DP Flow - ISO 5167 Venturi Tubes (Part 4)

Monday, June 3, 2019 | Steve Clark
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Part 4 of ISO 5167 covers three different manufacturing methods of classical Venturi tubes; as-cast, machined and fabricated.

The general shape, Venturi profile, surface finish and bore requirements of Venturi for each of the three manufacturing methods are described in detail. The differential pressure tapping size and location are detailed as well as the quality of tapping hole required to produce a reliable measurement.

The limitations of Venturi are listed along with corresponding uncertainty expectations for uncalibrated devices with equations to predict permanent pressure loss. Venturi tubes are well known as low permanent pressure loss devices. Flow through the measurement section is assumed to remain subsonic in all cases.

An extensive section is dedicated to the installation requirements of Venturi with detailed information on the upstream and downstream straight lengths required for differing inlet piping configurations all of which have been generated from empirical data.

Annexes to the main body of the standard give useful information on the use of venturi outside of the standard and the effect of surface roughness, Reynolds Number, divergent angle and truncation of a Venturi on the permanent pressure loss.

The Venturi tube has been established as a single-phase device for hundreds of years, but recently (since the early 1990’s) has also been adopted by a number of wet gas and multiphase meter manufacturers as a core element in their designs due to excellent robust and repeatable characteristics. Special consideration should be given when using single phase meters on multiphase applications. At Solartron ISA, we have been adapting the classical venturi design in our Dualstream wet gas and Seastream subsea meters for over 30 years.

Solartron ISA have been active participants for over 15 years in the ISO/TC 30/SC2 technical committee assigned to ISO 5167. The standard is due for ISO systematic review in 2019.