Susceptibility of Conventional Pressure Vessel Steel to Hydrogen-Induced Cracking and Stress- Oriented Hydrogen-Induced Cracking in Hydrogen Sulfide-Containing Diglycolamine Solutions

• Published in: Corrosion (Houston, Tex.) Vol. 55; no. 11; pp. 1101 - 1109
• Main Authors: Al-Anezi, M.A., Frankel, G.S., Agrawal, A.K.
• Format: Journal Article
• Language: English
• Published: Houston, TX NACE International 01.11.1999; NACE
• Subjects: Applied sciences; Corrosion; Corrosion environments; Corrosion rate; Crack sensitivity; Cracking (corrosion); Cracks; Exact sciences and technology; Hydrogen; Hydrogen sulfide; Hydrogen sulphide; Low carbon steels; Metals. Metallurgy; Pressure; Pressure vessels; Steel; Stress; Sulphides; Tests; Thickness ratio; Weight loss; Steel-ASTM-A516; Hydrogen Sulfides; Rupture; Mechanical properties; Pressure vessel; Corrosion rate; Stress corrosion cracking; Hydrogen embrittlement
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1.3283947

ABSTRACTHydrogen-induced cracking (HIC) and stress-oriented hydrogen-induced cracking (SOHIC) tests were conducted on a conventional type A516-70 (UNS K02700) pressure vessel steel exposed to hydrogen sulfide (H2S)-containing diglycolamine (DGA) gas-sweetening environments. Base-line HIC and SOHIC tests were conducted in NACE TM0284-96 Solution A. For the SOHIC tests, four-point double-beam specimens were stressed to 60%, 80%, or 100% of the yield strength of the steel to study the effect of applied stress. Test conditions included solutions containing 70 wt% DGA and 500 ppm H2S to 0.45 M-H2S/M-DGA and temperatures of 25°C, 45°C, and 80°C. Corrosion rates of the steel were calculated from weight loss of the HIC specimens to compare the severity of the test environment with the actual service environment. Cracks were characterized in terms of crack length ratio (CLR), crack thickness ratio (CTR), and crack sensitivity ratio (CSR). Results indicated that conventional type A516-70 pressure vessel steel was not susceptible to HIC or SOHIC in various H2S-containing DGA solutions at the temperatures studied.Various types of cracking associated with hydrogen are seen in pressure vessel steel such as type A516-70 (UNS K02700)(1) exposed to a wet-sour environment. Hydrogen-induced cracking (HIC), sulfide stress cracking (SSC), and stress-oriented hydrogeninduced cracking (SOHIC) are schematically represented in Figure 1 and are summarized below. HIC occurs in low-strength steel (typically < 80 ksi [550 MPa] such as type 516-70) during exposure to wet hydrogen sulfide (H2S) environments. It mainly occurs because of the buildup of internal pressure caused by the accumulation of molecular hydrogen at nonmetallic inclusions and other trap sites. HIC includes blisters near the surface of the steel plate and internal cracks that propagate in a stepwise or straight mode.1-2 HIC results in cracks that are created parallel to the rolling direction of the steel plate without the effect of external applied stress. SSC is hydrogen embrittlement cracking that occurs in high-strength and/or high-hardness steels under the influence of an external tensile stress and is caused by absorption of hydrogen from wet H2S corrosion.1 According to NACE standard MR0175, the steel has to have a hardness level > 22 Rockwell C hardness (HRC) and to be exposed to wet-sour environments containing 0.05 psia partial pressure of