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Title: The Effect Of Diameter Steps In Upstream Pipework On Orifice Plate Discharge Coefficients
Author: m J Reader-Harris And W C Brunton
Source: 2002 International Symposium on Fluid Flow Measurement
Year Published: 2002
Abstract: The present requirements for the diameter of pipework upstream of orifice plates are very restrictive. According to ISO 5167-1:19911 if there is to be no additional uncertainty there must be no diameter steps in pipework greater than 0.3 per cent at any point within the upstream pipework, till the first fitting is reached. The first fitting could be more than 100D from the orifice plate, where D is the pipe internal diameter. If the pipe size is small it may be necessary to machine the whole upstream length in order to meet this requirement. However, any requirement on steps which is the same at both 2D and 50D from the orifice plate is unlikely to be necessary at both locations. Moreover, it is important to know whether an existing orifice meter could be used in a different installation and what the pipework requirements are for a laboratory calibrating an orifice meter. Previous work has been undertaken by Zedan and Teyssandier2. They installed rings of width 12.7 mm (-inch) and of various internal diameters so that the downstream face of the rings was at a distance 2D upstream of an orifice plate of diameter 50.8 mm (2 inch). Large shifts in discharge coefficient were obtained, as might be expected with steps in pipe diameter so near to the orifice plate. The aim of the work presented here is to examine the effect of steps in pipe diameter at a distance from the orifice plate greater than or equal to 5D.

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