ASTM D4928-12(2018)

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.
Designation: D4928 − 12 (Reapproved 2018)
Manual of Petroleum Measurement Standards (MPMS), Chapter 10.9
Standard Test Method for
Water in Crude Oils by Coulometric Karl Fischer Titration
This standard is issued under the fixed designation D4928; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope 2. Referenced Documents
1.1 This test method covers the determination of water in
2.1 ASTM Standards:
the range from 0.02 to 5.00 mass or volume % in crude oils.
D1193Specification for Reagent Water
−
Mercaptan (RSH) and sulfide (S or H S) as sulfur are known
D4057Practice for Manual Sampling of Petroleum and
to interfere with this test method, but at levels of less than
Petroleum Products (API MPMS Chapter 8.1)
500µg⁄g [ppm(m)], the interference from these compounds is
D4177Practice for Automatic Sampling of Petroleum and
insignificant (see Section 6).
Petroleum Products (API MPMS Chapter 8.2)
D5854Practice for Mixing and Handling of Liquid Samples
1.2 This test method can be used to determine water in the
of Petroleum and Petroleum Products (API MPMS Chap-
0.005 to 0.02 mass % range, but the effects of the mercaptan
ter 8.3)
and sulfide interference at these levels has not been deter-
E203Test Method for Water Using Volumetric Karl Fischer
mined. For the range 0.005 to 0.02 mass %, there is no
Titration
precision or bias statement.
2.2 API Standards:
1.3 This test method is intended for use with standard
MPMS Chapter 8.1Practice for Manual Sampling of Petro-
commercially available coulometric Karl Fischer reagent.
leum and Petroleum Products (ASTM Practice D4057)
1.4 The values stated in SI units are to be regarded as
MPMS Chapter 8.2Practice for Automatic Sampling of
standard. No other units of measurement are included in this
Petroleum and Petroleum Products (ASTM Practice
standard.
D4177)
1.5 This standard does not purport to address all of the
MPMS Chapter 8.3Practice for Mixing and Handling of
safety concerns, if any, associated with its use. It is the
Liquid Samples of Petroleum and Petroleum Products
responsibility of the user of this standard to establish appro-
(ASTM Practice D5854)
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
3. Terminology
For specific warning statements, see Section 8.
3.1 The following terms are used with respect to sampling
1.6 This international standard was developed in accor-
(see Section 9).
dance with internationally recognized principles on standard-
3.2 Definitions of Terms Specific to This Standard:
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom- 3.2.1 aliquot, n—asmallportionofalargersamplewhichis
mendations issued by the World Trade Organization Technical analyzed and assumed to represent the whole sample.
Barriers to Trade (TBT) Committee.
3.2.2 sample, n—portion extracted from the contents of any
pipe,tank,orothersystem,andintendedtoberepresentativeof
that system, placed in a primary sample container for analysis.
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products, Liquid Fuels, and Lubricants and the API Committee on
Petroleum Measurement, and is the direct responsibility of Subcommittee D02.02
/COMQ, the joint ASTM-API Committee on Hydrocarbon Measurement for For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Custody Transfer (Joint ASTM-API). This test method has been approved by the contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
sponsoring committees and accepted by the Cooperating Societies in accordance Standards volume information, refer to the standard’s Document Summary page on
with established procedures. the ASTM website.
Current edition approved July 1, 2018. Published August 2018. Originally Published as Manual of Petroleum Standards. Available from American
approved in 1989. Last previous edition approved in 2012 as D4928–12. DOI: Petroleum Institute (API), 1220 L. St., NW, Washington, DC 20005-4070, http://
10.1520/D4928-12R18. www.api.org.
© Jointly copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, USA and the American Petroleum Institute (API), 1220 L Street NW, Washington DC 20005, USA
D4928 − 12 (2018)
3.2.3 test specimen, n—the representative sample taken in separate compartments. Instructions for operation of Karl
fromtheprimaryorintermediatesample(aliquot)containerfor Fischer titration devices are provided by the manufacturer and
analysis. The entire test specimen is used in the analysis. not described herein.
