External Corrosion of Tubes in Hydrocracker First Stage Reactor Effluent / H_2S Stripper Feed Breech-Lock Heat Exchanger

摘要

First stage reactor effluent/H_2S stripper feed Breech Lock Exchanger with CS tubes (A 210 Gr C) of Hydrocracker unit commissioned in 1988 was performing satisfactorily until 2003. Subsequently, the feed throughput was increased. Also the feed quality changed with higher nitrogen content. Due to the incomplete oil-water phase separation in a Cold Low Pressure Separator (CLPS), the entrained water containing ammonium chloride salts in the H_2S stripper feed was carried over to the shell of the exchanger. Tubes suffered external corrosion in the form of grooves and pits resulting in wall thinning and leaks.This paper describes results of a failure analysis using Energy Dispersive Spectroscopy (EDS), electron microscopy, metallography and various other conventional Non-destructive techniques on the damaged tubes and collected deposit scales. Corrosion occurred under deposits in wet and sour hydrocarbon streams containing ammonium chloride salts. Immediate remedial measures were taken to replace the coalescers of separators and long-term recommendation in the form of upgrading the tube metallurgy to high nickel Alloy 625 are discussed in the paper.