PTQ Q2 2025 Issue

further reduced with caustic addition to the desalted crude stream. Caustic treatment inhibits the formation of HCl from the remaining salts in the desalted crude when exposed to crude furnace conditions. Minimising consequences When all measures to reduce the risk of salt formation are exhausted, frequent equipment failures can still be avoided by reducing the corrosion rate of inevitable salt formation. As mentioned earlier, these salt deposits are concentrated acid solutions that react with equipment surfaces. The pH of these salt deposits is typically in the 3-4 range, which can be very corrosive on equipment surfaces. Experience has shown salt corrosion rates of 50-200 mpy (1.3-5.1 mm/y) on carbon steel equipment and up to 25 mpy (0.6 mm/y) on C-276 alloy. However, the presence of amines with stronger basicity than typical overhead neu- traliser amines can raise the pH of these salt deposits and significantly lower the associated corrosion rates.6 Treatments with Topguard salt control additive have reduced corrosion rates by 70-80% extending equipment life by three to five times as long and reducing the need for failure repairs between scheduled maintenance shutdowns. Figure 4 shows a treatment example where the average corrosion, as measured by electrical resistance probes, was reduced by about 70-80%. While tramp amines can have costly consequences in crude unit equipment, these threats can be managed to achieve operational goals. From flexibility in crude oil feedstocks to flexibility in overhead operation, refinery asset performance can be enhanced even when tramp amines are present. TOPGUARD and EXCALIBUR are marks of Baker Hughes company. References 1 Damage Mechanisms Affecting Fixed Equipment in the Refining Industry, Recommended Practice RP-571, 3rd. Ed., American Petroleum Institute (API), 2020. 2 Rechtien, R., Duggan, G., Identifying the Impacts of Amine Contamination on Crude Units, CORROSION/2006, paper no. 06581 (Houston, TX: NACE 2006). 3 Lack, J. E., Considering Mass Transfer in Refinery Crude Distillation Overhead Water Wash, CORROSION/2023, paper no. C2023-18757 (Houston, TX: AMPP 2023). 4 Lack, J. E., Applying Mass Transfer Principles to the Design and Operation of Refinery Crude Distillation Overhead Water Wash Systems, CORROSION/2025, paper no. C2025-00075 (Houston, TX: AMPP 2025). 5 Lack, J. E., An In-Depth Look at Amine Behavior in Crude Units Using Electrolyte-Base Simulation, CORROSION/2005, paper no. 05570 (Houston, TX: NACE 2005). 6 Lack, J. E., Harrell, B., Reducing Salt Corrosion Rates with Stronger Base Amines, CORROSION/2013, paper no. 2037 (Houston, TX: NACE 2013). Joel Lack is a Senior Application Engineer for Key Accounts and has more than 25 years of experience in the global oil refining industry, mostly focused on managing corrosion in the process units. He holds three patents and has authored several articles and conference papers. Lack is a member of AMPP and holds a BS in engineering with chemical concentration from McNeese State University.

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volume washes confirmed the build-up of salt deposits. After the water wash rate was raised to the appropriate levels, the after-wash salt ΔT values were almost always positive. Subsequent high-volume washes showed no evi- dence of salt accumulation following the change to a higher rate injection. Blocking threats While an effective water wash provides protection to the overhead condensers with valuable flexibility in crude feed quality, it cannot provide protection when the distil- lation tower top is at risk of salt formation. To remove the risk of salt corrosion in the tower top, either the tower top temperature must be raised to >25°F (>14°C) above the highest salt formation temperature, or the highest salt for- mation temperature must be lowered below the tower top temperature (by the same margin) via a reduction in salt- forming contaminants. Pretreatment demulsification in the tank farm can be very effective at removing water-soluble contaminants, especially if the crude tanks have dewatering facilities. Even without tank dewatering, earlier use of demulsification chemistry allows for increased interaction with microemulsions. With enhanced emulsion contact, more vigorous mixing can be tolerated, yielding better dehydration and greater desalting efficiency across the desalter. At the desalter, tramp amines can be removed via acid- ification. Many factors impact amine phase partitioning in the desalter, but the greatest impact is the pH of the water in the desalter.5 Acidic conditions push amines to an ionic form, which is insoluble in oil. A pH of approximately 5.5 is usually enough to maximise amine removal, which can sometimes lower the salt formation temperature by as much as 20°F (9°C) or more. Unfortunately, the same mechanism that removes bases from the oil phase can push oil-soluble acids into the oil phase. Using volatile acids, such as acetic acid, can sig- nificantly increase organic acids in the crude distillation overhead, driving up neutraliser consumption and the asso- ciated neutraliser salt risk. Excalibur additives are designed to be effective at lower desalter pH while minimising impacts to the crude distillation overhead. In addition to maximising desalter efficiency, overhead chlorides can be Figure 4 Impact on probe corrosion rates when Topguard 1130 salt control additive was applied

PTQ Q2 2025