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Mmagan (Industrial) (OP)
13 Jul 09 7:34
Hi all.

We are currently designing some piping to convey sea water. At first I thought 316L would be OK, but after reading a dozen of articles, it seems there are mixed experiences with it. I am currently considering Duplex 2205, but I would like to know a couple of things:

1) Is it much more costly than 316L? I just want to know that I am not going to ask the supplier for something outrageously expensive...

2) Is duplex 2205 OK for sea water (35g/l NaCl, 20ºC max), considering that the pipe will only convey seawater around 16h/day? I am concerned about having the water stagnant, although the docs I have read seem to point out that a few hours stagnant is not a problem. For longer stops (maintenance and such), I think we will just wash up the pipe with fresh water.

I welcome your tips. Many thanks in advance.  
Helpful Member!  EdStainless (Materials)
13 Jul 09 9:21
The material is more expensive, make sure that you reduce the wall thickness.  2205 is almost twice as strong as 316L so you can use less metal.

You are correct, you can't expect 316 to work in seawater, especially when it will not be continuous flow.
This may be a problem for 2205 also, but it will hold up better.
When you spec the material make sure that you order S32205, and require the ASTM A923 testing.
What will be done for biological control? chlorination? During the stagnant period I am worried about grow taking over.

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Plymouth Tube

Helpful Member!  strider6 (Materials)
13 Jul 09 11:49
i'll select a 2507 superduplex with a PREN (pitting resistance equivalent) above 40 for a seawater service.

Corrosion of Duplex
Stainless Steels in Seawater

"In all tests, components made of
316L and S31803 were attacked by
severe crevice corrosion after a short
time. The highly alloyed steels
S32760 and S31254 performed in an
excellent way, and so did titanium
and S32550"

hope this help


Corrosion Prevention & Corrosion Control

Mmagan (Industrial) (OP)
14 Jul 09 3:38
Thanks for you replys.
@strider6: Actually I had already seen that article, and noticed that they test at least at 30ºC, significantly higher than what we can expect. Nevertheless it is an interesting article, but I don't think the cost of the superduplex steel is assumible.

@EdStainless: Yes, we are thinking about 0.5 ppm chlorination, during 30~60 min a day. We must avoid all possible biological fouling as lead loss is also highly undesirable. According to the article attached, 2205 should do just fine as long as the temperature doesn't increase. Also, MANY thanks for the advice about S32205 instead of S31803 (I didn't even know the difference...). With the stress allowable values, it seems that it may be actually less expensive thanks to reduced thickness.  
Helpful Member!  moltenmetal (Chemical)
14 Jul 09 7:34
Wow- 2507 super duplex for seawater at less than 30 C?

Sounds like we're getting out the 12-pound sledgehammer to drive that square peg into that round hole!

Cold seawater is an ideal application for non-metallic piping.
Mmagan (Industrial) (OP)
14 Jul 09 7:48
Not at 60 bar...Sorry, I forgot that detail blush
EdStainless (Materials)
14 Jul 09 8:51
When you are not operating will the pipe be full of water, or only part full?  If it is part full then you can expect to get both biofouling and corrosion attack along the water line.  But that will take a while.  I still think that 2205 is a good option for this application.

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Plymouth Tube

Mmagan (Industrial) (OP)
14 Jul 09 10:01
I do not see why we couldn't have the pipe full of water while we are stopped. I will ask to my mates if they see any problem, but even if we couldn't, I do not see that as a huge problem, the pipe has over 500m height difference between extremes so it is not as if the water line is going to be at the same spot every day.
moltenmetal (Chemical)
14 Jul 09 14:52
OK, 60 bar is good enough reason for metal!

And at those pressures, the extra strength of the duplex grades WILL be of use to you!
stanier (Mechanical)
14 Jul 09 19:53
Super duplex is the material you should be using even then the pickling and passivation requirements 9ASTM A380 etc) is required.

Freom the pressure you have stated this probably a desalination plant using SWRO.

I have been working on plants for Veolia Water and Acciona Agua over the past 4 years. All use Super Duplex UNS 32507 with a PREN>40 for the sea water and brine services.

