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Overview of Hydrofluoric (HF) Acid Corrosion

Hydroflouric (HF) Acid Corrosion is an acidic environment damage mechanism associated almost exclusively with HF Alkylation Units. Although these units are usually carefully controlled, unexpected problems with process control can lead to wet acid carryover into carbon steel sections, which were never intended to be exposed to HF acid, resulting in corrosion and leaks. Carbon steel areas prone to HF acid corrosion include flange faces, deadlegs, overhead systems, and some heat exchanger bundles.

Corrosion and fouling in HF Alkylation Units tends to be closely linked to feed quality and operating conditions. Prior to entering the Reaction Section, the olefin and isobutane feed should be treated to remove water, sulfur and other contaminants.

Whenever the temperature of the acid phase exceeds 150 °F or water content of the acid exceeds 3% (or some combination thereof), there is the likelihood of higher corrosion rates on carbon steel equipment. In areas prone to corrosion on carbon steel, Alloy 400 has been very successful in minimizing and preventing corrosion in situations where oxygenates are minimized.

While HF acid corrosion isn’t widespread, there is no reason to get complacent. It is important for operators to continue to closely monitor the susceptible areas on carbon steel equipment and piping.

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