The effects of applied stress and test temperature on the environment-induced cracking (EIC) behavior of carbon steel in 5 kmol/m3 NH4NO3 solution were investigated by using constant load method. The three parameters (time to failure (tf), steady state elongation rate (lss) and transition time to time to failure ratio (tss/tf)) were obtained from a corrosion elongation curve. The relationships between applied stress and the three parameters were divided into three regions; the stress-dominated, the EIC-dominated and the corrosion-dominated regions. Under an applied stress of 225 MPa (in the EIC-dominated region), the test temperature dependences of the three parameters were investigated. Although tf decreased with increasing test temperature above 323 K, it became constant independent of test temperature under 323 K. Whenever the EIC takes place, the relationship between log tf and log lss become a good straight line with a slope of -1.1 irrespective applied stress and test temperature, which means that lss becomes a parameter for predicting tf. In addition, the fracture appearance in the EIC-dominated region was intergranular. From the results obtained, the intergranular cracking of carbon steel was discussed in terms of film formation, dissolution and hydrogen permeation.
Hydrogen Permeation Estimated by HMT in Carbon Steel Exposed to Gaseous Hydrogen
