Piping for sea water: Duplex 2205 vs 316L 3

[Mmagan]

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.

 

[Mmagan]

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]

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]

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]

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]

You could consider Halon coated carbon steel pipe.