Hydrochloric Acid Corrosion
General Information
Hydrochloric acid finds widespread use across various industries, serving as a crucial component in chemical manufacturing, food production, pharmaceuticals, rubber manufacturing, metal cleaning, and well activation (acidizing), among others. In the refining industry, HCl typically emerges as a by-product during the decomposition reactions of both inorganic and organic chlorides in the crude distillation process, impacting the integrity of the overhead (OVHD) section of the atmospheric distillation tower. Additionally, HCl is present in reforming and isomerization units where it either emanates from Cl-containing catalysts or forms during the regeneration of catalysts through the addition of chlorinated compounds. Moreover, HCl is also employed as a bulk chemical, serving as a neutralizing agent in tasks such as water treatment plants or within caustic treatment units.
The Cl- ions in aqueous HCl solutions can penetrate and break down the passive oxide layer of many CRAs (Corrosion-Resistant Alloys), resulting in accelerated corrosion. For instance, UNS S31603 (316L) may corrode at a rate similar to carbon steel under such conditions. Therefore, only a few alloys, such as molybdenum-rich C-276 (UNS N10276) and B-3 (UNS N10675), have demonstrated relatively good resistance — although not complete immunity — to HCl across a wide range of temperatures and concentrations.1 2 When using material selection tables for HCl, which are commonly employed in the industry, caution is advised as the data mostly originates from laboratory experiments in controlled environments. The presence of oxidizers like O2 from the air or ions such as Fe3+ or Cu2+ may significantly alter the behavior of the alloy.3 4
Choosing resistant materials for HCl is challenging, so the practice of lining internal steel pipelines/vessels with polymeric materials has become a popular strategy to reduce bulk HCl corrosion in specific regions.5 6 This method is effective but demands highly skilled personnel for assembly, maintenance, and inspection of internally lined systems. Table 1 outlines typical areas susceptible to HCl corrosion.
Table 1 Potential locations for HCl corrosion in process units.7
| Process Unit | Operation area affected by hydrochloric acid corrosion |
|---|---|
| Crude Distillation Unit (CDU) | • Atmospheric tower overhead |
| Catalytic Reforming Unit (CRU) | • Product separator • Debutanizer section (OVHD) |
| Isomerization (ISO) | • Stabilizing column OVHD • HCl scrubbing (caustic treatment) |
| Hydroprocessing Hydrotreating/Hydrocracking | • Inlet to REAC (relatively low probability as HCl will predominantly form NH4Cl in reaction with NH3) |
| Utility & Storage | • Condensate polishing unit (neutralization section) • Caustic unit (neutralization) • HCl tank, vapor lines/scrubber • Wastewater primary treatment (for alkaline wastewater) |
Hydrochloric Acid Corrosion is governed by a combination of several factors like chemical species and concentration, temperature, materials and/or flow regimes.
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References
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