Hydrogen Permeation Behavior of Steel under Wet/dry Corrosion with Changes in Relative Humidity at the Dry Period

Abstract

Wet/dry cyclic corrosion tests were conducted to investigate the effect of relative humidity (RH) at dry periods on the hydrogen permeation behavior of steel. Steel specimens were exposed to a temperature and humidity-controlled environment with an initial placement of NaCl droplet. The RH at the dry period was controlled at 20%, 55%, 60%, and 65%, which was lower than the deliquescence RH of NaCl (75%). Hydrogen permeation current was detected using electrochemical methods. The corrosion process on the steel was observed using optical techniques. The results show that the amount of permeated hydrogen through the steel increases with increasing RH at the dry period from 20% to 65%. The hydrogen evolution reaction is inhibited with the accumulation of corrosion products on the steel surface, resulting in a decrease in the amount of permeated hydrogen. Based on the results, the state of NaCl inside corrosion products is supposed to be a solid phase at 20% RH, a liquid-solid phase at 55% RH, and a liquid-rich phase above 60% RH. The increasing volume of the liquid phase contributes to the rise in the amount of permeated hydrogen at the dry period.