STRESS CORROSION CRACK INITIATION OF COLD-WORKED ALLOY 800 IN Pb-CONTAINING, ALKALINE ENVIRONMENTS

摘要

Steam generator (SG) tubing made of Alloy 800 haveexhibited good performance in service for over 30 years.Despite its excellent performance, the industry hascontinued to proactively investigate the limits of its stresscorrosion cracking (SCC) resistance, particularly forsecondary-side environments where boiling at occludedheat-transfer surfaces can produce more aggressiveenvironments compared with the well-controlled, benignchemistry of bulk secondary-side water. Previouslaboratory testing, predominantly using reverse-u-bend(RUB) specimens, has demonstrated the vulnerability ofAlloy 800 to SCC in modestly alkaline environments,containing lead (Pb). The present work builds onprevious RUB investigations by probing the limits to SCCsusceptibility using actively-loaded, blunt-notch tensilespecimens with in-situ crack monitoring via the directcurrent potential drop (DCPD) technique. ComparativeSCC initiation testing was performed to probe thesusceptibility of cold-worked Alloy 800 to Pb-inducedSCC at progressively lower pH values. Furthermore, thetest methodology was also used to investigate the relativeeffects of applied load and type of loading (cyclic vs.constant). This paper will discuss the effects of theseparameters on crack initiation in the context of themechanism of Pb-induced SCC of Alloy 800.