Pressure measurement in gas piping
Pressure measurement in gas piping
(OP)
All,
Can anyone recommend a good source of information for designing/locating pressure taps in an existing gas piping system?
I am trying to locate a tap for pressure control purposes in a 12" gas line (MAOP = 800psig). Unfortunately there is not much straight length of pipe available in the area where measurement is required. Ideally I would be looking to install the tap with 10 straight upstream pipe diameters. I am trying to determine if the 5 ft of straight pipe available will provide reliable pressure readings, and if not, how inaccurate the readings will be.
Thanks.
Can anyone recommend a good source of information for designing/locating pressure taps in an existing gas piping system?
I am trying to locate a tap for pressure control purposes in a 12" gas line (MAOP = 800psig). Unfortunately there is not much straight length of pipe available in the area where measurement is required. Ideally I would be looking to install the tap with 10 straight upstream pipe diameters. I am trying to determine if the 5 ft of straight pipe available will provide reliable pressure readings, and if not, how inaccurate the readings will be.
Thanks.





RE: Pressure measurement in gas piping
RE: Pressure measurement in gas piping
The reason for the straight-pipe requirements in square-edged-orifice gas-measurement is the assumption in the equations that the flow is "fully developed" prior to going through a known restriction. If the flow is swirling (for example) then it will tend to corkscrew through the orifice and get a significantly reduced dP for a given mass flow rate.
Measuring pressure does not have the same requirements. In fact, I will always prefferentially take a pressure reading in a dead leg above a gas flow (this keeps condensation from accumulating in the instrument).
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
The Plural of "anecdote" is not "data"
RE: Pressure measurement in gas piping
The instrument should be above the tap in pressure, especially if the lfuid is condensible. (If the pressure is fairly high, perhaps about 500 psig, then the potential head impact for a measurement a few feet below the tap is not such an issue.) If you were measuring steam it would be different. Steam may exceed the rating of the instrument. We typically come off the side or lower connection or if from the top add a siphon accessory to trap condensate thus isolate the high temperature from the instrument.
As previously stated, the upstream diameter requirements apply to flow meters, especially head type flow meters.
John
RE: Pressure measurement in gas piping
m777182
RE: Pressure measurement in gas piping
RE: Pressure measurement in gas piping
John