Hydrogen permeation behavior of X80 pipeline steel under alternating wet-dry environment in the South China Sea

The riser sections of offshore pipelines are subject to cathodic potentials, alternating wet-dry (AWD) cycles and stresses in the service environment. The hydrogen permeation of X80 offshore pipeline with different cathodic potentials, dry/wet ratios, and constant tensile stress in AWD environment were investigated by the self made experimental equipment, which includes the three modules, i.e., the constant stress loading, the two-component cell hydrogen permeation, and AWD environment. Results showed that hydrogen permeation current fluctuates with the AWD, which is different from that in the bulk solution. In one AWD cycle, the permeation increases in the wetting stage and decreases in the dry stage. The smaller the dry/wet ratio, the longer the hydrogen permeation current keeps high level which is caused by the dense corrosion product layer. The hydrogen permeation currents in the elastic stress are greater than those in the plastic deformation, and unstressed conditions is the smallest.