# 18-8/304/316/... SS fasteners?



## micheck (Sep 29, 2010)

I am told that one should use 316 Stainless Steel in a saltwater environment - that other 'grades' will not stand up to the environment. I also see that places like West Marine and my local fastener superstore both carry extensive 18-8 stocks of fasteners but very few (and expensive) 316 fasteners. Thoughts?

Charles


----------



## mitiempo (Sep 19, 2008)

Where are you using them? I would bet most of the bolts and screws on my boat are 304 and they look good after 33 years.


----------



## sailingdog (Mar 19, 2006)

I'd point out that 304 is generally stronger than 316 as well.


----------



## tommays (Sep 9, 2008)

18-8: 300 series stainless steel having approximately (not exactly) 18% chromium and 8% nickel. The term "18-8" is used interchangeably to characterize fittings made of 302, 302HQ, 303, 304, 305, 384, XM7, and other variables of these grades with close chemical compositions. There is little overall difference in corrosion resistance among the "18-8" types, but slight differences in chemical composition do make certain grades more resistant than others do against particular chemicals or atmospheres. "18-8" has superior corrosion resistance to 400 series stainless, is generally nonmagnetic, and is hardenable only by cold working.


18-8 is covers a bit to much ground BUT i have never seen many problems in above the water line use other than staining which is pretty easy to resolve these days with a product like spotless stainless


----------



## mitiempo (Sep 19, 2008)

I agree, have rarely seen problems above waterline. Stainless really should not be used underwater anyway.


----------



## Bloke (Sep 12, 2010)

Marine grade stainless steel is 316 or 316L - period.

Cliams like "built of high quality marine grade 304 stainless" are blatent lies. 

Stainless steel is a very big subject and if you want to learn it, there are plenty of resources on the web to do so. But if you haven't got the time then take the advices of the SS manufacturers - every one of them identifies 316 as the Marine grade. 

Parts manufacturers on the other hand are competing with other parts manufacturers who use claims like "built of high quality marine grade 304 stainless" and in a price driven market are using the cheaper SS to compete.
Boat manufacturers use 304 because it will last past their warranty period, beyond that they don't care, in fact they would prefer it to rust.

Easiest test to establish grade is to use a magnet - 304 is magnetic, 316 is not, (except where it has been welded)

A magnet is also useful when buying hose clamps - many have 316 bands but use 304 screws - a fact responsible for many failures and several sinkings...


----------



## sailingdog (Mar 19, 2006)

You'd be a lot more credible if you knew what you were talking about. A lot of good marine hardware is made of 304 grade stainless steel, which is non-magnetic. *The cheaper martenistic grades of stainless steel are magnetic, but the 300 series of austenitic stainless steels are not*.



Bloke said:


> Marine grade stainless steel is 316 or 316L - period.
> 
> Cliams like "built of high quality marine grade 304 stainless" are blatent lies.
> 
> ...


----------



## PorFin (Sep 10, 2007)

sailingdog said:


> You'd be a lot more credible if you knew what you were talking about.


Boy, I just had a flashback -- my Dad used to say that to me a lot!  

Other pearls were 
o "You could probably see a lot better if you'd get your head out of your a$$."
o "How's the light up there, dimwit?"
and truly a classic -- "Any damn fool can break a shovel handle."


----------



## JiffyLube (Jan 25, 2008)

I have this Harkin pad eye with a 3" base (heavy duty), that is 17-4 and magnetic. I read that 17-4 is suppose to be similar to 304, but I can safely say I don't know what I'm talking about on this subject.


----------



## Bloke (Sep 12, 2010)

sailingdog said:


> You'd be a lot more credible if you knew what you were talking about. A lot of good marine hardware is made of 304 grade stainless steel, which is non-magnetic. *The cheaper martenistic grades of stainless steel are magnetic, but the 300 series of austenitic stainless steels are not*.


ha! 
I used to think that too, was taught it fact.
Experience has proven my teachers to be wrong in so many things. - like the idea that the 300 series is all non magnetic... try it, you'll be surprised too.

Like I said, SS is a big subject - but as general rule 316 is the most corosion resistant and the only one I would consider "Marine grade" (even though it will still rust - they all will).

"Good marine hardware made of 304"? 
Just last week I had to throw away my boarding ladder - 304 and rusted out from the inside - Couldn't buy one in 316, so had to build one.

"If I knew what I was talking about"... cheap shot - You got shares in a chandlery or something?


