ToF-SIMS depth pro les of the passivation lm
Cross - section STEM images
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STEM BF
STEM BF
FeO
PO
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Figure 3 Surface characterisation of phosphorus-based corrosion inhibitor treated metal coupon
Patent-pending low-P multifunctional naphthenic acid corrosion inhibitor Although phosphorus-based corrosion inhibitors have demonstrated efficacy in mitigating high-temperature naphthenic acid corrosion, the excess phosphorus content can adversely affect catalyst performance in downstream processing units. Furthermore, the dislodgement of phos- phorus-based scale deposits from metal surfaces due to high shear conditions can result in subsequent fouling complications for downstream operations.4 For these rea - sons, new research was initiated to develop a low or non- phosphorus, non-metal-based, thermally stable, and non-fouling high-temperature corrosion inhibitor for the mitigation of naphthenic acid corrosion. To achieve the aforementioned objective, the synergies of various corrosion inhibitors and dispersant chemistries were studied to develop multifunctional products that could mitigate naphthenic acid corrosion. These were extensively evaluated for high-temperature corrosion inhibition, ther- mal stability, product corrosivity at elevated temperature, and dispersing and fouling tendencies, including their abil- ity to disperse iron phosphate and organic foulants. It was discovered that when using a combination of phosphorus- based corrosion inhibitor with a specific dispersant
chemistry, although the protective film is formed by the phosphate chemistry, the synergy of the dispersant com - ponent helped make it more effective at a much lower dosage. This enabled better corrosion inhibition at approx- imately half the phosphorus level of the conventional phosphorus-based inhibitors. This led to the filing of a pat - ent-pending treatment innovation, termed the new low-P multifunctional naphthenic acid corrosion inhibitor. The corrosion inhibition efficacy of conventional phos - phorus-based corrosion inhibitors and that of the new multifunctional corrosion inhibitor was evaluated by RCA for carbon steel and P5 metallurgy for a synthetic test fluid with a NAN ~3, at 310ºC (590ºC) and ~30 Pa shear stress. This represents the high TAN and low sulphur scenario mentioned earlier, which is typically very corrosive as there is no iron sulphide protective layer formation and the high shear stress tends to remove the protective layer. Through this analysis, it was demonstrated that the same corrosion inhibition efficacy shown by a conventional corrosion inhib - itor with 3.5 wt% phosphorus content could be achieved by the new low-P multifunctional corrosion inhibitor with only 1.7 wt% phosphorus content (see Figure 4 ). Impact of sulphur compounds on naphthenic acid corrosion The sulphur content in the crude oil can influence the naph - thenic acid corrosion at high temperatures. Based on the nature of the sulphur, it can form a tenacious iron sulphide layer on the metallurgy, providing a protective layer, or it can form a non-tenacious iron sulphide layer. The latter is typically a defective protective layer that leads to iron naph - thenate diffusion into the fresh metal surface, increasing the corrosion severity.5 In either case, the data presented in this section demonstrate that the new low-P multifunc - tional corrosion inhibitor can form a tenacious protective layer on the iron sulphide layer while demonstrating excel - lent corrosion resistance from naphthenic acid. Two HVGO samples from two US refineries (total sulphur content of >1.5 wt% and TAN >1) as well as a bottom resi - due from the atmospheric distillation unit of an Asian refinery (total sulphur of ~3 wt% and TAN ~0.5) were tested using
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C10 18 P5
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Conventional Cl (3.5% P)
Conventional Cl (1.7% P)
Low-P multifunctional Cl (1.7% P)
Figure 4 Naphthenic acid corrosion inhibition of conven - tional CI vs low-P multifunctional CI
12
PTQ Q2 2025
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