chloride/seawater stainless steels
chloride/seawater stainless steels
(OP)
I am familiar with the addition of molbdenum to improve stress corrosion crack resistance of austenitic stainless steels. However, I request this Boards expertise in suggesting to my customer, what readily avaiable off-the shelf stainless steel pipe is suitable for seawater. They currently specify Monel Cu-Ni, which is expensive, and also soft, therefore they over-kill design to accomodate the softness of this alloy. Alloy 20, Ferralium 255, Avesta 254 SMO.... ??





RE: chloride/seawater stainless steels
Ed should be coming on soon offering a whole boquet of solutions. Meanwhile you could browse through his company products with the link provided.
Cheers!
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: chloride/seawater stainless steels
RE: chloride/seawater stainless steels
First things first. 316 has better pitting resistance than 304. It does not have better chloride stress cracking resistance. It really take higher Ni content (or a lot lower Ni) to improve CSCC resistance.
If you need real seawater resistance you will need a 6%Mo stainless like 254AMO or AL-6XN. Both of these should be available as pipe.
If you need pretty good pitting resistance, and very good CSCC resistance then look at 2205. You will probably get a little pitting, eventually. But it is a lot stronger and very tough, and for this kind of low temp application it might be fine. If the forks get hosed off daily with fresh water it may last longer than they care about.
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Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: chloride/seawater stainless steels
RE: chloride/seawater stainless steels
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: chloride/seawater stainless steels
RE: chloride/seawater stainless steels
Is the Navy requesting this, or is it one of the major shipyards in New England that designs and builds Navy ships?
As to the original question, I wouldn't recommend any of the "more common" stainless steels for seawater service. Duplex grades, maybe, but I don't think the shipyards building Navy ships have much experience with these grades.
RE: chloride/seawater stainless steels
AL-6XN is under consideration for new double-hull designs of ships so the Navy has been researching the alloy for a signficant amount of time. Such research may carry over to consideration for piping systems and assist you in getting them to consider it. A quick search on the alloy and Navy on google or other search brings up several reference papers.
www.rolledalloys.com
RE: chloride/seawater stainless steels
A few small points - what temperature seawater does the Navy wish to put through this piping and is it raw or chlorinated?
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: chloride/seawater stainless steels
The extra nickel makes it significantly more expensive, but it's still >50pct iron.
It's surely not up to Navy expectations for longevity.
If 90/10 CuNi is too soft, suggest 70/30 CuNi.
Mike Halloran
Pembroke Pines, FL, USA
RE: chloride/seawater stainless steels
The company I work for produces this tube for subsea umbilicals used for control lines for subsea equipment in the oil field.
Temperature concerns were mentioned above... other issues for subsea use or "fit for purpose" include: expected life, fluid used, electrial cables near tube (potential differences), all these items determine overall "fit for purpose". I have seen 316L used in this environment with success, in short life expectancy situations...
RE: chloride/seawater stainless steels
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: chloride/seawater stainless steels
Superferritic alloys like S44660 (SeaCure) don't have enough ductility, and 70/30 probably isn't strong/hard enough for a wear application. Though for piping both of these are very good options.
Alloys like 316, 317 90/10 and 2205 will eventually suffer corrosion failure in ambiant temp seawater.
Relying on a sacraficial coating for long term corrosion protection of an alloy sucsetable to localized corrosion is a very risky plan.
Your choices really come down to K-500, 6%Mo stainless, superduplex, or nickle (Ni-Cr-Mo) alloys. These will offer you strength, ductility, can be fabricated, and have great long term corrosion resistance.
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Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: chloride/seawater stainless steels
I assume the intended application is SW cooling, probably clorinated, with a max design temperature of 140F.
Others above have asked similar but more specific questions.
Last, I'm still wondering who in the US Navy is promoting the use of stainless steels for SW use - heck, we've got enough problems using stainless in fuel systems!
RE: chloride/seawater stainless steels
You may want to consider using FRP pipe like Ameron, Fiberbond, Conley instead of stainless steel. More corrosion resistant than SS and may be comparably priced.
Does the Navy also require this piping to meet the IMO A753 fire testing standards? Some FRP products actually perform better than Cu-Ni pipe in this service.
Hope this helps.