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Orifice Plate Installation Factors

September 26, 2010
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David W. Spitzer
Orifice plates are often viewed as simple devices. Which of the following should be addressed during installation?

A. Center the orifice plate in the pipe.
B. Remove burrs from the weld at the orifice flange.
C. Make sure the pipe is round upstream and downstream of the orifice plate.
D. Measure the inside diameter of the pipe.
E. Make sure the inside diameter of the gaskets is the same as the inside diameter of the pipe.

Commentary
Examination of the standards for orifice plate installation may lead one to believe that the orifice plate is more than just a simple metal plate (with a hole) that is sandwiched between two flanges. Further, the wetted part of the flow measurement system is more than just the orifice plate itself – it includes the geometry of the upstream straight run, orifice plate assembly, and downstream straight run.

Simply put, all of the answers contain items that can affect the geometry of the flowmeter system and therefore affect the flow measurement. The extent to which each item affects the flow measurement may be different, but standards and practices either state or imply that all of these items should be addressed during installation.

Additional Complicating Factors
Often the orifice plate, flanges and piping have already been installed before you can check these items. I was recently asked to analyze the installation and operation of some 800 PSIG steam flowmeters that were in service for over 50 years. In this case, I was limited in my options and had to “accept” the installation noting that no access was available.

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.

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