API RP13C table.

API RP 13C[1] is a new physical testing and labeling procedure for shaker screens. To be API RP 13C compliant, a screen must be tested and labeled in accordance with the new recommended practice. Internationally, API RP 13C will become ISO 13501[2]. The greatest value of the new numbering system is that ALL conforming screens are measured using the same process which will allow cross-comparison of screen designs/types based on a uniform solids size removal value.

The new number describes the size at which particles will be rejected (removed) under laboratory test conditions. ALL screens which are tested according to RP13C and have the same API Screen Number will remove solids of a similar size. However, the new API number is NOT intended to describe how the screen (or indeed the shaker) will operate in the field. This will depend upon several other parameters such as fluid type & properties, shaker design, operating parameters, ROP, bit type, etc.

Any manufacturer labeling their screens as “conforming to API RP 13C” must supply the test data for that screen upon request to the end user/purchaser.



Mesh, as it relates to a piece of woven wirecloth[3], is a measure of the number of holes in a linear inch (such as 100 mesh) or in a linear inch in each direction (such as 100 x 60 mesh).

D50 Cut Point

The D50 cut point of a screen is the particle size at which half of those particles reporting to the screen will pass through the screen and half will be retained.

D100 Cut Point

The D100 cut point of a screen is the particle size at which no particles will pass through the screen.

API Screen Number

The API Screen Number is determined using a specific test procedure (as set out in API RP 13C). The test uses a specifically graded sample of Aluminum Oxide which is passed through a stack of sieves – including the test sieve – and mounted on a Tyler Ro-Tap®. The method determines the D100 cut point of the test screen and relates it to the D100 of an ‘equivalent’ standard ASTM test sieve.

Screen Conductance Conductance, measured in kilodarcies per millimeter (kD/mm), defines a Newtonian fluid’s ability to flow through a unit area of screen in a laminar flow regime under prescribed test conditions. All other factors being equal the screen with the higher conductance number should process more flow.

Non-Blanked Area

The non-blanked area of a screen describes the net unblocked area in square feet (ft²) or square meters (m²)available to permit the passage of fluid.


The use of the term “mesh” (when considering the capabilities of shaker screens) was made obsolete by the introduction of oblong mesh and multi-layer screens which resulted in variations in ‘aperture sizes’. Rig-based personnel continued to rely on the ‘mesh number’ indicated by the manufacturer. This may have borne little relationship to the actual separation potential of the screen being used. Hence, comparison of screens from different manufacturers (or even across one manufacturer’s series) could be difficult or inaccurate. The following photomicrographs (60x) show four different screens from four different manufacturers.

Comparison between ‘Non-Standard’ Screen Nomenclature and Standard API Labeling.

The lack of commonly accepted screen labeling procedures and great disparity in screen designations throughout the oil and gas drilling industry led to the development of API RP 13C. The new procedure is a revision of the previous API RP 13E, which was based on optical measurements of the screen opening using a microscope and computer analysis. Under API RP 13E, screen designations were based on individual manufacturer test methods, producing inconsistent labeling.

Following a review of labeling practices under API RP 13E, the API standards committee concluded that physical testing would be preferred for screen designations. API RP 13C was then developed as an objective method of describing shaker screens. Two tests were devised: cut point and conductance.

API Screen Number Determination

API RP 13C recommended cut point test

The D100 cut point, the absolute separation potential of a screen, is used for assigning screen designations. 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 designating 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. A representative section of the screen is mounted in a holder and is placed in the middle of a stack of ASTM test sieves (calibrated according to ASTM E-11[4]). Using a Ro-Tap® a defined amount of dry Aluminum Oxide is sieved and the results collated and graphed. The test is repeated three times and the results from each test are then averaged to determine the D100 cut point and the screen is given an API number of the test sieve having the closest D100 cut point.

For example, if the measured D100 cut point of the test screen is 114.88 microns (114.88μ), the table indicates that it compares to the ASTM 140 sieve. The test screen would then be classified as an API 140 screen. Important Note: RP13C states that this test describes the openings of the screen and does not predict the performance of the screen in the field. However, if all other variables are equal, a screen with a higher API Screen Number (smaller holes) should remove more and finer solids.

