Tube to tube sheet connections

[numberfive]

Experts,

We have a non-asme stamped air-ejector condenser located at a customer's facility that has numerous leaks at the tube to tube sheet connections.

The tube attachment is nothing that I have ever seen before (see attached photo). I'm assuming that this acts as some kind of a compression fitting to create a seal at the tube.

Maintenance personnel at the plant tried to tighten several of these fittings in an attempt to stop the leaks to no avail.

Has anyone seen this type of tube to tube sheet connection before and if so what do you suggest to stop the leaks?

All leaks are located at the interface of the OD of the tubes to the ID of the threaded fitting to the tube sheet.

Thanks in advance for your insight.

numberfive

 

[Fizza453]

I am also seeing first time threaded joint between tube and tubesheet, rules for such joints are not provided in Section I, IV, VIII-1 and VIII-2. Anyhow, further tightening and/or seal welding can stop the leakage.

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[SnTMan]

Odd looking duck. What are we looking at on the left hand side of the pic? It looks like a conventional rolled joint? Is this maybe an outlet pass? Could the fittings be a type of ferrule on the inlet pass?

Regards,

Mike

 

[numberfive]

What you are seeing on the left hand side of the pic are tubes that are expanded and flared into the tube sheet. All of the tubes have the threaded fitting on one end and are expanded and flared on the opposite end.

I'm not sure which side is the inlet and which side is the outlet but the change in tube to tube sheet connections definitely follow the flow of the water as there are multiple passes in the heat exchanger.

numberfive

 

[SnTMan]

You might normally see some kind of erosion protection such as ferrules on the tube inlet end. They usually play no part in sealing the tube-tubesheet joint.

Never seen any ferrules that look like that though. A puzzler.

 

[chicopee]

Well, you have not identified the areas of leakage and I don't think it is in the area of the threaded tube ends area because I seal that seal welding was done. It also appears that there is a baffle separating the areas where the tube ends were expanded/rolled/ flared and those that have threaded ends leading me to believe that the threaded end area is a colder temperature region susceptible to corrosion from condensed vapor. So you'll need to be more precise in identifying where the leakage is occurring.
Note the tube sheet holes where you have the threaded ends are probably threaded too, so if this is the area that is leaking, I would remove all the tubes from that section, resurface those tube holes, install new tubes with external ferrules on the side where the threaded ends are located, thereby, you would be consistent with NBIC.

 

[GenB]

I see no chance of fighting or remove the threaded bushings they are damaged. What you need is to remove all the bushings and install new ones. Lube the joint so it will be easy to tight the next time it leaks.

 

[numberfive]

Leakage is occurring between the threaded ferrules and the tube ends. There has been no seal welding performed.

I would agree that removing the existing ferrules, cleaning and installing new ones (properly lubricated) is the best option.

Thanks for the input!

numberfive

 

[chicopee]

Put the new ferrules on the outside of the tube ends and not on the inside; it they are inserted inside, you will thin out the tube wall thicknesses.