DESIGN AND FABRICATION OF ALLOY A-286 FOR RESISTANCE TO IGSCC IN PWRS

摘要

Alloy A-286 (UNS designation S66286) materialis an age-hardenable austenitic stainless steel alloythat has been extensively used in light water reactors(LWRs). The alloy was originally developed for usein high temperature applications where goodcorrosion resistance and high-strength are required,such as gas turbines. Alloy A-286 has been used forreactor vessel internals bolting, fuel rod springs,control rod drive mechanism parts, reactor coolantpump shafts and bolting, and external reactorcoolant system bolting. Intergranular stresscorrosion cracking (IGSCC) has been observed inmany of the locations in LWRs (i.e., pressurizedwater reactors (PWRs) and boiling water reactors(BWRs)) where Alloy A-286 material is in contactwith reactor coolant, particularly as a high-strengthbolting material. Alloy A-286 component items havebeen procured in accordance with various industryspecifications, such as ASTM A 453, Grade 660,Class A or Class B; SA-453, Grade 660, Class A orClass B; ASTM A 638 Grade 660 Type 1 or Type 2;and AMS 5737. Laboratory testing and failureanalysis efforts have shown that certain fabricationpractices and high levels of stress increase thesusceptibility of Alloy A-286 material to IGSCC inPWRs. This paper describes the operatingexperience with the many instances, including recentfailures observed in reactor coolant pump bolting, ofIGSCC that have been observed with Alloy A-286material and summarize the best available designand fabrication parameters for optimizing IGSCCresistance in PWR environments.