304 vs 316 stainless steel

[captaingregger]

Ok, I already know the answer to the question so I don’t even know why I’m asking.

304 vs 316. I know 316 is most corrosive resistant, that’s its key selling point. But the area where my boat is getting refit... 316 is 23x more expensive than 304. Quite frankly that’s just an expense I Have to accept however the project manager/ captain I recently hired to move the refit along claims he’s seen many owners use 304 SS during past projects.

On the one hand I don’t want to cut corners, on the other, I’m 1.5 yrs into a refit that was suppose to take 6 mo. Way over budget of course.

This is for stanchions and railings on the aft deck that we’re re-doing. So no real load bearing to speak of. I’ve already replaced the load bearing posts for the new coach roof with 2” 316. I have to assume the quality of the 316 isn’t all that great either.

I’ll also add that I’m not 100% sold on 316 as the savior metal, having dealt with many failures of stanchions, shackles, etc over the years. All it takes
is one hairline crack in the steel, invisible to the naked eye, and it dies a slow death as the rust gets in.

I’ve bought a few 304 shackles over the years off amazon or eBay. They actually held up surprisingly well. My biggest concern here is keeping corrosion at bay and rust off the decks.

I presently use Citrisurf (from the Rust Store) for cleaning existing 316 SS on the boat from rust.

Thanks for any thoughts.

[atoll]

304 will very quickly develop surface rust and staining if used outside,fine for inside brackets etc

316 for brightwork,stanctions outside in direct contact with saltwater etc 316,once polished will remain untarnished for a very long period,if staining or discolouring occurs oxalic acid or lemon juice will bring back the shine very quickly

[Pete7]

Originally Posted by atoll

304 will very quickly develop surface rust and staining if used outside,fine for inside brackets etc

316 for brightwork,stanctions outside in direct contact with saltwater etc 316,once polished will remain untarnished for a very long period,if staining or discolouring occurs oxalic acid or lemon juice will bring back the shine very quickly

I so wish I had asked this question 2 years ago before using 304 tube to join a large solar panel to the 316 arch. Although its hidden under the panel I notice it all the time. Not deep rust just looks like someone spilled tea on in. Will be replaced in due course when the solar panel is upgraded.

Pete

[a64pilot]

304 if it’s well passivated and well polished will do fine.
I’ll give you as an example Kato Marine, who’s davits, Radar Poles etc. are among the more expensive ones, but have a very good reputation, they are also mostly 304, but well passivated and highly polished.

300 series SS is 300 series SS, to see much difference you need to change series. I’m not saying they are identical but I am saying that the difference isn’t as much as many think and passivation and polish as well as how it was tooled has as much to do with it as whether it’s 316 or not, run 316 tubing through steel dies which is how it’s made, don’t passivate it well and polish, and it will rust profusely, from the steel contamination from the die of course, same for wire, maybe even more with wire.

[captaingregger]

Originally Posted by a64pilot

304 if it’s well passivated and well polished will do fine.
I’ll give you as an example Kato Marine, who’s davits, Radar Poles etc. are among the more expensive ones, but have a very good reputation, they are also mostly 304, but well passivated and highly polished.

300 series SS is 300 series SS, to see much difference you need to change series. I’m not saying they are identical but I am saying that the difference isn’t as much as many think and passivation and polish as well as how it was tooled has as much to do with it as whether it’s 316 or not, run 316 tubing through steel dies which is how it’s made, don’t passivate it well and polish, and it will rust profusely, from the steel contamination from the die of course, same for wire, maybe even more with wire.

Yes, passivation is key to either 304 or 316. I’ll agree there for sure.

I would imagine the reason Kato can get away with 304 is they’re in control of the metal grade selected. The problem here is I can’t be sure as to the specs of the 304 being offered. And that’s probably the same for the 316. I’ve seen 316 get deluged with rust if left unpolished as well.

[mvweebles]

Originally Posted by a64pilot

304 if it’s well passivated and well polished will do fine.

Never heard of Passivated SS. A quick Google search acidic etching to remove surface iron (and only surface iron). See a product below that claims to assist.

As a guy show is 10-months into a 6-month refit, I feel your pain. Don't be tempted to cut corners as it's a small overall cost in the grand scheme to deplete your children's inheritance. Sounds like you'll be 'passivating' for a while. Probably not a bad idea for 316 in tropical climates.

https://www.theruststore.com/What-is...ation-W85.aspx

[captaingregger]

Originally Posted by mvweebles

Never heard of Passivated SS. A quick Google search acidic etching to remove surface iron (and only surface iron). See a product below that claims to assist.

As a guy show is 10-months into a 6-month refit, I feel your pain. Don't be tempted to cut corners as it's a small overall cost in the grand scheme to deplete your children's inheritance.

Agreed. I’m certain on using 316 but since he said he’s had clients use 304, I thought I’d ask and see what’s up.

What I can’t understand is the price difference being so massive. Probably a typo in his WhatsApp text.

