Which Grade for Marine Use?
A practical comparison of the two stainless grades used in marine gas springs — what actually separates them, where each belongs, and how to avoid paying for the wrong one. For OEM engineers, procurement teams, and distributors.
- 1 Two Springs, Same Catalogue Photo, Very Different Lifespans
- 2 Four Marine Environments and the Grade Each One Calls For
- 3 Choosing Between 304 and 316L: A Straight Decision
- 4 When 304 Is Genuinely Enough — and When to Step Up
- 5 304 vs 316L: Side-by-Side Comparison
- 6 Why Specifiers Come to Newtone for the 304 vs 316L Decision
- 7 Frequently Asked Questions
- 8 Conclusion
- 9 Get a Grade Recommendation or Quote
Two Springs, Same Catalogue Photo, Very Different Lifespans
Two gas springs sit side by side on a bench. Both are bright, both are stamped “stainless steel,” both look identical in the catalogue. Fit one to a foredeck hatch and it is tea-staining within a season; fit the other and it is clean after five years. The difference is the question this page answers: 304 vs 316L Stainless Steel Gas Springs — Which Grade for Marine Use? The word “stainless” hides a gap in corrosion performance wide enough to decide whether a part survives salt water or quietly fails at the rod.
This page is written for the people who sign off the specification — OEM engineers choosing materials for a new build, procurement managers comparing quotes where one supplier offers 304 and another 316L, and distributors who need to explain the difference to a marine customer. Newtone manufactures gas springs in both grades, so what follows is grade selection without a thumb on the scale: where 316L earns its premium, and where 304 is a perfectly sensible economy.
The short version: 316L contains molybdenum that resists chloride pitting; 304 does not. For exposed, salt-water, or bilge positions, specify 316L. For dry interior or freshwater use, 304 saves cost without real risk. Most marine failures come from using 304 where 316L belonged.
Four Marine Environments and the Grade Each One Calls For
Grade selection is really about where the spring lives. The same hatch hardware can need either grade depending on how much chloride and moisture it actually sees. These four positions cover most marine cases.
Offshore & Coastal Decks
Foredeck hatches, cockpit lockers, anchor lids — green water, spray, and constant UV. The clearest case for 316L: 304 here pits and tea-stains within a season or two.
Engine Bay, Bilge & Exhaust Zones
Warm, humid, salt-laden, and full of crevices around fittings. Heat plus chlorides plus stagnant moisture is the worst combination for 304. Specify 316L throughout, including fasteners.
Sheltered Interior Cabinetry
Cabin sole lids, locker doors, and berth access that rarely meet salt water. 304 performs well here and trims cost, provided the position stays genuinely dry and ventilated.
Freshwater & Trailerable Boats
Lake and river craft that see little or no chloride exposure. 304 — or even a black nitrided rod with HNBR seals — is often sufficient, with 316L reserved for owners who store near the coast.
Choosing Between 304 and 316L: A Straight Decision
Stripped of marketing, the choice comes down to chloride exposure versus budget. These two columns are the decision most engineers actually face when specifying a marine gas spring.
⬤ Choose 304 When…
- The position is dry, interior, and ventilated
- The boat is freshwater or trailerable
- Chloride exposure is rare and brief
- Cost is a real constraint on volume
- The part is easy to inspect and replace
⬤ Choose 316L When…
- The spring is exposed on deck or in the bilge
- Salt spray, green water, or humidity is constant
- The boat is marketed to coastal or offshore use
- The part is hard to reach for replacement
- Long service life matters more than unit cost
When 304 Is Genuinely Enough — and When to Step Up
Specifying 316L everywhere is safe but wasteful; specifying 304 everywhere is cheap but risky. Matching the grade to the duty is the engineering decision.
When a Lower-Cost Option Is the Right Call
For a dry interior locker on a freshwater boat, 304 — or even a non-stainless spring with a black nitrided rod (900–1000 HV, 20–30 µm) and HNBR seals — gives good service at a lower price. The black nitrided option resists corrosion well in low-chloride air and is a sensible economy where the marine atmosphere never really reaches the spring. Over-specifying 316L for these positions adds cost without adding usable life.
