stainless 304 versus 316

316 is best. 304 will rust around salt water. Did you know you can use 7018 weld rod to weld ss, it works great and is way cheaper.

The 316 is much more "stainless" than 304. Standing water will rust the

304.

304 is a basic 18-8 stainless steel. 18% Chromium, 8% - 10% Nickle

316 has the same chromium content and a slightly higher nickle content.

18% Chromium, 10% - 14% Nickle This gives it better corrosion resistance.

316 is weld compatible with 304 unless immersed in a dielectric liquid such as salt water.

316 is tougher to machine, cut, bend, drill and form than 304.

304 is the most common alloy used in food service equipment.

316 is the most common alloy used in marine equipment.

Where is the cheapest place to get 304/316 parts online 1/4" ? Since we are at it... I got some compression fittings from McM (very expensive but great service!) But I can't really afford to pay

7 to 10 bucks per compression fitting even if it is 316ss. Anyhow any ideas? Thanks, Reno, Paul

Check my assumption here, won't the weld be subject to corrosion then?

Karl

Why would you waste your money on SS if your welds are going to rust?

Ted

I have some nice surplus pieces:

We are about to build an exhaust system for my neighbour's homebuilt, open cockpit, single seat biplane. IIRC, 316 is the best but much more expensive than 304. True???

We will be TIG welding it. I have 308, 309, 312, 316, 321 and 347 rod. Is it correct that any of those are fine for 304 but not all are good for 316?

Since this bird will likely only see a few 10's of hours per year, if that, are the advantages of 316 worth considering?

Any others?

Ted

They will all work on both, except that you will be pumping heated corrosive gasses through the piping which means you need the most stable combination possible.

If you are using 316 SS tube, then use 316L filler rod to match. Personally I would go with something more anti corrosive, like 321.

Well in that case the 316 should be fine.

304 might even work OK, but 316 would be a safer choice.

If you want to buy components check out these guys.

I've fabricated many marine exhausts from 316L schedule 5 pipe. Hot salt water from the engine's heat exchanger was injected into these systems right after the exhaust manifold, so it was a pretty nasty environment.

In your case, I doubt you'd ever be able to tell the difference, unless the tubing gets very hot. 316 has a higher service temperature than 304, but I don't recall the exact numbers.

On the other hand, 316L is only approx 50% more expensive than 304L. Back when I was doing that type of work (ca

1980) Schedule 5 and 10 pipe in both 304L and 316L were easily available and not awfully expensive here in northern New England.

Ned Simmons