structural stainless--unobtanium?

[HgTX]

I have a designer who wants stainless steel for corrosion protection & aesthetics, but assumed he could use typical carbon steel properties in the design. So he assumed yield strength of 50 ksi and ultimate tensile strength of 125 ksi.

I fear I may not be able to make this work.

These are rod & hanger assemblies for a bridge. Fatigue loading, some components welded, some machined. Outdoor exposure, but not to salt water and probably very little road salt, if any.

The bridge design specs say that the SS has to come from ASTM A 176, A 240, A 276, or A 666, or something that meets the chemical & mechanical requirements of something listed in one of those specs. Or "other published specifications that establish its properties and suitability and that it is subjected to analyses, tests, and other controls to the extent and in the manner prescribed by one of the listed specifications". Which I choose to interpret as "if I need to go elsewhere to make it work, so be it".

I am assuming we need some kind of austenitic SS, preferably 300 or 400 alloy group. 304 or 316 type would be best.

For starters, we need 1.75" threaded rod/bar.

Nothing in A 176 meets the strength requirements.

Nothing in A 240 meets both yield and ultimate strength requirements.

Nothing in A 666 meets the strength requirements unless I get into the cold-worked materials, but I think those are all just sheet, not plate or bar.

In A 276, I see:
XM-21 (S30452?), S30454, S31654, Condition B ("relatively severe cold work")
Are any of those available as 1.75" rod/bar? And threadable? (And available as melted & manufactured in the U.S.?)

But wait, there's more. That's for the threaded bar. There's also 1.5" and 1.75" plate that needs to be weldable, a pin with a 2.5" diameter head (needs to be machined down to 2" diameter where the head isn't), a clevis that needs to be machined from material originally at least 6.125" in diameter (not to be welded), and...rectangular tubing, 5"x4"x3/16", weldable. So far I can't find that rectangular SS structural (as opposed to ornamental) tubing even exists.

So...does any of this stuff exist? And would they be better off with a casting for the clevis?

Hg

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[HgTX]

Nope, won't go to lower-strength steel.
And still wants S20161 for the rods for Fu=125.
How's S20161 for outdoor exposure?

That's not to mention the discussion of the architectural finish.

Hg

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[MikeHalloran]

The shops you normally use to fabricate and machine mild steel are _not_ going to like the alloys being discussed, most especially the ones with high yield points. All of this stuff fights back when you work it or cut it.





Mike Halloran
Pembroke Pines, FL, USA

 

[rmw]

Where is this bridge? I think I want to plan an alternate route; better where are any bridges that this designer has designed using unobtanium?

rmw

 

[moltenmetal]

2205 "looks like" just about any other stainless steel. Surface finish will determine its initial appearance.

I'm not at all familiar with D1.6, but know that you can make nice, sound welds in 2205 which pass tensile and bend tests but have far too much ferrite in the weldment or HAZ to exhibit desireable corrosion resistance. So a little more care in welding will be required. Must it all be GTAW for your application? Probably not, but using a normal structural steel fabricator to do this work would be risky to say the least...

Again, suggest looking into LDX2101 or one of the other "lean duplexes" that others were raving about here when nickel prices went through the roof. 2205 is overkill from a corrosion resistance perspective. Never used it and hence never looked at its physical properties, but it would definintely be worth a look.

 

[HgTX]

I assume it wouldn't be--all the steel is these stainless hangers; the arch itself is concrete. I don't see why any conventional steel bridge fabricator would even bid on it.

Hg

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[EdStainless]

There are people fabricating 2205 structurals. Some of these are laser welded from cut plate. I don't have names at hand right now but I'll look.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[HgTX]

This just in--all structural welds will be encased in concrete (the weld is for an anchor plate). That helps with the corrosion issue.

That still leaves S20161 rod exposed. Adequate?

LDX2101 isn't listed in D1.6, which would add a whole new level of complication to dealing with this material.

Hg

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