316L stainless hydraulic fittings: what the range covers, and how it behaves differently

Stainless hydraulic fittings are bought for one reason — corrosion — and used in places where plated steel gives up: offshore decks, coastal plant, food and pharmaceutical washdown, chemical service. Our 316L range covers the same thread families as carbon steel, so a stainless upgrade rarely means changing the port. What it does change is how the parts are made up, and sometimes what they are rated for.

/01What is in the range.

Within those families the less common shapes are listed too: metric 24° cone female swivels and male studs, double-hexagon swivel females in BSP, JIC and NPSM, BSP and metric banjos, and the standpipes and nuts made for hydrowashing machines.

/02Flanges: the bolt grade matters.

Our 316L SAE flange fittings follow SAE J518 and ISO 6162. The Code 61 parts are rated up to 210 bar (3,000 psi) and bolted with SAE J429 Grade 5 bolts as a minimum; the Code 62 parts up to 415 bar (6,000 psi) with Grade 8 bolts. The flanges, counter-flanges and split flanges for hose are listed with an L-series rating of 210 bar and an S-series rating of 415 bar, and spare seal kits are sized by flange. The bolt grade is part of the rating: a Code 62 flange on Grade 5 bolts is not a 415 bar joint. The Code 61 / Code 62 distinction itself is covered in SAE J518 Code 61 and Code 62.

/03Galling, and how to avoid it.

Stainless threads cold-weld under load more readily than plated steel — the two surfaces pick up, the joint seizes during make-up, and both parts can be destroyed. The mitigations are ordinary: a suitable anti-seize paste on the threads and never on the sealing face, correct make-up by turns or flats from finger tight rather than brute force, and not repeatedly assembling and dismantling the same pair. A workshop meeting stainless for the first time should know this before its first seized joint.

/04Mixed metals and where to use it.

A stainless fitting screwed into a plated steel port makes a galvanic couple, and in salt air the plated side corrodes faster. Sometimes that is still the right trade; where the exposure is severe, match materials through the joint. The judgement of where stainless earns its cost — and where it is a downgrade — is in when stainless is worth it and galvanic corrosion in fittings.