Operators can help ensure accurate orifice measurement by following a basic calibration, inspection and maintenance schedule. Many measurement errors are caused by excessive pipe line deposit build-up, turbulence in the flow stream, and incorrect meter tube design. These errors can be eliminated by periodic inspection and cleaning. Having a fundamental operational understanding of the orifice meter's primary and secondary elements is key to a successful maintenance program. Primary elements such as the orifice plate must be regularly inspected for nicks and gouges; and the orifice plate holder must be checked for leaks, and to ensure that it is properly placed. The secondary element, whether a bellows meter, electronic flow computer or RTU, also must be regularly inspected and calibrated. In addition, operators must be familiar with the various types of differential pressure taps used with orifice meters, so that proper correction factors are used during calculation of gas volumes.
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