Paul Industries carries out corrosion assessment, materials consultation and passivation for North Dakota crush plants and oil refineries. The extraction side of a crush plant is a flammability problem. The refining side is a corrosion problem, and it is a more varied one than most operators expect, because refining vegetable oil means exposing equipment to free fatty acids, then strong caustic, then acidic soapstock, then high temperature under vacuum, in that order, in the same building.
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Each refining step presents a different problem
Crude oil leaving extraction is not a finished product. It carries gums, pigments, waxes and free fatty acids, and removing each of those is a separate operation with its own chemistry.
Degumming. Water or acid is used to hydrate and remove phosphatides. Where acid degumming is used, typically phosphoric or citric, the equipment sees a dilute acid at temperature. Mild, and it is the first of several acid exposures rather than an isolated one.
Caustic neutralizing. Sodium hydroxide reacts with the free fatty acids to form soapstock, which is separated out. Now the same plant that was handling acid is handling strong caustic at temperature, which is the environment described on our Wyoming caustic cracking page: carbon steel, low-alloy steel and 300-series stainless are all susceptible to caustic stress corrosion cracking, and the control is post-weld heat treatment rather than an alloy upgrade.
Soapstock acidulation. The separated soapstock is commonly treated with sulfuric acid to recover fatty acids, which produces a hot acidic stream that is considerably more aggressive than anything in the main oil line. This is frequently the single most corrosive service on the site and it is frequently housed in equipment specified as an afterthought, because it handles a by-product rather than product.
Bleaching. Adsorbent clay removes color and residual contaminants under vacuum at temperature. The clay is abrasive, so filtration and handling equipment wears, and spent clay retains oil, which makes it both a disposal question and a self-heating hazard if it is stored badly.
Deodorizing. Steam stripping under high vacuum at high temperature removes volatile compounds and the remaining free fatty acids. This is the most demanding duty in the plant: hot enough that material selection is governed by temperature rather than chemistry alone, under a vacuum that makes any air in-leakage both a process and an oxidation problem.
Free fatty acids, and why incoming quality matters to the equipment
Fatty acids are corrosive to carbon steel at elevated temperature, and the concentration arriving at the plant is not constant. It depends on how the beans were stored, how long they sat, the condition they were harvested in, and how the crush ran. A plant processing a poor crop year is running higher acid loads through the same equipment that handled a good one.
That gives two consequences worth designing for rather than tolerating.
Specify against the bad year, not the average. Material selection based on typical crude quality leaves a plant exposed exactly when conditions are already difficult. The incremental cost of specifying for the upper end is small compared with replacing a heated vessel.
Track incoming quality as a maintenance input. A plant that records fatty acid content at intake has a leading indicator of the corrosion load its refining equipment is about to see, and can plan inspection around it. Most plants record it for process reasons and never connect it to the asset condition, and the two are directly related.
| Step | Driver | Inspection focus |
|---|---|---|
| Degumming | Dilute acid at temperature | Heated surfaces, mixing zones |
| Neutralizing | Strong caustic at temperature | Welds and heat-affected zones; PWHT status |
| Soapstock acidulation | Hot sulfuric acid | Everything; usually the worst service on site |
| Bleaching | Abrasive clay plus vacuum | Filtration, handling, wear points |
| Deodorizing | High temperature under vacuum | Heated surfaces, vacuum integrity, packing |
| Storage and transfer | Fatty acids and water separation | Tank bottoms and the waterline |
The last row is the quiet one. Oil stored with any water content separates, and the water layer at the bottom of a tank concentrates whatever is soluble in it, including fatty acids and any chloride present. Tank bottoms and the waterline are where storage corrosion appears, and they are the least inspected part of any storage installation.
| Heating load | Per treatment | Per 20 treatments |
|---|---|---|
| 30 kW | $17.40 | $348 |
| 60 kW | $34.80 | $696 |
| 120 kW | $69.60 | $1,392 |
At 7.25 cents per kilowatt-hour, below the 8.13 cent national average (EIA, 2024), treatment energy is immaterial. What governs this work is access and availability, since most of it happens inside vessels during a turnaround, competing for the same window as the mechanical work described on our North Dakota shutdown page.
