Which is better for Heat Exchanger Tubes copper nickel 90/10 or 70/30?

[MaterialsDude]

I'm researching both Copper Nickel 90/10 and 70/30 as possible tube materials for heat exchangers as an alternative to Admiralty brass which the company has been usuing and is looking to replace. Basically I want to know if anyone has had experience with these materials and if they are ideal for erosion and corrosion resistance, and if they have sufficient heat transfer coefficients.
Thanks

 

[metengr]

Yes, we have used both materials in our Power Plant heat exchangers - feedwater heaters and large steam turbine condensers.

Thermal performance no real difference. The copper-nickel has better corrosion resistance in comparison to brass. The final selection really depends on service conditions followed by cost.

 

[Guest102023]

Is this for once-through cooling water systems using natural fresh water, or other?

In my area there is a lot of OTCW with admiralty brass tubes that have been replaced with 90-10 cupronickel, although it is not immune to the usual suspects (ammonia, shock chlorine treatment). I believe that in seawater applications the 70-30 is more resistant. The Nickel Development Institute (NiDI) could probably help you.

http://www.nidi.org

 

[EdStainless]

We replace a lot of 90/10 with super ferritic stainless.

CuNi works well if you have moderate flow rates, it has problems with stagnation and high velocity. It is also sensitive to S compounds.
The alloys are usually used one or two gauges lighter than brass.
Go to copper.org and do some research there.

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Plymouth Tube

 

[MaterialsDude]

Any idea where I could get some good info like design velocities etc for both these copper nickel alloys. The problem I am having is that a lot of websites provide info on these alloys in sea water applications......probably cuz they have historically been used in such applications.

 

[SnTMan]

MaterialsDude, what kind of HX? We use 90/10 almost exclusively in our air coolers, including seawater service. Conductivity of 90/10 is much greater that 70/30, per a quick look at a table of such data, like 5:3 at 200F, but under half of Admiralty.

It all depends on your service.

Regards,

Mike

 

[rmw]

HEI has good recommendations for tube velocities for various common power plant alloys.

rmw

 

[MaterialsDude]

Well we have determined that we may not go for the Copper nickel alloys due to their lower thermal conductivity relative to the admiralty brass. Anyone have any recommendations for a better material? Basically we need tubes that can withstand velocities of about 12 ft/s, resist corrosion from substances in water such as sulphates and chlorides, and fouling. The heat exchanger is a shell and tube exchanger. We also are looking into Titanium grade 2 and duplex 2205 stainless steel.

 

[SnTMan]

MaterialsDude, this is not really my area of expertise, but, rmw's HEI guidelines recommend fps 10 max for SS, NI alloys and Ti, less for other materials. This is for clean water, BFW, less for erosive fluids.

If you don't like the conductivity of 90/10 you sure won't like Ti or 2205.

Regards,

Mike

 

[MaterialsDude]

I checked out that website for HEI but couldn't find any such info. Isn't it

http://www.heatexchange.org/

 

[EdStainless]

Don't overlook SEA-CURE. It has better corrosion resistance than 2205 and better erosion resistance than Ti. It is also twice as stiff as Ti allowing thinner walls and better vibration resistance.
We did the erosion testing at 134 ft/sec in seawater.

What was your flow in the brass, 7 ft/sec?
If so then at 12 ft/sec with 0.028" SEA-CURE you will have about 30% increase in overall heat transfer than you had with 0.049" brass.
Flow velocity is your friend.

You would need to buy info from HEI. Their recommendations are not based on erosion resistance.

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Plymouth Tube

 

[MaterialsDude]

EdStainless,

It is funny that you mentioned that because I was doing research on the Sea Cure and it really does look like a good material. The only drawback that I read was that it isn't so good with fouling resistance due to no copper in its composition.

Well we did have velocities as high as 12 ft/s in the exchangers and we believe it caused erosion corroion problems with Admiralty brass tubes because it isn't designed for such high velocities.

So have you seen Sea Cure being used for ordinary shell and tube heat exchangers??

 

[rmw]

When I recommended the HEI as a source for velocities it was for CU-Ni and brass tubing. I think their recommendations there for those tube materials are right on. But, regarding their recommendation of 10 fps for stainless, I don't know where they are coming from. I am reminded that I intended to phone one of the HEI committee members and quiz him regarding that and forgot to do it.

Here is a link that will answer several of the questions that you have ask in this thread (and a paper that I wasn't familiar with - and one I need for other purposes, so thanks. I think the velocity recommendations in this paper are much more realistic for the 'better than copper' alloys.

http://www.plymouth.com/_tmp/IDA Presentation MP07-016.pdf

You were certainly right in your conclusions regarding using brass in a 12 fps application. Sheesh. And, yes, copper and brass do build up a nice patina resistant to further corrosion, but those velocities will wash it right off.

I for one am a huge fan of SeaCure. If there is a better metallurgy for low (meaning not high) temperature applications with all the stuff that can be found in less than DI water I want to know about it. I haven't found one I think to be better on an 'all around' basis.

What is causing your fouling?

rmw

 

[MaterialsDude]

Thanks rmw. Well scaling and fouling are problems in the tubes due to the water chemistry of the water flowing through them. The scaling issue can be handled mainly through regular cleaning. Fouling is a result of bacteria presence in the water.

 

[rmw]

Then I think you are a prime candidate for SeaCure. Underscale pitting is a real problem in the scenario you describe and SeaCure is superior for that. Especially if you have any Manganese in the mix.

Here is another good read on Cu-Ni. It is a pitch for SeaCure, but it goes into why one would want to make that change.

http://www.coalpowermag.com/ops_and_maintenance/219.html

The author has a background in copper based tubing as well, so this isn't just a lot of hype.

rmw

 

[EdStainless]

There is a chemical treatment on the market that you might consider. It is designed for once through systems.

http://mexel.fr/products-solutions/mexel-432/

This stuff coats surfaces and then slowly breaks down. In the process things that stick to it get shed off into the discharge.
It is about the option you have to slow scale formation in a once through system.
Using a hard tube alloy like SEA-CURE, with a plan to mechanically clean on a regular time table will go a long way to keep the unit running.

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Plymouth Tube