Tube to tubesheet joint

[asvipin]

hi,
I want to design a tube to tube sheet joint in U tube HX. Tubesheet thickness is 30 mm and tube thickness is 1.245 mm (material SS304L both) and ligament in tubesheet is only 4.5 mm. Since loads are less, a 2 mm strength weld(weld is preferred since leak tightness is important) is sufficient. I can use a simple fillet weld or a welded joint with groove around the hole. How to decide whether groove is required or not (ligament size is not enough to create groove)? In one forum it was mentioned that for SS weld without groove can be used since thermal conductivity is less. Is it actually correct?

Having an expanded and seal welded joint is an option but the cost will be high.


Thanks in adavance

 

[EdStainless]

Expanded and seal welded would be the normal route for this.
You have to expand the tubes anyway, even if just for mechanical support.
This is a low pressure application, don't mess with strength welds.

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P.E. Metallurgy, Plymouth Tube

 

[asvipin]

Thanks for ur reply.

You have to expand the tubes anyway

But a 2 mm fillet weld can provide the strength for pressure loading. Then is it necessary to expand the joint? (Crevices are not a concern). I am beginner in this field


Just for knowledge, In strength weld how to decide whether groove (surrounding the weld) is to be provided or not?

 

[EdStainless]

The spans between supports were probably calculated from the BACK of the tube sheet, if you just weld then that first span will be 30mm too long, that section of the tubes will vibrated, and as they hit the edge of the holes they will fracture.
Proper roll expanded joints will have more than enough strength and sealing for this application.
If leak tightness is critical I would add 15 shallow "V" grooves in the tubesheet holes.
If this is an acid cooler I would go ahead and seal weld.
the correct process is to do a light contact only roll, seal weld, hard roll the tube making sure to stay 5mm from the weld and 5mm from the back face. The rolling needs to be based on roll torque that was determined in a mock-up using the same tubesheet and tube materials.
It may seem like it costs money and takes time, but do you want the HX to last?
For every problem there is s solution that is quick, cheap, and wrong.

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P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

Th process engineer / process safety engineer may most likely have a say in whether the tubes need to be seal welded into the tubesheet, depending on the consequences of inter stream leakage. In some cases, where the consequences pose significant risks, a double tubesheet is used ( with inter tubesheet bleed to disposal).