Where passivation helps, and where it does not
We sell passivation and it is worth being specific about which of these problems it addresses.
It helps on the product-contact stainless. Cleaning per ASTM A380 and passivation per ASTM A967 removes free iron and weld heat tint and restores a coherent film. On refined oil equipment that matters for corrosion resistance and because iron contamination is itself a product quality issue, since trace metals promote oxidation and reduce oil shelf life. That is a direct product argument rather than only an asset one.
It does not address caustic cracking. As on our Wyoming page, the mechanism needs tensile stress, a caustic environment and a susceptible material, and passivation changes none of them. Post-weld heat treatment is the control, and it is the item most often omitted from a competitively priced fabrication.
It does not substitute for the right alloy in acidulation service. Hot sulfuric acid handling needs materials selected for it, and passivating an inadequate material produces a well-passivated component that still fails.
It is essential after every repair. Every cut, weld and grind on this plant introduces free iron and heat tint into services that will exploit both. Post-repair treatment belongs in the maintenance procedure rather than being treated as a construction activity.
We carry out corrosion surveys with thickness mapping, materials consultation across the refining train, post-weld heat treatment coordination, in-place and shop passivation, heat tint removal, and tank bottom and waterline inspection. Where a plant has a recurring failure we would rather establish which of the four regimes is responsible before recommending anything, because the answers differ completely.
Standards referenced: EIA electricity price data · ASTM A967 · ASTM A380 · ASME BPE
Frequently asked questions
Do you handle corrosion work at North Dakota crush and refining plants?
Yes, across Casselton, Spiritwood, Fargo, Grand Forks, Jamestown and statewide: corrosion surveys with thickness mapping, materials consultation, post-weld heat treatment coordination, in-place and shop passivation per ASTM A967 after cleaning per ASTM A380, heat tint removal, and tank inspection.
Why is refining harder on equipment than extraction?
Because refining exposes the same building to four different regimes in sequence: free fatty acids, then strong caustic, then acidic soapstock, then high temperature under vacuum. Extraction is dominated by one problem, flammability; refining is dominated by several corrosion mechanisms with different remedies.
Which service is usually worst?
Soapstock acidulation. Treating separated soapstock with sulfuric acid produces a hot acidic stream more aggressive than anything in the main oil line, and because it handles a by-product rather than product it is frequently specified as an afterthought.
Does incoming crude quality affect corrosion?
Directly. Free fatty acid content varies with storage, harvest conditions and how the crush ran, and fatty acids are corrosive to carbon steel at elevated temperature. A plant processing a poor crop year is running a higher acid load through equipment specified for a normal one.
How should we use that information?
Specify materials against the bad year rather than the average, since the incremental cost is small against replacing a heated vessel. And treat recorded intake fatty acid content as a leading indicator of corrosion load for inspection planning, which most plants measure for process reasons and never connect to asset condition.
What about the caustic neutralizing stage?
It presents caustic stress corrosion cracking, where carbon steel, low-alloy steel and 300-series stainless are all susceptible. The control is post-weld heat treatment to relieve residual stress rather than an alloy upgrade, and inspection should target welds and heat-affected zones rather than general wall thickness.
Where does storage corrosion appear?
At tank bottoms and the waterline. Oil stored with any water content separates, and the water layer concentrates whatever is soluble in it including fatty acids and chloride. It is the least inspected part of most storage installations and a common source of surprise.
Is passivation worth it on refining equipment?
On product-contact stainless, yes, and for two reasons. It restores corrosion resistance, and it removes iron contamination that is itself a product quality issue, since trace metals promote oxidation and reduce oil shelf life. That is a direct product argument rather than only an asset one.
What can passivation not fix here?
Caustic cracking, which needs stress relief rather than a surface treatment, and inadequate material selection in acidulation service, where passivating the wrong alloy gives a well-passivated component that still fails. Both are worth establishing before any treatment is specified.
How do I get a quote for North Dakota refining corrosion work?
