Failure analysis of structural steel subjected to long term exposure of hydrogen

Embrittlement of steel due to its exposure to hydrogen is a well-established phenomenon, which diminishes its ductility and toughness. However, there is limited research on how hydrogen, which evolves from the corrosion process, affects the yield strength of mild steel in the long-term. This paper presents the results obtained from a long-term investigation on hydrogen evolving from a corrosion reaction, which causes embrittlement of mild steel. Both mechanical tests and microstructural analyses on corroded steel specimens are performed at three different intervals for one year. Time-dependent relations for predicting the corrosion rate and its subsequent hydrogen release were derived by analysing the test results. Moreover, relations for predicting the change in yield strength as a function of hydrogen content, corrosion rate and compositional element change were developed, along with one single equation considering all these factors. Furthermore, fractography analysis was performed to observe HE effect and reasons for the decline in yield strength. The analysis revealed hydrogen induced micro cracks, micro pores, intergranular cracks, grains deformation and hydrogen blisters.