Abstract
Sulfide stress cracking (SSC), i.e., a form of hydrogen embrittlement (HE), is one of the main threats to pipelines transporting sour oil and gas. The ISO 15156-2 standard restricts the hardness and the allowable nickel content of carbon and low alloy steels (LASs) for sour service to reduce SSC risks. However, it is well accepted that the SSC resistance is primarily governed by alloy microstructure.
Dual-phase (DP) LASs are extensively used in the automotive industry due to their low cost and excellent mechanical and high technological properties. In addition, the combined features of ferrite and martensite make these steels promising candidates for the O&G sector. Snape et al. studied DP LAS on a commercial-grade AISI 4340 composition, which showed great potential for sour O&G applications in the tempered condition. However, no previous studies focused on the role of Ni on the HE for DP LAS.
This work quantifies the HE resistance of research-grade DP LASs with varying Ni content fixing the ferrite-martensite ratio using in-situ slow strain rate testing (SSRT). In addition, the hydrogen transport kinetics was evaluated using hydrogen permeation testing, and the trapping activation energies were studied by thermal desorption spectroscopy (TDS). Finally, the microstructural characterization was performed by scanning electron microscopy (SEM). Ductility loss due to hydrogen embrittlement and the hydrogen diffusion and trapping quantification results were linked to the microstructural characterization.