API 570 Piping Inspector Practice Test

Moisture trapped under insulation creates a wet, chloride-rich environment that accelerates corrosion. The two forms most commonly seen in this situation are localized attack on carbon steel and chloride-induced stress corrosion cracking in austenitic stainless steels. Carbon steel tends to corrode in a localized way, forming pits or crevice-like damage where water pools or where protective films are breached. Austenitic stainless steels, when exposed to chlorides and tensile stresses at the temperatures typical under insulation, can develop cracks that propagate through the metal—chloride stress corrosion cracking. The other listed forms—erosion from particle impact, uniform corrosion of aluminum with copper pitting, or galvanic corrosion from dissimilar metals—are not the predominant corrosion modes under insulation in most refinery or piping scenarios.