Use of full-length CRA HEX tube liners vs. partial ferrules

[kevlar49]

I have suggested that full-length liners be used in lieu of partial ferrules or solid alloy tubes for hex tubes that experience dew point corrosion since the salt point and dew point tend to move depending on operating conditions.

I have been told that the contact resistance would severely reduce heat transfer. Does anyone have any comment about this?

Some have said that organic coatings like Saekaphen and the type that Ed Curran apply do not decrease the heat transfer as much as full-length metallic liners. Any comments?

Is there any data out there to support either position?

many thanks.

 

[metengr]

kevlar49;
I can give you some real world experience on the application of thin sleeves used in steam condenser tubes. At one of our Generating Stations, we had come across external (ammonia) grooving of brass tubes in and outside of the air removal section of the condenser. This was past damage and it appeared to be no longer active. To avoid future tube leaks, and to extend the life of the condenser, austenitic stainless steel sleeves (I don't remember the sleeve thickness before expanding) were hydraulically expanded into each condenser tube, full length.

Despite taking great pains to clean the tube ID surface, and assuring proper pressure to radially expand the sleeve against the existing tube ID surface, the end result was a significant penalty in condenser performance. We were able to preserve tube life but we could not regain bogey performance of the condenser on hot summer days.

The interface between an expanded sleeve and tube wall was just to large of a barrier to overcome in terms of heat transfer by thermal conduction.

I would never recommend full length sleeves in a heat exchanger application again.

 

[EdStainless]

There are many excellent applications for full length liners. Regretably they neeed to be considered in design, not as retrofit. Consider the situation where the original design calls for CS tubes with 0.109" wall for pressure and an additional 0.062" for corrosion allowance. If instead you built using 0.109" CS tubes with full length hyro expanded liners in stainless or Ni alloy you can use 0.020" liners and get very long life with good heat transfer. In heavy walled tubes with a good surface the heat transfer penalty is less than most people suffer from fouling. If you do this in a low pressure hex you will see the impact, unless you design for it.

Now, your situation. In every case that I have seen you can measure the decrease in heat transfer. My experience is that the coatings hurt you worse than properly installed liners.
In your case there is another problem. You can look at the existing tubes and select a lenght for partial liners based on the corrosion. But when you intall the liners you will slightly reduce the heat transfer and this will move the corrosion further down the tubes.
Are you going to repalce the tubes? If so then use the lightest wall CS that code will allow and full length line them as new tubes before they ever go into service. Select a liner alloy with zero corrosion in you environment.
If this is a retro fit, then decide how much heat transfer you can afford to loose. Is it better to loose the entire hex, or a bit of capacity?

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