Hydrogen trapping in an API 5L X60 steel

Electrochemical hydrogen permeation tests were performed on an API 5L X60 steel to study trapping and diffusion properties in the as-received (AR) and in a cold-rolled (CR) state, at 30, 50 and 70 °C. Hydrogen trapping was characterized by assuming saturable traps in local equilibrium. Binding energies (ΔG) and trap densities (N) were determined by fitting a trapping theoretical model to experimental data. Both conditions AR and CR present a high density of weak traps |ΔG| < 35 kJ/mol, namely N = 1.4 × 10−5 and 7.9 × 10−4 mol/cm3 respectively. Strong trapping sites were detected (−72 < ΔG < −57 kJ/mol) and their densities increased markedly after cold-rolling.

► Hydrogen diffusion and trapping parameters were determined for an API 5L X60 steel. ► Parameters were obtained by using a model of saturable traps in local equilibrium. ► Apparent diffusion coefficient reflects weak trap effects. ► The use of an apparent diffusion coefficient improves calculation efficiency. ► Either weak or strong trap densities are increased with plastic deformation.