Characterization of Magnetite Scale Formed in Naphthenic Acid Corrosion

• Published in: JOM (1989) Vol. 69; no. 2; pp. 217 - 224
• Main Authors: Jin, Peng, Robbins, Winston, Bota, Gheorghe, Nesic, Srdjan
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.02.2017; Springer Nature B.V
• Subjects: Acids; Chemistry/Food Science; Corrosion; Corrosion resistance; Crude oil; Earth Sciences; Engineering; Environment; Experiments; Iron; Iron oxides; Magnetite; Mineral oils; Morphology; Naphthenic acids; Petroleum refineries; Physics; Refineries; Scale (corrosion); Scanning electron microscopy; Steel; Steels; Sulfur; Temperature; Transmission electron microscopy; Naphthenic Acid; Corrosion Rate; Sulfur Compound; Magnetite; Iron Sulfide
• ISSN: 1047-4838; 1543-1851
• DOI: 10.1007/s11837-016-2164-y

Naphthenic acid corrosion (NAC) is one of the major concerns for corrosion engineers in refineries. Traditionally, the iron sulfide (FeS) scale, formed when sulfur compounds in crudes corrode the metal, is expected to be protective and limit the NAC. Nevertheless, no relationship has been found between protectiveness and the characteristics of FeS scale. In this study, lab scale tests with model sulfur compounds and naphthenic acids replicated corrosive processes of refineries with real crude fractions behavior. The morphology and chemical composition of scales were analyzed with scanning electron microscopy and transmission electron microscopy. These high-resolution microscopy techniques revealed the presence of an iron oxide (Fe 3 O 4 or magnetite) scale and discrete particulates on metal surfaces under FeS scales, especially on a low chrome steel. The presence of the iron oxide was correlated with the naphthenic acid activity during the experiments. It is postulated that the formation of the magnetite scale resulted from the decomposition of iron naphthenates at high temperatures. It is further postulated that a nano-particulate form of magnetite may be providing corrosion resistance.