Electrochemical Corrosion Comparison of Seamless Tubes in UNS S31266 and UNS S31254 with New Testing Method

摘要

The super-austenitic stainless steel UNS S31266 is due to its optimum of alloying elements a suitable material for seawater applications as for example seawater cooled heat exchangers. Producing UNS S31266 as seamless tubes gives the possibility to build heat exchangers with both tubes and plates in UNS S31266. The super-austenitic stainless steel UNS S31254 also has excellent corrosion resistance in a variety of industrial environments. In this study the critical pitting temperature (CPT) for UNS S31266 was compared to UNS S31254 with the newly developed electrochemical method, modified ASTM G150 developed by K. Lund et al., using 3M magnesium chloride (MgCl_2) instead of 1M sodium chloride (NaCI). CPT-values measured by the modified ASTM G150-method were shown to be 10-20 °C lower than when using 1M NaCI. Also, the crevice corrosion resistance of UNS S31266 was compared to UNS S31254 measured in NaCI solution. The average CPT_(mod) in 3M MgCl_2 for UNS S31266 was 86 °C and for UNS S31254 it was 66 °C. The CPT_(mod) was thus 20 °C higher for the UNS S31266 seamless tubes compared to UNS S31254. The CCT in NaCI of UNS S31266 was approximately 85 °C and for UNS S31254 it was approximately 60 °C.