METERING

Going with the flow.

Although accuracy and repeatability are the perennial requirements in flow metering, there are other considerations too. Tank Storage magazine looked at the pros and cons of the different technologies that deliver the must haves.

Whichever side of the loading arm you stand - as buyer or seller - your money's on the line if the flow meter can't deliver a high degree of accuracy and repeat it time after time. Although all flow metering technologies used for custody transfer in the petroleum industry meet the required industry standards, some lay claim to greater accuracy or repeatability than others, and each has quite separate pros and cons that need to be considered. "It's fair to say that you get nothing for free, and so far no technology has emerged as clearly the best," asserts Peter Liptrot, at Daniel Measurement and Control, which produces metering equipment for high value custody transfer and fiscal duty applications, and has considerable expertise in the field of packaged flow measurement (skid) systems. Whether you opt for the traditional industry choices of turbine or positive displacement meters, or the newer technologies such as Coriolis or ultrasonic meters, depends on what you are trying to achieve, the limitations of your application, and how much money you have to spend, he explains.

The traditional turbine Turbine meters remain widely used in the petroleum industry for several reasons. "The advantages of traditional - or mechanical - flow meters stem from the simplicity of their designs and the fact that they offer a primary flow signal," says Liptrot. "The output signal is produced by (and therefore precisely proportional to) the movement of the measuring element, which almost always is a faithful reproduction of the actual flow rate."