Stainless steel fixings

[grantc]

From a previous thread, it was asked where to obtain 316 stainless steel fastenings, here are a few suggestions

Any respectable service dept should be able to supply 316 fastenings etc, because that is all they should use!!! But we know they don't!!

If unsure then you could go to a local industrial fastening wholesaler, if they don't stock them then they should be able to get them.

How do you know if they really are 316? That's the hard part!

There are many grades of stainless steel but the most common ones used for fixings are 304 and 316.
Both of these grades are non ferrectic which in simple terms means there are no ferrous elements (iron etc), also meaning that neither are magnetic. (However there are also ferrectic stainless steel grades that are magnetic).
But just because it says its 304 or 316 doesn't mean its good quality material especially in more recent years with the arrival of cheap chinese materials that will not have the same non corrosive qualities that they should.

Okay why 316, well it is about 40% more expensive but that is due to the different mixture of elements to create it, certified 316 stainless is fully inert in a salt laden enviroment even in contact with most acids it still remains inert. It also has a higher tensile strength.
304 on the other hand although it has many non corrosive qualities unfortunately is not inert in saltwater enviroments.
In fact when using stainless steel in construction you should only use 316 if any contact is with mortar, stonework or masonry.
Also if stainless steel is to be used in construction within 1 mile of the ocean, then 316 is the only grade used.
Now i would suggest that our fixings on our boats are considerably closer than one mile from salt water and 304 fixings will corrode quickly, 316 could be immersed for a thousand years and not corrode.

So why don't manufacturers use 316, because the additional 40%cost of a few screws on a $70,000 boat must equall a big saving.. right!!!

Probably the easiest way without a laboratory to test if the fixings you have are 316, is to get a bucket of seawater and drop the fixings in for a few days then leave them outside for a few days, then immerse again and so on, if after a couple of treatments you notice any sort of discoloration then they are not 316.

It would be nice to compile a list of manufacturers who do or do not use 316 fixings, this would say a lot about how they view the long term quality of their product.


If you can't get them locally i did find a supplier on the net, www.marchfasteners.com but they have minmum orders

Hope this helps!!

[EngEdge]

Actually, the best way to know what you are getting is to buy the fasteners to an industry specification. In the aviation, aerospace and other critical application industries this is what they do to ensure material and strength performance. To go a step further, when it really - really matters the fastener is ordered to a industry specification and trace-ability is required. Trace-ability is where the supplier ceritifies the material or hardware via material qualification testing.

Now as far as 316, this is a cost effective choice if you want quality, however 317L is tougher and more corrosion resistant. If you want the best then you might use 2205 (UNS S 32205) or 904L. These SS are pretty tough. However, keep in mind one can spend more on fasteners and the desired quality than the likely economical usable life of the boat...

Search the internet for "Aviation fasteners", "Aerospace fasteners" or "MIL specification fasteners". Now all you need is the applicable fastener type specification and material specification you need.

[WildeOne]

If you really want good, get monel. Way better against salt.

[76GMC1500]

Probably a little cheaper than av-grade 317L, too. Also, monel isn't subject to crevice corrosion like stainless is. That's why they make wooden boats with monel screws and not stainless.

[Mike Lovely]

Here's another industrial supplier that might work for you folks.
I use them all the time for business.

http://www.mcmaster.com/

[grantc]

It is true that there is no limit to the materials available to use in the manufacture of fixings, but certified 316L will not corrode in saltwater and will outlast any boat and is easily found, i cannot comment on monel because i've no experience.
When a supplier calls it marine grade stainless, it was always 316 but now suppliers cheat and use cheaper derivatives, so don't trust the marine grade label, also uncertified cheap imported 316 stainless may corrode.

[76GMC1500]

316 stainless is technically inert in salt water. Technically, in its passive state, it won't corrode in salt water, but a lot of things can start it corroding and once it starts it's hard to stop.

[deltarome]

The above is partly correct. Problem is he is not a metallurgist or an engineer, which I am both.
Both 304 and 316 Stainless Steel contain iron. The 316 has the least. It is really 18 Cr 8 Nickel and most of balance is iron. Both alloys are Austenitic in microstructure so they are not magnetic.
Since it does contain iron, it will corrode on surfaces that can get wet but are readily exposed to the oxygen of the atmosphere. They will then corrode in tight cavities like behind a screw head or a hinge.
While a lot has been said about "cheap" 316 alloys from overseas, the fact is as long as it is the correct alloy, it doesn't matter where it is made. The higher Chrome the better and that is why 347 is better than 316 which is better than 304. The difference in parts is that some are Chrome plated so none of the iron bearing alloy is exposed to the water and the underlying material is protected by the 100% Chrome plating.
I rest my case.

