what are the main parts in hot tapping machine?

Answer 1

Currently in the Gulf of Mexico doing hurricane remediation work on oil wells, with 3 different industrial hot tap units on board.

Main parts:
1) Sealing surface, e.g. teflon or other compressible material, in order to contain the pressure of the pipe you're tapping
2) clamping mechanism, to hold the seal firmly against the pipe
3) sealing sleeve, to allow liquid or gas inside the pipe to pass back out to your return hose, but not along the drill shaft
4) drilling mechanism (bit + power source), with enough length to get past the sealing sleeve and any in-line valves
5) return hose, to contain any fluids coming back to your containment vessel.

Usually you'll have a valve on your return hose to contain the pressure if needed. Sometime you'll have a valve to isolate the drill from the sleeve once the bit is retracted. In the set-up we're using, we also pre-pressurize the sleeve to give us an indication that the tap is complete.