Simulation of hydrogen embrittlement requires a coupled approach; on one side, the models describing hydrogen transport must account for local mechanical fields, while on the other side, the effect of hydrogen on the accelerated material damage must be implemented into the model describing crack initiation and growth. The present study presents a review of coupled diffusion and cohesive zone modelling as a method for numerically assessing hydrogen embrittlement of a steel structure. While the model is able to reproduce single experimental results by appropriate fitting of the cohesive parameters, there appears to be limitations in transferring these results to other hydrogen systems. Agreement may be improved by appropriately identifying the required input parameters for the particular system under study.

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Simulation of hydrogen embrittlement requires a coupled approach; on one side, the models describing hydrogen transport must account for local mechanical fields, while on the other side, the effect of hydrogen on the accelerated material damage must be implemented into the model describing crack initiation and growth. The present study presents a review of coupled diffusion and cohesive zone modelling as a method for numerically assessing hydrogen embrittlement of a steel structure. While the model is able to reproduce single experimental results by appropriate fitting of the cohesive parameters, there appears to be limitations in transferring these results to other hydrogen systems. Agreement may be improved by appropriately identifying the required input parameters for the particular system under study.

A coupled finite element and cohesive zone modelling approach has been applied to simulate hydrogen induced fracture initiation in a hot rolled bonded clad steel pipe. The results are compared in terms of experimental fracture mechanical testing in air and under in situ electrochemical hydrogen charging. A best fit to the experimental CTOD fracture initiation toughness value in air was achieved for an initial cohesive stiffness k n = 4 • 10 6 MPa/mm and a critical cohesive stress σ c = 1210 MPa. For simulating under hydrogen influence, the hydrogen induced lowering of the cohesive strength was computed both in terms of the lattice concentration and the total hydrogen concentration. Two different formulations for calculating the dislocation trap density was considered. The simulated results revealed that both hydrogen in lattice and hydrogen trapped at dislocations can be responsible for the observed hydrogen induced reduction in CTOD fracture initation toughness. The choice of trap density formulation appeared significant only under the assumption that both lattice and trapped hydrogen infer an influence on the hydrogen induced lowering of the cohesive strength. Further effort is needed to provide a reliable description of the interface hydrogen content and distribution, providing a model able to transfer between different material systems.

The objective of the present work has been to study the fracture properties of the interface between clad and base material of two 316L austenitic stainless steel-X60/X65 carbon steel hot roll bonded clad pipes; with and without a Ni-interlayer. Fracture mechanical tests were performed in air and under in situ electrochemical hydrogen charging to establish crack growth resistance curves and fracture initiation toughness for both systems. The results revealed that an electroplated Ni-interlayer reduces the fracture initiation toughness for testing in air, while it raises the fracture initiation toughness for testing in hydrogen environment. The samples with a Ni-interlayer revealed little influence of hydrogen on the fracture resistance, with a reduction in the fracture initiation toughness of 20 %, attributed to crack propagation mainly occurring in the nickel layer. The samples without a Ni-interlayer revealed a strong influence of hydrogen on the fracture resistance, with a reduction in the fracture initiation toughness of 85 %. An alternating crack path was proven, shifting between the dissimilar interface and the base material adjacent to the interface.