The results of an analysis of a CA6NM plug and cage control valve which seized in hydroprocessing service are presented. The valve was found to have seized due to the accumulation of corrosion deposits resulting from a relatively brief exposure to a high temperature hydrogen / hydrogen sulfide environment. Wear surfaces on the valve were nitrided to prevent galling. Nitrided surfaces were found to have a significantly lower corrosion resistance than predicted by the Couper-Gorman curves for 12 Cr stainless steels. This high corrosion rate is explained by depletion of chromium in solution due to the formation of chromium nitrides.

Subject
Materials, Corrosion rate, Predicted corrosion rate, Valves, Iron sulfides, Chromium, Iron, Micrography, Base metals, Scale, Carbon, Stainless steel, Nitriding
Keywords:
CA6NM, hydroprocessing, nitriding, galling, hydrogen, hydrogen sulfide
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2005
Association for Materials Protection and Performance (AMPP)
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