Failure analysis of stress corrosion cracking of 316L stainless steel bend pipe in the atmospheric tower

The top circulation system of the atmospheric tower maintains the fractionation balance inside the tower by refluxing and condensing the liquid. During operation, cracking and leakage occurred in the 316L stainless steel elbow of the recirculation line. A detailed failure analysis was conducted through experimental testing, along with stress analysis and fluid flow simulations. The results showed that a small amount of water in the gasoline tends to accumulate on the outer side of the elbow under the effects of by centrifugal forces, creating a chloride and sulfur corrosive environment. The inner wall of the elbow underwent localized pitting corrosion due to the combined effects of welding thermal influence and chloride ion corrosion, resulting in the formation of numerous corrosion pits. Under the influence of external tensile stress and welding residual stress, these corrosion pits served as crack initiation sites and gradually propagated, ultimately leading to leakage failure. This failure was the result of the combined action of multiple factors, including welding residual stress, corrosive environment, and external loading. Based on the failure analysis, a series of targeted protective measures were proposed as well.