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Please describe what is feasible if joint for tube to tube sheet is expanded and strength welded. (Consider fixed tubesheet heat exchanger)

1-Welding after expanding
2-Welding before expanding

Please elaborate ur answer with some reference from TEMA/ or other related codes.

There are certain merits and demerits of both the sequences you mentioned.
Codes including ASME Sec. VIII Div. 1 and TEMA do not say anything regarding the recommended sequence to be followed.
But the preferred and recommended sequence is 2, that is welding before expanding based upon following reasons:
1. Welding shall be performed in an atmosphere where welding gases can escape; welding after expansion will surely result in bad tube-to-tubesheet joints having porosity or weld inclusions by lubricants (if cleaning not done properly)
2. Welding after expansion would cause adverse effects on expansion (can get loosened) due to welding heat. Such tubes would be requiring re-rolling.

On the other hand, the de-merits of above mentioned recommended solution include:
a. No foolproof check would be in place for leak tightness of expansion done
b. Chance of welding getting damaged during expansion process. The later can be overcome by increasing the starting distance of expansion towards shell side (recommended is > 15 mm from the toe of the weld joint, used by manufacturers)

Hope this would help.

Very rightly said by Ashfaq Anwer.
I also recommend welding and then rolling of tubes based on above reasons.
"Heat Exchanger Design and Fabrication" Book by Stanly Yokell also recommends to do welding and then rolling.
In case of PWHT requirements, rolling should be performed by after welding and PWHT.

Thanks Asfaq and Zahid.

Rana Ghulam Rasool
KSA

Dear Mr.Ashfaqanwer,
Thanks for your explanation.
The leak tightness of expansion generally done only through Mock-up test.After mock-up test the test piece is cross sectioned and leak path is measured under microscope.

The % of expansion is strictly done as per TEMA Rules and it is measure by GO and NOGO gauge and Bore dial gauges.

To carryout full expansion after welding also induce more stresses into the tube to tubesheet weld joint.
Generally initial rolling i.e 25% to 50% expansion done initially to make sure that the tube is in position and does not move inward or outward during welding and complete the final expansion after welding and this will reduce stress on the tube to tubesheet weld joint.

Thanks
NNREDDY

NNREDDY,
Thats seem to be the ideal approach to go.
I agree with your comments.
Can you please confirm about carrying out the leak tightness only through mock-up test by giving any reference to the applicable code?

Thanks in advance.

Dear Mr.Ashfaqanwer,
Specification for the Tube to Tubesheet welding you may find in ASME SEC III indetail. I have followed both section III and Nuclear Power Corporation of India specification which will be more stringent.

Thanks
NNREDDY