Fitting and crevice corrosion behaviour of high alloy stainless steels in chloride-fluoride solutions

The localised corrosion resistance (pitting and crevice corrosion) of two h igh alloy stainless steels, namely superduplex (SD) and superaustenitic (SA ), has been studied in chloride-fluoride solutions at pH values ranging fro m 2 to 6.5. The pitting potential (E-pit) and crevice potential (E-cre) hav e been calculated for these test media using electrochemical techniques (co ntinuous current). The Critical Pitting Temperature (CPT) and Critical Crev ice Temperature (CCT) are in both materials lower then the room temperature . In spite of this fact and due to the high repassivation rate, the resista nce of these materials to localised corrosion is high in the tested media. At the highest tested concentration of aggressive anions and pH 6.5 both ma terials undergo a generalised attack.