1、_ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there
2、from, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions. Copyright 2016 SAE International All rights reserved. No part of this p
3、ublication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-497
4、0 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/ARP5991 AEROSPACE RECOMMENDED PRACTICE ARP5991 Issued 2002-12 Reaffirmed 2016-09
5、Test Method for the Determination of Water Concentration in Polyol Ester and Diester Aerospace Lubricants by Coulometric Karl Fischer Titration RATIONALE ARP5991 has been reaffirmed to comply with the SAE five-year review policy. 1. SCOPE:The test method describes the procedure for the direct determ
6、ination of water concentration in polyol ester and diester based aerospace lubricants by the commercially available automated coulometric Karl Fischer titration instrument. The method was validated to cover the water concentration range of 150 to 3500 g/g. The method may also be suitable for the det
7、ermination of water concentrations outside this range and for other classes of fluids, however, the precision statement shall not be applicable for such uses.1.1 Purpose:Knowledge of the water concentration in polyol and diester aerospace lubricants is required since the presence of excess amounts o
8、f water can lead to hydrolysis of the lubricant, resulting in corrosion and wear of the lubricated components and degradation of the lubricant. Significant variability observed in inter-laboratory Karl Fischer test results for these lubricants highlighted the need for a standardized Karl Fischer tes
9、t procedure, specifically suited for these lubricants. 2. APPLICABLE DOCUMENTS:The following publications form a part of this document to the extent specified herein. The latest issue of SAE publications shall apply. The applicable issue of other publications shall be the issue in effect on the date
10、 of the purchase order. In the event of conflict between the text of this document and references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained.SAE INTERNATIONAL AR
11、P5991 Page 2 of 11 2.1 ASTM Publications:Available from ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959.ASTM D 6304-98 Standard Test Method for the Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl Fischer TitrationASTM D 6300-99 Standard
12、 Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products and Lubricants3. TEST REQUIREMENTS:3.1 Outline of Method:An accurately weighed aliquot of the fluid sample is injected into the titration vessel of a coulometric Karl Fischer apparatus in which iodi
13、ne for the Karl Fischer reaction is generated coulometrically at the anode. Upon the completion of the titration of the water in the sample, the electrometric end point sensor detects excess iodine and the titration is terminated. The quantity of water is determined by the integration of the total a
14、mount of current consumed by the reaction, which, based on the stoichiometry of the reaction, is proportional to the molar concentration of water in the sample.4. APPARATUS:4.1 Coulometric Karl Fischer Apparatus (using electrometric end point):A number of automated coulometric Karl Fischer apparatus
15、 consisting of a titration cell, platinum electrodes, magnetic stirrer and a control unit are commercially available. The instructions for the operation of these devices are provided by the respective manufacturers and are not discussed in this document.4.2 Syringes:Fine glass syringes with luer fit
16、tings and hypodermic needles are recommended. Disposable plastic precision syringes can be used for routine sample analysis but not for the validation. The bores of the needles shall be kept as small as possible, but large enough to avoid problems arising from excessive back pressure or blocking whi
17、le obtaining a sample. Suggested syringe sizes are as follows:4.2.1 Ten microliters fine glass syringe graduated for readings to the nearest 0.01 l or better. This syringe is used in the standardization step.SAE INTERNATIONAL ARP5991 Page 3 of 11 4.2.2 One and five ml capacities, accurate to the nea
18、rest 0.01 ml. A quality gas-tight glass syringe with a TFE fluorocarbon plunger and luer fitting is recommended. Disposable plastic precision syringes can be used.NOTE: Rinse all glass syringes and needles with anhydrous acetone (or equivalent) after cleaning. Then dry in an oven at 100 C and store
19、immediately in desiccators.4.3 Balance:An analytical balance with a resolution of 0.0001g.5. REAGENTS/MATERIALS:Reagent grade chemicals, conforming to the specifications of the Committee on Analytical Reagents of The American Chemical Society shall be utilized in all tests, unless indicated otherwis
