ASTM D6728-01
(Test Method)Standard Test Method for Determination of Contaminants in Gas Turbine and Diesel Engine Fuel by Rotating Disc Electrode Atomic Emission Spectrometry
Standard Test Method for Determination of Contaminants in Gas Turbine and Diesel Engine Fuel by Rotating Disc Electrode Atomic Emission Spectrometry
SCOPE
1.1 This test method covers the determination of contaminants and materials as a result of corrosion in gas turbine or diesel engine fuels by rotating disc electrode atomic emission spectroscopy (RDE-AES).
1.1.1 The test method is applicable to ASTM Grades 0-GT, 1-GT, 2-GT, 3-GT and 4-GT gas turbine fuels and Grades Low Sulfur No. 1-D, Low Sulfur No. 2-D, No. 1-D, No. 2-D and No. 4-D diesel fuel oils.
1.1.2 This test method provides a rapid at-site determination of contamination and corrosive elements ranging from fractions of mg/kg to hundreds of mg/kg in gas turbine and diesel engine fuels so the fuel quality and level of required treatment can be determined.
1.1.3 This test method uses oil-soluble metals for calibration and does not purport to quantitatively determine or detect insoluble particles.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only. The preferred units are mg/kg (ppm by mass).
1.3 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 and health practices and determine the applicability of regulatory limitations prior to use.
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An American National Standard
Designation:D6728–01
Standard Test Method for
Determination of Contaminants in Gas Turbine and Diesel
Engine Fuel by Rotating Disc Electrode Atomic Emission
Spectrometry
This standard is issued under the fixed designation D 6728; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope D 6299 Practice for Applying Statistical Quality Assurance
Techniques to Evaluate Analytical Measurement System
1.1 This test method covers the determination of contami-
Performance
nants and materials as a result of corrosion in gas turbine or
diesel engine fuels by rotating disc electrode atomic emission
3. Terminology
spectroscopy (RDE-AES).
3.1 Definitions:
1.1.1 The test method is applicable to ASTM Grades 0-GT,
3.1.1 burn, vt—in emission spectroscopy, to vaporize and
1-GT, 2-GT, 3-GT and 4-GT gas turbine fuels and Grades Low
excite a specimen with sufficient energy to generate spectral
Sulfur No. 1-D, Low Sulfur No. 2-D, No. 1-D, No. 2-D and
radiation.
No. 4-D diesel fuel oils.
3.1.2 calibration, n—the determination of the values of the
1.1.2 Thistestmethodprovidesarapidat-sitedetermination
significant parameters by comparison with values indicated by
of contamination and corrosive elements ranging from frac-
a set of reference standards.
tions of mg/kg to hundreds of mg/kg in gas turbine and diesel
3.1.3 calibration curve, n—the graphical or mathematical
engine fuels so the fuel quality and level of required treatment
representation of a relationship between the assigned (known)
can be determined.
values of standards and the measured responses from the
1.1.3 This test method uses oil-soluble metals for calibra-
measurement system.
tion and does not purport to quantitatively determine or detect
3.1.4 calibration standard, n—a standard having an ac-
insoluble particles.
cepted value (reference value) for use in calibrating a measure-
1.2 The values stated in SI units are to be regarded as the
ment instrument or system.
standard. The values given in parentheses are for information
3.1.5 detection limit, n—the smallest concentration of an
only. The preferred units are mg/kg (ppm by mass).
element that can be measured for specific analysis conditions
1.3 This standard does not purport to address all of the
and data collection periods.
safety concerns, if any, associated with its use. It is the
3.1.6 emission spectroscopy, n—measurement of energy
responsibility of the user of this standard to establish appro-
spectrum emitted by or from an object under some form of
priate safety and health practices and determine the applica-
energetic stimulation; for example, light, electrical discharge,
bility of regulatory limitations prior to use.
and so forth.
2. Referenced Documents 3.2 Description of Terms Specific to This Standard:
3.2.1 arc discharge, n—a self-sustaining, high current den-
2.1 ASTM Standards:
sity, high temperature discharge uniquely characterized by a
D 975 Specification for Diesel Fuel Oils
3 cathode fall nearly equal to the ionization potential of the gas
D 2880 Specification for Gas Turbine Fuel Oils
or vapor in which it exists.
