TiHabanero

Working on replacing the top tube on a bike, and am trying to salvage the tube to use on another project. In the past I have not had to preserve the tube as it was damaged anyway, so I cut the tube and was able to pull it out as the joint came to temp. This time I need to keep the tube in tact. Any guidance on this? Can it even be done?

Cynikal 

Assuming that the frame is lugged, I doubt you could without cutting the rest of the frame up.

TiHabanero

Cynikal, yes, the frame is lugged. Forgot that little detail!

unterhausen

are you salvaging anything else?

Andrew R Stewart 

Consider cutting through the HT just below the upper lug. Then heat and pull the TT from the ST lug.

This is not what I would want to do though as pulling a tube from a lug is ripe for a few problems that make the repairs get more involved or less nice looking. (metal likes to do weird things when it gets to filler melting temps. Lug tips break off, tubes tear, the heat level is hard to maintain evenly so usually there's a way too hot area and almost but not quite to temp area).

For the cost of a new TT I would suggest not saving the old one. Andy

unterhausen

steel gets really weak at temperatures well below the melting point of fillers. I was a bit surprised at that, The conclusion I draw from this is you don't want to put much force on a tube when removing it from a lug.
When I removed the bb shell from a frame recently, I was pretty careful to not push on the tubing very hard. And I cut everything up except the tubing I was saving. I think you need a lot of heat to do this, as in multiple torches or firebricks and a gas burner.

There used to be some pages on a repair done by Yellow Jersey in Madison Wi. I would go look for that.

JohnDThompson 

…and make sure the joints are not pinned before trying to pull them apart!