Industries we serve

Marine & Fishing Industry

Deck hardware, boatyard fasteners and processing-plant fittings finished for chloride service — with a straight answer about what a coated carbon-steel bolt can and cannot do near the sea.

Our shop is in Samut Sakhon, a short drive from the Mahachai fishing port, so the air that corrodes our customers' parts is the same air outside our own door. Marine and fishing work is the one sector on this site where the honest answer is often that a coated carbon-steel fastener is the wrong part for the position, and saying so is more useful than selling a plating job that will be back within a year. Where coated carbon steel IS the right answer — sheltered dockside fittings, processing-plant hardware, gear that is washed down and re-greased — the specification is thickness, the sealer and where exactly the part sits relative to the water.

Typical specification bands in this sector

Typical specification bands in this sector
Property class	4.8 / 8.8 preferred · ISO 3506 A4-70 where the buyer specifies stainless
Hardness	≤ ~32 HRC — high classes are a liability in chloride service
Materials	S45C · SWCH10B21 · SUS304 / SUS316 supplied by the buyer
Coating system	Zn + Cr3+ + sealer · zinc phosphate + oil on greased, re-greased deck gear
Coating thickness	12–25 µm Zn (ASTM B633 SC4) — the heaviest electroplated class
Salt spray (NSS)	480–1,000 h NSS asked for; NSS ranks coatings, it does not convert into months at sea
De-embrittlement bake	ISO 4042 bake by hardness — service hydrogen adds to what plating already introduced
Inspection methods	ISO 3497 local minimum · ISO 9227 with the criterion stated · visual at crevice sites

The bands below are what buyers in this sector write down. The limit worth stating plainly is that no electroplated zinc system converts a carbon-steel bolt into an immersion-service fastener; it buys time in an atmosphere, and how much time depends on where the part sits.

Standards commonly cited

ISO 9227 ISO 4042 ISO 2081 ASTM B633 ISO 898-1 ISO 3497 All standards →

Steel grades commonly specified

S45C SWCH10B21 SUS304 All steel grades →

How fasteners actually fail here

1Chloride dissolves the film zinc depends on

Zinc does not survive by being noble; it survives by building a stable, poorly soluble surface film. Chloride converts that film into soluble products, so the coating goes on being consumed instead of settling down, and a bolt that would last years in an inland factory can rust through a season on a boat. That is the whole reason marine specifications ask for the heaviest coating classes and a sealer, and the reason a thickness that is generous inland is merely adequate here.

2Crevice attack in the gaps the joint itself creates

Under a washer, in the thread engagement, between two lapped plates and beneath a fitting bedded on a deck, water is trapped, oxygen is used up and chloride concentrates. This is the failure mode that surprises people who switched to stainless: austenitic stainless resists general attack but is comparatively vulnerable in exactly this oxygen-starved, chloride-rich pocket, and a 304-type part in a wet crevice is a very different proposition from the same part in open air. The crevice is created by the joint design, not by the material, so it is a detailing problem before it is a purchasing one.

3A galvanic couple with the area ratio pointing the wrong way

Seawater and salt-laden condensate are far better electrolytes than inland rain, so a bimetallic couple that would be tolerable elsewhere runs hard here. The damage concentrates on the smaller, less noble member, and that is usually the fastener holding a large bronze, stainless or aluminium fitting. The practical rule that follows is uncomfortable but simple: in marine service the fastener should be the more noble member of the joint, or it should be isolated, and a cheap fastener into an expensive fitting is exactly the wrong way round.

4Hydrogen that arrives after the part is in service

Hydrogen embrittlement is usually discussed as a plating-line problem, but corrosion in seawater and the cathodic protection systems used on boats and structures both generate hydrogen at the steel surface. A high-strength fastener can therefore keep accumulating the very thing the relief bake was meant to remove, long after installation. It is one of the reasons marine practice tends to keep fastener strength moderate rather than reaching for the highest class available, and it is worth asking your designer about before specifying a high class near the water.

