This guide is written by the team at Kelly Steel, marine steel fabricators based in Dandenong, Melbourne. It covers how to select the right steel for saltwater and coastal structural environments, material options, corrosion considerations, and coating systems. If you have a project underway and need fabrication support rather than a material guide, see our industrial marine fabrication service.
Marine projects don’t usually fail because the steel looks wrong on day one. They fail later when salt exposure, trapped moisture, and hard-to-maintain details start doing damage.
If you’re planning marine structural steel for a wharf upgrade, port access structure, coastal platform, or industrial site near saltwater, the best results come from lining up three things early:
materials + detailing + protection system
Kelly Steel’s Industrial & Marine capability follows that same approach, with common coastal material options including 316 marine-grade stainless and aluminium where appropriate.
What “marine grade steel” means in practice
“Marine grade steel” gets used as a catch-all, but it usually refers to one of these realities:
- Stainless steel selected for chloride exposure (often 316 family)
- Aluminium chosen for corrosion behaviour/weight and handled with the right interfaces
- Carbon steel that relies on a correctly specified protective coating system (and sometimes other protection methods) to meet service life expectations
So instead of asking “What’s the marine grade?”, the practical question is:
What’s the exposure, what service life do we need, and how will the structure be maintained?
Start with exposure: coastal air, splash zone, sheltered crevices
Salt corrosion isn’t uniform. A member that’s washed clean and dries quickly can outlast another member in a “protected” corner that never dries.
Common exposure types you’ll want to name in the design review:
- Coastal atmosphere (salt-laden air, intermittent wetting)
- Splash / tidal zone (wet–dry cycling; aggressive)
- Sheltered crevices (stagnant moisture + salt = trouble)
- Immersion / intermittent submersion (different protection requirements again)
This is where standards frameworks help. ISO 12944-9 specifically covers performance requirements for protective paint systems for offshore and related structures exposed to marine atmosphere and immersion.
Material selection for marine structural work
1. 316 stainless
For many coastal projects, specifiers commonly step up to 316 because it generally performs better than 304 in chloride-prone environments.
Kelly Steel explicitly positions 316 marine-grade stainless and aluminium products/solutions for marine manufacturing and fabrication support.
Where people get caught: “316” doesn’t mean “maintenance-free.” If you design in crevices, create water traps, or ignore dissimilar metals, stainless can still suffer localized corrosion over time.
2. 304 vs 316
A practical way to think about it:
- 304 can be fine in many mild environments.
- 316 is often selected when chloride exposure is meaningful (coastal air, splash, recurring wetting) or the cost of rework/maintenance is high.
If the budget is tight, the best question is usually: Where do we truly need 316, and where can we justify alternatives based on exposure and detailing?
3. Aluminium
Aluminium can work very well in coastal applications, but it’s sensitive to detailing around interfaces (especially when paired with other metals). Treat it as a system, not a standalone material choice.
The common trap: dissimilar metals and galvanic corrosion
A lot of “mystery corrosion” in marine structures comes from galvanic corrosion typically at fasteners, brackets, mixed-metal interfaces, and wet joints.
ASSDA’s guidance explains galvanic/dissimilar metal corrosion clearly and focuses on how to avoid it (it also notes the three conditions required for galvanic corrosion to occur).
Practical controls you can build into drawings early:
- Avoid mixed-metal contact in wet zones where possible
- Isolate metals (non-conductive washers, gaskets, sleeves)
- Choose compatible fasteners (don’t treat fasteners as an afterthought)
- Detail joints so they drain and dry
- Be careful with “wet battery” details (stagnant seawater trapped in a joint)
This is one reason marine steel fabricators who understand service exposure often save projects money: they spot these issues before fabrication locks them in.
Marine structural detailing that reduces corrosion and rework
The “marine” part of marine structural steel is often a detailing discipline:
Design for drainage and drying
- Avoid flat ledges that hold water
- Add slopes, weep points, and sensible drainage paths where appropriate
- Don’t create pockets that stay damp
Reduce crevice risk
- Minimise tight lap joints in wet zones
- Avoid hidden gaps that trap salt and moisture
- If a joint needs to be sealed or coated, detail it so that’s actually achievable
Keep tolerances realistic (so installation doesn’t blow out)
Marine parts can look simple on paper and become complicated fast at fit-up especially in upgrades and refits. Clean drawings, repeatable fabrication, and consistent checks reduce site rework.
