USE OF ON-LINE MONITORING TECHNIQUES FOR EVALUATIONS OF LEAD STRESS CORROSION CRACKING (PBSCC) AND A PBSCC INHIBITOR

摘要

Stress corrosion cracking (SCC) of steam generatortubing is no longer the leading cause of pressurized waterreactor outages and repairs in large part because moreresistant alloys are in much wider use. Specifically, Alloy690 and Alloy 800 tubing is now used at well over 50% ofthe operating steam generators around the world.However, despite the superior performance of these alloysfor nominal water chemistries, both of these alloys alongwith Alloy 600MA and Alloy 600TT have been shown tobe susceptible to lead stress corrosion cracking (PbSCC)in faulted chemistries that could plausibly occur during aplant chemistry excursion event. Therefore, EPRI hasbeen investigating the use of an inhibitor to PbSCC thatcan be applied on the secondary side of steam generators.One significant complication for development of aninhibitor is the limited ability of traditional SG tube SCCtest methods (e.g. reverse u bend tests) to provide directdata on the initiation time for PbSCC and on crackgrowth rates. Newer testing that utilizes active load anddirect current potential drop (DCPD) for crackmeasurements can provide additional data, but the testsetup may not be as representative of plant materials andstress states. This paper will review the testingmethodologies previously used for evaluations of PbSCCand inhibitor evaluations, and then discuss the state-ofthe-art for testing utilized today including the latestresults available from on-going testing, and discuss thesteps remaining to qualify a PbSCC inhibitor for plantuse.