This paper deals with Environmentally-Assisted Cracking (EAC) resistance data, that is, SSC and SCC resistance for martensite-based stainless steel OCTG materials of (1)Modified-13Cr (13Cr-5Ni-2Mo: generic classification of Super-13Cr), (2)15Cr (15Cr-6Ni-3Mo-Cu: UNS No.S42625) and (3)17Cr (17Cr-4.5Ni-3Mo-Cu-W: UNS No.S42825) by autoclave-based Four-Point Bent Beam (FPBB) testings. It was experimentally proved that martensitic stainless steel do not have a specific cracking-susceptible temperature range at around 80 °C to 100 °C (175 °F to 210 °F) where duplex stainless steel is said to specifically fail, as far as the authors investigated the EAC resistance in the corrosion environment of acetic-buffered 20%NaCl solution saturated with 5MPa CO2 and 0.01MPa H2S by testing at temperature from room temperature (24 °C/75 °F) to 200 °C (390 °F) and at pH3.0 to pH5.0.

Judging from the domain maps of EAC for 13%Cr-added to 17%Cr-added martensite-based stainless steel, the non-failure domain for each sample is limited by “cracking” and/or “corrosion rate”. In terms of cracking in martensitic stainless steel, EAC does not occur above a certain temperature, in the same manner as carbon-sour steel is more SSC-susceptible at lower temperature and can be also regarded as crack-free above 80 °C (175 °F). In terms of corrosion rate, the general corrosion phenomenon is directly related to temperature. As temperature is lower, the corrosion rate decreases and it can stay below the upper limit of corrosion rate at less than a certain temperature. Higher-alloyed martensite-based stainless steel has better performance with respect to both cracking and corrosion rate, and the non-failure domain is expanded.

Subject
Environmental cracking, Test methods, Corrosion failures, Materials, Corrosion rate, Autoclaves, Corrosion cracking, Pitting, Duplex stainless steel, Stainless steel, Sulfide stress cracking, Stress corrosion cracking, Martensitic steel
Keywords:
SSC, SCC, EAC, sour environment, martensitic stainless steel, OCTG, 13%Cr, modified 13Cr, Mod-13%Cr, 15%Cr
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2019
Association for Materials Protection and Performance (AMPP)
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