7.2 Mixer, to homogenize the crude sample.
4. Summary of Test Method
7.2.1 Non-Aerating, High-Speed, Shear Mixer—The mixer
4.1 After homogenizing the crude oil sample, a test speci-
shall be capable of meeting the homogenization efficiency test
men of that sample is injected into the titration cell of a Karl
described in Practice D5854 (API MPMS Chapter 8.3). The
Fischer apparatus in which iodine for the Karl Fischer reaction
sample size is limited to that suggested by the manufacturer’s
is generated coulometrically at the anode. When all the water
specifications for the size of the mixer.
has been titrated, excess iodine is detected by an electrometric
7.2.2 Circulating Sample Mixer—A device such as used
endpoint detector and the titration is terminated. Based on the
with automatic crude oil sampling receivers, is acceptable
stoichiometry of the reaction, one mole of iodine reacts with
providing it complies with the principles of Practice D5854
one mole of water thus the quantity of water can be deter-
(API MPMS Chapter 8.3).
mined.
7.3 Syringes—Test specimens are most easily added to the
4.2 The precision of this test method is critically dependent
titrationcellbymeansofaccurateglasssyringeswithLuerLok
on the effectiveness of the homogenization step. The accept-
fittings and hypodermic needles of suitable length. The bores
ability of the mixing used to achieve a homogeneous sample is
of the needles used should be kept as small as possible but
determined by the procedure given in Practice D5854 (API
largeenoughtoavoidproblemsarisingfrombackpressureand
MPMS Chapter 8.3). In addition, if the test method is per-
blocking while injecting a test specimen. The syringe size
formed on a volume basis, the precision of the test method is
should be selected such that the test specimen is not less than
critically dependent on the accuracy and repeatability of the
half the total volume contained by the syringe, the needle
volume injected.
should be long enough to permit the injection of the test
specimen into the fluid, below the surface of the fluid in the
4.3 Two procedures are provided for the determination of
titration cell.
water in crude oils. In one procedure, a weighed test specimen
7.3.1 Syringes for Gravimetric Determination—For gravi-
is injected into the titration cell and the mass % of water is
metric determination, any type of syringe that does not leak is
determined. The other procedure provides for the direct deter-
appropriate. Syringe should have physical dimensions to fit on
mination of the volume % of water in the crude oil by
the balance appropriately.
measuring the volume of crude oil injected into the titration
7.3.2 Syringe for Volumetric Determination—For volumet-
cell.
ric determination a certified syringe capable of delivering the
5. Significance and Use volumetric quantity with an accuracy 0.5% of the contained
volume is required.
5.1 Theaccurateanalysisofacrudeoilsampletodetermine
thewatercontentisimportantintherefining,purchase,sale,or 7.4 Balance for Mass Determination—Any analytical bal-
ancewithanaccuracyandresolutionof0.1mg,andcapableof
transfer of crude oils.
weighing up to 100 g can be used.
6. Interferences
7.4.1 The balance for determining the weight of the test
specimen injected into the titration cell shall be calibrated.
6.1 A number of substances and classes of compounds
associated with condensation or oxidation-reduction reactions
NOTE 1—The use of balances on structures that are in motion may not
interfereinthedeterminationofwaterbyKarlFischer.Incrude be appropriate.
oils, the most common interferences are mercaptans and
7.5 Titration Cell—Sunlight can cause disassociation of the
sulfides (not total sulfur). At levels of less than 500 µg/g
iodine in the Karl Fischer reagent, resulting in false results.A
[ppm(m)](assulfur),theinterferencefromthesecompoundsis
titration cell made of opaque material may reduce this effect.
insignificant.Mostcrudeoils,includingcrudeoilsclassifiedas
“sour crude,” have mercaptan and sulfide levels of less than
8. Reagents and Materials
500 µg/g [ppm(m)] as sulfur. For more information on sub-
8.1 Purity of Reagents—Chemicals of reagent grade or
stances that interfere in the determination of water by Karl
higher purity shall be used in all tests. Unless otherwise
Fischer titration method, see Test Method E203.
indicated, it is intended that all reagents shall conform to the
6.2 The significance of the mercaptan and sulfide interfer-
specifications of the Committee onAnalytical Reagents of the
ence on the Karl Fischer titration for water levels in the 0.005
American Chemical Society, where such specifications are
to 0.02 mass % range has not been determined experimentally.
available. Other grades may be used, provided it is first
At these low water levels, however, the interference may be
significant for mercaptan and sulfide levels of less than
500µg⁄g [ppm(m)] (as sulfur). 4
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For Suggestions on the testing of reagents not
7. Apparatus listed by the American Chemical Society, see Annual Standards for Laboratory
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
7.1 Karl Fischer Apparatus, using electrometric endpoint
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
detector.Theinstrumentmusthaveanodeandcathodereagents MD.
