Elastoplastic constitutive modeling for subsea pipeline steels considering hydrogen-induced dislocation pinning and depinning

Abstract

Four-stage elastoplastic constitutive models for subsea pipeline steels in gaseous hydrogen environment are proposed, in which the impact of hydrogen-induced dislocation pinning and depinning on the elastoplastic mechanical behavior of pipeline steel is taken into accounted. The proposed constitutive models are developed in terms of the phenomena observed in nanoindentation experiments. The variation of yield strength of pipeline steel during hydrogen-induced dislocation pinning and depinning, as well as the subsequent strain hardening, are reflected in the proposed constitutive models. Developed constitutive models are then incorporated into a cyclic cohesive zone model (CCZM) for predicting hydrogen-assisted fatigue crack growth (FCG) rate. A comparison between predicted results of the CCZM incorporated with the proposed elastoplastic constitutive models and experimental data of hydrogen-assisted FCG rates of API pipeline steels is conducted and the results show that the predicted FCG rates agree well with the experimental data. In addition, the impact of model parameter for describing the depinning stage on the hydrogen-assisted FCG rate are also discussed.