Hydrogen trapping in an API 5L X60 steel

Abstract

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 (DG) 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 |DG| < 35 kJ/mol, namely N = 1.4 105 and 7.9 104 mol/cm3 respectively. Strong trapping sites were detected (72 < DG < 57 kJ/mol) and their densities increased markedly after cold-rolling.