API 570 Piping Inspector Practice Test

Chloride-induced stress corrosion cracking happens when chloride ions disrupt the protective passive film on stainless steels, allowing cracks to grow in a humid, warm environment like what forms under insulation in CUI conditions. Austenitic stainless steels have a high chromium-nickel content that gives them excellent corrosion resistance in many environments, but that same protective film can be attacked by chlorides when there is tensile stress and moisture under insulation. In these conditions, cracking can initiate and propagate along grain boundaries or through the grain structure, often without noticeable overall metal loss, making it a common failure mode for austenitic stainless steels in CUI. Copper alloys, aluminum, and carbon steel don't exhibit chloride SCC as routinely or predictably under CUI. Copper alloys may suffer other chloride-related effects, aluminum can pit or corrode, and carbon steel is more prone to general corrosion or hydrogen-related issues rather than classic chloride SCC, especially under insulation.