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ChrisV82 (Mechanical)
22 Dec 08 15:28
I am working on a project which requires a heat exchanger that can handle sea water on one side and deionized water on the other.  Additionally, because of the application, no copper alloys can be used.  

For deionized water only, I would typically use 316 stainless, but I believe the sea water will pose an issue to this material.  I know brass is generally good for sea water, but this will be problematic for DI water, and as it contains copper, cannot be used.  Titanium has been suggested, and seems to be a good fit, but is fairly expensive.  Does anybody have any suggestions of other materials to look into?  Thanks.
EdStainless (Materials)
22 Dec 08 16:32
For this service people generally use either a super-austenitic stainless (such as AL-6XN), or a super-ferritic stainless (such as Sea-Cure), or Ti.
All three alloys have long track records for successful use in seawater.
The super-ferritic will have the lowest cost of the three options.  Using Sea-Cure for tubes and AL-6XN for the rest of the seawater exposed parts would be a typical construction.

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

ChrisV82 (Mechanical)
23 Dec 08 6:47
Do either of the stainless options have a track record for use with DI water?  I know it poses its own set of issues that are different from sea water.
EdStainless (Materials)
29 Dec 08 8:18
All of these high alloy material have been used with high purity water.  I have been associated with applications in power generation handling feedwater as well as in pharma with water-for-injection.

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

MJCronin (Mechanical)
31 Dec 08 13:11
I agree with EdStainless...

Titanium is your best overall choice and has a proven track record with both fluids. If the HX is not too big, the additional cost of TI, will not be too bad.

But, part of your choice of materials will depend on the style of the HX that you require..? Is this a shell & tube. plate-frame or what ? Will you need to periodically clean the seawater side of the HX ?

-MJC
 

   

rmw (Mechanical)
31 Dec 08 17:36
I think Ti is a little bit of an overkill, unless this is a plate & frame type Hx and then I'd consider it seriously.  I think the super ferritics should do just fine in this service if it is a shell & tube Hx.

MJC, did you get your words out of order?  I think your last sentence should read "You WILL need to periodically clean the seawater side of the Hx.

rmw
SJones (Petroleum)
1 Jan 09 18:10
Could we also have an idea of the temperatures of the two fluids so that we can make a more informed materials selection?

Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
 

ChrisV82 (Mechanical)
5 Jan 09 8:09
Thanks for all the suggestions.  The plan right now is to use a plate-frame HX since it should be smaller in size, although I do want to evaluate all of my options.  The hot side (DI water) inlet temperature is approximately 167 F max, and the cold side (sea water) should be around 85 F max.  Any additional advice would be greatly appreciated.  Also, could anyone suggest some possible manufacturers of such a HX?  Thanks.
EdStainless (Materials)
5 Jan 09 12:19
That temp in a P&F, you will want to use Ti.
The cooling water side will need to be well filtered or you will end up fouling the passages in the plates.

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

Helpful Member!  Johnnybv (Industrial)
23 Mar 09 20:20
I don't know if it is still made, however if it is it could be a solution for you.  George Fischer (+GF+) used to make a thermoplastic heat exchanger.

It was not good for any applications which required a great deal of heat, nevertheless, if the volume of water is not too great, and the delta t is not too great it could be an option.

http://www.us.piping.georgefischer.com/go/85FD4C79D60EB5F06E88713117408325
 
MJCronin (Mechanical)
27 Mar 09 12:33
rmw...

Yup....words out of order...

I agree with EdStainless on material selection

But, for a plate frame HX, I suggest that you get a price on Ti as well as one of the super-austenitics.

Also, be sure to get as much junk as possible out of the sea water incoming stream. A duplex strainer with a fine mesh seems to make sense. These will not be cheap either.
 
(Yes... I know that the maintenance people will complain about periodic cleaning of the system....thats the way it goes...)

-MJC

   

rmw (Mechanical)
27 Mar 09 19:59
MJC, couldn't agree more.  If you don't put a good serviceable strainer in front of a P&F, the P&F will itself become a strainer for everything too large to get through the narrow flow passages.  They make wonderful strainers even though that isn't what they were bought for.

rmw

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