Interaction effect of temperature and cathodic protection on electrochemical corrosion and stress corrosion cracking behavior of E690 steel in artificial seawater

Abstract

This study investigates the interaction effects of seawater temperature (0–30 °C), cathodic protection (−950 mV_SCE), calcareous deposition (CaCO₃), and tensile loading on the electrochemical corrosion, hydrogen permeation, and stress corrosion cracking (SCC) behavior of E690 steel in marine environment. The results show that under open circuit potential (OCP) condition, the anodic dissolution-driven SCC occurs due to the combined effects of anodic dissolution of Fe and tensile stress, resulting in ductile fracture. A large number of corrosion pits form at 30 °C, which become crack sources under load and promote SCC. The hydrogen-induced SCC occurs to E690 steel under a cathodic potential of −950 mV_SCE due to hydrogen evolution and hydrogen permeation, which causes brittle fracture. Temperature has a dual impact on SCC. On the one hand, increase of temperature promotes both electrochemical reactions and hydrogen permeation rate, which aggravates SCC sensitivity. The amount of hydrogen evolution increases from 4.1 C cm⁻² at 0 °C to 6.2 C cm⁻² at 30 °C. On the other hand, a CaCO₃ deposition layer is formed on steel surface at 20 °C and 30 °C, with the average thickness of 7 and 17 μm, respectively. Its physical covering effect slows down the rate of cathodic hydrogen evolution and hydrogen permeation, which reduces SCC sensitivity. Therefore, with the increase of temperature, the SCC sensitivity presents fluctuating changes of first increasing, then decreasing, and then increasing again. E690 steel is proved to have low SCC sensitivity at low temperature of 0 °C.