fluid cleanliness counting procedure mar 2010

5/19/2018 Fluid Cleanliness Counting Procedure Mar 2010

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Fluid Cleanliness: Counting ProcedureIssue No. 2Date: March 2010Page 1 of 11

Fluid CleanlinessSAE ARP598 Determination of Particulate Contamination

in Liquids by the Particle Count Method

SAE AS4059 / NAS 1638 Cleanliness Classification forHydraulic Fluids

Some companies may wish to carry out particle counting in-house, or to submit samples to alocal laboratory for particle counting. This section lays down details of the particle countingprocedure approved by MacDermid Offshore Solutions, for use with Oceanic HW subseaproduction control fluids. The method is based on Aerospace Recommended Practice (ARP)598B, for the determination of particulate contamination in liquids by the particle count method.

It is recognised by MacDermid Offshore Solutions that the oilfield industry has in recent yearsbegun to use a variety of automatic particle analysers for carrying out particle counting.MacDermid Offshore Solutions have examined several of these methods and the specific piecesof equipment involved in considerable detail, and have reservations about the accuracy andreproducibility of the results that they produce. It is the opinion of MacDermid Offshore Solutionsthat these methods and instruments are largely intended for use with particulate matter of veryregular profiles, and that the interpretation of signals generated with irregular particles such asare encountered in hydraulic systems can lead to inaccurate and misleading results. In addition,it has been observed that the physical nature of Oceanic HW and other water based fluids cangive false readings.

On-site tests using particle counts obtained from automatic particle counting instruments have

revealed differences in particle counts of several orders of magnitude when compared withphysical microscope counts carried out using ARP 598B. The microscope count is regarded asthe most accurate method, as it relies on visual detection of particles, rather than electronicinterpretation of signals. MacDermid Offshore Solutions would only advocate the use of particlecounting by automatic particle counting instruments where this was being used as an indicationof contamination levels and not for certification of equipment to NAS1638 standards. Suchinstruments could be used, however, where calibration of the instrument had been carried out onthe control fluid under investigation and results verified using a microscope counting technique.

The "Conpar" comparative test method is also often used for establishing levels of particulatecontamination. This method uses comparison of standard slides to obtain an estimate of thelevel of particulate contamination present in a fluid sample. This method may be used as an

indication of the level of contamination, but it should be noted that this is not a particle countingtechnique, and only infers the number of particles present in each size band. In the opinion ofMacDermid Offshore Solutions, therefore, the Conpar method could not be used to certifyequipment as it does not meet the criteria for counting of particles as laid down in NationalAerospace Standard (NAS) 1638 or AS4059.

The following sections show the requirements of NAS1638, AS4059 and the particle countingmethod recommended by MacDermid Offshore Solutions and based on ARP 598B.


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National Aerospace Standard (NAS) 1638

Hydraulic System Cleanliness Requirements

Maximum Contaminant Limits (per 100ml)

Size Maximum Contamination Limits

Optical Count 5-15 m 15-25m 25-50m 50-100m > 100m

Class

00 125 22 4 1 0

0 250 44 8 2 0

1 500 89 16 3 1

2 1000 178 32 6 1

3 2000 356 63 11 2

4 4000 712 126 22 4

5 8000 1425 253 45 8

6 16000 2850 506 90 16

7 32000 5700 1012 180 328 64000 11400 2025 360 64

9 128000 22800 4050 720 128

10 256000 45650 8100 1440 256

11 512000 91200 16200 2880 512

12 1024000 182400 32400 5760 1024


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SAE Aerospace Standard (AS) 4059

Hydraulic System Cleanliness RequirementsMaximum Contaminant Limits (per 100ml)

Size Maximum Contamination Limits

Optical Count > 1m > 5m > 15m > 25m > 50m > 100m

APC Count > 4m > 6m >14m >21m >38m >70m

Size Code A B C D E F

000 195 76 14 3 1 0

00 390 152 27 5 1 0

0 780 304 54 10 2 01 1560 609 109 20 4 1

2 3120 1220 217 39 7 1

3 6520 2430 432 76 13 2

4 12,500 4860 864 152 26 4

5 25,000 9730 1730 306 53 8

6 50,000 19,500 3460 612 106 16

7 100,000 38,900 6920 1220 212 32

8 200,000 77,900 13,900 2,450 424 64

9 400,000 156,000 27,700 4,900 848 128

10 800,000 311,000 55,400 9,800 1,700 256

11 1,600,000 623,000 111,000 19,600 3,390 512

12 3,200,000 1,250,000 222,000 39,200 6,780 1,020

Limits are cumulative and should not be quoted within a range limit, i.e. all particles over the setsize are recorded. For most counting unless specified otherwise use the AS4059 groups B-F andquote the worst count as the AS4059 classification (same as NAS1638).


