Case of External SCC of Type 304 Stainless Steel Under Insulation in Natural Gas Plant

Abstract This paper presents a case study of stress corrosion cracking (SCC) in Type 304 stainless steel, which occurred under the insulation of an acid gas removal unit at a natural gas plant. The external SCC were primarily observed near the welds located at high temperature acid gas removal unit tower's reinforcement ring under insulation. The reinforcing ring, made of Type 304 stainless steel, was welded to the outer periphery of the tower, creating conditions for water accumulation under the insulation. Elemental analysis of the cracks revealed a high concentration of chlorides. Since the plant is located far from the coast, marine chloride contamination was unlikely; it is considered highly probable that the detected chlorides originated from leakage within the insulation. It was concluded that external SCC was caused by a combination of internal pressure and residual stress in the welds under insulation in high temperature with chloride environment.