The rising threats to FCC units
Combined operational influences on severe corrosion and its countermeasures
Keisuke Karaki Kurita Water industries Ltd. Arthur Lamm Kurita America, Inc.
F luid catalytic cracking (FCC) units remain indispensa- ble in modern refining due to their ability to convert low-value heavy fractions into a wide range of high- value light products, as well as their operational flexibility to accommodate market volatility. However, despite these advantages, FCC units are subject to significant corrosion risks – not only from cyanides, but also from various acids such as hydrogen sulphide, organic acids, and strong min - eral acids, including sulphuric acid, hydrogen chloride, and hydrogen bromide. Therefore, appropriate corrosion control is a critical concern for the operation of FCC units.1 Furthermore, recent developments have introduced additional corrosion risks, driven by two emerging trends: changes in operational preferences and variations in feed - stock impurities. The former is influenced by shifting mar - ket demands for gasoline and diesel, while the latter arises from the increased use of chemical additives in upstream processes, some of which remain in the feedstock. This article explores the mechanistic basis of these evolv - ing challenges, their potential impact on refinery assets, and available mitigation strategies. A case study is also presented to illustrate practical approaches to managing these risks. Operation mode trends Historically, FCC operations have prioritised naphtha pro - duction. However, structural shifts in fuel demand and increasing regulatory pressures have led refiners to favour light cycle oil (LCO) production for the diesel pool. This trend is expected to persist, driven by the rapid growth of alter - native fuel sources for gasoline, such as ethanol, biodiesel, and electricity. In response to these market dynamics, refiners are evaluating strategies to maximise FCC middle distillate yields. Achieving this objective typically involves coordinated adjustments to reactor conditions, catalyst for - mulations, and fractionator cut points. Fractionator cut points are commonly adjusted in two approaches. One involves lowering the gasoline end point by reducing the tower top temperature, thereby promoting condensation of hydrocarbons in the upper section of the tower.³ The other involves increasing the column bottom temperature to enhance recovery of light ends trapped in the slurry oil. While the first approach effectively increases LCO yield, it also narrows the safety margin against salt deposition and heightens fouling and corrosion risks. Conversely, the sec - ond approach can lead to increased asphaltene alike fouling, coke formation, and catalyst fine accumulation in the slurry
pumparound section. It may even lead to off-spec sediment values in some cases. Each approach presents its own set of advantages and trade-offs, which must be carefully evalu - ated within the context of unit performance and reliability. Feedstocks trends Recent trends in FCC unit feedstocks include: u Shift toward heavier fractions or an increased ratio of heavy fractions. v Transition toward lighter fraction feedstocks. w Emergence of feedstocks containing elevated levels of halogens, such as chlorides and bromides. x Co-processing of low-carbon feeds, such as bio-oils and pyrolysis oils derived from waste plastics. The adoption of heavier feedstock has long been prac - tised to improve profitability or in response to the declin - ing availability of high-quality crude. Conversely, the shift to lighter fraction feedstocks is often associated with the growing integration of FCC operations into petrochemical production. Trends 1 and 2 are closely linked to the declin - ing demand for heavy oils and gasoline/naphtha fractions. Forecasts suggest that demand for heavy oil will continue to fall, prompting increased utilisation of heavy fractions in cracking units, such as FCC units and cokers. In some cases, the recycling ratio of slurry oil (SLO) into FCC unit feed has been increased to reduce the output of heavy fractions. Regardless of the reasons, heavier fractions tend to contain high levels of corrosion-promoting species, such as chlo - rides, sulphur, and nitrogen. Trend 3 concerns halogen contamination in FCC unit feedstocks. While chloride has long been recognised as a corrosive component in refinery processes, there has been a growing trend in Bromide detection in refinery feed - stocks. Although bromide can equally cause severe acidic corrosion and salt deposition as chloride, bromide may not be detected by conventional chloride analysis methods. Potential sources of bromide include seawater contamina - tion, crude origin, or chemical additives used in upstream production stimulation. Trend 4 reflects broader efforts toward decarbonisation and circular economy initiatives. In this context, various bio- based and low-carbon feedstocks, such as used cooking oil, animal fats, wood pyrolysis oils, and waste plastic pyrolysis oils, are being introduced into hydrotreating and cracking units to support transition while utilising existing refinery infrastructure (for example, co-processing). However, these alternative feedstocks are reported to contain extremely
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PTQ Q1 2026
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