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SAE ARP598 - Determination of Particulate Contamination in Liquids by theParticle Count Method

1. Scope

SAE Aerospace Recommended Practice (ARP) 598 describes a procedure for the sizingand counting of particulate contamination in liquid samples by membrane filtration. Theprocedure will allow measurement of particulate contamination five micrometres orgreater in size with a maximum variation of + or - 20% in results over an average of tworuns. This procedure can be used for all samples where the membrane filter iscompatible with the sample liquid and rinse liquid.

Section II of this procedure may be used to count any sample on a gridded membranewhere particles are evenly distributed.

This procedure is an alternative to counting with an automatic particle counter althoughresults by each method from identical samples might not be equivalent due to individualidiosyncrasies in each technique.

NOTE :Apparatus described in this method may be obtained from:USA : Millipore Corporation, 290 Concord Road, Billerica, MA 01821. Tel: (978) 715-4321U.K.: Millipore, Croxley Green Business Park, Watford,WD18 8YH. Tel : 0870 900 46 45.Norway : Millipore AS, Karihaugveien 89, 1086 Oslo. Tel : (+47) 81062 645.

Or via the internet: www.millipore.com

2. Outline of Method

A known volume of liquid is filtered through a membrane filter. The particulatecontamination is deposited on the surface of the membrane filter. The residualcontamination is then sized and counted by microscopic analysis.

3. Materials

3.1 Membrane filter, pore size less than 1.0 micrometres. The filter shall have animprinted grid on 3.10 + or - 0.2mm centres. The colour shall be chosen formaximum contrast with the particulate contamination to be observed.

3.2 Petri dishes, plastic or glass.

3.3 Glass bottles, small mouth, screw capped, permanently marked to indicatesample volume. (1)

3.4 Plastic film, 0.5mm (0.002 in) minimum thickness. (2)


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4. Apparatus

4.1 Filtration Apparatus

4.1.1 Funnel, Filtration : The lower hole shall have a diameter of approximately35mm ID. The effective filtering area shall be calibrated by filtering acontrasting particulate pigment through a membrane filter. The diameterof the residual pigment shall be measured at quadrature diameters. If thereceiver is to be used for measuring the sample volume, the funnel shallbe calibrated within + or - 2% of the required volume.

4.1.2 Membrane filter support - Either a fritted glass, sintered metal or stainlesssteel screen may be used. The support shall be so designed as toenable attachment to a vacuum source.

4.1.3 Vacuum flask

4.1.4 Funnel holding device. A provision should be made for the dissipation ofstatic electricity from the funnel.

4.1.5 Funnel cover - to prevent extraneous contamination.

4.1.6 Vacuum source - minimum vacuum of 457mm (18 in) of mercury.

4.1.7 Forceps un-serrated tips.

4.1.8 Rinse dispenser(3).

NOTES :1) The standard sample volume shall be 100 + or - 5ml to allow complete use of fluid and to

allow the bottle to be rinsed with solvent.2) Plastics, membranes and films must be compatible with sample and rinse liquids.3) A pressurised container equipped to pass rinse liquid through membrane filter having apore size of 1.2 micrometers or finer.

4.2 Particle Count Apparatus

4.2.1 Microscope - Binocular or monocular (Stereo microscopes shall not beemployed with this procedure).

4.2.2 Objectives and oculars (eyepieces) in combinations to givemagnifications of 50 + or - 10x and 100 + or - 10x. The higher powerobjective shall have a minimum Numerical Aperture (N.A.) of 0.15. Theocular shall not be greater than 15x.

4.2.3 Ocular Micrometer - linear scale installed in one eyepiece. The smallestdivision shall not subtend a distance larger than the smallest particles tobe counted at a particular magnification.

4.2.4 Mechanical Stage - capable of traversing the entire area of themembrane filter. It shall have provision for holding a membranecontainer.


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4.2.5 Stage Micrometer - divisions of 0.1mm and 0.01mm.

4.2.6 Microscope Light - external, focusing - It shall be equipped with anexternal adjustable arm to give oblique incident light. It shall provide anillumination of 54 to 65 kilolumens per square metre (5000 to 6000 ft) atthe counting surface.

5. Reagents

5.1 Liquid detergent solution that leaves no solid residue.

5.2 Distilled or de-mineralised water.

6. Filtration of Reagents

The filtration of reagents shall be performed with the apparatus described in paragraph4.1.8.

7. Preparation of Apparatus

The apparatus used in the filtration of samples shall be prepared as follows :-

7.1 The apparatus shall be thoroughly washed in a solution of liquid detergent andhot water.

7.2 Rinse with hot distilled or de-mineralised water.

7.3 Rinse with 1 micrometre filtered distilled or de-mineralised water.

7.4 Allow to dry keeping away from particulate contamination.

7.5 Sample Bottle Preparation - repeat paragraph 7.1 through 7.4. Place a piece ofplastic film, which has been rinsed with filtered liquid, over the mouth of thebottle. Hold the film while screwing on the cap to prevent the film from rotating (4).

