Stress Corrosion Cracking Testing Of Laboratory Processed 304/304L Stainless Steel Elbows And Pipe

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Stress corrosion cracking (SCC) of austenitic stainless steels, while not as prevalent as that in nickelbased alloys such as Alloy 600 and Alloys 82/182, has been observed in the primary system of commercial pressurized water reactors. These instances of SCC have been associated with water chemistry issues and/or occluded regions; however, in many cases high levels of cold work were also present in the material as well.

Product Number: ED22-18591-SG

Author: Denise J Paraventi, Justin R Hesterberg, Tyler E Moss, and Stephen C Healey

Publication Date: 2022

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Conventional stress corrosion crack (SCC) initiation and growth understanding relies on the testing of fracture mechanics specimens such as uniform gage tensile and compact tension specimens. However, these specimens are restricted to Mode I loading and usually a uniform material condition per sample (e.g., heat treatment, cold work level). In contrast, actual components are likely subject to varying
stresses and material conditions through-thickness. While some conditions have been reproduced in laboratory testing (e.g., varying cold work), and unique specimen designs can be used to simulate multiaxial loading in high temperature water environments, it can be difficult to translate these results to real world situations. A program was conducted to test elbows and pipes that had been processed to include
varying through-thickness cold work and residual stress. These “specimens” were assembled into a piping loop arrangement and exposed to 274°C (525°F) water for up to 1.09 years. The specimens were monitored for SCC using in situ electric potential drop and periodic ultrasonic testing inspections to detect and monitor SCC initiation and growth. The observed cracking was confirmed via destructive evaluation
to be intergranular SCC. The results will be discussed in the context of the influence of varying cold work and residual stress on the initiation and growth in these novel test specimens. The extension of fracture mechanics-based SCC testing to complex component stress/material conditions will also be discussed.