Paul Industries carries out corrosion assessment, materials consultation and surface treatment for Alaska seafood and marine processing plants. Seawater is the most aggressive chloride service any food plant handles, and Alaska plants run it through pumps, piping, chillers and tanks continuously through the season. The finding that surprises operators is that most of the damage is not done while the plant runs. It is done during the eight or nine months the system sits still.
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Why a stopped system corrodes faster than a running one
Chloride attack on stainless is local rather than general. An ion penetrates the passive film at a weak point, a pit initiates, and the chemistry inside that pit diverges from the bulk solution and becomes progressively more aggressive as it deepens. Crevice corrosion is the same mechanism assisted by geometry: a gap, a lap joint, a gasket face or the space under a deposit where solution cannot exchange with the bulk.
What both mechanisms need is for the local chemistry to stay different from the bulk. Flow works against that. Moving seawater continually exchanges solution at the surface, disrupting the concentration gradients that a developing pit depends on, and carries away the products that would otherwise accumulate.
Stop the flow and the opposite happens. Every crevice, every gasket face, every low point holding a residue, every deposit becomes a site where chemistry can diverge undisturbed for months. Oxygen is consumed locally and not replenished, differential aeration cells establish, and the attack proceeds steadily with nothing to interrupt it.
That is why a plant that ran hard and cleanly through a season can open a system in spring and find damage that was not there in September. The damage is not evidence that the season was harsh. It is evidence that the layup was wet.
Layup, which is the highest-return maintenance activity available
The sequence that protects a seawater system costs very little and is routinely compressed because it happens when everyone is leaving.
Flush with fresh water, thoroughly. The objective is to remove chloride before the system dries, and a partial flush that leaves seawater in the low points achieves very little. Flush long enough and at enough velocity to displace the contents rather than dilute them, and flush the branches, not just the main runs.
Drain completely, and verify it drained. This is the step that separates a protected system from an exposed one. Low points that hold a residue are exactly where the remaining chloride concentrates as the rest dries, so a system that is ninety percent drained has concentrated its problem rather than removed it. Verification means opening the drains and confirming flow stops, not opening the valve and assuming.
Dry it if you can. Air circulation through a drained system removes the residual moisture that a drain alone leaves behind on surfaces. Where the layout allows a low-volume air purge, it is worth the effort.
Leave it open where practical. A system left open to atmosphere dries; a system sealed damp stays damp. Where closing is necessary, closing it dry matters considerably more than closing it quickly.
Write down what was done. The crew that lays the plant up is not the crew that starts it, and a layup record tells the spring team what to inspect and what to expect.
| Heating load | Per treatment | Per 20 treatments |
|---|---|---|
| 30 kW | $46.34 | $927 |
| 60 kW | $92.69 | $1,854 |
| 120 kW | $185.38 | $3,708 |
At 19.31 cents per kilowatt-hour, 2.38 times the national average (EIA, 2024), treatment energy is a real if modest cost. The larger consideration on a remote site is that mobilizing a crew and materials for a treatment is expensive, which argues strongly for doing corrosion work within the pre-season visit that is already happening rather than as a separate trip.
Materials, passivation, and being clear about which does what
Alloy selection sets the ceiling. In full-strength seawater, particularly where crevices exist and where the system sits stagnant, type 316 is frequently not sufficient. The reasoning is set out on our Washington alloy page: resistance to chloride pitting and crevice attack tracks chromium, molybdenum and nitrogen content, and duplex, super duplex and 6-moly grades sit well above 316. Where the duty is genuinely severe, specifying the higher alloy is cheaper than replacing 316 twice, and fabrication procedures must match the material rather than being borrowed from 316 practice.
One Alaska-specific nuance is worth noting. Chloride stress corrosion cracking, the mechanism described on our Oklahoma page, requires temperature as well as chloride and stress, and a cold seawater system largely sits below the range where it becomes a practical concern. That is genuine good news and it is narrow: it removes one mechanism and leaves pitting and crevice corrosion entirely intact, and those are what damage these systems.
Passivation restores the film and does not raise the ceiling. Cleaning per ASTM A380 and passivation per ASTM A967 removes free iron and re-establishes a coherent chromium oxide layer, which genuinely matters here because every weld, cut and field repair reintroduces both free iron from tooling and heat tint. In seawater service those defects are exploited quickly. What passivation cannot do is make 316 behave like super duplex, and we would rather say so at specification stage than be called back.
