Super duplex stainless steel is susceptible 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 (SSRT) technique. The testing, at strain rate of 1x10-6 s-1, was performed on specimens polarized in the range of -1050 mV to -400 mV at ambient temperature in ASTM artificial seawater conditioned with and without hydrogen pre-charging. The impact of HISC was evaluated through an assessment of the ratio of the elongation at fracture in the seawater to that in air (ε/εair). The influence of CP potential, hydrogen content, and microstructure of the tube were examined. The ductility and fracture mechanism of the samples were studied by SEM.

The results show that the ratio of ε/εair increases with the increase of CP potential applied down to threshold potential where the ratio of ε/εair was close to 1. Below the threshold potential, the influence of CP potential on the ductility of the material is less pronounced.

Subject
Super duplex stainless steel, Test methods, Materials, Stainless alloys, Microstructure, Tubes, Seawater, Mechanical failure, Electric potential, Fracture, Protection potential, Austenite, Hydrogen
Keywords:
Super Duplex Stainless Steel tube, Cathodic Protection Potential, HISC, Slow Strain Rate Testing
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2009
Association for Materials Protection and Performance (AMPP)
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