The change from RP13E to RP13C is a positive step because the new procedure moves away from measuring openings in the screen to an actual physical test using real solids. One further advantage of RP13C is that any screen with any aperture shape can be tested using the same procedures.

Conductance Test

Conductance Test Setup.jpg

Conductance is a measure of the ability of a fluid to pass through a screen. This property is determined by flowing 5W30 motor oil through a screen sample and then applying the pressure differential to a formula to calculate the conductance. Motor oil was selected because it oil-wets the screen and has a high viscosity. A large volume of motor oil is needed to allow equilibrium and to prevent large temperature changes.

Rig Site Performance

RP13C does not predict rig site performance given the myriad combinations of screens, shakers, fluids, flow-rates, solids loadings, etc. Performance will depend upon various factors including the properties of the fluid, the operational parameters of the shaker and the particle size distribution of the drilled solids presented to the screens.

Required Screen Label Information

API RP13C labeling example.jpg

RP13C states that the designation system (labeling) will consist of no fewer than the following minimum elements:

  1. API Screen Designation or API number (this must be 2X larger than any other information);
  2. D100 (Equivalent Aperture) in microns (μ);
  3. Conductance in kilodarcies per millimeter (kD/mm);
  4. Non-blanked screen area in square meters (m2) or square feet (ft2);
  5. Manufacturer’s Designation and/or Part Number (although not currently required to conform to API 13C, API recommends manufacturers use the API screen designation in the part number)
  6. Conforms to API 13C

The following information is optional (but recommended):

  1. Manufacturer’s name
  2. Application or description
  3. Country of origin
  4. Lot number
  5. Date of manufacture
  6. Order number
  7. Bar code

The label/tag must be permanently attached to the screen in a visible place.

Label Interpretation and Application

Because screens that conform to RP13C have all been tested using the same procedure, the labels are very helpful when it comes to comparing different screens. For example, if it is determined that there is a need for the cut point provided by an API 170 screen then a screen labeled API 170 can be selected regardless of the manufacturer of the screen.

All other factors being equal the screen with the higher conductance number should process more flow. Alternatively, if there is excess shaker capacity but longer screen life is desired, selecting a screen with larger diameter wires and perhaps more bonding material should provide increased screen life. Using screens conforming to RP13C can help the operator can make a more informed decision.

FAQs Regarding RP13C

  1. What is the D100?
    • The D100 cut point of a screen is the particle size at which no particles will pass through the screen.
    • D100 is a single number determined from a prescribed laboratory procedure – the results of the procedure should yield the same value for any given screen.
    • The D100 should not be compared in any way to the D50 value used in RP13E.
    • The method used in RP13C provides only the D100 value with no provision for D16, D50, or D84values.
  2. What does the API Screen Number tell us?
    • The API Screen Number corresponds to the API defined range of sizes into which the D100 value falls.
  3. What does the API Screen Number NOT tell us?
    • The API Screen Number is a single number which defines solids separation potential under specific test conditions. It does NOT define how a screen will operate on a shaker in the field as this will depend upon several other parameters such as fluid type & properties, shaker design, operating parameters, ROP, bit type, etc.
  4. Will a screen with a D100 of 172μ remove solids finer than 172μ?
    • By definition, every particle of the D100 size or coarser will be discarded.
    • In practice some portion of solids finer than 172μ may be removed.
  5. Why is there such a large variance between the old and new labeling values?
    • The biggest variation is due to the shift from using D50 to D100.
    • The previous test procedure (RP13E) measured the distribution of the apertures in the screen. RP13C uses a physical and repeatable test using actual solids (dry aluminum oxide) which measures the coarsest particle that can pass through the screen.
  6. Should I use the old screen number or the new API Screen Number when ordering replacement screens?
    • Although some companies are changing their part numbers to reflect their conformance to RP13C, others are not. It is therefore best to specify the RP13C value you want.
  7. Should I screen with a finer screen now if what used to be called a ‘200 mesh’ screen is now labeled API 120?
    • Users are advised to determine the screens that work best in their applications regardless of what the new API Screen Number happens to be.
  8. What is the practical value of RP13C to the end user?
    • RP13C provides an unequivocal procedure and benchmark for comparing different screens.
    • The primary intent of RP13C is to provide a standard measuring system for screens