chloride/seawater stainless steels

[joeswoes]

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.... ??

 

[arunmrao]

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

 

[davefitz]

as with the Trent tube link, Sea-cure S44660 is a preferred solution

 

[EdStainless]

OK, I am a little slow this morning.
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.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[joeswoes]

let us also consider that this customer is the US Navy, does that effect peoples ideas on suitable alloys ?

 

[EdStainless]

IF you have no influence over the use, and they want it to last forever, I would use AL-6XN or 254SMO.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[rorschach]

In addition to 2205, I'd also suggest SAF2507 and other 25% chrome super duplex stainlesses (Foroni 918, Zeron 100, others) as well. It is 85 KSI, virtually immune to CSCC, and can be sucessfully welded using TIG without a whole lot of hoop jumping using SAF 25-10-4L filler wire.

 

[mshimko]

The US Navy is wanting to use stainless steel for seawater piping?

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.

 

[rolledalloy]

Another advantage to the AL-6XN or 254SMO is they are more tolerant of sulfur compounds, like H2S in polluted water than alloy 400. They are also significantly stronger which can save weight if lighter wall piping can be used.

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.

http://www.rolledalloys.com

 

[SJones]

Colleagues,

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/

 

[MikeHalloran]

Six-M-O lasts longer than 316L in _hot_ seawater. I'm not convinced that it's any better in cold seawater.

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

 

[texaswildcat98]

As mentioned above the Super Duplexes offer an excellent resistance to seawater. There are lean duplexes like 19D (UNS 32001) which can also be used, these tubes typically will have an extruded zinc coating for cathodic protection and can have service lifes exceeding 30 years in seawater.
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...

 

[SJones]

Anything above 30 degrees C and there could be trouble with any of the alloys mentioned above. Take a look at NACE 98 Paper 707 from Statoil.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[EdStainless]

For a mechanical/structural application exposed to seawater there are not that many choices.
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.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[mshimko]

For Joeswoes - we need more info.

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!

 

[kevlar49]

Joe,

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.