The corrosion condition in the vacuum tower does not match the iron ion analysis

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The crude oil processed in my unit is high-acid and low-sulfur crude, resulting in severe corrosion of the composite wall panels, packing, and internal components within the vacuum distillation tower. Corrosion collapse of fillers (316L) for subtractive two-line segments, subtractive three-line segments, and subtractive four-line segments ； Large-scale pitting on the vessel wall composite plate (316L); local corrosion has disappeared ； The internal components of the tower (packing support grids, crossbeams, trough distributors and V-shaped plates), yet the levels of iron ions at high temperatures were all within the specified limit (≤3μg/g), which is quite different from the severe corrosion observed in the vacuum tower. It seems to me that the high-temperature corrosion inhibitor used contained interfering substances; these additives, being part of the overall mixture, reacted with iron ions through complexation, masking, or reduction processes, affecting the accuracy of the analysis results for iron ion levels. Have you all encountered such situations? What other insights do you have? Please share! How to conduct a rapid analysis and judgment if the additive contains interferents.