NOTES :4) It is important to hold the film when applying and removing to prevent serration.

8. Liquid Samples

8.1 The standard sample should be 100 + or - 5ml except in the following cases:When the particle count from this volume is greater than 100,000 or less than

500 particles total, the sample volume may be altered. For counts less than 500particles, the volume should be a minimum of 200ml. For counts greater than100,000 particles, the volume may be decreased to allow proper particledifferentiation. In all cases, the sample volume shall be recorded.

8.2 Sampling Procedure - samples shall be as representative of the system aspossible. Procedures for sampling shall be established by individual plants orlaboratories. To assure reproducibility, the sampling programme should bechecked by testing replicate samples from the sample port.


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9. Sampling Preparation Procedure

9.1 Blank Analysis Filtration

9.1.1 Remove a membrane filter using forceps from the container and rinse thefiltered liquid.

9.1.2 Place the filter on the support, lower the funnel, and secure with theholding device. Cover the funnel.

9.1.3 Place an amount of membrane filtered liquid from the rinse dispenser,equivalent in volume to the fluid to be tested, in a bottle(5) and agitate.

9.1.4 Remove the cover and pour the contents of the bottle into the funnel.

9.1.5 Pour approximately 50ml of rinse liquid into the bottle and agitate.

9.1.6 Pour the contents of the bottle into the funnel and replace the funnelcover.

9.1.7 Turn on the vacuum and allow the sample to filter until approximately50ml remain.

9.1.8 Remove the cover, rinse the funnel walls and replace the cover(6).

9.1.9 Allow the sample to filter until dry.

9.1.10 Remove the cover, holding device and immediately turn off the vacuum.

9.1.11 Remove the membrane filter using the forceps and place in a petri dish

and label.

9.1.12 Perform a particle count as specified in paragraph 11.

9.1.13 The blank count shall not exceed 10% of total allowable sample count. Ifthe blank analysis exceeds 10% of the count of an acceptable sample, orone particle, whichever is greater, and the total count exceeds the countof an acceptable sample, the apparatus shall be re-cleaned to produce alower blank and the procedure should be re-run.

NOTES :5) This procedure is designed to utilise glass bottles. If other containers are to be used, this

procedure should be deviated and proper identification given to the containers used.6) When the fluid filtration rate is excessive, causing a vortex, the vacuum should bereleased to allow adequate rinsing of the funnel walls and to eliminate the possibility of upsettingthe particle distribution by the rinse liquid.


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9.2 Sample Filtration

9.2.1 Repeat steps 9.1.1 through 9.1.2.

9.2.2 Thoroughly agitate the sample and then remove the cap.

9.2.3 Remove the funnel cover and pour the contents into the funnel.

9.2.4 Pour approximately 50ml of rinse liquid in the bottle and agitate.

9.2.5 Pour the rinse liquid into the funnel and cover.

9.2.6 Turn on the vacuum and allow the sample to filter until approximately50ml remain.

9.2.7 Lift the cover and carefully wash down the funnel walls with rinse liquid (6).

9.2.8 Replace the cover and filter until the membrane is dry.

9.2.9 Remove the cover, clamp and funnel and then release the vacuumimmediately.

9.2.10 Using the forceps, transfer the membrane filter to the petri dish.

9.2.11 Label the petri dish giving the sample volume and identification.

9.2.12 The filter is now ready for microscopic examination.

10. Microscope Calibration

10.1 Place the stage micrometer on the mechanical stage and adjust the light.

10.2 Place the required objective and oculars in the microscope and focus on themicrometer.

10.3 Calibrate the ocular micrometer located in one eyepiece(7)at each magnificationto be used. Each operator shall perform this calibration when using a binocularmicroscope(8). The calibrated method requires that the length of the entire linearscale be measured rather than only a portion.

10.4 The operator shall calculate the number of linear divisions required to measureeach range at all magnifications. For example : If an ocular micrometer with 100divisions measures 250 micrometers at 50x, then each division would equal 2.5

micrometers. By calculating the ranges, you would measure as follows : over100 micrometers equals 40 division, 50 to 100 micrometers equals 20 - 40divisions, 25 to 50 micrometers equals 10 to 20 divisions.

NOTES:6) When the fluid filtration rate is excessive, causing a vortex, the vacuum should bereleased to allow adequate rinsing of the funnel walls and to eliminate the possibility of upsettingthe particle distribution by the rinse liquid.7) Do not place the eyepiece containing the ocular membrane in an adjustable draw tubeeyepiece because the calibration will change as the ocular is adjusted.8) When the binocular microscope is used, the focal length and calibration will changewhen the interpupillary distance changes


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11. Particle Counting Procedure

While certain details of the counting procedure depend somewhat upon the specificequipment used, the procedure specified herein must be followed exactly as stated toprovide the required accuracy and reproducibility.

