Slow Strain-Rate Technique: Application to Caustic Stress Corrosion Cracking Studies

Abstract

This paper describes slow strain-rate test equipment, operable at elevated temperatures and pressures, that includes electrochemical potential control capability. Applications in caustic stress corrosion cracking (SCC) studies of both nuclear steam generator and fossil boiler materials are presented. Electrochemical potential regions for stress corrosion cracking of Inconel alloy 600, Incoloy alloy 800, and Type 304 stainless steel are compared to results obtained using constant load specimens. Tests with titanium stabilized Alloy 800 (Sanicro 30) tubular specimens also demonstrate the effect of potential on cracking mode. A comparison of SCC test results, using both long term exposure tests and short term straining electrode tests, is made between a mild steel and its weld metal. In these examples, favorable comparisons are obtained with tests using conventional methods, proving the value and usefulness of the slow straining device in accelerating SCC studies and in defining more accurately conditions under which SCC can occur.

On the suitability of slow strain rate tensile testing for assessing hydrogen embrittlement susceptibility

“…For example, specimens may be (1) exposed to the environment prior to testing (i.e. pre-exposed or precharged) and/or during the experiment (in-situ), (2) smooth or notched, (3) cyclically loaded prior to monotonic testing to generate a 'fatigue pre-crack', and (4) modified to include specific features of interest (coatings [23], different microstructural zones induced by welding [24,25], tubular cross-sections [26], etc.). Metrics of interest depend on the specimen geometry [21], with reduction in area (i.e.…”