Hi good morning

We have orifice plate in natural gas line where flow is in 557 kg/hr in orifice date sheet supplied by vendor. Our dp transmitter flow reading presently showing 367. What will be unit of flow? We know orifice give volumetic flow.

 

Sanjib,

An orifice does not give direct volume flow or mass flow, unless the P&T is exactly as in orifice calculation, if the actual density same it will impact by half in both volume and mass.

You will need a compensation for both P&T to get correct measurement.

 

Your datasheet should state the minimum, nominal and maximum design mass flow (since the units are kg/hr) at the design pressure, temperature, gas composition and associated differential pressures. If your current reading is 367, you should be utilizing the same units. However, much more information is required in order to verify your flow calculation.

Regarding your last statement, an orifice plate provides a differential pressure signal from which you can calculate volumetric flow. When dealing with natural gas, AGA-3 is often followed, which requires density and expansion factor inputs for mass flow.

 

Is it possible that your DP transmitter is really a multivariable transmitter that knows the static working line pressure and has a temperature sensor wired to it so that it calculates inferred mass flow?

 

How we get P&T calculation for accurate reading in orifice plate.