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 (Δ G) 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 |Δ G| < 35 kJ/mol, namely N = 1.4 × 10 −5 and 7.9 × 10 −4 mol/cm 3 respectively. Strong trapping sites were detected (−72 < Δ G < −57 kJ/mol) and their densities increased markedly after cold-rolling.