Use the form on this page or call 201-450-8280. Useful inputs are which refining stages are in scope, typical and worst-case incoming fatty acid levels, where failures appear, whether welds in caustic service were post-weld heat treated, and what turnaround window is available.
What does free fatty acid do to equipment?
Free fatty acids in crude oil are mildly corrosive to carbon steel and attack it at elevated temperature, and crude with high acidity corrodes storage, piping and the front of the refining train faster. Incoming crude quality affects how long the equipment lasts.
What materials are used in refining heat exchangers and why?
Stainless tubes in the grades that resist the wash water's chloride and the neutraliser's caustic, with titanium or duplex where the water quality or the temperature demands it, because exchanger tubes see the process fluid on one side and water on the other. Tube failures mix water into the oil, which starts the corrosion elsewhere.
What corrodes in bleaching and filtration?
Bleaching earth is mildly acidic and abrasive, and spent earth holds oil that can self-heat. Filters and earth handling equipment wear and corrode, and stainless is common at the filter.
What does deodorising do to equipment?
High temperature under vacuum with stripping steam, which is a demanding duty for the vessel and its internals, and where fatty acid distillate condenses it is corrosive. Stainless and careful design of the condensing sections are standard.
How does phosphoric acid degumming affect equipment?
Phosphoric acid added to remove gums is hot and corrosive to carbon steel and low-grade stainless, and the gums it produces foul surfaces, so the degumming stage runs in stainless with cleaning provision. It is an acid service inside a plant that is otherwise oil.
What damage do bleaching clay and filters cause?
Bleaching clay is abrasive and, when wet, acidic, so the slurry lines, filter housings and leaves wear and corrode together, with the filter housing's crevices the worst site. Materials and inspection at the bleaching stage are chosen for both mechanisms.
What does hydrogenation equipment need?
Pressure-rated vessels and piping for hydrogen service, with materials chosen to avoid hydrogen attack, and handling of the nickel catalyst that keeps it out of the product and away from surfaces it could foul. Hydrogenation is a pressure and materials discipline distinct from the rest of the refinery.
How is wash water chloride controlled in refining?
By treating the wash water to remove chloride and hardness before it contacts the oil, and by monitoring it, because chloride carried into the neutraliser and washer is the source of pitting on the stainless equipment downstream. Wash water quality is a corrosion control.
What does a North Dakota winter do to oil storage corrosion?
Cold roofs and walls condense moisture in the tank's vapour space, producing water that settles beneath the oil and corrodes the bottom, and cold oil holds water in suspension longer. Tank heating, insulation and regular water draw-off are winter controls on storage corrosion.
How is corrosion under insulation handled at a crush plant?
Hot, insulated refining and steam equipment corrodes under wet insulation, and the North Dakota climate drives condensation at every insulation break. Inspection at breaks and sealed jacketing are the controls.
How is passivation scheduled?
During turnaround, after cleaning, on the stainless equipment identified for it, with the work planned into the turnaround scope. It is combined with inspection so that the surface condition is recorded.
What inspection programme suits refining equipment?
Thickness monitoring on carbon steel at the corrosion locations, inspection of stainless at welds and condensing sections, and tank bottom inspection on a schedule. The programme follows the mechanisms found.
How is spent passivation chemistry handled?
Through the plant's effluent treatment after neutralisation, with the oil and soap load from cleaning accounted for. Refining effluent treatment already handles oily, alkaline streams.
Does biodiesel or renewable diesel processing change the picture?
Feedstock pretreatment for renewable fuels adds acid and adsorbent steps with their own corrosion, and the same logic applies: identify the mechanism at each stage and match the material and treatment to it.
What is the commonest refining corrosion finding?
Water accumulating in crude storage and at the front of the refining train, corroding equipment that was specified for oil rather than for wet oil. Draining water and monitoring moisture prevent most of it.
Corrosion in a North Dakota refining train?
Tell us which stage is failing and what your incoming fatty acid levels look like across a year. Those two usually identify the mechanism. Call 201-450-8280 or use the form below.