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Old 14-10-2012, 17:45   #16
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Re: check out this bolt

Someone asked what properties of mild steel elevate it above stainless steel in the marine environment.

The only two key advantages of stainless over mild steel in this service are freedom from generalised corrosion, and higher tensile strength.

The former is addressed by galvanising, and the latter by increasing the dimensions. (I would add that it's not in the interests of longevity or reliability to cash in on the increased tensile strength of stainless over mild: it just makes the nasty behaviour I'm about to describe more likely)

What is needed for crucial fittings like this is a material which does not easily tip across the dividing line between two failure mechanisms: yielding (like hot toffee/ taffy) and brittle fracture (like cold toffee)

You want the material you choose to be consistently inclined to the former rather than the latter. IOW, You want it tough, rather than strong.

Mild steel is a very tough material indeed, and requires quite a lot of provocation to tip into a brittle failure mode.

Stainless 30x alloys have a number of different mechanisms which will tip them towards - and into - brittle failure, most of which are difficult to detect. This is even more true of stainless weldments.

These include anoxic or depassivation corrosion, stress corrosion cracking, strain hardening, HAZ carbide precipitation (when welded), and others more subtle.

They are not really 'shelf life' issues, mostly coming into play when the material is ridden hard and stabled wet.
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Old 14-10-2012, 19:32   #17
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Re: check out this bolt

Like anything, there is stainless and there is stainless. 316 is probably the base point, and for many applications, 316 is just fine. But there are much stronger variants available; for example, check out 2205 duplex stainless... probably a better choice than 316 for a high load application.
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Old 14-10-2012, 21:32   #18
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Re: check out this bolt

Andrew,

While I would generally agree with what you said, you made a mistake to some degree. While the difference between titaniums yield and tensile is relatively low, the actual value is roughly the same as that for 6000 grade aluminium. And yield strength is not a measure of the force it can absorb, but the point at which the material has permanently deformed.

Titanium for insurance has roughly the same Young's modulus as steel, but a much higher yield strength. This means it is flexible (in that it can bend) but still return to is original shape long after steel would have permanently deformed, and should be discarded.

As an example lets assume a stainless lifeline stantion with a designed yield strength of 10,000psi, and a tensile strength of 20,000psi. If someone falls against the lifelines and exerts 15,000psi to them the stantions will deform from original shape, and not return. Hopefully they stayed on the boat, but either way you are going to be replacing the stantion.

By comparison a titanium stantion designed to a tensile of 20,000psi would have a yield of roughly 18,000 (just quick math in my head, so I'm sure it's off a bit). When the same force is applied the stantion would likely bend to the same point at the stainless one, since the YM is roughly the same, but when the person gets up, the titanium stantion would return to shape, because its yield strength was never reached. Thus there would be no permanent distortion in the part.


Hello,

I doubt titanium is nearly as expensive as you might think... Right now a major sailboat part manufacturer is selling 32" lifeline stantions for $99 each. Gurhaur is asking $39 each. Both of these are made from the same stainless grade.

Our Grade 9 titanium ones (the standard tube and pipe titanium grade) will set you back about $65, slightly less if you order a number of them at a time. For manufacturing purposes we actually use the same thickness titanium as they use stainless, so ours will be roughly three times as strong, and half the weight.
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Old 14-10-2012, 21:59   #19
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Re: check out this bolt

You know one thing I was sort of wondering about titanium is the longevity of it. I know everyone loves the stuff, but I remember hearing a story in the navy about Russians building submarines out of titanium that once cycled in pressure a few times became so screwed up that they were effectively out of service and the steel versions (what modern subs are still made of) held up fine.

Anyone thing there's just something work remembering that stainless, for all its faults, is a known quantity? I'm sure there is some dude who's been using titanium for a long time but it has nowhere near the pile of data to go along with it that 316 does.
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Old 14-10-2012, 22:07   #20
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Re: check out this bolt

Rebel, I think the USSR --not the Russians-- built exactly one of them, because eventhough they owned "all" the titanium it was still damned expensive, and again, doubly damned expensive to work, cut, or weld. It is just that much simpler to make mistakes when there aren't experienced workers.

Consider, if the Gulf oil industry wants pipe welders to have a minimum of TEN YEARS PIPE WELDING EXPERIENCE before they are interviewed, and out of those every inch of every weld still has to be examined preferably twice because the job is so hard to get right...

Now where so you get titanium pipe welders with ten years of military high pressure experience?

It isn't hard to run the numbers or develop the procedures, butI'd bet tht since most of the serious work was for things like the armored "bathtub" in the WartHog cockpit, the folks who have the had information would be sent to Levinworth for even aditting they knew what color it was. The rest? Well, with a limited demand, you don't get many shops willing to invest in working it.

