Influence of hydrogen embrittlement on the Wierzbicki – Xue failure strain criterion

The influence of hydrogen embrittlement on Wierzbicki and Xue (W-X) model parameters is studied. This model has 4 parameters (D, C, δ*, and e 0/f) which have been obtained by tensile test on smooth specimens, tensile notch specimens, single notch tensile specimens (SENT) and pure shear specimens. Hydrogen embrittlement has been obtained by electrolytic method. For the steel API 5L X60, the relative values decrease for the parameters D and C of the W-X plasticity model is in the range after HE. The δ* parameter increases after HE but its influence is limited because the values of the Lode angle are low. For the studied pipe exhibiting a crack-like defect and submitted to internal pressure, soil reaction and lateral seismic displacement Δ, the local failure strain indicates that for high values of Δ, the effect of HE is hidden by the stress triaxiality effect. Improvement of the W-X plasticity model is necessary to consider the thickness and the geometry effects. This can be done by introducing a constrain parameter. Application of the (W-X) model has been done to get the local critical resistance used to predict fracture by the Volumetric Method (VM). An example is given for the case of an embedded pipe submitted to service pressure and lateral seismic displacement.