Tube to Tubesheet Joint Question 3

[Fizza453]

Tube to tube sheet joint is expanded plus seal welded.
Is it better to expand the tube withing tube sheet prior to welding?
rather than expanding after welding?
Expansion prior to welding is an essential variable while qualifying the welding procedure, I have to make sure expansion before welding is preferable or after? so that same I can exercise at the time of qualification.



Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[puigi]

What code of construction are you using? Typically expansion is performed prior to seal welding.

 

[Fizza453]

Sorry for not mentioning design Code.

Design Code is Section VIII Division 1 and welding procedure qualification standard is Section IX.



Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[SNORGY]

I would roll (expand) the tubes prior to seal welding. If you did it the other way, you would likely re-stress the weld and HAZ. I think the welding after expansion makes more sense to me.

Regards,

SNORGY.

 

[rmw]

This discussion has been had in these fora many times before and there is disparity of consensus.

I for one having had experience with several manufacturers of high pressure Hx's - people who had to do it right the first time or pay some expensive warranty costs - NEVER welded after rolling EXCEPT in the case of Titanium. For all other metals, the process is to (1) contact roll first to size the tube out to fill the tube hole and center the tube, (2) weld, then (3) strength roll the tube.

And, when strength rolling the tube post seal welding, don't roll the seal weld because cold working it can break it as well. Begin the roll inside of the weld with some margin, say 1/2 inch or 12 mm.

The answer is weld process dependent. In a weld process where gasses are created during the welding, strength rolling first doesn't permit the gasses created to have a way to escape and when the weld finished, trapped gas behind the weld can cause a blow out defeating the purpose of the seal weld. A "contact rolled" tube still has enough porosity to permit the gasses to escape.

Welding Ti (to Ti) is an autogenous process and the gas creation problem is not an issue.

Other valued posters to this forum disagree and have firmly stated that they have done it the other way with success. My hat is off to them. The guys who weld tubes by the thousands per week/month/year year-in and year-out do it as I have prescribed above. I have no other experience to offer.

rmw

 

[SNORGY]

rmw:

Thanks. Your explanation reflects a much greater amount of knowledge in this area than I have.

I learn something every day.

Regards,

SNORGY.

 

[racookpe1978]

Nasir (user_id FIZZA453)


Please, as a matter of professional courtesy, note that you've started 28 threads since enrolling, but have replied only once, and that on this thread while clarifying your original question.

When asking for help from others, remember you are taking from them, from their free time, to gain information for your professional use. Thank you's are appropriate and appreciated in all cultures.

Robt

 

[EdStainless]

RMW's comment at spot on.
In thick tube sheets they usually contact roll at hte face of the tube sheet and only in the depth of the rolls. You just want the metals to touch but not seal.
When you go back for the hard roll you need to stay away from both edges.
Both location and torque of the rolling is critical to reliable joints.

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Plymouth Tube

 

[rmw]

Thanks Ed S. for clarifying that the contact roll prior to welding is only for a very limited amount of the full depth up near the face.

In my experience, in most cases, even in high pressure Hx's, the full strength of the joint was developed by usually no more than 2.5 in (63 mm) of roll. The tubes were expanded full depth (except for at the very end as Ed S. also noted) by explosive or hydraulic expansion. The tube sheets of the Hx's I dealt with were just too thick to spend all that time mechanically rolling. The full depth expansion was for crevice corrosion prevention among other reasons.

rmw

 

[Fizza453]

RMW

Quote from your reply

"And, when strength rolling the tube post seal welding, don't roll the seal weld because cold working it can break it as well. Begin the roll inside of the weld with some margin, say 1/2 inch or 12 mm."

Such requirement is mentioned in clause 6.10.2 of API 660 of February 2001, where it reads out as " when expanded and welded joints are specified, tube wall reduction should begin a minmum of 6 mm away from welds".



Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[rmw]

Fizza,

I gave you a star for that one. I don't use API but that was a reference that will come in real handy where I work right about now.

rmw