[CassidyNZ]

I built my own radar arch which after a couple of months had sections that gleamed like new, other tarnishing to the yellow colour one expects from 304 SS. I contacted the materials vendor, saying that some of the materials they had supplied were not 316 as requested but that they must have mistakenly mixed in some 304. They confirmed it was all 316 and said I should drill and send cuttings to them to test.

Rather than do that, I took the time to polish the whole structure which, as expected, shone like new. The interesting thing is it all still gleams the same after not being polished for some time. I still wonder what the difference was that caused some of the 316 to tarnish before being polished but not after.

Where I live, there is a difference in the price of 316 v 304 but it is certainly not 23x! I would be surprised if it was even double although I haven’t tested it recently. No need because I never consider 304 as a first choice for anything.

[hpeer]

I bought some 316 last spring. 304 was not a lot more than mild steel, roughly $4/lb. 316 was running $13/lb.

I was looking for 1” tube to make hand rails but filling my supplier had 1/2” 316 grade 1/2” PIPE (0.86 overall diameter and 0.18 wall thickness) for about $4/lb. I bought a bunch.

[Rogue Brit]

Hey guys, I've always understood that neither SS304 or SS316 rust, although both can appear to rust, but what really happens often is that the fabricator has either used tool blades that are carbon steel or used tools that have previously worked carbon steel. This leaves tiny carbon steel particles embedded in the stainless steel surface, which rust. Unsightly, but not structurally significant.

Also have always understood that the extra expense of SS316 is justified only if chlorine is present. The minor concentration of chloride ions in sea water should not be a problem.

Is there disagreement about this?

[a64pilot]

The tools themselves are almost always carbon steel. By tools I mean for example the dies that tubing is pulled over to make tubing and or wire as an example. I believe it’s that way because the dies have to be incredibly resistant to wearing out and that pretty much leaves carbon steel as the best material.
But you will get many replies telling you that 304 is much inferior, I don’t believe that myself I believe how well it’s finished etc determines whether the steel stains or not and that light staining is easily removed, yes it’s a chore, but not nearly as difficult or as time consuming as say waxing the boat.
304 is slightly structurally superior to 316, and 316 is in fact slightly more resistant to corrosion.

316 would be preferred unless there are other considerations that make 304 a better choice, but as with everything there is a value associated with it, I’d pay more for 316, just not of course 23 times as much.

That to me tells me that they offer it so that they say they do, but have not intent on fulfilling the offer, but if your foolish enough to pay the price that they set so high to intentionally discourage you, well a fool and his money are soon parted.

[atoll]

Originally Posted by Rogue Brit

Hey guys, I've always understood that neither SS304 or SS316 rust, although both can appear to rust, but what really happens often is that the fabricator has either used tool blades that are carbon steel or used tools that have previously worked carbon steel. This leaves tiny carbon steel particles embedded in the stainless steel surface, which rust. Unsightly, but not structurally significant.

Also have always understood that the extra expense of SS316 is justified only if chlorine is present. The minor concentration of chloride ions in sea water should not be a problem.

Is there disagreement about this?

experince says different......next time you bolt or screw something to the outside of your boat use 304 screws or nuts bolts and washers.....you will soon change your mind and wish you had used 316

[a64pilot]

Originally Posted by atoll

experince says different......next time you bolt or screw something to the outside of your boat use 304 screws or nuts bolts and washers.....you will soon change your mind and wish you had used 316

Probably 90% or better of the marine hardware, especially nuts and bolts that you buy are in fact 18-8, which is 304. 316 common hardware in a place like West Marine is rare.
316 is almost always advertised as such, and there is a lot of 316 that isn’t 316.
There is a whole lot of counterfeit stuff out there, the minute an unscrupulous supplier finds they can put something on a label and charge more, they do.

[atoll]

Originally Posted by a64pilot

Probably 90% or better of the marine hardware, especially nuts and bolts that you buy are in fact 18-8, which is 304. 316 common hardware in a place like West Marine is rare.
316 is almost always advertised as such, and there is a lot of 316 that isn’t 316.
There is a whole lot of counterfeit stuff out there, the minute an unscrupulous supplier finds they can put something on a label and charge more, they do.

in the uk we have a different classification,that is A2 for magnetic stainless
or 304
A4 is non magnetic and basically 316
i always use a magnet to check the grade

plus i never buy fastners from chandlers,i buy from engineering suppliers,much cheaper and quality is assured

[chasmains]

I’m retired Navy, served in submarines. There were lots of SS components on board that were exposed to moisture, including seawater. Almost all show rust after not much time. When they welded or drilled or otherwise machined or worked that SS with tools, the base metal absorbed iron atoms on the surfaces. I do nuclear plant stuff now. We passivate all machined SS parts we make for the plants. Otherwise, they will show rust. Any commercial parts or tubing we buy are factory passivated. So we don’t do them again.
You should always ensure you buy passivated SS parts. If you have parts made, include passivation in the work order. If not, live with the rust marks.
The Passivation process is covered in QQ-P-35 under the Type VI process. (You can get any Mil-STD or QQ doc free in PDF online.) It’s not hard to do but you use nitric acid in high concentrations, which is dangerous. And you have to soak the parts for 30 minutes in an acid proof tank.

Be damned careful!!!