Mass of Nitrogen Inside the Coil

You can, if you are willing, help yourself.

converting volume of nitrogen into mass

830cm³ is the volume of the pipe and of the nitrogen therein. However, I expect a higher pressurized (higher packed/denser) N₂ to weigh more than lower pressurized contained in the same volume pipe. Also the temperture, which the original post doesn't specify, is a factor.

0.391m³ of N2 weighs 0.454 Kg at 70°F and 1 atm. source

I suggest keeping the temperature and pressure constant, perharps based on operating conditions, then do the calculation.

the nitrogen prevents corrosion until the coil is ready to be in service. it also prevents air and moisture from entering the coil