----------



## PorFin (Sep 10, 2007)

Bloke said:


> ha!
> I used to think that too, was taught it fact.
> Experience has proven my teachers to be wrong in so many things. - like the idea that the 300 series is all non magnetic... try it, you'll be surprised too.
> 
> ...


Bloke,

OK, so what you're really asking for is for others to validate and agree with your opinions -- you could have saved a lot of time if you had just labeled your thread that way to start with.

BTW -- my guess is that your "304" ladder either wasn't 304 or that it had other issues going on inside it.


----------



## nickmerc (Nov 2, 2008)

sailingdog said:


> You'd be a lot more credible if you knew what you were talking about. A lot of good marine hardware is made of 304 grade stainless steel, which is non-magnetic. *The cheaper martenistic grades of stainless steel are magnetic, but the 300 series of austenitic stainless steels are not*.


You are correct, in general 300 series is not magnetic. However, when it is cold formed (like on a screw machine) it becomes magnetic. So, fasteners will be magnetic. Your answer seems like it came from Wikipedia. If it did you need to be careful. No one verifies if the information is correct.

I am curious what information you are referring to comparing strengths of 304 and 316. The numbers for tensile strength and 0.2% yield strength are:

304 85 ksi tensile and 35 ksi yield
316 85 ksi tensile and 35 ksi yield

And in case you are confusing the low carbon varients:
304L 80 ksi tensile and 30 ksi yield
316L 78 ksi tensile and 30 ksi yield
in this case there is a 2.5% difference in tensile strength which is well within any reasonable safety factor.

I agree with your statement "You would be more credible if you knew what you are talking about".

If you want to verify my numbers they came from the Machinery's Handbook, 25th edition on page 440.
________
Lenya


----------



## Bloke (Sep 12, 2010)

PorFin said:


> Bloke,
> 
> OK, so what you're really asking for is for others to validate and agree with your opinions -- you could have saved a lot of time if you had just labeled your thread that way to start with.
> 
> BTW -- my guess is that your "304" ladder either wasn't 304 or that it had other issues going on inside it.


Oh I'm sorry, I thought this thread was because someone asked for advice on the use of 304 versus 316 in a marine environment, I must be right off topic.

I was just offering a little bit of advice on that specific subject, based on 21 years of real world experience messing with old boats and fabricating stainless.
My opinions are based mostly on the 304 failures that I have personally witnessed - that does not mean that 304 will always fail but I have seen it fail too often to accept it when there is a better option available in 316.

If there is credible evidence to dispute my humble opinion, I would like to hear it.

Baggging the author is not what I would call credible evidence, that is just argementative tactic. This is supposed to be a discussion not an argument...

I am currently working on an 9 year old Hunter 380 which has the same rust problem with its boarding ladder - I suspect 304 because it holds a strong magnet and because is very rusty and because it is an American built production boat. 
Compare that to the 30 year old main boarding ladder on my boat which is I believe 316. The indicators for that, are: no rust, will not hold a magnet (except on the welds) and is is a New Zealand built custom.


----------



## newhaul (Feb 19, 2010)

if you are concerned with rust and corrosion just spend the money and go straight for monel or inconel expensive hard to weld but lasts forever if not inside a us navy nuc reactor. just my 2 cents worth


----------



## tommays (Sep 9, 2008)

Well we were talking about nuts and bolts used above the waterline 

BUT i buy all my work stainless with certifications and the stuff without is a LOT cheaper most likely with good reason and there there is Chinese material


----------



## cpeteod (Jun 8, 2012)

Funny, I came across this posting and know it is old, but figure I would help out anyone looking for good strong fasteners that will last forever. One catch, they usually don't sell one or two at a time, but can get their products sometimes on McMaster-Carr. Type in BUMAX on McMaster-Carr and that is how I was able to obtain some of the bolts I am using. This BUMAX 316L fasteners are almost fully non magnetic, extremely corrosive resistant, and as hard as SAE J429 Grade 5 & 8. I think they have a US warehouse, but good luck getting small quantities. www.bumaxus.com


----------



## deniseO30 (Nov 27, 2006)

This makes me wonder if the stainless bolts on my boats prop shaft flanges should be replaced with carbon steel bolts like it had.


----------



## cpeteod (Jun 8, 2012)

deniseO30 said:


> This makes me wonder if the stainless bolts on my boats prop shaft flanges should be replaced with carbon steel bolts like it had.


