Failure analysis of stress corrosion cracking of 316L structured packing in a distillation tower

The present study was done to find the probable causes of AISI316L structured packings (SPs) failure in a dewatering phenol tower. In this tower, the SPs would provide a high contact surface between streams to maximize and accelerate the distillation process. Increasing vibration of discharging pump showed that there were detached pieces of SPs in pump's strainer. During plant overhaul, corrosion inspection was done and some of the broken packings were gathered for further analysis. The samples were evaluated by visual observation, optical and scanning electron microscope. Transgranular cracks in packing sheets and screws, used for restraining layers of packing together, were seen. Energy-dispersive X-ray spectroscopy (EDS) of corrosion products on packing and the fracture surface of the screw was conducted. The results showed the occurrence of chloride stress corrosion cracking. Even though the chlorine contents of tower streams were low, it seemed that process fluids have been mal-distributed leading to the local concentration of the chlorine on SPs surface. In addition to chlorine, high working temperature and applied stress provided a favorable condition for stress corrosion cracking.