Expanded plus seal welded tube to tubesheet joint

[Fizza453]

How to calculate seal weld size that supplemts expanded joint? Design Code is Section VIII-1, UW-20 does not provide rules forthe seal weld sizing.
Appendix A of Division 1 provides a method of qualifying the expanded plus seal welds.
Are there rules in any other design code to calculate seal weld? and we may use these rules under U-2(g).

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[SnTMan]

Fizza453, for a seal weld, no strength is required, therefore there are no rules (or requirements) for calculating its size, see UW-20.2(c). As Appendix A is about establishing allowable loads, it is not applicable to a seal weld.

For thin tubewalls it is common to weld without filler, just by fusing the tube to the TS. For thicker tubes filler may be added, but again no particluar weld size is required.

All that is needed is to get a good weld. The weld size obtained I think would be very much a function of the process used.

Regards,

Mike

 

[Fizza453]

Mike,

Thanks for the input.
I do not agree with you if you say Appendix A is not applicable to expanded plus seal welded joints.
A-1(a) only excludes, from scope, full strength and partial strength joints (as defined in UW-20) and U-Tube construction (see A-1(b). Rest of all joints are included Appendix A scope. Although expanded plus seal welded joints not shown in Fig. A-2 yet A-1(c)(1) includes this joint in Appendix A scope.


Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[SnTMan]

Fizza453, you are correct regarding Appendix A, however it is concerned only with allowable joint load. I meant that it gives you no basis for sizing a seal weld.

It used to be common to consider a weld where a >= 1.4t as a "strength weld" and a weld where a < 1.4 t as a "seal weld". UW-20 gives a more rational basis for distinguishing between them.

Regards,

Mike

 

[Fizza453]

Mike,

Yes, Appendix A guides how the allowable load is to establish for the tube to tube sheet joints.
t is tube thickness in your above post?
I am little disagreed with you, UW-20 only distinguishes partial strength and full strength welds. UW-20.2(c) briefly describes seal weld only. UW-20 distinguishes partial strength and full strength welds by making calculations.
Thank you.

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[SnTMan]

Fizza453, yes, t is tube wall thickness, Appendix A.

"UW-20 distinguishes partial strength and full strength welds by making calculations.", exactly. No calculation, its a seal weld.

For the type of welds without filler I spoke of earlier, there is essentially no measurable weld leg, so UW-20 calculations are not possible. However if the process used gives a measurable weld leg, it looks to me like it should be possible to treat it as a partial strengh weld at the least.

Regards,

Mike

 

[lganga]

Fizza453

The tube to tubesheet joint, it is seal welded as way that no leaking will appear after service along the grooves and whe the service of ones side is corrosive in contat with the other side of the shellside
The resistance is done by the 2 gooves expanded.

In some cases you expand without groove (for example to avoid SCC) but we use a resistant weld.

But the problems with the tube to tubesheet joint is to get a dependable vendor (you must teach him what you want) and follow up of the expansions and weldings. The cleaning of the weld.To avoid contamination with the expansion lubricant and the welded joint

For this weld, orbital welding is preferred, but a very detailed inspection should be needed if you want a dependable heat exchanger.

Consider that when you weld, if you want to change in site the tube, the contamination will not let you weld it again after changing.

This is my experience after 10 years of failures in reboilers and HX
When we do a resitnt weld alway are two passes adn tested in between
Regards
Luis

 

[Fizza453]

Bundles of Thanks Luis,Mike

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[EdStainless]

When the seal welds are done correctly the tubes are not tightly rolled into the tubesheet, only enough to have contact.
In this way gasses from the weld can vent and you can actually leak test the welds. Then after this the hard rolling is done for tube support. This final roll needs to stay away from both the welds and the back edge of the tubesheet.

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Plymouth Tube