An Influence of Cathodic Protection Potential on the Mechanical Properties of the Super Duplex Stainless Steel Tube

Super duplex stainless steel is susceptibility to Hydrogen Induced Stress Cracking (HISC) under the influence of a Cathodic Protection (CP) system. A study has been carried out investigating the influence of CP potential on mechanical degradation of UNS S32750 Super Duplex umbilical tube using a slow strain rate testing technique. The testing, at strain rate of 1x10⁶ S^-1, was performed on samples polarized at -1050mV,-950mV,-850mV, -650mV and -400mV at ambient temperature in seawater conditioned with and without hydrogen pre-charging. The impact of HISC was evaluated through an assessment of the ratio between the time to fracture (R) in the seawater and in air. The influence of CP potential, hydrogen content, and degree of cold deformation of the tube were examined. The ductility and fracture mechanism of the samples was studied by SEM.
The results show that the ratio of R increases with the decrease of negative CP potential applied down to threshold potential where the ratio of R close to 1. Below the threshold potential, the influence of CP potential on the ductility of the material is less pronounced.