ASTM D6426-22

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D6426 − 18 D6426 − 22
Standard Test Method for
Determining Filterability of Middle Distillate Fuel Oils
This standard is issued under the fixed designation D6426; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This test method covers a procedure for determining the filterability of distillate fuel oils within the viscosity range from
2 2
1.70 mm /s to 6.20 mm /s (cSt) at 40 °C.
NOTE 1—ASTM specification fuels falling within the scope of this test method are Specification D396 Grade No. 2, Specification D975 Grade No. 2-D,
and Specification D2880 Grade No. 2-GT.
NOTE 2—The test method has been used with lower viscosity middle distillate fuels such as Specification D396 Grade No. 1, Specification D975 Grade
No. 1-D, and Specification D2880 Grade No. 1-GT, but the precision has not been studied and therefore the stated precision has not been validated for
these grades.
1.2 This test method is not applicable to fuels that contain undissolved water.
1.3 The values stated in SI units are to be regarded as standard.
1.3.1 Non-SI units, specifically U.S. customary units such as temperature in degrees Fahrenheit and pressure in pounds per square
inch gauge (psig), are included for information.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D396 Specification for Fuel Oils
D975 Specification for Diesel Fuel
D2880 Specification for Gas Turbine Fuel Oils
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricantsand is the direct responsibility of Subcommittee
D02.14 on Stability, Cleanliness and Compatibility of Liquid Fuels.
Current edition approved Dec. 1, 2018Dec. 1, 2022. Published February 2019December 2022. Originally approved in 1999. Last previous edition approved in 20132018
as D6426 – 13.– 18. DOI: 10.1520/D6426-18.10.1520/D6426-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6426 − 22
D4176 Test Method for Free Water and Particulate Contamination in Distillate Fuels (Visual Inspection Procedures)
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
D4860 Test Method for Free Water and Particulate Contamination in Middle Distillate Fuels (Clear and Bright Numerical
Rating)
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in this test method, refer to Terminology D4175.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 filterability, n—a measure of the rapidity with which a standard filter medium is plugged by insoluble matter in fuel and may
be described as a function of pressure or volume:
3.2.2 filterability (by pressure), n—the pressure drop across a filter medium when 300 mL of fuel is passed at a rate of 20 mL ⁄min.
3.2.3 filterability (by volume), n—the volume of fuel passed when a pressure of 104 kPa (15 psig) is reached.
3.2.3.1 Discussion—
Filterability by volume is used when less than 300 mL passes at a pressure up to 104 kPa (15 psig).
3.2.4 filterability quality factor (F-QF), n—a value that defines the filter plugging tendency of a fuel caused by particulates.
3.2.4.1 Discussion—
The F-QF value is calculated using the volume and pressure attained at the end of the test cycle, according to one of two equations,
depending on the outcome of the test. (See Section 10, Calculations.)
4. Summary of Test Method
4.1 A sample is passed at a constant rate (20 mL ⁄min) through a standard porosity filter medium. The pressure drop across the filter
and the volume of filtrate are monitored. The test is concluded either when the pressure drop across the filter exceeds 104 kPa
(15 psig) or when 300 mL have passed through the filter.
4.2 Results are reported as either the volume that has passed through the filter when a pressure of 104 kPa (15 psig) has been
reached or the pressure drop when 300 mL have passed through the filter.
4.3 Verification of the apparatus is required when there is a doubt of a test result, or when the apparatus has not been used for three
months or more. It is not necessary to verify apparatus performance prior to each test.
5. Significance and Use
5.1 This test method is intended for use in the laboratory or field in evaluating distillate fuel cleanliness.
5.2 A change in filtration performance after storage, pretreatment, or commingling can be indicative of changes in fuel condition.
5.3 Relative filterability of fuels may vary depending on filter porosity and structure and may not always correlate with results
from this test method.
5.4 Causes of poor filterability in industrial/refinery filters include fuel degradation products, contaminants picked up during
storage or transfer, incompatibility of commingled fuels, or interaction of the fuel with the filter media. Any of these could correlate
with orifice or filter system plugging, or both.
D6426 − 22
NOTE 1—Fuel flow from reservoir, through pump, to container.
FIG. 1 Schematic Diagram of Filterability Apparatus
6. Apparatus
6.1 Micro-Filter Analyzer:
NOTE 3—The Micro-Filter can display the pressure in either kPa or psig units by changing an internal jumper wire.
6.1.1 The apparatus is shown diagrammatically in Fig. 1 and photographically in Fig. 2. It is capable of measuring pressure
upstream of the filtering element and the volume of sample passed through the filter at a preset pressure level. The apparatus is
comprised of the following parts:
6.1.1.1 Peristaltic Pump, variable speed/flow rate, with feedback speed control, adjusted to provide fuel delivery at a constant rate
of 20 mL ⁄min 6 1 mL ⁄min, and incorporating a pulse dampening mechanism to produce a smooth flow.
6.1.1.2 Pressure Transducer—Pressure transducer capable of measuring gauge pressure in the range from 0 kPa to 104 kPa, in
1.0 kPa increments (0 psig to 15 psig, in 0.1 psig increments).
