Stress corrosion cracking (SCC) of carbon steel in fuel ethanol service has been observed in an increasing number of failures in the last few years. In the presence of oxygen, all of the samples evaluated in this study produced varying degrees of SCC, except for one of the producer ethanol samples. The reason for the high corrosion potential in this sample is still unknown and more detailed analysis of the sample chemical make-up is needed.
Low alloy steels (LASs) combine relatively low cost with exceptional mechanical properties, making LASs commonplace in Oil and Gas equipment. However, the strength and hardness of LASs for sour environments and for applications that generate atomic hydrogen at the surface, e.g., cathodic protection, is limited to prevent different forms of hydrogen embrittlement (HE) such as hydrogen stress cracking (HSC) and sulfide stress cracking (SSC). As a result, the specified minimum yield strength (SMYS) of forged LASs for, e.g., subsea components, rarely exceeds 550 MPa (80 ksi), while the most common pipeline steels are API(1) X65 to X70, with a SMYS of 450 MPa (65 ksi) and 482 MPa (70 ksi), respectively. Moreover, ISO(2) 15156-2 restricts LASs to a maximum of 1.0 wt% Ni due to SSC concerns. The LASs that exceed the ISO 15156-2 limit have to be qualified for service, lowering their commercial appeal.
In this work, the HSC resistance of the high-nickel (3.41 wt%), quenched and tempered (Q&T), nuclear-grade ASTM(3) A508 Gr.4N LAS was investigated using slow strain rate testing (SSRT) as a function of applied cathodic potential. Results showed that the yield strength (YS) and ultimate tensile strength (UTS) were unaffected by hydrogen, even at a high negative potential of -2.0 VAg/AgCl. HE effects were observed once the material started necking, manifested by a loss in ductility with increasing applied cathodic potentials. Indeed, A508 Gr.4N was less affected by H at high cathodic potentials than a low-strength (YS = 340 MPa) ferritic-pearlitic LAS of similar nickel content. SSRT results were linked to microstructure features, which were characterized by light optical microscopy (LOM), scanning electron microscopy (SEM) coupled to electron backscatter diffraction (EBSD).
Flexible pipes are frequently used both as flowlines and risers in the oil and gas industry. A flexible pipe has a complex structure consisting of layers of polymer and metallic materials. The armor wire layers – shielded with polymer materials from seawater on the outside and well fluid on the inside – are the load and pressure bearing parts. Due to diffusion from the well fluid and/or damage of the outer polymer layer, the annulus can be water-filled, and armor wire can corrode. In this work, the susceptibility to hydrogen embrittlement (HE) with the presence of atomic hydrogen due to cathodic polarization has been investigated for six different tensile armor wire materials. Samples were exposed to Slow Strain Rate testing (SSRT) in 3.5% NaCl solution and cathodic polarization to -1.1 and -1.4 VAg/AgCl at room temperature. Reference samples without hydrogen charging were tested in air for comparison. Stress-strain curves, reduction in area (RA) and the microstructure of the fracture surfaces were investigated. The HE susceptibility tended to increase with the carbon content, strength and hardness and the materials tended to be more brittle when charged to -1.4 VAg/AgCl than -1.1VAg/AgCl.