Application of the Critical Pitting Temperature Test to the Evaluation of Duplex Stainless Steel

This paper presents the results of a laboratory testing program whose objective was to evaluate the localized corrosion resistance of duplex stainless steel weldments and to validate screening test methods for this task. The results of sodium chloride (NaCl) critical pitting temperature (CPT) tests, ferric chloride tests, electrochemical polarization (pitting) scans, and simulated service environment tests are presented. These studies revealed that the sodium chloride CPT screening test provided the best correlation with long-term simulated service environment tests in terms of rank ordering resistance to pitting and in the morphology of attack. In terms of pitting resistance of duplex stainless steel weldments, it was found that pitting susceptibility could be related to both ferrite content and pitting index (PI) of the weld metal. At equivalent values of PI and ferrite content, the weld metal had higher resistance to pitting than the base metal.