Defect guides that matter in this sector

Early red rust on plated fastenersRed rust well before the specified salt-spray hours: thin coating in thread roots and recesses, damaged passivation, handling damage and test-plan mismatches, with the checks that find the real cause.White rust on zinc-plated partsWhite powdery zinc corrosion in storage and transit: passivation, drying, sealer and packaging faults that cause it, and how to judge it against a salt-spray acceptance criterion.Poor phosphate adhesion — coating rubs off, paint liftsPhosphate that wipes off, coarse powdery crystals and paint peeling from a phosphated fastener: cleaning, activation, bath control and post-treatment causes, with the practical checks that identify each.Hydrogen embrittlement — delayed fracture after platingWhy class 10.9 and 12.9 fasteners crack hours or days after zinc plating, how the preloading test to ISO 15330-1 confirms it, and the ISO 4042 baking rules — ≥ 390 HV, start within 4 hours — that prevent it.

All defect guides →

Documentation a buyer in this sector should receive

The exposure zone written down: dockside atmosphere, deck and spray, the splash and tidal zone, or permanently immersed. These are four different problems and no single coating report speaks to all of them.
Coating thickness as a local minimum with the method and the position, against the classification ordered — marine work is normally at the heavy end of the electroplated range, and the thinnest point is what the sea finds.
A salt-spray report to ISO 9227 / ASTM B117 with the criterion, interval and significant surfaces, together with the honest caveat that neutral salt spray is a comparative process check: it ranks coating systems against each other, it does not convert into months of service in a real marine atmosphere.
For stainless parts you supply, the mill certificate from your own supplier. A 304-type and a 316-type fastener are indistinguishable by eye and behave very differently in chloride, and we will not certify a material we did not buy.
A plain statement of scope: we electroplate zinc with a trivalent passivate and apply phosphate coatings, and we do not hot-dip galvanize, thermally spray, pickle or passivate stainless. Where the right answer is one of those, the part should go to a supplier who runs it.
Lot traceability from the delivered box back to the plating run, and every report carrying job and lot identity, material and agreed specification, position, method and instrument, values against limits, date, inspector and approval, under ISO 9001:2015.

What to send us for an accurate quote

1Where the part actually sits: a covered dockside store, an exposed deck, the splash zone, or under water — and whether it is ever rinsed with fresh water.
2The material as specified now: carbon steel for us to coat, or stainless you are supplying, and which stainless type if so.
3What it bolts to — bronze, stainless, aluminium, galvanised steel, GRP or timber — and roughly how large that part is compared with the fastener.
4Property class or hardness, and whether the designer will accept a lower class in exchange for better corrosion behaviour.
5Coating classification or thickness range and whether a sealer is wanted; for greased deck gear, whether phosphate with oil is acceptable instead.
6Lot quantity and piece weight, whether parts should ship oiled, packing for a humid store, and the documents required at delivery.

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Recommended services

Zinc Plating Cr3+Phosphate Coating Testing Laboratory Heat Treatment

Common parts we finish

Bolts Nuts Washers Pins Screws All part types →

Questions buyers in this sector ask

Zinc-plated steel or stainless for fittings near the sea?+

They fail differently rather than one simply lasting longer. Coated carbon steel is protected everywhere while the zinc lasts and then deteriorates fairly predictably; stainless does not rust generally but is vulnerable to pitting and crevice attack in the still, chloride-rich pockets a joint creates, and a 316-type is the usual marine choice over a 304-type for that reason. A stainless fastener into a steel structure also creates a galvanic problem of its own. We plate, coat and test carbon steel; the material decision is yours, and we will not pretend that zinc turns a bolt into a marine fastener.

Our customer asks for 1,000 hours salt spray. Can you meet that?+

The number depends on the whole system — zinc thickness, the passivate, whether a sealer or top-coat is applied — and on which criterion counts, first white corrosion or first red rust. Tell us the hours, the criterion and the significant surfaces and we will say honestly what our process can be expected to deliver. It is worth knowing what the number is not: neutral salt spray is a comparative chamber test used to control a process, and 1,000 hours in a cabinet is not a statement about how many seasons a fitting survives on a working boat.

Can you re-finish fittings taken off a boat?+

Usually not, and it is better to say so up front. Our line is built for production lots of small new parts, and used marine hardware arrives with embedded salt, rust in the threads, sealant and old coating that a production line cannot reliably remove — parts finished over that contamination fail early and the customer rightly blames the plating. For new production lots of small fasteners in the same sizes, that is exactly what the line is for.

The bands on this page are typical industry values, not a guarantee for any specific part. The governing drawing, customer specification and standard always take precedence, and every value is confirmed against your part before production. V.S. Heat Treatment operates under ISO 9001:2015; no other certification or sector approval is claimed.