A Ni-P coating was applied to coupons made from a common valve stem material (AISI 4140) used in geothermal steam that was known to experience localized pitting corrosion in the valve stem packing area. The coated coupons were exposed in geothermal steam test chambers with 160 °C saturated steam, and 105 °C 10 % wet low temperature steam with and without 3 % air added at the Broadlands Ohaaki well BR22 test site in New Zealand. This paper documents the properties of the tested Ni-P coating and presents corrosion performance comparisons for aerated vs non-aerated geothermal steam with reference to the anticipated valve stem environment. The results show that Ni-P coated valve stem material would not be expected to perform well in geothermal applications.

Subject
Scanning electron microscopy, X-ray diffraction, Nickel coatings, Vapor pressure, Geothermal energy, Materials, Valves, Nickel based alloys, Metal coupons, Corrosion products, Corrosion coupons, Nickel, Steam
Keywords:
Coating, Nickel-Phosphorous, Geothermal, Non-aerated, Aerated, Steam, Low Alloy Steel, Valve Stem, Corrosion
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2019
Association for Materials Protection and Performance (AMPP)
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