For what “complete” steel documentation typically includes, the Australian Steel Institute notes that structural steel detailers prepare shop drawings for manufacture and erection, based on the engineer’s drawings and project specifications.
Coatings and surface preparation
Coatings aren’t a “finish.” They’re a system and the wrong system can burn time and budget in rework.
ISO 12944-9 is specifically aimed at protective paint systems for offshore and related structures exposed to marine atmosphere and immersion, which makes it a useful reference point when coating performance matters.
Things to lock in early:
- Exposure assumptions (coastal, splash, sheltered, immersion)
- Surface preparation requirements
- Coating system selection appropriate to the exposure and service life goal
- Handling/touch-up plan after transport and installation
- Edge/weld treatment expectations (coatings often fail first at edges)
Where this shows up in real projects
Marine structural steel decisions show up most in:
- Ports and wharves (upgrades, access structures, platforms)
- Coastal industrial sites (walkways, ladders, safety access)
- Maintenance scopes where repeat parts need a predictable fit-up
If you’re delivering a marine or coastal scope in Melbourne or across Victoria, the same principles apply: choose materials for the exposure, detail for drainage and maintenance, and match the protection system to service life.
Quick checklist before fabrication starts
Use this to sanity-check the scope before drawings are approved:
- Exposure type confirmed (coastal / splash / sheltered / immersion)
- Material choice justified (not just “marine grade” as a label)
- Dissimilar metals reviewed and isolation detailed where needed
- Drainage/drying confirmed; crevices minimised
- Coating/protection system selected early (ISO 12944 referenced where relevant)
- Shop drawings cover what’s needed for manufacture + erection
- Maintenance access considered (inspection, washdown, touch-up)
Align Materials, Detailing and Protection
Marine steelwork lasts when the decisions are made early, not after parts are already fabricated. Material choice matters, but so do the details that control moisture, crevice points and dissimilar-metal contact. When materials, detailing and the protection system are aligned from the start, installation is smoother and long-term maintenance is far more predictable.
FAQs about Choosing Marine Grade Steel for Structural Work
What is marine grade steel?
It usually means a material and protection approach suited to chloride exposure, often 316 stainless, aluminium, or coated carbon steel depending on the environment and the service life you’re targeting.
Is 316 always required near the ocean?
Not always. 316 is a common choice for coastal exposure, but performance still depends heavily on detailing (crevices/drainage), interfaces, and maintenance.
What causes galvanic corrosion in marine steelwork?
It occurs when dissimilar metals are electrically connected in the presence of an electrolyte (like seawater). Avoidance focuses on isolation, compatible selections, and joints that drain and dry.
Why do coating specs reference ISO 12944?
ISO 12944 is widely used to guide protective paint system selection by exposure category. Part 9 focuses on offshore and related structures exposed to the marine atmosphere and immersion.
What should I look for when choosing a marine steel fabricator?
Look for a fabricator who understands the service environment — not just the material spec. Key questions to ask: How do they handle drainage and crevice detailing in the drawings? What coating systems do they use and how do they align to ISO 12944 exposure categories? Can they fabricate to engineer’s drawings and maintain dimensional consistency across repeat batches? For projects in Melbourne and Victoria, Kelly Steel’s industrial marine team handles all of these as standard practice.
What’s the biggest cause of early corrosion in marine structural steel?
Usually it’s a combination of water traps/crevices, poor drainage, unplanned dissimilar-metal contact, or a protection system that doesn’t match the actual exposure rather than the steel “looking wrong” in the workshop.
Is marine grade steel the same as 316 stainless steel?
Not exactly. ‘Marine grade steel’ is commonly used to describe materials suited to chloride-heavy environments, 316 stainless is the most frequent choice, but marine aluminium and correctly coated carbon steel are also used depending on the application. The right choice depends on the exposure zone (coastal atmosphere, splash zone, or submersion), the service life target, and how the structure will be maintained. Our guide above covers this in detail.
Where can I get marine grade steel fabricated in Melbourne?
Kelly Steel fabricates marine grade steel components from our workshop in Dandenong South, servicing ports, coastal industrial sites, and infrastructure projects across Victoria. We work with 316 stainless, marine aluminium, and coated carbon steel, and we fabricate to drawings for both structural and component-level scopes.
