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Title: Large Capacity Gas Orifice Measurement Skid
Author: Steve Baldwin, Trilochan Gupta
Source: 2007 South East Asia Flow Measurement Conference
Year Published: 2007
Abstract: Natural Gas volumes passing through an orifice meter are commonly calculated following the standards dictated in API Manual of Petroleum Measurement Standards (MPMS) Chapter 14.3. The standard has specific installation requirements for many piping configurations. For the use of high performance flow conditioning devices, the standard allows these to be used as long as the manufacturer has data to show that their devices comply with the performance criterion of the standard. The configuration of the metering skid is such that upstream and downstream of the meter tubes, there are 4 elbows out-of-plane including splitting the flow to the meters by a header that seemed to be under-sized. API MPMS 14.3. Part 2 Appendix 2-D defines minimum upstream length for orifice meter with pipefitting of two 90 degree elbows out-of plane. There is no test data for 4 elbows out-of-plane and restrictive headers upstream of the orifice fittings. The combination of undersized headers and no public domain test data lead to the need of flow calibrating the whole metering skid. Therefore, it was likely that the combined measurement uncertainty of the complete system, including the secondary instrumentation could not possibly achieve the uncertainty limits of 1% In order to achieve the measurement uncertainty of less than or equal to 1%, the options defined in API 14.3 Part 2 Appendix 2 C and 2 D would have to be followed. The standard requires, if possible, the designed flow metering system with all upstream and downstream piping configurations be flow calibrated preferably at operating conditions to achieve improved measurement accuracy. A test matrix was developed that would allow the metering skid to be sufficiently calibrated to meet the intent of the standard. This test matrix and the testing results will be presented showing the difference in volumetric calculation using the standard API MPMS RHG equation and the actual volume.

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