My experience with NPT fittings has taught me that the torque required varies with the material, the diameter & the quality of the threads.
I have seen PVC joints fail after several months in service
from being assembled too tight. After time the female fitting split. I have never seen bronze fittings split after assembly, even when very tight, unless water
froze inside of them.
Naturally, a 2" NPT fitting will need a lot more torque than a 1/4" NPT fitting.
There are different flavors of NPT. There is standard NPT, NPT level seal, NPT rail, etc. If you try to mate two different versions, you will have difficulties.
If you are using name brand bronze fittings in standard NPT, then I would start at around 25 foot pounds for a 1" fitting & check for leaks
. If leaks are present, then I'd go a little tighter until things seal up. If you get much past 50 foot pounds & still have trouble, then maybe your dope wasn't very good or else your thread quality was poor.
I have generally had good luck with plain white Teflon tape. I have also had good luck with non-hardening paste type pipe-dope from Permaseal. I know some people who recommend using both tape & paste at the same time, but I haven't tried that myself. When wrapping the tape, be sure to wrap it on the male in the same direction that the female will screw onto it. I start wrapping at the large end of the male & then work towards the small end when using tape that is more narrow than the thread width.
With good quality brass NPT fittings & white Teflon tape, I have been able to get good seals
on every gas I have tried that had a molecule larger than Helium. I don't have experience piping fuel