Pay attention to stress corrosion cracking of stainless steel pipes under insulation (case study)

Thread Content

Attention should be paid to stress corrosion cracking of insulated stainless steel pipes (case study). Example: In a certain plant, a stainless steel pipe with a diameter of 30.5 cm was used to transport a hot (80°C) weakly acidic solution. There is an insulating layer outside the tube to maintain the temperature. The insulation material is covered with an aluminum sheet to prevent rainwater from wetting it, and the pipes have been in use for several years without any problems. Due to the marine environment, the pipeline support frames suffered corrosion; to repair them, the aluminum covers and insulation materials were removed, and they were reinstalled after the repairs were completed. But just a few months later, the repaired pipe section began to leak. It was found that stress corrosion cracking had occurred on the outer surface of the stainless steel pipe. The reason is that the workers did not install the aluminum covers properly as required, failing to provide protection against rain. Rainwater seeps in, wetting the insulation material. Chloride ions in rainwater and those leached from insulation materials accumulate and concentrate on the surface of stainless steel pipes. Combined with the residual stresses present in the pipeline, this led to chloride stress corrosion cracking, with the cracks penetrating and causing leakage. Analysis: Once again, this is a corrosion problem caused by poor maintenance quality. During equipment maintenance, it is often necessary to remove the insulation layer, and it should be restored in accordance with the requirements of the construction specifications after the maintenance is completed. During the operation of the equipment, the insulation layer may sometimes get damaged; once damaged, it should be repaired promptly. For stainless steel equipment and piping, it is very important to prevent the insulation from absorbing moisture and becoming wet. Additionally, during maintenance, do not use water-absorbent materials (such as burlap) to cover stainless steel equipment. This helps prevent damage and contamination of the stainless steel surface; it is also an important measure for protecting stainless steel equipment.