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An Exploratory Investigation of the Cracking Susceptibility of Three Corrosion Resistant Alloys under Thermal Cycles and Conditions Exceeding the Traditional NACE MR0175/ISO 15156 Recommendations

The environmentally-assisted cracking (EAC) of three wrought corrosion-resistant alloys (CRAs) with a minimum yield strength of 110ksi (760MPa) was investigated between 70°F (21°C) and 450°F (232°C) through weekly thermal cycles totalizing 42 days. The thermal cycling was introduced to approximate service equipment conditions and gain additional confidence on the EAC-free limits of all three CRAs. Alloys 17-4PH, K-500, and 925 were selected and exposed to a 180,000-ppm NaCl brine (pH=2.75) in equilibrium with 1000 psi (68.95 bar) H2S, 1000 psi (68.95 bar) CO2, and 2500 psi (172.37 bar) CH4. All three CRAs were (a) acquired as per the NACE MR0175/ISO 1516 requirements (1), (b) tested as per NACE TM0177 Method C at 30-to-90% of the CRA minimum specified minimum yield strength (SMYS), and (c) also compared for their weight-loss corrosion and localized corrosion. The results show: (a) Alloy 17-4PH remains resistant to EAC below 45% of its SMYS, (b) Alloy K-500 resists cracking at an estimated 80% of its SMYS, but uniformly corrodes by sulfide conversion under film at a rate of 64 mpy (1.63 mm/yr.), and (c) Alloy 925 continues to be immune to EAC at 90% of its SMYS. Alloy 17-4PH also corroded at a rate of 22.8 mpy (0.58 mm/yr.) in comparison to only 0.6 mpy (15.2 mm/yr.) for Alloy 925, with no CRA showing experiencing crevice corrosion.
Product Number: 51324-20455-SG
Author: Manuel Marya
Publication Date: 2024
$40.00
$40.00
$40.00