How can I seal the fittings, in connection of Pressure Transmitter, on a HIGH PRESSURE gasoil line?
The pressure is around 200 bar.
Is it enough to use Teflon (PTFE) Tape?

 

Consider using the Swagelok SWAK Anaerobic Thread Sealant or similar from Loctite or other manufacturers.

This sealant is rated by the manufacturer for 689 bar and will lubricate as well.

Do not rely on tape for sealing high pressure services. The tape is primarily a lubricant to tighten up the the threads.

Hope this helps.