Stress Corrosion Cracking of Low Strength, Low Alloy Nickel Steels in Sulfide Environments

Abstract

Factors governing stress corrosion cracking (SCC) of low strength, low alloy nickel steels (e.g., ASTM A203 Grade E) in sulfide environments were investigated using a three point loaded bent beam specimen. Cracking occurred in both weld and base metal at low H2S partial pressures (to 0.001 atmosphere) and stress levels, but could be inhibited by a neutralizing amine (morpholine) and methanol addition as used for control of ice and hydrate formation in cryogenic gas plants. Cathodic polarization experiments showed cracking was retarded under these conditions. This indicates the cracking phenomenon involved is not that of hydrogen embrittlement (i.e., sulfide stress cracking) as has been heretofore assumed, but involves localized anodic attack as does the cracking of other low strength alloys in environments such as nitrate, caustic, CO/CO2, etc. Sulfide corrosion stress cracking (SCSC) is suggested as a term for this type of localized anodic cracking attack in sulfide environments.

Sulfide stress cracking of nickel-containing low-alloy steels

“…Several investigators have reported surface damage in the form of pits, trenches, and/or small blunt cracks when Ni-containing LAS were exposed to sour environments (Dunlop, 1978;Kaneko & Ikeda, 1988;Yamane et al, 1986;Yoshino & Minozaki, 1986). It is implicit in the papers that the depth-to-diameter ratio increases in the order those features were mentioned above; however, limits in aspect ratio to distinguish between them were not established.…”

“…Those tests include NACE TM0177 Method B bentbeam test (NACE, 1996), and SSRT. Trenches and cracks were reported near the stress raisers of the bent-beam test by Treseder and Swanson (1968) and Dunlop (1978) in steels with Ni contents above 1-wt%. Kaneko and Ikeda (1988) reported increased tendency to trench formation in this test even in samples with 0.48-wt% Ni.…”

“…Several authors (Biagiotti, 1995;Snape, 1968;) stated that Ni does not affect SSC resistance unless susceptible phases, such as untempered martensite, are present in the final microstructure. Others (Dunlop, 1978;Craig et al, 1990;Kaneko & Ikeda, 1988;Yamane et al, 1986;Yoshino & Minozaki, 1986) have shown an increase in surface trenching in Nicontaining steels exposed to sulfide-containing solutions.…”

“…The limitation suggested by ISO and NACE is mostly based on a body of research conducted during the 1960s and 1970s (Dunlop, 1978;Treseder & Swanson, 1968). In their pioneer work, Treseder and Swanson (1968) and Dunlop (1978) found that LAS with more than 1.0-wt% Ni were more susceptible to SSC under similar loading and environmental conditions.…”

“…In their pioneer work, Treseder and Swanson (1968) and Dunlop (1978) found that LAS with more than 1.0-wt% Ni were more susceptible to SSC under similar loading and environmental conditions. Treseder and Swanson reported that steels with a Ni content higher than 1.0-wt% were susceptible to SSC even if hardness was kept under 235-BHN, which is equivalent to the 22-HRC limit now adopted by ISO 15156-2.…”