Hi. I am currently doing my internship in the oil and gas industry (contractor) as process engineer. My supervisor give me a task to do some reverse engineering where i need to study how a spreadsheet (calculation) construct by other process engineer was been constructed. Ok the situation is the natural gas source is coming from NPS 18 and flow through NPS 8 and i need to calculate the mass and volumetric flow rate of the natural gas in the NPS 8 pipeline. The problem is i don't know the formula to calculate mass and volumetric flow rate as it involves gas phase and what i found on internet is the formula to calculate in liquid phases. Can someone help me ?