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Ammonium Chloride Corrosion in the Refining Industry

This paper summarizes key case studies where Ammonium Chloride (NH4Cl) corrosion was observed. Best practices for process control and corrosion mitigation strategies have been recommended based on the learnings from these failures.

 

Product Number: 51317--9574-SG
ISBN: 9574 2017 CP
Author: Sudhakar Mahajanam
Publication Date: 2017
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Ammonium Bisulfide (NH4HS) corrosion is an aggressive form of localized corrosion commonly found in hydroprocessing units throughout the reactor effluent air cooler (REAC) and associated piping. This happens when sulfur and nitrogen in the feed get converted to ammonia (NH3) and hydrogen sulfide (H2S) which react to form NH4HS. Depending on the NH4HS concentration it can also affect FCC SWS amine or delayed coker units. When liquid water is absent NH4HS deposits can form leading to fouling and under-deposit corrosion. Wash water is typically added upstream of the REAC to prevent this problem which can lead to the formation of a corrosive NH4HS solution. Currently there are no effective chemicals or inhibitors available to control this localized corrosion phenomenon. NH4HS corrosion prevention depends on the following critical factors: NH4HS concentration limits flow rates oxygen contamination in the stream corrosion resistant materials and process flow design. In this paper efforts have been made to characterize this corrosion mechanism using available literature and materials performance histories. Mitigation strategies and novel corrosion control methods have been proposed.

Keywords: ammonium chloride corrosion, underdeposit corrosion, under-salt attack, neutralizer, salt fouling, NH4Cl corrosion mechanism, ionic equilibria modeling

Ammonium Bisulfide (NH4HS) corrosion is an aggressive form of localized corrosion commonly found in hydroprocessing units throughout the reactor effluent air cooler (REAC) and associated piping. This happens when sulfur and nitrogen in the feed get converted to ammonia (NH3) and hydrogen sulfide (H2S) which react to form NH4HS. Depending on the NH4HS concentration it can also affect FCC SWS amine or delayed coker units. When liquid water is absent NH4HS deposits can form leading to fouling and under-deposit corrosion. Wash water is typically added upstream of the REAC to prevent this problem which can lead to the formation of a corrosive NH4HS solution. Currently there are no effective chemicals or inhibitors available to control this localized corrosion phenomenon. NH4HS corrosion prevention depends on the following critical factors: NH4HS concentration limits flow rates oxygen contamination in the stream corrosion resistant materials and process flow design. In this paper efforts have been made to characterize this corrosion mechanism using available literature and materials performance histories. Mitigation strategies and novel corrosion control methods have been proposed.

Keywords: ammonium chloride corrosion, underdeposit corrosion, under-salt attack, neutralizer, salt fouling, NH4Cl corrosion mechanism, ionic equilibria modeling

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