During a turnaround inspection of a Gasoil Hydrotreater, severe metal loss was observed in the Reactor Effluent Product Condenser Inlet piping. The thickness loss was on the straight horizontal piping portion downstream of continuous wash water injection point. Metal loss is confined to top portion i.e., 10 to 2 o'clock position of the piping only. Corrosion rates in excess of 1mm/year were noticed. The unusual observation was that there was no significant thickness loss at point of water injection or immediate downstream piping, but loss was predominantly on straight portion after 5 directional change. Process simulation, Ionic Equilibria modelling and Computational Fluid Dynamics (CFD) study of the REAC inlet system was performed. This paper explains how the location of wash water injection and type of injection device has influenced the corrosion in the REAC inlet piping. Based on the study, it was identified that stratification of flow and inadequate scrubbing of reactor effluent vapor by wash water has led to HCl/NH4Cl corrosion. Subsequently it was recommended to shift the wash-water injection location to vertical section of the piping and to change the injection type from quill to spray nozzle
Gas Oil Hydrotreating Unit uses a catalytic hydrotreating process employing a selective catalyst and a hydrogen-rich gas stream to decompose organic sulfur, oxygen and nitrogen compounds contained in the feed. The products of these reactions are the contaminant free hydrocarbon, along with H2S and NH3. Other Treating reactions include halide removal and aromatic saturation. Reactor effluent is cooled in series of Combined Feed Exchangers followed by REAC for product separation. The reactor effluent system is prone for corrosion and fouling due to salting of NH4HS and NH4Cl. Most of the failure analysis studies and literature available in public domain regarding reactor effluent corrosion deals with the corrosion in the REAC and its outlet piping. Even though unusual failure in the form top-half pipe corrosion was reported in few instances of REFINCOR1 forums, not much has been written on this subject. This paper discusses the methodology and analysis carried out to understand the factors influencing such corrosion in the inlet piping of REAC.
