As fatigue and overload have been quantified in design codes, environmental cracking (stress corrosion cracking (SCC) and corrosion fatigue) has become more common, and is less well understood than other corrosion phenomena. When environmental cracking develops rapidly, the challenges in quantification and modeling are not nearly as immense as when long life (such as 20 – 80 years) is a requirement. Short term tests that represent a time-acceleration of 100 – 2000X cannot be expected to be (nor are they) adequately sensitive, and tests that focus on initiation cannot account for the evolution of the surface over long-time environmental exposure – indeed, often the nature and consistency of engineering surfaces are poorly known. Functionality (on stress, concentration/pH, temperature, microstructure, etc.) cannot be extrapolated by 100 – 2000X in time with any confidence. Such tests have value, but their shortcomings must be understood.
SCC growth rate tests with high resolution crack following hold the greatest promise for quantifying SCC susceptibility and identifying dependencies, and they characterize the response of the overall structure, not just the surface. Such tests involve experimental sophisticated and testing expertise, and a recently published SCC Guidelines (www.epri.com) provides detailed examples of historical errors and recommended practices.