20、e.5.1 Karl Fischer Reagent:Standard commercially available reagents for coulometric Karl Fischer titration.5.2 Cathode Solution:Standard, commercially available cathode Karl Fischer solution.5.3 1-Octanol:ACS grade, 99% pure, 5% withdraw an additional specimen and add to the titration vessel as per
21、8.3.1. If the difference in the results of the last 2 trials is 5%, validate the equipment as per Section 7.8.6 Replace the anode and cathode reagents when one of the following occurs and then repeat the preparation of the apparatus as in Section 6.8.6.1 Persistently high and unstable background cur
22、rent.8.6.2 Phase separation in the titration vessel or oil coating the electrodes.NOTE: Phase separation and oil coating the electrodes can be due to insufficient solubility of the fluid in the anode reagent. Thirty percent xylene (by volume) mixed with the anode reagent has shown improved solubilit
23、y for polyol ester based fluids.8.6.3 The fluid level in the titration vessel reaches the maximum recommended by the manufacturer.SAE INTERNATIONAL ARP5991 Page 6 of 11 8.6.4 The instrument displays error message that directly or indirectly suggests replacement of the electrolytes, as per the instru
24、ments operating manual.8.6.5 The reagents in the titrator are over one week old.8.6.6 The result of validation with 1000 g pure water is outside of 1000 g 10 g or with saturated 1-octanol is outside of 47,300 g/g 1000 g/g.8.7 Thoroughly clean the anode and cathode compartments with xylene if the ves
25、sel becomes contaminated.9. CALCULATION OF RESULTS:Most automatic Karl Fischer apparatus have integral calculation methods or can be programmed for a specific application. Calculate the water concentration in g/g of the sample as follows: (Eq. 1)where:W1= mass of water titrated, gW2= mass of sample
26、used, g10. REPORT:Report the water concentration to the nearest whole g/g based on the average of the two trials for a fluid sample. The test report shall contain at least the following information relating to the analysis:1. Identification of the fluid sample tested2. Reference to the method3. Resu
27、lts of the test4. Date of the testNOTE: The presence of free or emulsified water in the sample shall be mentioned in the report with a note indicating that the result does not take into account the free water in the sample.Water, g/g W1W2=SAE INTERNATIONAL ARP5991 Page 7 of 11 11. PRECISION AND BIAS
28、:The precision of this test method as determined by the statistical examination of the inter-laboratory test results is as follows:11.1 Repeatability:The difference between successive results obtained by the same operator with the same apparatus under constant operating conditions on identical test
29、materials, would, in the long run, in the normal and correct operation of the test method, exceed the following values only in one case in twenty:Repeatability = 0.003875 (x)1.287Where x is the mean value of duplicate measurements11.2 Reproducibility:The difference between the results obtained by di
30、fferent operators, working in different laboratories on identical test materials, would, in the long run exceed the following values in only one case in twenty:Reproducibility = 0.02187 (x)1.287Where x is the mean value of duplicate measurementsPREPARED UNDER THE JURISDICTION OFSAE COMMITTEE E-34, P
31、ROPULSION LUBRICANTSSAE INTERNATIONAL ARP5991 Page 8 of 11 APPENDIX AHELPFUL HINTS FOR COULOMETRIC KARL FISCHER WATER ANALYSISFollowing are some suggestions to obtain accurate and precise results by this test method. Some of these suggestions are also described in the test method, but are reiterated
32、 here for easy reference.A.1 All equipment should be thoroughly cleaned of moisture. Rinse all glass syringes and needles with anhydrous acetone (or equivalent) after cleaning. Then dry in an oven at 100 C and store immediately in a desiccator until needed for use.A.2 Keep the sample bottles tightly
33、 sealed before and after withdrawing a sample aliquot with a dry hypodermic needle.A.3 Although standardization is not necessary in coulometric titrations, reagent performance can deteriorate with use, hence it should be monitored by accurately injecting 1000 g of pure water or 10 l water saturated
34、1-octanol after the starting up of the equipment and after each reagent change. If the fluid is suspected of interfering with the titration, utilize procedure in A.9 for the validation of the apparatus with the fluid.A.4 Rinse the internals of the clean and dry syringe at least once with the sample
