Dioxide and Hydrogen Sulfide Removal

Carbon steel is the predominant construction material for carbonate and amine solution containers. Corrosion in the overhead lines (hydrogen sulfide or carbon dioxide plus water from the regenerator) is prevented by adding corrosion inhibitors. Although amine carry-over can act as a corrosion inhibitor in the overhead line, SCC of carbon steel has occurred when amine added as a corrosion inhibitor became concentrated. Copper and copper base alloys should be avoided in amine service and are questionable in carbonate seivice. Nickel or cobalt base alloys (e.g., Monel00 400 and Inconel 600) except for Stellite01 should be avoided in carbonate service. Monel 400 should be avoided in amine service if UCC Amine Guard02 corrosion inhibitor is used. 

Hydrogen, Methanol, Ammonia, Gas Treating, Hydrodealkylation, Polymerization, Phenol, and Solvent Treating 

Recent work reveals that SCC occurs only in hot MEA solutions when the electrochemical potential of the steel surface is more negative than -700 mV vs a silver-silver chloride electrode. The tendency for SCC increases with an increase in solution concentration and in temperature. Saturating the hot MEA solution with hydrogen sulfide makes the potential of the steel more positive (i.e., decreases the tendency for SCC). This latter result raises a question about the practice of some operators who require stress relief only for steels exposed to amine solutions containing hydrogen sulfide. 

There is some question about the need to stress relieve carbon steel in a carbonate solution, which normally contains corrosion inhibitors. Oxygen is usually added to maintain the inhibitor, which is often vanadium pentoxide in the active (oxidized) state otherwise, SCC can occur. 

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