Measuring the maximum pore size of sand screens – choosing the most statistically robust parameter

G. Rideal*, K. Brocklehurst, Whitehouse Scientific Ltd, UK

Bubble Point is often used to measure the largest opening in a filter medium, but it can give variable results, partly because the area of the sample required is infinitesimally small compared to the area of mesh on a roll, and partly because of the uncertainty of converting bubble point to a maximum pore size/Maximum Penetrating Particle (MPP).

Fig 1. For irregular challenge particles, different measurement techniques give different pore size results


An alternative method is Challenge Testing, where particles are presented to the filter and those passing measured. Here again shape is an important factor in aligning an irregular particle shape to an irregular shaped pore, as different measuring techniques will give different pore sizes, figure 1.

Ideally, spherical glass beads should be used in Challenge Testing in order to accurately measure the Geometric Pore Size although, because they are produced from a melt process, they are not always totally spherical and any misshapes will have a profound effect on the Maximum Penetrating Particle (MPP).


The PoreSizerTM Image analyser in conjunction with a glass bead Challenge Test has been used because of its ability to electronically remove any non-spherical beads and thereby reduce the measurement uncertainty.


This work examined several sand screens and measured over 140,000 spherical beads passing through 6 specimens of the same mesh in search of the MPP. The variation between the samples was up to 45%, making comparisons impossible. However, when specifying the ‘maximum’ aperture as d99.5 rather than the absolute maximum (d100), the uncertainty dropped to below 7.5% and in one case, to below 2% making it a much more reliable parameter than the MPP for comparing meshes....

Session: F1 - Filter Media - Quality Control and Pore Size Analysis I
Day: 13 March 2018
Time: 13:00 - 14:15 h

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