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Go Back   SailNet Community > On Board > Gear & Maintenance > 18-8/304/316/... SS fasteners?
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Topic Review (Newest First)
06-12-2012 09:55 PM
Stumble
Re: 18-8/304/316/... SS fasteners?

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.
06-12-2012 09:25 PM
casey1999
Re: 18-8/304/316/... SS fasteners?

Quote:
Originally Posted by Stumble View Post
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.
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.
06-12-2012 09:20 PM
Stumble
Re: 18-8/304/316/... SS fasteners?

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.
06-12-2012 09:14 PM
casey1999
Re: 18-8/304/316/... SS fasteners?

Quote:
Originally Posted by Stumble View Post
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.
06-12-2012 09:03 PM
Stumble
Re: 18-8/304/316/... SS fasteners?

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.
06-12-2012 07:55 PM
casey1999
Re: 18-8/304/316/... SS fasteners?

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
06-12-2012 06:33 PM
Stumble
Re: 18-8/304/316/... SS fasteners?

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
06-12-2012 03:32 PM
casey1999
Re: 18-8/304/316/... SS fasteners?

Quote:
Originally Posted by Stumble View Post
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.
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.
06-12-2012 03:13 PM
Stumble
Re: 18-8/304/316/... SS fasteners?

Quote:
Originally Posted by casey1999 View Post
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.
06-12-2012 02:47 PM
casey1999
Re: 18-8/304/316/... SS fasteners?

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/...e_strength.htm
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