CHLORIDE STRESS CORROSION CRACKING OF PUMP SEAL FLUSH COOLER COILS IN OPEN RECIRCULATION WATER

摘要

Frequent leaks were observed in the seal flush coolers of pumps in crude distillation unit where shell side is open recirculation cooling water. These coolers are in small size and low value items. However, repeated coil leaks resulted in failure of pump seals (increased maintenance cost) & reduced standby redundancy of the pumps. Moreover, cooling water is often contaminated with hydrocarbon (seal oil media) causing increased wastage of treated water by blowdowns (environmental concern), additional consumption of fresh water & treatment chemicals. Further, there is an increased threat of microbiological induced corrosion (MIC) in the open recirculation cooling water system.The coil tube material of coolers is Type 304 stainless steel [UNS S30400] as per original design. The typical mean time between failure (MTBF) of these coils is approximately 2 years. The failures are attributed to chloride stress corrosion cracking (CISCC) of susceptible 300 series stainless steels in aqueous chloride environment. This paper details the investigation of cracking degradation mechanisms, microstructural study, assessment of cooling water quality, and review of design conditions & suitability of selected material. Also presented are suggested alternate techno-economical solutions for affected cooler materials.