Expansion sequence for Heat Exchangers
Expansion sequence for Heat Exchangers
(OP)
We are in the process of fabricating heat exchanger where the shell side is to be tested at 770PSIG. The tube sheet has 2 grooves and the tubes will be welded with 2 passes.
My question is as follows.
1) should expansion be performed before or after welding
2) Is Hydraulic expansion a better option than coventional roller expansion.
3) Is helium test required prior to Hydrostatic test to ensure no leakage .
Thanks
My question is as follows.
1) should expansion be performed before or after welding
2) Is Hydraulic expansion a better option than coventional roller expansion.
3) Is helium test required prior to Hydrostatic test to ensure no leakage .
Thanks





RE: Expansion sequence for Heat Exchangers
1) If adding filler metal, light contact roll, weld, full roll - this lets welding gasses escape
2) Hydraulic expansion is usually used with materials that work harden rapidly and heavy wall tubes. It will require a wider groove than a rolled joint.
3) Not required, depends on the consequences of a leak.
Regards,
Mike
RE: Expansion sequence for Heat Exchangers
I agree that you need to make provisions for the welding gasses to escape, but if you're adding filler metal, why would you still need to do a full roll?
A light roll might be advisable to reduce the likelihood of crevice corrosion, but a full roll is usually considered unnecessary with a full strength weld.
-Christine
RE: Expansion sequence for Heat Exchangers
rmw
RE: Expansion sequence for Heat Exchangers
RE: Expansion sequence for Heat Exchangers
http:
"When a strength weld is employed and properly tested it is not necessary to perform the tube end expansion step. However if only seal welding is done then expansion of the tube end is needed in order to achieve the required mechanical strength at the joint."
"The preferred method of making the tube-to-tubesheet joint is first to expand and then seal weld. When this sequence is followed a higher quality expanded joint is possible and the risk of cracking the seal weld during the expansion step is eliminated. In addition a higher quality seal weld can be made."
-Christine
RE: Expansion sequence for Heat Exchangers
I have been closely associated with three of them and speak from their experience and practices. Others have stated success with the roll then weld method, but I hold out for the position of those that do tens, no maybe hundreds of thousands of tube welds each and every year.
Expansion can be done so that the welded end isn't disturbed. And the question was raised about hydraulic expansion. I'll mention explosive as well. Both lend themselves to protecting the welded end.
rmw
RE: Expansion sequence for Heat Exchangers
Two passes of weld are calling for full strength weld, not seal. Hence no roll is required (it also depends on the tube wall thickness).
However, to prevent the crevice corrosion, after weld a light roll might be justified. Also, the uneven weld heat and progressive heating of the tubes may loosen up the expansion if performed before welding.
Amazingly, another fabricator needs to expand first the tubes to prevent them moving in the tubesheet during weld!
That only proves that the fabricator experience and his equipment determine the priority of weld and expansion, not theoretical documentation.
On the other hand, I don't think is correct to leave this issue to the welder discretion, probably is time to get some proper code or similar ruling.
Cheers,
gr2vessels
RE: Expansion sequence for Heat Exchangers
Regards,
Mike
RE: Expansion sequence for Heat Exchangers
RE: Expansion sequence for Heat Exchangers
Cheers,
gr2vessels
RE: Expansion sequence for Heat Exchangers
And I suppose in the old days when electric utilities in the USA made guaranteed mark up on the cost of building plants, it made the power companies money by requiring and paying for Helium leak tests. Much more common way back then as were Hx's that were grossly oversized.
Then deregulation happened.
rmw