Study On The Effect Of Cathodic Polarization On The Hydrogen Embrittlement Sensitivity Of Ocean Engineering Steels And Welds

Ocean engineering steels, such as E460, E500, E550 and XXXX, are prone to corrosion as serving in seawater. Thus, cathodic protection is widely used to protect these structural steels from corrosion. It is known that high strength steels are normally sensitive to hydrogen embrittlement, which becomes more serious as the strength of the steel increases. Hydrogen evolves from the metal surface caused by more negative cathodic polarization potential, which diffuses into the metal structure and results in hydrogen embrittlement fracture. Therefore, selection of reasonable cathodic polarization potential range is very important for the cathodic protection design of high strength steels. In this paper, electrochemical techniques and slow strain rate tensile tests methods were used to study the hydrogen embrittlement sensitivity of E460, E500, E550 and XXXX steel at different polarization potentials. The effect of cathodic polarization potential on the hydrogen embrittlement sensitivity of high strength steels were discussed in details.The E460 steel behaved ductile fracture as the potential was in the range from Ecorr to-0.85V(SCE). In the potential range from-0.85V to-0.95 V, quasi cleavage morphology characteristics of the steel appeared. When the potential ranged from-0.95V to-1.05 V, the steel showed brittle fracture.The E500 steel was dominated by anodic dissolution and ductile fracture when the potential was in the range from Ecorr to-0.85V. In the potential range from-0.85V to-0.90 V, quasi cleavage morphology characteristics of the steel appeared. While the potential ranged from-0.90V to-1.05 V, the steel showed brittle fracture.The E550 steel behaved ductile fracture as the potential was in the range from Ecorr to-0.90V. When the cathodic protection potentials was lower than-0.90V, the tendency of brittle fracture of the E550 steel increased. When the cathodic protection potentials further shifted lower than-1.00V, the E550 steel’s fracture mode changed into brittle fracture.In the potential range from Ecorr to-0.90V, the dominated fracture mode of the XXXX steel was ductile fracture. When the cathodic protection potentials was lower than-0.90V, the tendency of brittle fracture of the XXXX steel increased. When the cathodic protection potentials further moved lower than-0.95V, the XXXX steel’s fracture mode changed into brittle fracture.In the potential range from Ecorr to-0.875V, the fracture mode of XXXX weld seam was ductile fracture. When the cathodic protection potentials was lower than-0.90V, the XXXX weld seam showed tendency of brittle fracture. When the cathodic protection potentials was lower than-0.95V, the fracture mode of the XXXX steel weld seam behaved brittle fracture.