Analysis of hydrogen diffusion and trapping in a 13% chromium martensitic stainless steel

Abstract

A theoretical analysis has been made of the combined effects of reversible and irreversible trapping, with varying degrees of occupancy, on hydrogen transport in steels. The analysis has been coupled with repetitive electrochemical permeation measurements to characterise the diffusion and trapping parameters associated with a 13% Cr martensitic stainless steel commonly used for oil production tubing. The density of reversible and irreversible traps was (3.0 ± 1.0) × 10 19 sites cm −3 and about 1.5 × 10 19 sites cm −3 respectively. The binding energy of the reversible traps was (− 38.7 ± 1.0) kJmol −1. The capture rate constant for the irreversible traps was (4.8 ± 1.3) × 10 −19 cm −3 s −1. Assuming the same value for the reversible traps a release rate constant for the reversible traps of about (3.4 ± 1.6) × 10 −2 s −1. Knowledge of these parameters enables improved calculation of hydrogen charging times, which is essential for establishing reliable test methodology. It is recommended that the use of an effective diffusion coefficient, as a quantitative parameter for characterising hydrogen transport, be abandoned in systems for which irreversible trapping is dominant.