[76GMC1500]

That's what I was saying, I just didn't feel like elaborating as I've done it many times before.

[grantc]

That it what is wrong with this forum, this thread was to help someone out who wanted a simple response to a question as to how to tell if fixings were good quality stainless or not and how to tell the difference between 304 and 316,
It was not to open a debate about what the best materials are available to mankind are, we could of course all fit our boats out with aviation/aerospace grade fixings but economically 316 is one of the more easily sourced materials.

Who said i wasn't an engineer, in fact i own a large engineering company specialising in stainless and alloy fabrication, i admit i am not a metalurgist but my father was chief design engineer for hawker siddeley helping to design the harrier as well as concorde so i've had a good tutor.

What i am not is a person that jumps on a thread to try and tell everyone how good they are, and rubbish what others say.

So in resting your case, what have you proved, that there are better materials than 316, of course there are! but did i say otherwise. That you are more qualified, that too may be true, that's the idea of this forum so that people get the best advice from a range of people.

But in all honesty all you have proved is that you need to justify you own existence and little life by trying to find fault in others, go back read the thread and ask yourself why did i attack this guy.

I believe that my point was to state that 316 is better for use on boats than 304, is economically viable and easily sourced but not easily identified against other grades for the average user.

[DonAustin]

It is not harrier or concorde grade, but for me about to rig up a small aluminum boat for floundering, I did learn a little on fasteners from this discussion and hope I can now find some 316 fasteners to use. Thanks, Don

[paxfish]

What exactly is a "fixing?" Is that a term synonymous with a "fitting?"

[grantc]

deltarome - 5/23/2007 8:16 PM

The above is partly correct. Problem is he is not a metallurgist or an engineer, which I am both.
Both 304 and 316 Stainless Steel contain iron. The 316 has the least. It is really 18 Cr 8 Nickel and most of balance is iron. Both alloys are Austenitic in microstructure so they are not magnetic.
Since it does contain iron, it will corrode on surfaces that can get wet but are readily exposed to the oxygen of the atmosphere. They will then corrode in tight cavities like behind a screw head or a hinge.
While a lot has been said about "cheap" 316 alloys from overseas, the fact is as long as it is the correct alloy, it doesn't matter where it is made. The higher Chrome the better and that is why 347 is better than 316 which is better than 304. The difference in parts is that some are Chrome plated so none of the iron bearing alloy is exposed to the water and the underlying material is protected by the 100% Chrome plating.
I rest my case.

I am surprised that you didn't suggest using 2205 duplex s/s!

[bmkshort]

I have to ask this question. For us average Joes with our average boats, couldn't we just use a simple magnet to tell good stainless vs. cheap. Thats what I've always done when buying hardware. Maybe I've been wrong but I would like to know for sure.

[76GMC1500]

The magnetism of stainless steel has little to do with its quality and everything to do with its microstructure. Generally, everything in the 300 series is non-magnetic with the exception of 312. Some alloys, including 316, become slightly magnetic after cold working.

[gemlux]

grantc
Your intent was good but your post conained a lot of incorrect information mixed with good information. Deltarome is correct and very justified in correcting you. I do not know why that would bother you. To me, the benifit of this fourm is for everyone to exchange information that might lead to better boats and happier users.

Since all SS has Fe (Iron) it is all subject to corrosion. As DeltaChrome satated a Chrome plating will eleminate such, but only for as long as the Chrome Plating stays in-tact. Once the plate is chipped the situation gets far worse than if the item had never been plated.

In our experiece, the best solution for standard marine fastenting is either an electropolished SS fastner or a Chrome plated SS fastener. Since the EP is not easy to get we reccomend that our builders use the Chrome plated SS fasteners or at least 316 SS when attaching our hardware. We reccomend caution when installing the CP SS fasteners so the installer does not chip the chrome plate with his screw-driver.

I hope that helps.
Gemlux

[dingbat]

grantc - 5/24/2007 4:35 AM

I believe that my point was to state that 316 is better for use on boats than 304, is economically viable and easily sourced but not easily identified against other grades for the average user.

Nothing wrong with your attempt to educate but you made statements which are inaccurate and or misleading in the process. Is there something wrong with someone with more in-depth knowledge on the subject setting the record straight?

I started to elaborate upon some of the discrepancies in your post but decided it wasn’t worth my time….. nor effort at this point.


BTW: Determining the physical properties of metals of all types at the rolling mill level has been my game for the last 29 years. Chances are I had sometime to do with determining and or classifying the properties of the materials you have in your shop right now.

[Reel-Rascals]

FWIW www.go2marine.com sells 316 SS hardware. I've often had to the buy more than I needed or the longer length and then cut it down, but it is great stuff.