We carry out corrosion surveys timed to the pre-season window, in-place and shop passivation, weld heat tint removal, materials consultation for replacement decisions, layup procedure design, and fabrication in higher alloys with matched procedures.
Standards referenced: EIA electricity price data · ASTM A967 · ASTM A380 · ASME BPE
Frequently asked questions
Do you handle corrosion work for Alaska seafood plants?
Yes, across Kodiak, Dutch Harbor, Bristol Bay, Southeast and the remote sites: corrosion surveys timed to the pre-season window, in-place and shop passivation, weld heat tint removal, materials consultation, layup procedure design, and fabrication in higher alloys.
Why does a stopped system corrode faster?
Because pitting and crevice attack depend on local chemistry staying different from the bulk, and flow disrupts exactly that. Moving seawater exchanges solution at the surface and carries away accumulating products; stagnant seawater lets every crevice and low point diverge undisturbed for months.
So spring damage is not from the season?
Usually not. A plant that ran hard and cleanly can open a system in spring and find damage that was absent in September. That is evidence the layup was wet rather than that the season was harsh, which is a more encouraging diagnosis because layup is cheap to fix.
What is the single most valuable layup step?
Draining completely and verifying it drained. Low points holding a residue are where remaining chloride concentrates as everything else dries, so a system ninety percent drained has concentrated its problem rather than removed it. Verification means confirming flow stops, not opening a valve and assuming.
Is a fresh water flush worth it?
Yes, and it must be thorough. The aim is to displace the contents rather than dilute them, which means enough time and velocity, and flushing the branches rather than only the main runs. A partial flush leaving seawater in the low points achieves very little.
Should we leave systems open or closed over winter?
Open where practical, because an open system dries and a system sealed damp stays damp. Where closing is necessary, closing it dry matters considerably more than closing it quickly, which is the opposite of what end-of-season pressure encourages.
Is 316 stainless adequate for seawater?
Frequently not, particularly where crevices exist and the system sits stagnant. Resistance to chloride pitting and crevice attack tracks chromium, molybdenum and nitrogen, and duplex, super duplex and 6-moly grades sit well above 316. Where the duty is severe, the higher alloy is cheaper than replacing 316 twice.
Does cold water reduce the risk?
For one mechanism only. Chloride stress corrosion cracking needs temperature as well as chloride and stress, and a cold seawater system largely sits below the practical range. That removes cracking from the list and leaves pitting and crevice corrosion entirely intact, and those are what damage these systems.
Can passivation substitute for a better alloy?
No. It removes free iron and restores the passive film, which matters a great deal here because every weld, cut and field repair reintroduces free iron and heat tint that seawater exploits quickly. It cannot make 316 behave like super duplex, and we would rather say that at specification stage.
How do I get a quote for Alaska corrosion work?
Use the form on this page or call 201-450-8280. Useful inputs are which systems are affected and their materials, your current layup procedure, where damage appears at start-up, how the site is reached, and what pre-season window is available.
What does a layup passivation treatment involve?
A fresh water flush to remove salt, cleaning to remove organic and mineral deposits, a citric acid passivation to restore the film, a final rinse to a verified endpoint, and complete drainage and drying. The equipment then sits in the condition the treatment left it, which is why it is done last.
What should the winter layup checklist for a seafood plant contain?
Draining and drying or fully filling each system, fresh water flushing of seawater-contacting equipment, passivation of stainless that has seen chlorides, protection of open ends against salt air, and a record of what was done so that spring start-up follows from it. The checklist is the plant's corrosion control for half the year.
What is galvanic coupling in a seafood plant?
Different metals in electrical contact in seawater form a cell where the less noble metal corrodes faster. Stainless fittings on aluminium or carbon steel, brass valves in stainless lines and mixed fasteners are common examples, and the seawater makes the coupling severe.
How is galvanic coupling avoided?
By using one metal family in seawater systems where practical, by isolating dissimilar metals with non-conducting gaskets and sleeves, and by keeping fastener metallurgy consistent with the joint. A materials survey finds the couples that exist.
Where does crevice corrosion appear in seafood equipment?
Under gaskets, in threaded joints, at lap welds, under deposits, and in the gaps at bolted flanges, wherever seawater can enter and not exchange. Crevice attack on 316 in seawater is expected rather than unusual.
What are the alloy options above 316 for seawater-contacting equipment?
Duplex and super duplex stainless steels, 6% molybdenum super austenitic grades, and nickel alloys for the most severe service, each with a higher pitting resistance and a higher cost. The choice is made for the components that fail, not for the whole plant.
