VAWELDER,
I don't know that there is any easier way than cutting your way in and welding your way out. But with regard to identifying the leaking tube we have a tool for just this task. It essentially perform a hydro on individual tube joints by sealing in side the tube and crushing a seal...
roniprabowo,
You may want to consider Hydraulic Expansion. This process utilizes direct water pressure inside the tube and produces minimal wall reduction. Expansion pressure is calculated off of the yields and tensiles of the materials involved the tube & tubesheet. It also does not cold work...
