Stress Corrosion Cracking (SCC) Testing

Stress Corrosion Cracking (SCC) Testing Overview

Stress corrosion cracking (SCC) is a failure mode in which a susceptible material, subjected to sustained tensile stress in a specific corrosive environment, develops and propagates cracks at stress levels well below the material’s yield strength. Neither the mechanical stress alone nor the corrosive environment alone would cause cracking under these conditions – the failure results from the synergistic interaction of both. SCC is particularly dangerous because it can occur with little or no visible surface corrosion and progresses with limited warning before catastrophic fracture.

SCC testing applies controlled tensile stress to specimens immersed in or exposed to a defined corrosive medium and monitors for crack initiation and propagation over time. Stress is applied by constant load, constant displacement (bent beam or C-ring specimens), or slow strain rate methods, each of which emphasizes different aspects of the cracking behavior. The choice of method depends on whether the objective is determining a threshold stress below which cracking does not occur, measuring crack growth rate, or assessing susceptibility ranking across different materials or heat treatments.

Materials commonly evaluated for SCC susceptibility include high-strength aluminum alloys (particularly in the 2xxx and 7xxx series), stainless steels in chloride environments, titanium alloys in specific media, copper alloys in ammonia environments, and high-strength steels in hydrogen-generating conditions. SCC test data informs design allowable stress levels, alloy and temper selection, and protective measure requirements for structural components.