Expansion Versus Weld Repair
Expansion Versus Weld Repair
(OP)
1978 TEMA C recommended that for 300 psig+ and 350 degF + heat exchangers with 5/8" dia and larger tubes you should either expand the tubes over 1-1/4" min. length in a two-grooved tubesheet or use full strength seal welds.
If the 5/8" dia tubes are presently rolled 3" long in a 6" thick tubesheet without grooves and SSC has cracked through the tubes next to the seal welds, is there a case for expanding the 3" un-rolled section rather than re-welding the seal weld?
If the 5/8" dia tubes are presently rolled 3" long in a 6" thick tubesheet without grooves and SSC has cracked through the tubes next to the seal welds, is there a case for expanding the 3" un-rolled section rather than re-welding the seal weld?





RE: Expansion Versus Weld Repair
No. Roll expansion mechanically locks the tube into the tubesheet. Seal welding provides the leak tight boundary. If you attempt to roll expand the remaining three inches with no seal weld repair, you may have roll joint leaks over time.
During thermal cycling in service, the roll joint can relax resulting in tube roll joint leaks. The seal weld is necessary at high pressures and temperatures to ensure a leak tight joint. I am curious as to how stress corrosion cracking was determined. Are you sure it was not fatigue crack propagation? What is the tube material and service conditions?
RE: Expansion Versus Weld Repair
I was trying to "re-package" the problem statement to draw out more opinions, like yours.
If you could take a moment and read my problem description in the other thread, it should answer all of your questions.
I am convinced that re-rolling should eliminate the tubesheet/tube thermal gradient problem, making seal welding redundant.
RE: Expansion Versus Weld Repair
Patricia Lougheed
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RE: Expansion Versus Weld Repair
RE: Expansion Versus Weld Repair
Another option if you truly have SCC is to stress relieve the tube to tube sheet joint. I have done this on several occasions, including to prevent SCC of zirconium tubes.
RE: Expansion Versus Weld Repair
You posted both around the same time so I made the apparently erroneous assumption that they were related -- part of a bigger problem, if you will.
Patricia Lougheed
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RE: Expansion Versus Weld Repair
Sorry for the late reply, I didn't see your reference to the Nooter Corp study - I will look into that, thanks.
The annular gap may be filled with water, which would defeat uniform hydraulic expansion and cause ripples, unless it was incrementally applied in order to squeeze the water past the upper or lower rolled joints.
RE: Expansion Versus Weld Repair
RE: Expansion Versus Weld Repair
I suspect a final, incremental roll from top to bottom or vise-versa would be required to smooth out the 'squeeze path' or line of partially buckled tube where the water made it's escape. It has been suggested that the 5/8" OD x .0445" thick Inconel 800 tubes shouldn't be expanded more than 7% total (wall thickness reduction).