Marine and offshore
Operators spend heavily on premium marine systems and still see failures within a few years. The material is rarely the problem. On coastal and marine steel, the outcome is usually settled before the first coat goes on.
Viram Mariv Ltd · Tema, Ghana · 8 min read
Marine steel corrodes faster than anything else we work on. Constant salt, constant wetting and drying, mechanical damage from waves and handling, and strong UV on everything above the waterline. Under ISO 12944, marine atmospheric steel is classified C5-M, and splash zone steel sits in CX and Im2 — the most severe categories the standard defines.
Everyone involved knows this, which is why marine specifications are demanding and marine coating materials are expensive. And yet the failures keep happening. Blistering on a hull eighteen months after docking. A jetty pile losing its coating in the splash zone within two years. Ballast tanks that were lined at the last survey coming up rusted at the next.
The common factor is almost never the paint.
Steel that has been sitting in marine air holds chloride salts in its corrosion pits. Every port structure, every vessel, every piece of equipment cycling through a supply base in Takoradi or Tema. The salts are microscopic and invisible.
Blasting does not remove them. Abrasive skips across the mouth of a pit, cleans the surrounding surface to a perfect Sa 2½, and can drive contamination deeper. The steel passes visual inspection with the problem still inside it.
Then the coating goes on, and the chlorides start doing what chlorides do — pulling moisture through the film by osmosis. Water accumulates against the steel. Blisters form. Within a year or two the coating lifts from underneath.
The most valuable check in the entire marine coating process costs a fraction of a percent of the job. It is a salt test, and it is the one most often skipped.
Where levels exceed the coating manufacturer's limit, the answer is a fresh water wash before coating — because water is the only thing that flushes chlorides out of a pit. That is also why wet and hydro blasting feature so heavily in marine work.
| Element | Requirement |
|---|---|
| Corrosivity category | C5-M for marine atmospheric. CX and Im2 for splash zone and immersion. |
| Blast grade | ISO 8501-1 Sa 2½ minimum for atmospheric. Sa 3 for immersion and tank internals. |
| Salt testing | Standard practice, not an optional extra. |
| Total film thickness | Typically 260 microns or more for C5-M. Splash zone systems run considerably heavier. |
| Stripe coating | Every weld, edge, bolt, handrail joint and cut-out brush coated before spray. |
| Conditions | Humidity and dew point logged before every coat. Dockside, these are the limiting factor. |
The band between low water and the top of the wave crest is where marine structures fail first, and by a wide margin. It gets full oxygen from the air, full salt from the sea, constant wetting and drying, and mechanical impact from waves and floating debris. Corrosion rates there run several times higher than in the permanently immersed steel directly below it.
It is also the hardest band to work on, because it is only accessible on tides and in workable sea states. You cannot programme it like a flat area of deck.
Which means it needs its own method: heavier film builds, surface-tolerant or moisture-cured systems where the steel cannot be brought fully dry, and sometimes mechanical protection — sleeves, wrapping or jacketing — rather than coating alone.
If you are pricing jetty piles or fender steel, price the splash zone band separately. Rolling it into the general area rate is one of the most reliable ways these projects overrun.
Marine work is programme-driven in a way shore work is not. The vessel sails. The dock slot ends. The supply run leaves whether the topcoat has cured or not.
What makes it work is mobilising properly rather than optimistically:
The mistake that costs most is starting the blast before confirming the coating can follow. Bare marine steel flash rusts in under an hour in Ghana's humidity. Blasting a large area on Friday afternoon and priming on Monday means blasting it again.
Antifouling is applied to the manufacturer's scheme, and it carries a launch window — a maximum period between final coat and the vessel entering the water. Exceed it and the antifouling's performance drops, sometimes sharply.
That window is fixed by the product, so it has to be built into the docking programme from the start rather than discovered near the end. It is a common source of dispute when a docking overruns and nobody flagged that the clock had started.
Equipment that cycles between the supply base and offshore — containers, baskets, skids, frames, handrails, gratings — should be blasted and coated onshore, not offshore. It is safer, far cheaper per square metre, easier to inspect, and the conditions can actually be controlled.
The planning question worth asking is which items can be brought ashore on the next rotation and serviced properly, rather than patched in place until they need replacing.
Yes, subject to port and terminal permissions. Dust and overspray containment is normally the condition attached. Where open-nozzle blasting will not be permitted, wet or hydro blasting is the route.
Because chlorides are the failure mechanism in a marine environment. They survive blasting, sit in the pits, and blister the new coating off from beneath. Inland steel without chloride exposure does not have the same problem.
A high-durability C5-M system is designed for more than fifteen years to first major maintenance. That assumes salt testing, correct blast grade and profile, correct film thickness, stripe coating and inspection. Cut any of them and the number falls quickly.
Only if the preparation and application are controlled. A premium system over contaminated steel fails faster than a mid-range system over clean steel. The money is better spent on preparation first.
Often yes, working to tides and sea state, with methods chosen for damp substrate. It is slower and needs a separate programme from the rest of the structure.
Viram Mariv is based in Tema and mobilises nationwide, including Takoradi and the supply base. We have delivered surface preparation and coating on offshore support equipment and on gas pipework at the Tema LNG terminal. Send us the scope and the window you are working to.
Written by the Viram Mariv team. We are an industrial surface preparation and protective coating contractor based in Tema, Ghana, working across West Africa.