I hear you, the way I found out about this BUMAX stuff was from the guys on the Volvo racing team in the Volvo Ocean Race. Wow i sound like a volvo sales man. Joking aside the PM for the boat told me the switched everything to BUMAX 109 316L and reduced the size of many of their fasteners by almsot half. Ok now I sound like a BUMAX sales guy. Hope my small expereiance helps. Best way to stop salt water eating at everything is switch to fresh water sailing lol.


----------



## Stumble (Feb 2, 2012)

I am certainly biased here, but I have been switching to titanium. It solves all the corrosion problems, and is much stronger than 300 series steel. Since fastener prices have started to come down, it is not nearly as bad as it used to be. Figure between 20 and 50% more than 316 stainless, the more commonly used sizes are cheaper regardless of size for fasteners typically.

Check the prices at McMaster Carr for type 2 or 5 titanium nuts and bolts. Type 5 is the go to for the Marine environment for its strength, but a lot of bits are only commonly available in type 2. 

If McMaster doesn't have what you need let me know, our catalog covers fasteners from 1mm up to around 4 inches.


----------



## SVAuspicious (Oct 31, 2006)

deniseO30 said:


> This makes me wonder if the stainless bolts on my boats prop shaft flanges should be replaced with carbon steel bolts like it had.


Assuming your flanges are carbon steel or cast iron I would use carbon steel bolts. Stainless bolts, particularly passivated, are much more noble than carbon steel. Over time the flanges could corrode under and around the bolts and nuts (unless you used something to isolate them electrically, like Tef-Gel) and the resulting lash will result in damage.

This isn't time critical in my view - just swap back this year. Use an anti-seize compound on the nuts and either lock washers or safety wire. I have a drilling jig for wire holes if you want to borrow it.


----------



## casey1999 (Oct 18, 2010)

SVAuspicious said:


> Assuming your flanges are carbon steel or cast iron I would use carbon steel bolts. Stainless bolts, particularly passivated, are much more noble than carbon steel. Over time the flanges could corrode under and around the bolts and nuts (unless you used something to isolate them electrically, like Tef-Gel) and the resulting lash will result in damage.
> 
> This isn't time critical in my view - just swap back this year. Use an anti-seize compound on the nuts and either lock washers or safety wire. I have a drilling jig for wire holes if you want to borrow it.


I have read where carbon steel is recommended over stainless for the bolts in the coupling due to the fact stainless will fatigue (and then fail) at a greater rate than carbon steel (use high strength US made). That said my coupling also has stainless bolts from PO. I plan to switch out to a high strength carbon bolt in the future.


----------



## casey1999 (Oct 18, 2010)

316 is superior in corrosion resistance when compared to 304 (18-8). The reason 316 is superior is that it has more chromium. Chromium is what makes stainless, stainless.

316 is generally recommend over 304 in salt water tropical areas (like Florida and gulf coast). Take your standing rigging, in tropical areas 316 wire is recommended over 304. The 304 will be about 10% less strong when compared to 304 (same would go for bolts), therefore the rigging would need to be one size up to have similar strength.

If you are replacing a bolt, if properly designed there should be significant safety factor (at least 3) and 10% reduction of strength should not matter.

In salt water tropics 316 should be used for everything. This is not just my opinion, but reflects every publication and book I have read.

316 stainless should not be magnetic. 304 stainlless can exhibit magnetic qualities, especially if it has been work harden (rolled threads for example).

For 304 and 316 strengths, refer to:
http://www.americanmachinetools.com/tensile_strength.htm


----------



## Stumble (Feb 2, 2012)

casey1999 said:


> I have read where carbon steel is recommended over stainless for the bolts in the coupling due to the fact stainless will fatigue (and then fail) at a greater rate than carbon steel (use high strength US made). That said my coupling also has stainless bolts from PO. I plan to switch out to a high strength carbon bolt in the future.


I don't know of anyone who would recommend carbon steel over stainless for boat use. Unless you are talking about boats made from the ground up with carbon steel, and have full time work crews aboard to scrape and paint.

304 is ok, 316 is better, I would argue that titanium is best (I am biased as a salesman, but I became a salesman because I believe in the products).

The reality is that strength alone is a poor determiner of which part to buy. It is important, but most rigging is built far stronger than it needs to be to handle the loads imparted by a rig. Almost always the failure point is from corrosion attacking the rigging, and weakening the something that leads to failure. In engineering this is called the Corrosion Allowance, and it is the designed amount of material that can fail before the system does.

304/316 both suffer from crevice corrosion, which is particularly dangerous in areas like chain plates that have a portion of the material bedded into a sealed environment. This causes a low oxygen environment, which prevents the chromium from oxidizing and forming a protective cover over the part. Because of the way that stainless (all grades) corrodes though this can start with just a scratch, and slowly dig its way into the metal littlerly rotting it from the inside out.

