Failure analyses were performed on three fractured 6061-T6 Aluminum alloy turbo-expander wheels that were exposed to a mercury-bearing natural gas environment. This investigation showed that failure of the 6061 Al-alloy was due to corrosion attack by liquid metal embrittlement (LME). Mercury corroded and embrittled the 6061-T6 Al-alloy resulting in several crack initiations along the edges of several blades and inside the expander wheel holes. LME also caused a loss of toughness, which led to corrosion fatigue, stress corrosion cracking and premature wheel failure. Minimizing direct contact of the aluminum alloy surfaces with mercury will prevent liquid metal embrittlement and improve the service life of these wheels. This can be achieved by anodizing whenever the mercury level is low (<10 ppm) or by using a more corrosion resistant coating when the mercury level is high and other corrosive species (chloride and sulfide) are also present.

Subject
Corrosion fatigue, Water, Coatings, Aluminum, Natural gas, Corrosion attacks, Mercury, Solutions, Mechanical failure, Metals, Carbon, Aluminum alloys, Liquid metal embrittlement
Keywords:
Liquid metal embrittlement, mercury, oil and gas processing plants, mercury/aluminum amalgam process, corrosion fatigue, coatings
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2004
Association for Materials Protection and Performance (AMPP)
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