When 316L Is Non-Negotiable, and a Note on Locking Springs
Any exposed, bilge, or coastal position should be 316L stainless for both body and rod. The same logic applies to locking gas springs on engine hatches and anchor lockers: a locking unit is usually fitted exactly where corrosion is worst and replacement is hardest, so the grade decision matters even more. Where a locking spring holds a heavy hatch open for servicing, specify 316L and qualify the release mechanism for the load at the design stage.
304 vs 316L: Side-by-Side Comparison
| Property | 304 Stainless | 316L Stainless | What It Means at Sea |
|---|---|---|---|
| Molybdenum content | None | 2–3% | Mo is the key to chloride resistance |
| PREN (approx.) | ~18 | ~25+ | Higher resists pitting |
| Chloride pitting resistance | Moderate | High | Salt spray, green water, bilge |
| Carbon (weld zones) | ~0.08% | <0.03% (low) | 316L corrodes less at welds |
| Best-fit position | Dry interior, freshwater | Deck, bilge, offshore | Match grade to exposure |
| Relative cost | Lower | Higher | Premium worth it in salt |
Note that grade is independent of force. A hatch weighing 6 kg (13 lb) needs the same force — say 150–300 N (34–67 lbf) depending on hinge offset and open angle — whether it is built in 304 or 316L. Choose the grade by environment and the force by geometry; shifting a bracket 20–30 mm (0.8–1.2 in) changes the force far more than the steel grade ever will. Send us the panel weight and geometry and we will calculate force, then recommend a grade; you can also review the stainless steel gas spring range or ask for a grade recommendation.
Why Specifiers Come to Newtone for the 304 vs 316L Decision
We manufacture in both grades, so we have no reason to push one over the other. We build what the environment actually needs — and say so when 304 is enough.
Frequently Asked Questions
For corrosion resistance in salt water, yes — 316L’s 2–3% molybdenum resists chloride pitting that 304 cannot. But 304 is not useless: for dry interior cabinetry or freshwater boats that rarely meet salt, it performs well at lower cost. 316L is non-negotiable for exterior and bilge use; 304 is a reasonable economy for genuinely sheltered, low-chloride positions.
It stands for low carbon — under 0.03% versus about 0.08% in standard 316. Lower carbon reduces chromium carbide formation at welds and machined areas that would otherwise corrode. For a welded, machined gas spring, 316L gives more consistent corrosion resistance across the whole part, which is why it is the grade worth specifying for marine hardware.
It can. In a chloride-rich environment 304 is prone to pitting and tea-staining — small rust spots and surface discoloration that work inward. On a gas spring rod, that pitting scores the sealing surface and lets the spring lose pressure. 304 will not dissolve overnight, but on an exposed marine part it degrades far faster than 316L.
Grade does not change the force calculation — a 6 kg (13 lb) hatch needs the same force in N whether 304 or 316L. What grade changes is service life: a pitted rod from an under-specified grade destroys the seal, so the spring loses force over time. Choose grade by environment and force by geometry; both have to be right.
Yes. We manufacture in 304 and 316L, plus black nitrided rod options for non-marine use, and we advise which grade suits your environment rather than upselling by default. Springs are supplied for OEM and aftermarket from the same platform. We manufacture in Turkey and export to more than 60 countries.
Conclusion
The 304-versus-316L question is not really about which steel is “better” — it is about matching corrosion resistance to exposure. The failures that show up as warranty claims almost always trace back to the same decision: a part labelled simply “stainless” turned out to be 304 fitted where chlorides demanded 316L, and it pitted from the rod inward until the seal gave up.
Newtone manufactures gas springs in both grades and has supplied marine builders for over two decades. That means genuine 316L where the environment is harsh, 304 or a black nitrided rod where it is not, HNBR seals as standard, and a matched-grade approach across spring, fittings, and brackets so the joint does not corrode before the spring does.
Tell us where the spring will live and what it has to lift. We will recommend a grade, calculate the force, and send a datasheet and quote — typically within 5 business hours.
Get a Grade Recommendation or Quote
Tell us the position, exposure, and panel weight. Our engineering team handles the rest — grade selection, force calculation, sample datasheet, and competitive marine-grade pricing.
