Corrosion and Cracking Behavior of the API X-52 and API X-65 Steels with Cathodic Protection

Cathodic protection is one of the most useful methods to stop corrosion when the deterioration process has started. It is always a concern when applying cathodic protection the efficiency of this protection method under different experimental conditions. However, high pH generally induces stress corrosion cracking (SCC) phenomena and occurs only in a relatively narrow cathodic potential range in the presence of a carbonate/bicarbonate environment and  for pH’s greater than 9. In this work, the resistance to the stress corrosion cracking of the API X-52 and API X-65 steels was investigated using a modified wedge opening loading (WOL) fracture mechanics specimens. The specimens were loaded with 95% of the yield strength. The resistance of crack growth and the corrosion were evaluated under different protection potentials (-850 and -650 mV). The used electrolytes were simulated soils (carbonate-bicarbonate solution). Evidence of crack propagation of the API X-52 and API X-65 steels was obtained by scanning electron microscopy. The results showed susceptibility to SCC on specimens even with cathodic protection. The applied protection potential (-850 mV vs Cu/CuSO4 electrode) decreases considerably the corrosion rate on the evaluated steels. In this work the loaded stress showed to be a very important variable on the susceptibility to SCC.