Code calculations to determine the thickness of the flat plate to blank leaking tubes

[Gears6580]

Hi All,

Looking for code calculations to determine the thickness of the flat plate to blank leaking tubes in the shell and tube heat exchanger and the weld thickness.

Shell:
Material - 304L
Medium - Air
Pressure - 6 bar
Temp - 120 C

Tube
Material - 304L
Medium - Saturated steam
Temp - 215 C
Pressure - 25 bar
thickness - 1mm
Tube dia - 16mm

Tube plate
thickness - 20mm
material - 304L

We have found some leaks in the heat exchanger tube, the manufacturer recommended that we cut the leaking tube flush with the tube plate and weld a flat plate on the tube plate. The removed tubes will be sent to manufacturer to determine the failure cause.

My two major questions

1. I have used the UG-34 calculation to determine the thickness of the plug. I understand this calculation is for heat exchanger/pressure vessel heads but can this be used to determine the thickness of the flat plate required to plug holes and corresponding weld thickness.

2. The tubes are seal welded on the shell side of the HX. Adding a fillet or bevel weld on the tube side will restrict the thermal growth of the tube with the 20mm tube plate. Is this going to be an issue?

Thank you for your help/advice in advance.

 

[NovaStark]

Hello Gears6580,

Are you referring to welding a flat plate onto the tubesheet where the tube is being extracted ? You can consider putting a tapered plug of suitable dimensions as that may be easier depending on the configuration. UG-34 would generally be the way to go once you select the correct attachment factor based on welding.

In certain cases, you would have to drill through the tubesheet so that any expansion rolls or seal welds are cut to alleviate the thermal expansion issue (if any) as well as for venting purposes.

 

[goutam_freelance]

1. I think that the plate you are welding will be like a miniature unstayed flat head or cover. So your proposition could be acceptable by code.

2. Since tube as well as tube plate materials are the same this should not be a problem as thermal growths will almost match. Some temperature difference still will exist between the shell side and the tube plate. You could remove some portion of the old tube inside the tube plate near the new cover plate welding using grinding etc. and create a small gap between the old tube end and the plate. This could solve the problem.

One apprehension though, it looks like there will be a dead space within the tube plate due to the removal of the tube. Please ensure that this does not give rise to corrosion.

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[r6155]

Insert a bar with a diameter of 14 mm x 20 mm and fillet weld.

Regards