316/316L stainless is bought when the environment outside a fitting is more aggressive than the fluid inside it. Its corrosion resistance is the metal itself rather than a coating: a chromium oxide film that re-forms wherever the surface is scratched or re-machined, with molybdenum in the 316 grade to resist chloride pitting from seawater, brine and washdown chemistry. A zinc-plated fitting there is on a countdown from the first wrench mark.
The premium is real — commonly four to six times the equivalent plated steel part, with longer lead times on less common shapes — so it is specified where a corroded joint means a shutdown, a contamination event or a seized fitting. Geometry is untouched: the same SAE J514, J1453, J1926 and ASME B1.20.1 dimensions apply, so stainless drops into any joint the steel range fits.
Where it's specified
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Marine, offshore and coastal — deck machinery, dredging, dock and lock gear, where airborne chloride alone strips zinc plating inside a season
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Food, dairy and beverage — daily caustic and acid washdown, and no plating layer that can flake into a product zone
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Chemical process and water treatment — chlorinated, brine and effluent circuits where plated steel is attacked from outside faster than from within
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Permanent, hard-to-reach runs — buried, potted, high-level or submerged assemblies where the fitting costs less than reaching it
Range and materials. Several thousand part numbers in 316/316L with no plating to break down, covering the same connection families as the plated range in straight, elbow, tee, cross, bulkhead, swivel and reducer forms.
Ordering notes. Stainless galls: threads seize and cold-weld if run in fast or dry, so use an anti-seize compatible with your fluid, start every thread by hand and assemble slowly. Expect a lower pressure rating than carbon steel in the same size and check it against the relief setting. Avoid pairing stainless with zinc-plated steel in a wet joint — the plated part turns sacrificial.
