PTQ Q4 2025 Issue

Corrosion control in refinery distillation

How advanced corrosion control in Chinese refineries’ distillation units ensure safe and efficient operation

Shaofeng Lin Veolia

I n the complex world of petroleum refining, distillation processes are at the forefront of transforming crude oil into valuable products. At the heart of these operations lie atmospheric and vacuum distillation towers. Both dis - tillation towers are critical components within the refin - ery, facing persistent challenges, chief among them being corrosion. The corrosion conundrum Corrosion in refinery distillation units represents far more than a routine maintenance challenge; it poses a substan - tial threat to operational integrity, safety, and profitability for refineries worldwide. This issue is especially critical in atmospheric and vacuum distillation devices, where the synergistic effects of elevated temperatures, corrosive chemicals, and fluctuating pressure conditions create an ideal environment for accelerated metal deterioration. The journey of crude oil through a refinery’s first unit begins with desalting and dehydration, then moves through atmospheric distillation, and often concludes with vacuum distillation. Each stage presents unique corrosion challenges:  Desalting: Chlorides in crude oil can hydrolyse to form hydrochloric acid, attacking equipment at the top of the distillation tower and subsequent condensing system (overhead system). The chloride removal efficiency by the desalter is crucial to corrosion control. v Atmospheric distillation tower (ADT): The atmospheric furnace increases the temperature to the level where chlo - ride hydrolysis starts and accelerates to form hydrochloric acid (HCl), which goes through the trays in the atmospheric tower. The corrosion becomes more complicated, particu - larly in the presence of sulphur compounds and organic acid. Along with temperature decreases, the HCl enters water, causing serious corrosion. Also, the high temper - atures create an environment for naphthenic acid and/or sulphide corrosion. w Vacuum distillation tower (VDT): The high temperature and concentrated naphthenic acid, along with occasionally high active sulphur in gas oil or residue, increase high-tem - perature corrosion risks. As there is still hydrogen chloride in the system, with an even higher concentration of hydro - gen sulphide and organic acid, the corrosion potential can

be higher in the overhead system of vacuum towers than in atmospheric towers. To address corrosion control challenges in atmospheric distillation towers (ADT) and vacuum distillation towers (VDT), refiners have implemented comprehensive mitiga - tion strategies. These include strategic equipment metal - lurgy upgrades, precise process parameter adjustments, optimised crude oil blending ratios, and advanced chemical treatment protocols. Such multifaceted approaches have proven effective in minimising corrosion-related risks and enhancing operational reliability. In the National Association of Corrosion Engineers (NACE) publication 341091, the corrosion mech - anisms and mitigation methods for ADT and VDT overhead systems are discussed in detail. Titanium or nickel- based alloy has been widely used in overhead dew point or salt deposit impact heat exchangers. Desalter operation must be optimised to best control hydrolysing salts. Caustic injection into desalted crude is a common practice to main - tain a low chloride level in boot water. Wash water injection management can be highly bene - ficial to refineries, both in terms of the dew point and salt deposits, as it can dilute the acid and dissolve the ammo - nium/amine chloride salts that may form in the overhead system. Chemical injection is the core part of overhead corrosion control, as it builds a barrier between the metal surface and corrosive matter, neutralising the acids. In API RP 571², the study focuses on naphthenic acid and high-temperature sulphidation corrosion. The corrosion is affected by factors such as the total acid number (TAN), velocity, temperature, and shear energy. Typical mitigation involves using higher molybdenum content metal and cor - rosion inhibitors. Among the mitigation methods, chemical treatments are critical. After years of application knowledge and experience, we have developed a suite of innovative tools to combat multifaceted challenges experienced in the four key areas of the crude unit operations.  Corrosion control through stable desalting operation The Embreak series of chemical products to assist with electrical desalting performance includes: • Advanced primary demulsifiers for efficient oil-water separation.

PTQ Q4 2025