Hydrogen permeation through mild steel in temperature range 20–500°C measured by hydrogen collection method

Abstract

Hydrogen permeation through steel plate maintained at various constant temperatures between 20 and 500°C was investigated using the hydrogen collection method. Fused salts were employed at elevated temperatures. Hydrogen entry was induced by step changes in cathodic charging current density. Emanating flux transients obtained at the hydrogen exit face corresponded closely to a model for permeation determined exclusively by bulk hydrogen diffusion through steel, induced by stepped changes in hydrogen concentration at the steel entry face subsurface, and zero hydogen at the exit face subsurface. An Arrhenius plot of log (D) v. 1/T, using diffusion coefficients D derived from permeation transients was approximately linear in the range 20–310°C. The values derived for activation energy E _a of 17 kJ mol ^-1 and for the pre-exponential factor D ₀ of 2·6 × 10^-3 cm2 s^-1, according to D = D ₀ exp (-E _a/RT) were similar to literature values. Between 310 and 500°C, stable permeation conditions were difficult to obtain, but flux measurements were repeatable and unaffected by moisture in air.