Sizing a pipe for a piece of equipment

[TG0626]

Hello,

My facility is putting in a new piece of equipment, and I need to determine the size of the service line to it. I know the heater input rating, and thus know the CFH the equipment will use. I have seen tables that show the maximum capacity (in CFH) of gas pipe for various diameters and lengths of pipe. However, a lot of these tables note that the capacity is at low gas pressures - 0.5psig or less. Do these pipe capacities change when the system operates at a higher pressure?

I'm a bit lost on what other information I need to make this decision.

Thank you

 

[1503-44]

Yes, higher pressure increases flow capacity, roughly by CFH2 = CFH1 / P1 X P2
Pressures are absolute pressures.
Doubling the pressure, P1=30 to P2 = 60psia, tends to double the flow.
100 CFH at 30 psia becomes 100/30 x 60psia = 200 CFH

But there will also be double the friction due to the increased gas density, so capacities may not be doubled if pipe lengths are long and you cannot increase pressure drop too, but basically that's what you can expect over short distances.

You must know the flow you want and the length of pipe and have some idea of the maximum and minimum equipment operating pressure.

 

[PEDARRIN2]

Since you stated "heating equipment" I would assume your requirements are in inches water column or maybe 2-5 psig or less.

In general you need.

1. All equipment loads in CFH/BTUH on the pipe system you are adding equipment.
2. Total length of pipe and diameters from upstream regulator. This should also include equivalent lengths for all fittings and valves.
3. Pressure at the discharge of the regulator.
4. Min/Max pressure of the equipment being added.

The tables in the IFGC allow you to size the piping system. Since you have an existing system, you will need to determine if adding the new piping will require increasing pipe sizes upstream of the new equipment. You find the table with the system pressure (or as close to it as you can - but never lower pressure) and use the row with your total length. Each column in the table is the maximum CFH allowed for that pipe size. You use this to size the pipe to your new equipment.

This method is conservative as it assumes all equipment operating simultaneously, but it typically also accounts for increased pipe roughness due to age of pipe and miscellaneous other things that are typically missed.