35、and discard the aliquot before taking an aliquot for injecting in the titration vessel.A.5 High background current for a prolonged period may be due to moisture on the inside wall of the titration vessel. Gentle swirling of the vessel will wash the inside with electrolyte. Keep the titrator on to al
36、low stabilization to a low background current.A.6 The frit separating the vessel compartments may get clogged with sample residue. Disassemble the apparatus and acid clean the frit per the manufacturers recommendations.A.7 Replace the anode and cathode reagents when one of the following occurs and t
37、hen repeat the preparation of the apparatus as in 6.2.A.7.1 Persistently high and unstable background current.A.7.2 Phase separation in the titration vessel or oil coating the electrodes.NOTE: Phase separation and oil coating the electrodes can be due to the insufficient solubility of the fluid in t
38、he anode reagent. Thirty percent xylene (by volume) mixed with the anode reagent has shown improved solubility for polyol ester and diester based fluids.A.7.3 The fluid level in the titration vessel reaches the maximum recommended by the manufacturer.A.7.4 The instrument displays error message that
39、directly or indirectly suggests replacement of the electrolytes, as per the instruments operating manual.A.7.5 The reagents are over one week old.A.7.6 The result of validation with 1000 g pure water is outside of 1000 g 10 g or with saturated 1-octanol is outside of 47,300 g/g 1000 g/g.A.7.7 Thorou
40、ghly clean the anode and cathode compartments with xylene or other solvent recommended by the manufacturer if the vessel becomes contaminated.A.8 PROCEDURE FOR THE PREPARATION OF WATER SATURATED 1-OCTANOL (WSO) FOR THE VALIDATION OF THE APPARATUS:A.8.1 Mix 5 parts 1-octanol with 1 part distilled wat
41、er in a clean glass container over a magnetic stirrer using a Teflon stirring bar for 24 hours at room temperature. Let the mixture stand un-stirred for three days.A.8.2 Decant the water saturated 1-octanol into a dry and clean, sealed glass container. The water concentration of the WSO is stable ov
42、er the temperature range of 50 to 86 F.A.9 PROCEDURE FOR THE VALIDATION OF THE APPARATUS WITH A WATER-SPIKED FLUID SAMPLE:A.9.1 Accurately weigh a clean and dry glass sample bottle, including the cap.A.9.2 Fill the sample bottle with fresh fluid, approximately 90% full.A.9.3 Determine the water conc
43、entration of the sample in the bottle as per 8.3.1.A.9.4 Weigh the sample bottle. Subtract the weight of the empty bottle to obtain the weight of the fluid in the bottle.A.9.5 Calculate the amount of water required to bring the water concentration to 2000 g/g.NOTE: Most polyol ester and diester base
44、d lubricants have water solubility in the range of 2500 to 3500 g/g.A.9.6 Add the calculated amount of water to the sample bottle by accurately weighing the syringe before and after the injection of water in the sample bottle.A.9.7 Install the cap and shake the bottle by hand for 2 minutes, followed
45、 by 15 minutes in an ultrasonic bath, followed by 2 minutes of shaking by hand.A.9.8 Determine the water concentration of the sample in the bottle as per 8.3.1.SAE INTERNATIONAL ARP5991 Page 9 of 11 A.7.5 The reagents are over one week old.A.7.6 The result of validation with 1000 g pure water is out
46、side of 1000 g 10 g or with saturated 1-octanol is outside of 47,300 g/g 1000 g/g.A.7.7 Thoroughly clean the anode and cathode compartments with xylene or other solvent recommended by the manufacturer if the vessel becomes contaminated.A.8 PROCEDURE FOR THE PREPARATION OF WATER SATURATED 1-OCTANOL (
47、WSO) FOR THE VALIDATION OF THE APPARATUS:A.8.1 Mix 5 parts 1-octanol with 1 part distilled water in a clean glass container over a magnetic stirrer using a Teflon stirring bar for 24 hours at room temperature. Let the mixture stand un-stirred for three days.A.8.2 Decant the water saturated 1-octanol
48、 into a dry and clean, sealed glass container. The water concentration of the WSO is stable over the temperature range of 50 to 86 F.A.9 PROCEDURE FOR THE VALIDATION OF THE APPARATUS WITH A WATER-SPIKED FLUID SAMPLE:A.9.1 Accurately weigh a clean and dry glass sample bottle, including the cap.A.9.2
49、Fill the sample bottle with fresh fluid, approximately 90% full.A.9.3 Determine the water concentration of the sample in the bottle as per 8.3.1.A.9.4 Weigh the sample bottle. Subtract the weight of the empty bottle to obtain the weight of the fluid in the bottle.A.9.5 Calculate the amount of water required to bring the water concentration to 2000 g/g.NOTE: Most polyol ester and diester bas
