The super duplex stainless steel grade UNS S32750 was studied with regard to susceptibility to hydrogen embrittlement when cathodically protected in chloride containing media. Test specimens were connected to zinc creating an open circuit potential commonly occurring in cathodic protection systems subsea. The methods employed consist basically of constant load and slow strain rate testing techniques and the chloride solutions used were 3% NaCl and synthetic sea water. The duplex grade UNS S31803 was included in the constant load tests in the latter solution. Reference testing was conducted in air.

In order to investigate the effect of cold work, test specimens with up to 20% of cold deformation were prepared and tested. In addition, specimens pre-charged with hydrogen were compared with uncharged samples with exposure to hydrogen exclusively in the strained condition. Amounts of hydrogen uptake during pre-charging and testing were evaluated.

It is shown that hydrogen has a notable effect on the material properties with regard to ductility. Whereas the yield and tensile strengths remain almost unaffected, the fracture strain is reduced as an effect of the increased hydrogen levels. In the constant load test series, no cracking was observed at loads exceeding the yield strengths of the materials, irrespective of the degree of cold work. The critical factors when designing super duplex systems for use in connection with cathodic protection subsea are discussed.