A Limited Evaluation of the Applicability of NACE MR0175/ISO 15156 H₂S Limits to Supercritical CO₂ Pipelines Available to Purchase

In an earlier paper one of the authors raised the question of whether the hydrogen sulfide (H₂S) partial pressure threshold of 0.05 psia (0.3 kPa) for cracking of steels from sulfide stress cracking is pertinent to dense phase carbon dioxide (CO₂) systems in which there is no free gas phase. This paper presents a limited test of the pertinence of this threshold value in Supercritical CO₂. Autoclave tests of four-point bend beam specimens of API 5L Grade X80 line pipe steel at 0.05 psia (0.3 kPa) and 0.20 psia (1.38 kPa) H₂S were performed and the samples were examined after testing for cracking. In addition, the test conditions were modeled with the OLI Studio software to determine the H₂S fugacities and H₂S concentrations in the brine phase. No cracking was found after 30 d of exposure.