Fuselage tube replacement technique

For the welders out there.
When you replace a tube in a fuselage, what is your technique? For example, once you've cut the old tube out, do you grind the old weld off down to the original tube profile or do you leave some of the old weld in place to be sure you haven't ground into the longeron? What about replacing a tube in the middle of a cluster? Once the new tube is in place and welded, do you add a finger patch. AC 43.13 has lots of great info on repairing tubes but not a lot on replacing them.

Thanks
Marc

Carefully get rid of it completely if it's bad enough. But beware of cutting something out that's critical for fuselage alignment.
Otherwise you may be able to splice it.

don't get to fancy and grind original tube, get most of weld... over grinding worse than under.....

It was more of an issue gas welding with old partial/weld penetration... but if Tig welding, some old weld is no problem.. what they really were truing to avoid is someone welding over say a crack in a gear fitting and really just adding a layer of weld on top of the crack.... with old crack still in there...

no finger patch....

(longeron on replacement technique) using a cutoff wheel in a die grinder, lob off old tube at each end of cluster, cut outer part of tube to replace off, then grind from inside to remove rest of old tube.... put new tube in and weld per original....

don't let things get all misaligned when doing this.... it may move.....

Mike has got it right--as per usual. I might finger strap a dented longeron at a cluster as per 43.13. But not necessary if replacing a section. Remember to mitre tubes at 30* and install liner tubes with rosette welds at both ends of the tube, again as per 43.13

Mike has got it right--as per usual. I might finger strap a dented longeron at a cluster as per 43.13. But not necessary if replacing a section. Remember to mitre tubes at 30* and install liner tubes with rosette welds at both ends of the tube, again as per 43.13