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Quenched and tempered martensitic steels for Oil Country Tubular Goods can be subject to Sulfide Stress Cracking (SSC) when exposed to a sour environment. Basically, the failure mechanism of SSC includes an initiation step followed by a propagation step of a crack. Focusing on the latter, it is essential to model the conditions for crack propagation in order to discern the levers that enable to avoid propagation or to stop the crack. With this view, a hydrogen stress driven model was built that describes stress field and hydrogen activity at the direct vicinity of a crack tip. In complement, a second model based on the cohesive zone simulates the kinetic of a crack growth. In parallel, experimental works using hydrogen permeation under stress on flat un-notched and notched tensile specimens brought experimental data that were compared to simulation outputs. The respective influence of diffusible and trapped hydrogen on the cracking mechanism received a specific focus, based on fractographic analyses.