Failure Analysis of Reactor Effluent Air Cooler (REAC) in Hydrocracker Unit

摘要

A major fire incident took place in the Reactor Effluent Air Cooler (REAC) of the Hydrocracker Unit (HCU). The air cooler was severely affected. Cracks were observed on the welding joints between the top plate and the tube sheet, between the bottom plate and the tube sheet of the floating header. The material of construction of the air cooler is Duplex Stainless Steel (DSS). Visual inspection was carried out on the failed portion and its surrounding area. A systematic metallurgical investigation including mechanical testing, macrostructural and microstructural analysis, Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS) was conducted on the failed air cooler. The failure at the weld root and at the fusion line is attributed to crevice and pitting corrosion in the presence of the process fluid containing Chlorides, Hydrogen Chloride (HCl) and Ammonium Chloride (NH_4Cl). The remaining portion of the weld exhibited characteristics of brittle failure. The failure is attributed to a combination of ductile fracture at the weld root and brittle fracture in the remaining portion of the weld caused by the very high pressure process fluid containing Chlorides, HCl and NH_4Cl.