OTOH there are at least nine different makers of titanium sporks and serveral single and double-wall titanium coffee cups out there. i keep meaning to get the lead out of the galley.VBG.
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Old 14-10-2012, 22:16   #21
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Re: check out this bolt

Well I guess another knock against titanium is that since local fabrication is almost non existent, fitting beyond simple bar stock stuff is a lot more complicated. My stem fitting wraps around my bowsprit, and my stern fitting drapes around the canoe stern and then comes up onto the deck. Probably fifteen pounds of stainless, welded and shaped. Couldn't even imagine the cost of having that done in titanium.
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Old 14-10-2012, 23:10   #22
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Re: check out this bolt

Rebel,

There is an issue with non-expert fabrication, but we have developed a pretty simple fix. We work exclusively from 3D CAD files. This means for many simple pieces (say chainplates) we just ask customers to make tracings onto heavy construction paper and send it to us. We then convert that to a CAD drawing for fabrication.

For something more complicated we recommend having a local engineer draw the part into a CAD program. Of course price may vary, but generally costs are pretty reasonable. Once we have the CAD file we can price the part in a couple of days, with prices including shipping and any associated costs.

For really simple parts, like some chainplates, we don't even need a tracing. Just a detailed description can be enough. To some extent it just depends on the part, and it's complexity. As well as the comfort level of the owner in using a micrometer and measuring tape.
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Old 14-10-2012, 23:24   #23
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Re: check out this bolt

Don't forget that the strongest solution is not necessarily the best.
Titanium bolts are scary expensive (or they were last time I checked). A decent stainless bolt, regular inspection and periodic replacement probably make more sense.
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Old 15-10-2012, 01:14   #24
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Re: check out this bolt

FWIW, Any welding of any material, the procedures and tecniques required can be obtained from the technical services departments of the companys that make the electrodes or wire to weld it,
Its also a free service, The info can be obtained instantly over the phone,
I have used the quite a few times over the years, especially with specialized steels, and the procedure and electrodes to weld them up,

I had a delivery by the manager of one steel electrode supplier, who delivered the 10 x 1.5 mm electrodes to me personally.

He came into the office and asked for me, The manager of the company I worked for said to leave the electrodes on his table,

No, I cant do that, I will give them to the Boilermaker personally, These electrodes, tiny as they are, are worth $150-00 each, he had $1500-00 dollars worth in his hand, thats going back 20 odd years, What they would be worth now, Who knows,

And he did place them in my hand, He would not give them to any one else under any circumstances,

They were for welding up the excess bolts holes in the mould cases for forming refactory bricks, and came with a big list of do's and donts, along with the weld procedure I needed to use them for the welding,

They were a magnificent electrode to weld with, Nice and easy running, the finish was perfect,

But hard as the hobs of hell,
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Old 15-10-2012, 02:21   #25
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Re: check out this bolt

Weyland,

Right now comparing apples to apples (at least by size).

West marine has 1/4 x 1" 304 stainless bolts for .31 each
We would sell you 1/4 x 1" Grade 5 titanium for 2.13 each.

So ya were more, but scary more, well not to me. And bolts are still hard for us to compete because they sell hundreds of thousands a year, we sell thousands. If the number made was similar (which on some parts it is getting closer) the prices are much more comparable.

Like a 1/2" turnbuckle that would run $90 at West I can sell you for $130. Again our prices are higher, but given the expected life since ours won't corrode and are roughly 5 times stronger than what they replaced, it isn't such a bad deal.



In fact we are currently working with a few engineers that can take your current part in stainless and re-size it to take advantage of the strength of titanium. In many cases the reduction in size allowable, while keeping the same safety margins allows for a part that is only nominally more expensive than the stainless one would be.

As an example (and these are really rough numbers) if you currently have 1" 316 keel bolts on your boat they will have a cross section area of a fraction more than .75 square inches. For a nominal yield strength of 26,100lbs.

To get the same strength titanium bolt you would need a bolt that is (26,100lbs/128,000psi=.2 square inches of surface area) only 1/2 an inch. Now when you start comparing the prices of 1/2" titanium bolts to 1" stainless steel bolts the prices get really close together.

Assuming I did the calculations right, a 1 foot section of 1" 316 stainless threaded rod for keel bolts would run $33.50 at Granger. For the comparable strength 1/2" 1 foot section of titanium threaded rod, we would charge $29.

Now this assumes I did the math right, but as you can see, when you take advantage if the properties of titanium it very well may not cost any more than to make the part out of stainless. But you get a part that is significantly better in many ways.
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