Developments In Diagnostic Capabilities Of DP Meters

By Kim Lewis and Jennifer Rabone | February 2012, Vol. 239 No. 2

Figure 1: A 4-inch, 0.6 beta ratio dual chamber orifice meter test at CEESI.

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Differential Pressure (DP) flow meters have been widely used since Herschel first developed the Venturi meter in the 1880s. The orifice plate meter, possibly the most popular flow meter ever, is a derivative of the Venturi meter. Weymouth introduced the orifice meter a century ago.

There are also other successful DP meter designs developed from the original Herschel Venturi meter concept such as nozzle, Venturi nozzle, cone and wedge DP meters.

DP meter designs are widely considered simple, sturdy and therefore reliable. They are also usually relatively inexpensive flow meters. These traits have led to DP meters being one of the most widely used flow meters in the oil and gas industry. However, in recent years with the value of hydrocarbon product increasing, with more hydrocarbon assets owned by multiple parties, and with an increase in safety requirements, the need for precise flow metering throughout the production system has become more pressing. The industry has been increasing its demand for meters that have diagnostics internal to the meter system.

Figure 1 shows a 4-inch, 0.6 beta ratio dual chamber orifice meter at the CEESI wet gas flow test facility. Due to the DP meter’s simplicity it has long been held as an axiom that DP meters cannot have any diagnostic system. Traditionally, all DP meters operate by having an obstruction (primary element) in the pipe that changes the local pressure as the fluid passes the obstruction. For example, in Figure 1, the orifice plate is the primary element. Measuring the difference in pressure between upstream and in the vicinity of this obstruction gives the “differential pressure” or “DP”. This DP can be related to the flow rate through simple physical laws.

Due to the simplicity of this method of flow measurement, it was long assumed that a DP meter can have no significant diagnostics capabilities, as there apparently wasn’t enough information from the meter to work with. As such, in the last two decades other meter designs with various levels of internal diagnostics have taken significant market share. However, in 2009 the axiom that DP meters can have no diagnostics was challenged. DP Diagnostics released details of the successful development of a comprehensive diagnostic system internal to any DP meter system, e.g. orifice, Venturi, nozzle and cone meters.

In 2008 and 2009 DP Diagnostics carried out a substantial test program to research and develop the first ever diagnostic system for DP meters. These tests were supported by Colorado Engineering Experiment Station Inc. (CEESI). Every major CEESI flow test facility was utilized. CEESI even offered existing non-confidential DP meter data sets that could be of extra help in the diagnostic system development.

In 2009 this comprehensive DP meter diagnostic concept was revealed to the industry. By 2010 DP Diagnostics (a DP meter manufacturer) and Swinton Technology (a leading UK system integrator) had partnered to produce a DP meter diagnostic system. The initial disbelief through out the oil and gas industry was followed by questions of “just how does it work!?”

Figure 2: A single chamber orifice plate diagnostic ready meter.