6.1.1.3 Three Digital Displays—One for pressure readout capable of interfacing with transducer (see 6.1.1.2) with display range
from 0 kPa to 104 kPa in 1.0 kPa increments (0 psig to 15 psig in 0.1 psig increments), one for volume readout with display range
from 0 mL to 300 mL in 1 mL increments, and one for F-QF.
6.1.1.4 Fuel Reservoir Container—PTFE-fluorocarbon, funnel shaped, 500 mL capacity.
6.1.1.5 Collection Container—Glass or plastic Erlenmeyer flask, 500 mL capacity.
6.1.1.6 Tygon Tubing, fuel compatible, 3.1 mm (0.12 in.) inner diameter.
6.1.1.7 Plastic In-line Splice Coupler, fuel compatible, capable of being inserted into, and making a seal in Tygon tubing (see
6.1.1.6).
6.1.1.8 Plastic Tee Coupler, fuel compatible, capable of being inserted into, and making a seal in Tygon tubing (see 6.1.1.6).
6.1.1.9 Plastic Luer-Loc Coupler, fuel compatible, one end capable of being inserted into, and making a seal in Tygon tubing (see
6.1.1.6) and the other end into filter unit (see 6.2).
The sole source of supply of the apparatus (Model 1143 Micro-Filter Analyzer) known to the committee at this time is available from EMCEE Electronics, Inc., 520
Cypress Ave., Venice, FL 34292. If you are aware of alternate suppliers, please provide this information to ASTM International Headquarters. Your comments will receive
careful consideration at a meeting of the responsible technical committee, which you may attend.
Tygon tubing was used in the round robin test program to generate the precision and bias. Tygon is available from most laboratory supply houses.
D6426 − 22
FIG. 2 Micro-Filter Analyzer
6.2 FCell (trademarked) Filter Unit—Disposable, precalibrated assembly consisting of a shell and plug containing a 25 mm
diameter nylon membrane filter of nominal 5.0 μm pore size, nominal 60 % porosity, with a 158.9 mm effective filtering area. It
is labeled in a white background with black lettering:
D6426, DIESEL (5.0), FCell®
6.3 Accessories for Apparatus Verification Test:
6.3.1 Measuring Cylinder, 500 mL capacity, with 1 mL graduations.
6.3.2 Pressure Gauge, 350 kPa (50 psig) capability, graduations 0.5 kPa (0.1 psig).
6.3.3 Temperature Measuring Device, having a range of 0 °C to 60 °C and accurate to 0.5 °C. Temperature measuring devices that
cover the temperature range of interest, such as liquid-in-glass thermometers, thermocouples, or platinum resistance thermometers
that provide equivalent or better accuracy and precision may be used.
7. Sampling
7.1 The fuel sample from which an aliquot is being drawn for the purposes of this test shall be representative of the lot of fuel.
Obtain the sample in accordance with the procedures of Practice D4057 or D4177, and report (see 11.1.1) how and from where
it was obtained. The maximum sample size is dictated by the quantity that can be mixed thoroughly (see 9.3).
7.2 If any undissolved water is visually apparent (as determined by Test Method D4176 or D4860, or both), discard and replace
with a fresh sample.
7.3 After thoroughly mixing, if the sample container such as a drum is too large to readily handle, use an epoxy-lined can or dark
glass bottle as a transfer container to store an aliquot of the test sample. Prior to drawing the aliquot, rinse the transfer container
three times with the product to be tested. Draw a representative 1 L to 2 L aliquot from the sample container into a transfer
container. (Warning—Because the situations under which samples are taken vary from laboratory to laboratory and from situation
to situation, no firm recommendation for sampling can be given. It is the responsibility of the user of this test method to ensure
the aliquot used in the test is representative of the lot of fuel.)
8. Preparation of Apparatus
8.1 Locate the apparatus on a level surface in an area where the temperature is between 15 °C and 25 °C (59 °F and 77 °F).
A registered trademark of EMCEE Electronics, Inc., 520 Cypress Ave., Venice, FL 34285.
D6426 − 22
FIG. 3 Threading the Tubing in the Pump
8.2 Open the case, and assemble the apparatus as shown in Fig. 2. If the Tygon tubing (see 6.1.1.6) is not attached as shown, carry
out 8.2.1 to 8.2.2.
8.2.1 Attach one end of the Tygon tubing to the fuel reservoir container (6.1.1.4) and insert the plastic in-line splice coupler
(6.1.1.7) into the other end.
8.2.2 Insert the plastic in-line coupler into another piece of Tygon tubing, thread the tubing in the peristaltic pump (see 6.1.1.1),
as shown in Fig. 3, and clamp it in place by moving the lever arm counterclockwise.
NOTE 4—The splice fitting prevents the tubing from being pulled into the pump during operation. This also allows easy replacement of the portion of
the tubing that is depressed by the pump rollers. To extend the life of the Tygon tubing, when not in use, leave the clamp open or remove the tubing from
the pump.
8.2.3 Insert one end of the horizontal section of the plastic tee coupler (6.1.1.8) into the tubing that is clamped in th
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