The performance of Alloy K-500 has been revisited considering its extensive oilfield experience across short and long-term applications and a recently completed test program. Specifically, three heats of Alloy K-500 were sulfide-stress cracking tested between 70°F (21°C) and 275°F (135°C) in two sour and coexisting phases, a 120,000ppm chloride brine and a dense phase with 400psi (2.76 MPa) H2S and 1600psi (11.03 MPa) CO2; complementarily, the same heats were evaluated for hydrogen embrittlement in NACE TM0177 Solution A with and without -1050mV vs. Ag/AgCl potential. In all corrosion tests under tensile loads, Alloy K-500 was only stressed 30-to-80% of its minimum specified yield strength (SMYS) in an effort to validate historical tool practices, with all new results confirming that Alloy K-500 is environmentally-assisted cracking resistant when used per recommended guideline. Additionally, the alloy was characterized for weight-loss and pitting corrosion, including in three heavy brines with pH between 2.8 and 12.2. This testing reveals that Alloy K-500 does not suffer from elevated weight-loss, pitting, or crevice corrosion in the absence of sour gas, and thus may be safely operated up to the investigated temperatures. However, when exposed to a sour environment, Alloy K-500 can experience a rapid sulfide scale conversion with a characteristic tarnishing, overall limiting the alloy useful time in oilfield applications. Despite often being out of favor, Alloy K-500 still has its place as an oilfield alloy, particularly among niche and specialized applications in drilling, wireline, artificial lift, among others.

Subject
Hydrogen embrittlement, Corrosion resistant alloys, Corrosion rate, Valves, Nickel based alloys, Copper alloys, Heat, Equipment, Brines, Monel alloys, Sulfide stress cracking, Alloys, Uniform corrosion
Keywords:
K-500, corrosion, sulfide-stress cracking, hydrogen embrittlement, operational limits
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2023
Association for Materials Protection and Performance (AMPP)
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