Corrosion of carbon steel and alloys in ammonium chloride salt

Kazuhiro Toba*, Koji Kawano, Jun'ichi Sakai

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    5 Citations (Scopus)


    The corrosion behavior and the hygroscopic properties of solid ammonium chloride (NH4Cl) salt are investigated. This study was conducted to determine the root cause of aggressive corrosion due to wet NH4Cl salt deposition in reactor effluent streams in hydroprocessing units. In addition, the corrosion resistance and behavior of carbon steel and alloys in high-concentration NH4Cl solutions were investigated. Corrosion and water-absorption tests were performed under various relative humidity (RH) conditions with solid NH4Cl salts using a temperature- and humidity-controlled chamber. Eight types of materials commonly used in refineries were examined. UNS K02702 (carbon steel) was corroded above 20 % RH. Its highest corrosion rate was observed at 60 % RH and 80 °C. It was suggested that the corrosion of NH4Cl is the most severe around a critical RH, above which water absorption becomes significant. Immersion tests were performed in boiling 20 wt% and 40 wt% NH4Cl solutions with eighteen materials. The corrosion rates of carbon steel were as high as 25.4 mm/y and 60.4 mm/y in 20 wt% and 40 wt% NH4Cl solutions, respectively. Pitting was observed in UNS S41000, UNS S40500, UNS S32100, UNS S30403, UNS S31603 and UNS N08800. The maximum pit depth had a close relationship with the Pitting Resistant Equivalent Number (PREN). Neither general corrosion nor pitting was observed in titanium alloys and alloys with a PREN of 40 and higher. The corrosion rate of UNS K02702 increased with increasing temperature, and the increase was especially rapid in the higher temperature range.

    Original languageEnglish
    JournalNACE - International Corrosion Conference Series
    Publication statusPublished - 2014


    • Ammonium chloride
    • Carbon steel
    • Corrosion
    • Hydroprocessing unit
    • PREN
    • Refinery
    • Relative humidity
    • Salt

    ASJC Scopus subject areas

    • General Chemical Engineering
    • General Chemistry
    • General Materials Science


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