Mild steel just flakes apart in marine environments. It can be slowed down by painting, and scraping, but it requires a lot of upkeep, and for parts with pad bearing surfaces (the holes in a Chainplate) it is almost impossible to keep these areas from rusting.

Honestly the best solution is titanium, yes it is expensive (though likely not as bad as you might think), but it is completely immune to corrosion in ambient marine environments. Strait size for size replacements will also save around 50% the weight of stainless parts, while increasing the strength by about 250%. A designed from scratch titanium part can save even more weight, as much as 80% depending on the part.

I don't want to overstate the risks of stainless steel though, it has been used for years, and is a very corrosive resistant metal. There is nothing wrong with 300 series steel, but there are better alternatives.


----------



## casey1999 (Oct 18, 2010)

Stumble said:


> I don't know of anyone who would recommend carbon steel over stainless for boat use. Unless you are talking about boats made from the ground up with carbon steel, and have full time work crews aboard to scrape and paint.
> 
> 304 is ok, 316 is better, I would argue that titanium is best (I am biased as a salesman, but I became a salesman because I believe in the products).
> 
> ...


For the carbon steel bolt use- I am refering only to the drive components of the engine- like where you need to bolt a carbon steel coupling together. This area should not see siginificat sea water and the engine components are carbon steel. Agree all other areas of the boat should use corrosion resistant materials.

As far as Titanium, I was considering going that route. Practical Sailor had an article about a boater whom changed his chain plates to titanium. But in the next issue a letter to the editor stated there could be corrosion issues between the titanium chain plates and stainless rigging. The letter writer recommended Duplex Stainless 2205- duplex. I am still confused by the whole issue.


----------



## Stumble (Feb 2, 2012)

Casey,

Certainly for internal parts like engines, I would just go with OEM stuff and not worry about it.

The concern with titanium and electrolysis is a real issue, but not really a major concern for things like fasteners. 

First a primer on electrolysis - when two different metals are in contact, and there is an electrolyte (salt water works great) in contact with them, one of the metals will slowly corrode due to the electrical difference between those two metals. The speed of the reaction is dependent on a few things 1) the electrical potential between the two metals, 2) the size of the pieces relative to each other, 3) the strength of the electrolyte. 

When looking at common metals on a boat (stainless, titanium, monel, bronze and aluminium) anywhere any of these comes into contact there will be corrosion. But the process of eliminating it is also well understood. Insulators either in the form of plastic bushings, loctite, rubber pads, ect will prevent the contact and thus prevent electrolysis. 

The other way to minimize the problem is to have a large anode in contact with a small cathode. Since the rate of corrosion is distributed over a larger area. So a titanium bolt (cathode) in contact with an aluminium mast (anode) will have a negligible effect, while a titanium mast in contact with an aluminium bolt would eat it apart relatively quickly. 

The third way to reduce the problem is to regularly rice your boat with fresh water. Small salt crystals actually pull water out of the air, and create a super salty electrolyte right at the location where the salt crystal is (this is also what causes crevice corrosion). So regular rincing a boat with water washes away the salt crystals, thus preventing corrosion as well. 

The better each of these can be implemented the smaller the problem of electrolysis, and thus the longer parts will last. However titanium is no more of a problem than any other metal, and is often used where there is one part that absolutely cannot be allowed to fail. 

Chainplates for instance are often the failure point for rigging due to crevice corrosion in the area hidden by the deck. So a lot of boats are going to titanium since it doesn't suffer from corrosion problems pretty much at all. Or for clevise pins that cannot be allowed to fail, since it puts the entire rig in jeopardy. Additionally since the size of a chainplate is relatively small compared to the size of a mast or rigging the concern over electrolysis is minimized.

Chart of the potential between some common marine metals (generally not alloy specific)
Metal------------potential
Titanium-----------.30
Monel------------- .31
Bronze----------- .40
Stainless----------.50
Steel --------------.85
Aluminum---------.90
Galvanized steel- 1.2
Zinc--------------1.25


----------



## casey1999 (Oct 18, 2010)

Greg,
Good explanations. I do try to rinse my boat once per week and also after each use as you recommend. It makes a huge difference. My stainless is mostly shiney when the boats near me that never get rinsed have all rusted stainless. Our boats will normally be covered with salt on a weekly basis due to the nearby surf breaks and trades blowing towards the boat harbor.

