Which of the following flowmeter primaries can be used for custody-transfer applications?
A. Magnetic
B. Orifice plate
C. Positive displacement
D. Ultrasonic
E. Venturi tube
Commentary
All of these flowmeters can be used in some form of custody-transfer application. Magnetic flowmeters are often used for the custody transfer of clean water, sewage and wastewater. Orifice plate and positive displacement flowmeters are commonly used for the custody transfer of natural gas. Both can also be used for hydrocarbon liquids and water. Ultrasonic flowmeters have been developed for natural gas and liquid hydrocarbon custody-transfer applications. Venturi tubes are commonly used for the custody transfer of water. The correct answers are Answers A, B, C, D, and E.
Additional Complicating Factors
There are standards that describe the use of certain flowmeters for the custody transfer of certain fluids. These standards provide guidance and can have the effect of law in some jurisdictions, as local statutes often stipulate conformance with a certain standard. This is particularly prevalent when sales are made to the public such as the sale of gasoline, natural gas, and potable water.
Notwithstanding the above, it is my understanding that the custody transfer of fluids (in the USA) can be measured by a flowmeter that is agreed upon by both the buyer and seller. In these applications, the actual flowmeter may or may not be well-suited for its service. Needless to say, such flowmeters can cause problems if the buyer or seller questions its performance.
David W. Spitzer is a regular contributor to Flow Control with more than 35 years of experience in specifying, building, installing, startup, troubleshooting and teaching process control instrumentation. Mr. Spitzer has written over 10 books and 150 technical articles about instrumentation and process control, including the popular “Consumer Guide” series that compares flowmeters by supplier. Mr. Spitzer is a principal in Spitzer and Boyes LLC, offering engineering, expert witness, development, marketing, and distribution consulting for manufacturing and automation companies. He can be reached at 845 623-1830.
