In the flow

Whether it is for tracking upstream oil flow or monitoring rogue environmental emissions, accuracy is the watchword when it comes to selecting flow-metering equipment.

Because flow measurement is used for both gases and liquids, there is an abundance of different devices on the market – some highly specialised and others created for more general use.

Their common objective is to allow companies to monitor and record the most important flow data in their processes, with minimal day-to-day intervention.

Even so, there is no guarantee any device will escape so-called “installation effects,” says Craig Marshall, project engineer at NEL (formerly known as the National Engineering Laboratory).

“These are to do with the nature of fluid flowing through a pipe. Because the middle is a hollow cylinder, where the fluid meets the wall you have frictional forces,” says Marshall.

“A flow meter only stands a chance of living up to the manufacturer’s accuracy and uncertainty claims if it is installed correctly.”

The primary objectives for deploying a flow meter are to track fiscal transactions (for custody transfer in the energy or water industries, or for government taxation), environmental monitoring for regulatory purposes, or process optimisation and safety.

To satisfy each of these, there are four main categories of flow-meter devices, says Marshall.

At the top end are Class 1 devices offering the absolute accuracy required for custody transfer applications. Down at the lower end of the spectrum are class 4 devices for servicing less critical operations such as flare measurement for waste gas disposal.

But regardless of its ranking, any number of physical limitations can undermine device accuracy, says Marshall. This is especially so in areas where space is at a premium, such as an offshore oil or gas site.

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