sulfur, analyzed with EDX, was found on the fracture surfaces and at other locations. Hardness was found to be within specification for sour service as per ISO 15156. Residual stress was measured using X-Ray diffraction in two directions. Results of the various investigations are presented. From the investigation, the following conclusions could be drawn. The surface of the diffuser was covered in corrosion products indicating active corrosion. Crack initiation was found to be from pitting corrosion. Several secondary intergranular cracks were found in cross sections. The fracture face showed striations in some areas indicating fatigue crack growth. The failure was because of changed gas chemistry and/or physical parameters which deposited elemental sulfur, leading to active corrosion causing hydrogen embrittlement.

Subject
Scanning electron microscopy, Hydrogen embrittlement, Materials, Crack initiation, Fracture surfaces, Corrosion cracking, Corrosion products, Mechanical failure, Elemental sulfur, Deposit corrosion, Fracture, Residual stress, Hydrogen
Keywords:
Diffuser, Gas compressor, failure, sour gas, failure investigation, hydrogen embrittlement
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2017
Association for Materials Protection and Performance (AMPP)
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