Screen Cut Point Determined by ASTM* Sieves
The API RP 13C cut point test is based on a time-proven testing method used by ASTM to classify particles by size. The procedure utilizes a series of standard-size screens (sieves), which have been used for such analysis since 1910. The API standards committee simply adapted the use of these sieves to designated shaker screens. The shaker screen designation is identified by matching the screen's cut point to the closest ASTM sieve cut point.
The cut point test uses aluminum oxide, a Rotap, a set of ASTM sieves, a test screen, and a digital scale for weighing the quantity of test particles retained by the test screen. The D100 cut point is used for assigning screen designations. D100 means that 100 percent of the particles larger than the test screen will be retained, and all finer particles will pass through. After conducting three Rotap tests, the results are averaged, and the screen is given an API number of the test sieve having the closest D100 cut point.
For example:
Using the table below (a section from Table 5 of API RP 13C, pages 40 and 41), the average of three Rotap tests = 114.88 microns. Therefore, the API designation = API 140
ASTM sieves mounted on a Rotap with the test screen in the center. Sieves used for this test range from 70 to 140. Cut point is determined by comparing the quantity of test particles trapped by the test screen with quantities in the ASTM sieves above and below the test screen.
* ASTM (American Society for Testing and Materials