How is a mixed-alloy system passivated?
Each alloy responds to different chemistry, so the system is surveyed first and the treatment is matched to the alloys present. A single citric procedure across a system with titanium, duplex and 316 does not serve all three.
How are pumps and heat exchangers protected through layup?
Drained, flushed, opened where possible, dried and stored with protection against condensation. Pumps left full of seawater over winter corrode at the seals and impellers; exchangers left wet pit at the tube sheets.
Does passivation help brine and glaze systems?
Yes. Brine and glaze systems run cold and salty and are among the most chloride-exposed equipment in the plant. Cleaning and passivation at layup, with a fresh water rinse, extend their life materially.
How is corrosion inspected at spring start-up?
By opening and inspecting the locations where crevice and pitting attack are expected, before the system is refilled, so that failures are found while they can be repaired. A quick visual on a sealed system finds little.
What about corrosion of the building and structure?
Marine air corrodes structural steel, fasteners and roofing, and a seafood plant's building corrodes from outside and inside at once. Coating maintenance and material selection are part of the corrosion programme.
Can passivation be done at a remote site?
Yes, with chemistry and equipment brought in for the layup period, and the spent solution neutralised and disposed of under the plant's permit. Planning the layup treatment into the end-of-season schedule is what makes it happen.
Why does cold seawater still corrode stainless?
Because chloride and oxygen are present and the cold water holds more oxygen, so while the corrosion rate is lower than in warm water, it does not stop, and crevices and stagnant conditions concentrate the attack regardless of temperature. Alaska plants see pitting in equipment that never gets warm.
What comparison settles whether to re-alloy a failing component?
The cost of the upgraded component against the cost of the repeated repairs, passivation and lost production the current one causes, over the plant's planning horizon. For components that fail every season the upgrade usually wins; for those that fail every decade, passivation and inspection do.
What is the commonest corrosion finding at Alaska seafood plants?
Crevice and pitting attack that progressed through the idle months on equipment that was shut down wet and salty. Layup treatment is the highest-return maintenance in the plant.
Galvanic coupling, which a seafood plant creates without meaning to
There is a second corrosion mechanism running alongside pitting in these plants, and unlike pitting it is created by how the plant was assembled rather than by what it processes.
Seawater is an excellent electrolyte. Put two different metals in electrical contact with it between them and current flows, and the less noble metal corrodes preferentially to protect the more noble one. In a seafood plant that arrangement appears constantly and mostly by accident: a bronze or cast-iron pump body on stainless pipework, a carbon steel support bracket bolted to a stainless tank, galvanized fixings on a stainless frame, copper alloy fittings in a seawater line, aluminium equipment sharing a structure with stainless.
Three features make it worse here than the textbook case suggests.
Area ratio decides severity. A small area of less noble metal connected to a large area of more noble metal corrodes fast, because the whole cathode drives the reaction at a small anode. That is precisely the geometry of a carbon steel bolt holding a large stainless component, which is why fixings fail first in seawater service and why substituting a cheaper fastener is a more consequential decision than it appears.
The reverse geometry is far more forgiving, which gives a practical rule: if a dissimilar-metal joint is unavoidable, make the less noble part the large one.
Stainless changes sides. Stainless steel is noble while its passive film is intact and considerably less so where that film has been compromised, in a crevice or where oxygen is depleted. A joint that behaves well in flowing aerated seawater can behave differently in a stagnant crevice during layup, which is another reason the shutdown condition matters.
Coupling is often invisible. The electrical connection does not need to be obvious. Two components bolted to the same frame are coupled through the frame, and a pump and a valve are coupled through the pipework between them even where nobody thought of them as connected.
The controls are straightforward once the mechanism is recognized. Select fixings and supports to at least the standard of what they hold rather than as general hardware. Isolate deliberately where dissimilar metals must meet, using an insulating gasket set and sleeved fasteners, and confirm the isolation actually works rather than assuming the kit did its job. Where isolation is impractical, sacrificial anodes give the cell something to consume that is cheap and replaceable, and they need inspecting and replacing rather than installing and forgetting. And keep the area ratio in mind on every dissimilar joint.
We survey for galvanic couples during pre-season corrosion work, specify and install isolation and anode arrangements, and correct the fixing and support specifications that cause most of these failures.
Finding corrosion at spring start-up in Alaska?
Tell us what your layup procedure covers. If draining is an intention rather than a verified step, that is where the damage is coming from. Call 201-450-8280 or use the form below.