One question. If I went with Titanium chain plates, would they last "forever" (assuming they were properly engineered for stresses involved)?
Regards


----------



## Stumble (Feb 2, 2012)

Casey,

I can't promise they would last forever. I am a salesman, not an engineer. The proper person to tell you the lifespan of something like this would be a PE (Professional Engineer). However I can address a few things.

1) Titanium is the most cathodic metal commonly used for structual purposes (the only metals I know higher on the chart are gold, silver, and platinum). Though carbon fiber masts are actually more cathodic than any metal, as far as I know. 

2) Like steel, titanium has an infinite fatigue limit, which means so long as cycle loads are kept below a % of breaking strength cycle loads will never effect the part. The limit for 316 stainless is around 30%, for grade 5 titanium it is around 50%

3) titanium has roughly 2.5 times the tensile strength of 316 stainless. 

4) Titanium weighs about 1/2 of 316

5) Titanium is considered immune to salt/brackish/polluted water corrosion

6) Titanium can be subject to crevice corrosion at tempratures in excess of 200 degrees F

7) Titanium is much more abrasion resistant than 316 (sand laden water pipes can carry about 3 times the flow rate if using titanium vs steel tubing)

Generally titanium is just a better metal that 316 for marine use. Of course the primary brake on adoption by the marine market place has been it higher costs (which are justified to some extent), and concerns about machining (which are not). 

Figure a non-standard part, like a single chain plate it will run about 3 times the price of stainless, but will last much longer, are stronger, and lighter. If you are looking to have multiples made (say all your chainplates at once) then I can probably get a volume discount that would reduce cost (likely in the twice the price range). I can't promise the prices though until I run them through our quoting system. If you could get a whole fleet of boats to purchase at once (say an owners group of the same boat) the price would come down again. 

The best price I have seen comparing titanium to stainless was for a couple of our most commonly used bolts, where the price was about 20% more than stainless, but to get this low we have to make a lot of something.


Edit - After retreading this, I wanted to note that while I do sell titanium, all of this information is strait out of engineering texts, not advertising publications. If you would like to confirm any of the above, we use primarily Grade 5 titanium for marine uses due to its strength, and is the alloy I was referencing in the above. A number of different alloys are commercially available, and they do have different physical properties.


----------



## casey1999 (Oct 18, 2010)

Stumble said:


> Casey,
> 
> I can't promise they would last forever. I am a salesman, not an engineer. The proper person to tell you the lifespan of something like this would be a PE (Professional Engineer).


Greg,
Thanks for your honesty.

I am a Mechanical Engineer (PE) and cannot tell you how long Titanium chain plates would last. But I think they would last longer than 316 stainless. I have been involved in the design of salt water evaporaters and we did use titanium- it is good stuff.


----------



## Stumble (Feb 2, 2012)

LOL,

well Casey, if you can't tell me, I promise I can't tell you. My company has been in business for a little over 5 years, and have made a number of chainplates for boats. So far we haven't had a single one fail. 

As I read the mechanical properties I don't see what the failure mechanism would be absent being damaged by a pretty strong impact, but that isn't to say it couldn't happen.

Honestly my best guess as to failure would be if someone were to design a chainplate specifically taking advantage of the material properties of titanium (and so made them smaller), and miscalculated something, or failed to take something into account.


----------



## casey1999 (Oct 18, 2010)

Stumble said:


> LOL,
> 
> well Casey, if you can't tell me, I promise I can't tell you. My company has been in business for a little over 5 years, and have made a number of chainplates for boats. So far we haven't had a single one fail.
> 
> ...


I actually was on the Allied web site several months ago pricing some titanium chain plates. I liked what I saw. The only thing that concerned me was the titanium was from China, maybe that is not a problem. If I were to replace my stainless, I would go with titanium of the same size and end up with a safety factor of over 6 times. Should be good enough for cape horn.


----------



## Stumble (Feb 2, 2012)

Casey,

I actually work for Allied, and while some of our shops are in China, titanium has been a strategic metal there for decades, so the quality control is very high. Basically the same guys who made titanium parts for Chinese Mig fighters are now making titanium chainplates. We do have shops elsewhere though, and can send a part order to another country if the buyer prefers. Generally we send the order to our shop with the lowest cost to manufactur, which can vary depending on what other jobs are running at the time. 

Either way once parts are made we ship everything to our QC shop here in the states and check them for quality, and conformity with what was ordered. If a part doesn't meet our standards we ship it back and remake the part. Only once CQ has approved it does it get shipped to the end user.


----------

