Surface Condenser Corrosion. 2

[Corgas]

A local lab doing chem analysis of deposits found Cu & Zn inside "water tube" of packaged type "D" boiler.

Where Cu was found inside the tube, there was also some wall thining. Lab concluded thining was due to Cu present.

Looking at the system, it seems that Cu is coming from surface condenser tubes (Inhibited Admiralty). This condenser has > 3,000 tubes and about 60 are plugged.

Is it correct to assume that Cu is coming from those condemned tubes ? Is retubing those 60+ tubes the solution?

Cooling water closed-loop. Steam is 600 #. Steam system does not operate continuously. Condenser was Eddy current tested in 2001 and > 1,000 tubes showed wall loss. Back in 2002, corroded tube was taken for analyis and local lab concluded that corrosion of the inside surface was by dezincification.

Concern is source of Cu and its effect (corrosion) on Boiler.

Any thoughts and suggestions are welcomed.

 

[EdStainless]

You may be getting some ammonia attack on the steam side of the tubes, or it may just be the natural general slow release of Cu.
I suspect that the Cu is coming from ALL of your condenser tubes. Low pressure plants tend to see it in the boiler tubes. As temp and pressure go up it movers to superheaters and turbines.
Yes, your boiler tube thinning is probably a result of galvanic corrosion from the Cu deposits. If they get too thick you may get failures from localized overheating or liquid metal embrittlement.
This is why almost no one puts Cu alloys into condensers (or any BOP heat exchangers) any more.
There are chemical treatments to minimize Cu transport. But they may be costly and they may not be compatible with other chemicals that you are using.

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Plymouth Tube

 

[Corgas]

Thanks Ed,

Yes, Brass tubes were selected before my time!!

I'll look into ammonia on the steam side.

Wouldn't you expect higher general corrosion rates on OD of plugged tubes?

Can you suggest a chem treatment to minimize Cu transport? It's probably cheaper than repair or replace boiler and/or turbine in the long run.

 

[metengr]

Corgas;
I would expect you have ammonia grooving on the steam side of your condenser tubes. The copper plates out on the waterside deposit of high pressure boiler tubes and will promote under deposit corrosion.

I would be less concerned with copper embrittlement, which is the least likely problem to occur. I would be more concerned with local plug corrosion damage that results in hydrogen that is liberated and diffuses into the carbon steel tubing causing local hydrogen damage. This will cause window type tube failures that cannot be repaired other than wholesale tube replacement!

 

[MJCronin]

Talk with NALCO....

This damage can be somewhat mitigated via control of pH

http://www.emersonprocess.com/RAIhome/documents/Liq_AppData_4900-85.pdf

http://www.parkerboiler.com/pdf/bulletins/Water Treatment/1001B-C.PDF

-MJC

 

[EdStainless]

The OD metal loss will be a function of local chemistry more than the tubes being plugged.

I doubt that it will cost less to use chemicals, over the next 20-40 years. Treatment in mixed metallurgy system is always a compromise. You can't fully protect your boiler and superheater and also fully suppress Cu transport.

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Plymouth Tube