D4928 − 12 (2018)
ascertained that the reagent is of sufficiently high purity to 9.3 Sampling Apparatus—Sample lines and other sampling
permit its use without lessening the accuracy of the determi- apparatus that comes into contact with the fluid being sampled
nation. shall be constructed of a material to which water does not
adhere. The apparatus shall be constructed so that water does
8.2 Purity of Water—Unless otherwise indicated, references
not collect in deadlegs and low spots. There may be unique
to water shall be understood to mean reagent water as defined
requirements specified in the sampling method listed in 9.5.
by Type IV of Specification D1193.
Prior to extracting a sample, sample apparatus should be
8.3 Xylene—Reagent grade. Less than 0.05 % water.
appropriately purged or cleaned to prevent contamination.
(Warning—Flammable. Vapor harmful.)
9.4 Sample Storage and Handling—Samples should be
8.4 Karl Fischer Reagent—Standard commercially avail-
properly labeled and secured as appropriate to prevent tamper-
able reagents for coulometric Karl Fischer titrations.
ing.Samplescanbestoredindefinitelyaslongasthecontainer
8.4.1 Anode and cathode reagents shall not be used past the
is constructed to prevent ingress or egress of vapors, and the
manufacturer’s expiration date.
fluid being tested can be rehomogenized. No additional envi-
8.4.2 The need to replace the anode and cathode reagent is
ronmental constraints apply to properly sealed containers.
a function of number of tests run and the amount of water
9.5 Sampling Method—Representative samples obtained as
previously titrated. An abnormally slow titration is an indica-
specified in Practice D4057 (API MPMS Chapter 8.1) and
tion that the reagents should be replaced.
Practice D4177 (API MPMS Chapter 8.2) should be used to
8.4.3 Anode Reagent—A mixture of commercial coulomet-
obtain the sample.
ric Karl Fischer anode reagent and reagent grade xylene,
9.5.1 Sampling Viscous Crude Oil—Application of this
typically in a 6:4 mixture. Other proportions of anode reagent
method of viscous crude oils may present challenges in two
and xylene can be used and should be determined for a
different areas; sample mixing and test specimen extraction.
particular reagent and apparatus. The precision and bias were
Mixing apparatus may operate less efficiently. It may be
established using a 6 parts Karl Fischer reagent and 4 parts
difficult or impossible to extract and deliver an exact quantity
xylene. (Warning—Flammable, toxic by inhalation and if
of test specimen (see Section 15). Equipment or procedure
swallowed, avoid contact with skin.)
modifications if required may invalidate the precision state-
8.4.4 Cathode Reagent—Use standard commercially avail-
ment in this method. Validation of any modifications are
able coulometric Karl Fischer cathode reagent. (Warning—
required.
Flammable, can be fatal if inhaled, swallowed, or absorbed
through skin. Possible cancer hazard.)
9.6 Sample Mixing:
8.4.5 Check Solution—NIST Traceable check solution used
9.6.1 In order for the test specimen to be representative of
for verifying the calibration of the Karl Fischer instrument. In
the sample, the sample must first be homogenized. This is
the absence of an available check solution, pure water may be
accomplishedbymixingthesampleusinganappropriatemixer
used.
for a specified period of time.
9.6.2 Themixershallmeetthespecificationsforthehomog-
9. Sampling and Test Specimens
enization test, Practice D5854 (API MPMS Chapter 8.3).
9.1 Sample Container—It shall be constructed of a material Reevaluate the mixer for any changes in the type of crude,
volume of crude in the container, the shape of the container, or
to which water does not adhere with a sealable lid or other
mechanismtopreventrainorhumidityfromcontaminatingthe the mixing conditions (such as mixing speed and time of
mixing).
sample.
9.1.1 Ifanon-aeratinghigh-speedshearmixeristobeused,
9.6.2.1 For small sample containers and volumes in the 50
the sample container shall be of sufficient dimensions to allow to 500 mL range, a non-aerating, highspeed, shear mixer may
mixing as described in 9.6 and consistent with
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