Duplex vs Admiralty Brass 4

[rustbuster]

Hello all,

I'm lookin for some quick comparison numbers for 2205 to compare to SB 111. I want to know how much heat transfer I will give up if re-tube insitu. Thanks all.

 

[rmw]

It is an interesting question but you haven't given us enough information to do squat for you.

rmw

 

[EdStainless]

For one thing you will reduce the wall thickness by about 60%, and still have better stiffness and pressure rating.
The real trick in the tube side flow, what happens when you reduce the pressure drop? Do you get much more flow?
If this is directly fed by centrifugal pumps then you will prob not see any change in overall heat transfer.

Can you keep the duplex from biofouling? SS isn't toxic like Cu is so things can grow on it if you don't treat the water.

We need to know fluids, flows, and system dynamics to give a better answer.

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Plymouth Tube

 

[rustbuster]

My apologies,

These exchangers are in clarified cooling water service with varying process fluids and ar gases. We should be able to keep bio-fouling to a minimum.

I've heard that many operators are standadizing on duplex vs. ad. brass. Thought someone would have a rule of thumb or have knowledge and experience.

We will do the engineering but I want to hear others' experiences.

Thanks all

 

[EdStainless]

Duplex is all that is used in pulp and paper. No 300 series and no Cu alloys.
If you go this route throw out old rules about wall thickness and do the pressure rating and vibration calculations yourself.
Remember that there is no corrosion allowance with SS, since all corrosion failures are localized.
And remember to raise flow velocities as high as you can. A good place to start is 10 ft/sec, there will be no flow erosion unless you have a lot of abrasive solids.


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Plymouth Tube

 

[rustbuster]

Thank You Ed,

A star for you!

 

[Guest102023]

SB-111 is many Cu alloys.

 

[rmw]

Chances are that if you have copper now and your pumps are sized right, when you thin down your wall thickness to get equal or as near equal as possible heat transfer, it will run your pumps way too far out on their curve. If you have the ability to increase your pump rate (by adding an additional pump for example) you can make the change. If you can't change your flow the change in metallurgy probably won't benefit you.

rmw

 

[rmw]

You did mention re-tubing insitu and my answer was based on that. Another question would be - what is the tubesheet metal that you are planning to roll these duplex tubes into? If your water has any electrolytes in it all, you may have galvanic incompatibility.

On another tack, if you change the bundle out altogether, with a tubesheet metallurgy to compliment or match the duplex, then you can change tube size, pitch, count; any of these, all of these in order to match your pump flow to your heat transfer surface. Give it a thought.

rmw

 

[rustbuster]

Thanks for your comments rmw, I hadn't considered the tubesheet couple. We'll consider that as well.

 

[EdStainless]

1. It is common in cooling water service to keep the bronze tubesheets and epoxy coat them, IF they are in good condition.
If there is any doubt then look at having an entire bundle with new tubesheets made. If you do this you could possibly change tube size or count to reengineer the heat exchanger.
2. You need to analyze the flow. Is the restriction of the tube bundle really what is controlling the flow? Where are your pumps running on their curve now? If the bundle is the major restriction and the pumps are above the BEP then you might be in great shape. Otherwise a new impeller designed for lower head/higher flow might be what you need.

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Plymouth Tube