11.1 The particle size shall be determined by measuring the largest dimension.

11.2 The size ranges shall be as follows : 5 to 15 micrometers, 15 to 25 micrometers,25 to 50 micrometers, 50 to 100 micrometers, over 100 micrometers & fibres (9).

11.3 Remove the container lid and place the sample on the mechanical stage.

11.4 Select the proper magnification and focus on the membrane grid lines.

11.5 Turn the petri dish until the grid lines are aligned with the vertical and horizontalstage axis.

11.6 Focus the light, adjust the angle(10)and intensity to obtain maximum particledefinition.

11.7 Examine the membrane by scanning the surface to determine that the particleshave a random distribution. If the membrane shows evidence of spottydistribution or rings of heavier particle concentration around the outside edge ofthe filtration area, the statistical counting procedure shall not be used. The liquidsample should be re-run or a total particle count performed.

11.8 This procedure defines a method of sizing and counting particles 5.0micrometers and greater.

11.8.1 In obtaining the number of particles given particle size range, thenumbers of particles on a representative number of grid squares on thefilter disk are counted. From this count, the total number of particles,which would present statistically on the total effective filtration area of 100imprinted grid squares, is calculated.

11.8.2 If the total number of particles of a given particle size range is estimatedto be between 1 and 50, count the number of particles over the entireeffective filtering area.

11.8.3 If the total number of particles of a given particle size range if estimatedto be between 50 and 1,000, count the number of particles in 20

randomly chosen grid squares and multiply this number by 5 to obtain thetotal statistical particle count.

11.8.4 If the total number of particles of a given particle size range is estimatedto be between 1,000 and 5,000, count the number of particles on 10randomly chosen grid squares and multiply this number by 10 to obtainthe total statistical particle count.

NOTES :9) A fibre is defined as a particle greater than 100 micrometers whose length exceeds thewidth by at least 10 times.10) The recommended angle is 15 - 45 deg. from the horizontal.


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11.8.5 If the estimated total number of particles of a given size range exceeds5,000, count the particles within at least ten (10) randomly chosen unitareas. To arrive at the total statistical count, the sum of the particlescounted in 10 or more unit areas is multiplied by the calibration factor.

11.8.6 Count the number of particles in each field (11) for each size range by"gating"(12)the membrane filtration area. As the particles pass by eachocular micrometer measure(13)and record the number of particles in eachsize range(14).

11.8.7 If a particle lies on the upper or left boundary line of a counting area,count this particle as if it were within the boundaries of the counting area.Particles on the lower and right hand boundary lines of the counting areashall not be counted.

12. Particle Count Calculations

12.1 The total particle count for each range shall be calculated using the followingformula :

Total Count = A x PtFnx Fa

Where A = Filtration area of membrane (normally 960 mm2).

Fn= Number of fields (unit areas) counted.

Fa= Area of each field (unit area) mm2.

Pt= Number of particles Fnfields or unit areas.

12.2 Particle counts shall be expressed in particles per 100ml. If the volume is otherthan 100ml, the results shall specify the sample volume.

NOTES :11) Select a field size so that there are no more than about 50 particles of the size to becounted in the field. Optional fields are : a grid square; a rectangle defined by the width of a gridsquare and the calibrated length of the ocular micrometer scale; a rectangle defined by the width

of the grid square a portion of the length of the ocular micrometer scale as shown in the diagrambelow.12) Gating is the technique where one starts at a reference point and traverses the entirefiltration area in a systematic manner.13) For particles improperly oriented relative to the ocular micrometer, an estimate shall bemade. The eyepiece containing the ocular micrometer should not be rotated to size specificparticles.14) More than one size range can be counted simultaneously providing the magnification isthe same.


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13. Counting Proficiency

13.1 Check Samples

Membrane filters containing contamination, representative of the system to becounted, should be permanently mounted between glass. These samples shouldbe counted by all operators to determine the mean particle count. This samplemay then be sent to outside laboratories for additional counting. Care must betaken with these slides because the particle count may change as a result ofhandling.

13.2 Competence

Individual laboratories, with experienced counters, should be able to count with a10% mean deviation thus providing the operator and optical accuracy.

14. Dispute Clause

In case of dispute, this clause shall be used to test laboratory competence in filtering andcounting clean fluids.

14.1 Place 10ml of 0.45 micrometer membrane filtered fluid in a glass bottle cleanedas specified herein.

14.2 Perform a filtration as specified herein.

14.3 Count all particles 5 micrometers and above and record.

14.4 The total particle count shall not exceed a total of 250 including a maximum of 10particles above 50 micrometers.

fluid cleanliness counting procedure mar 2010

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