The question of stagnation is also a cuase for concern for super duplex. Whether you use SAF 2507 Sandvik or Zeron 100 Outokumpu doesnt matter; they both warn of stagnant conditions.

If cost is an issue why not use carbon steel pipe coated with FBE inside and out? You may have a little more maintenance in the future if the external is damaged but is far simpler than the stainlesses.

strider6 (Materials)
15 Jul 09 2:55
it's just my opinion but.. i'll select a 2507 for a seawater service.. it depends also on the criticality of the service, what are the consequence in case of failure??, and  it's possible to make maintenance??
you can select also a cupro nickel alloy but there are limitations on the max velocity...
Sea water System Design


Corrosion Prevention & Corrosion Control

Mmagan (Industrial) (OP)
17 Jul 09 3:32
Well, the consequences in case of failure is essentially having to stop the whole plant, since this is the whole point of the facility is to use seawater to store energy. Also, I don't think the local environment authorities would be terribly happy about spilling seawater...

As I said, the plant does stop during several hours a day, but there is only so much maintenance you can do during 6~8 hours. During the weekends, it could be possible to make maintenance at little cost, but that ultimately depends on the market, so it's hard to tell.

@stainer: We do not trust coating solutions a lot, to be honest, my bosses have had rather poor experiences with it
SJones (Petroleum)
17 Jul 09 21:39
Would somebody care to elaborate upon why, specifically, GRP has to be ruled out?  I haven't seen anything convincing against it yet.

Steve Jones
Materials & Corrosion Engineer

MikeHalloran (Mechanical)
17 Jul 09 22:03
Uh, 60 bar?

Not that GRP pipe couldn't take it, but connections might be a challenge.


Mike Halloran
Pembroke Pines, FL, USA

SJones (Petroleum)
18 Jul 09 2:05
Come on!  I've been using GRP in 120 bar pipelines.  Screwed connections.  No problemo.  Not straightforward, granted, but no reason to toss it in the 'too hard box' just because one sees 60 bar pressure.

Steve Jones
Materials & Corrosion Engineer

MikeHalloran (Mechanical)
18 Jul 09 11:33
Okay, now you've got _me_ curious.
Where can I get GRP pipe and screwed connections for pressure like that?


Mike Halloran
Pembroke Pines, FL, USA

SJones (Petroleum)
18 Jul 09 20:51
MikeHalloran (Mechanical)
18 Jul 09 21:35
That's impressive stuff.

Mike Halloran
Pembroke Pines, FL, USA

moltenmetal (Chemical)
20 Jul 09 7:22
Wow- never seen FRP service pressures anything close to that.

Mmagan (Industrial) (OP)
20 Jul 09 7:45
Interesting stuff, but at 8", we would need an afwul lot of pipes to have a decent lead loss, I'm afraid. We are thinking about 36" or 48" (if feasable) pipes!

We even had a proposal to make a tunnel-like piping in concrete, with an impermeabilization sheet. I can't find any freely available examples to show you, though. But in any case that option is not my field, and I'm rather clueless about it.  
EdStainless (Materials)
20 Jul 09 10:27
At 48" concrete sounds like a better option to me.  There are some great lining material available that make the surface smoother, easier to clean, and more durable.
And yes, for seawater there are special concrete formulations.  Not to mention the re-bar.

My opinion is that for a reasonable life and a reasonable cost 2205 would be suitable for handling cold seawater.

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Plymouth Tube

stanier (Mechanical)
20 Jul 09 19:20
What is th design life of the asset?
Will the line be stagnant and can the temperature rise above 25C?
CEGB in the UK used to make all their seawater intakes to powerstations in carbon steel powder coated with PE. Flanges may be a problem at 60bar wit the gasket/PE thickness.

EdStainless (Materials)
21 Jul 09 14:00
I have talked with someone that makes PP lined steel pipe.  The liner is heavy, but the steel carries all of the load.  This system is more reliable than a coating.  Look for this as an option.

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Plymouth Tube

stanier (Mechanical)
22 Jul 09 21:30
You could consider Halon coated carbon steel pipe.

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