D 4057 Practice for Manual Sampling of Petroleum and
3.2.2 check sample, n—a reference material usually pre-
Petroleum Products
pared by a single laboratory for its own use as a measurement
D 5854 Practice for Mixing and Handling of Liquid
control standard, or for the qualification of a measurement
Samples of Petroleum and Petroleum Products
method.
3.2.3 contaminant, n—material in a fuel sample that may
cause ash deposition or high temperature corrosion.
This test method is under the jurisdiction of ASTM Committee D02 on
3.2.4 graphite disc electrode, n—a soft form of the element
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
carbon manufactured into the shape of a disc for use as an
D02.03 on Elemental Analysis.
Current edition approved Nov. 10, 2001. Published January 2002. electrode in arc/spark spectrometers for oil and fuel analysis.
Annual Book of ASTM Standards, Vol 05.01.
Annual Book of ASTM Standards, Vol 05.02.
4 5
Annual Book of ASTM Standards, Vol 05.03. Annual Book of ASTM Standards, Vol 05.04.
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D6728–01
3.2.5 graphite rod electrode, n—a soft form of the element 6. Interferences
carbon manufactured into the shape of a rod for use as a
6.1 Spectral—Mostspectralinterferencescanbeavoidedby
counter electrode in arc/spark spectrometers for oil and fuel
judicious choice of spectral lines. High concentrations of some
analysis.
elements can have an interfering influence on the spectral lines
3.2.6 profiling, n—to set the actual position of the entrance
used for determining trace levels of contaminants. Instrument
slit to produce optimum measurement intensity.
manufacturers usually compensate for spectral interferences
3.2.7 standardization, n—the process of reestablishing and
during factory calibration. A background correction system,
correcting a calibration curve through the analysis of at least
which subtracts unwanted intensities on the side of the spectral
two known oil standards.
line, shall also be used for this purpose. When spectral
3.2.8 uptake rate, n—the amount of oil or fuel sample that
interferencescannotbeavoidedwithspectrallineselectionand
is physically carried by the rotating disc electrode into the arc
backgroundcorrection,thenecessarycorrectionsshallbemade
for analysis.
using the computer software supplied by the instrument manu-
facturer.
4. Summary of Test Method
6.2 Viscosity Effects—Differences in viscosity of fuel
samples will cause differences in uptake rates. Internal refer-
4.1 A fuel test specimen is excited by a controlled arc
ences of the instrument will compensate for a portion of the
discharge using the rotating disk technique. The radiant ener-
differences. Without a reference, the analysis will be adversely
gies of selected analytical lines and a reference are collected
affected if the test specimen has a different viscosity from the
and stored by way of photomultiplier tubes, charge coupled
calibration samples. The hydrogen 486.10 nm spectral line
devices, or other suitable detectors. A comparison is made of
shall be used for light fuels, and the carbon 387.10 nm spectral
the emitted intensities of the elements in the fuel test specimen
line shall be used for heavy fuels as an internal reference to
againstthosemeasuredwithcalibrationstandards.Theconcen-
compensate for viscosity effects.
tration of the elements present in the fuel test specimen are
6.3 Particulate—When large particles over 10 µm in size
calculated and displayed.
are present, the analytical results will be lower than the actual
concentration they represent. Large particles may not be
5. Significance and Use
effectively transported by the rotating disk electrode sample
5.1 Operating experience of gas turbines and diesel engines
introduction system into the arc, nor will they be fully
has shown that some of the ash-forming substances present in
vaporized.
a fuel can lead to high temperature corrosion, ash deposition,
and fuel system fouling. Ash-forming materials may be in a
7. Apparatus
fuelasoil-solublemetallo-organiccompoundsaswater-soluble
7.1 Electrode Sharpener—an electrode sharpener to remove
salts or as solid foreign contamination. Their presence and
the contaminated portion of the rod electrode remaining from
concentrationvarieswiththegeographicalsourceofacrudeoil
the previous determination. It also forms a new 160° angle on
and they are concentrated in the residual fractions during the
the end of the electrode.
refining process. Although distillate fuel oils are typically
7.2 Rotating Disc Electrode Atomic Emission
contaminant free, ash-forming materials may be introduced
Spectrometer—a simultaneous spectrometer consisting of ex-
later in the form of salt-bearing water or by contact with other
citation source, polychromator optics, and readout system.
petroleum products during transportation and storage. Specifi-
Suggested wavelengths are listed in Table 1. When multiple
cations of gas turbine and diesel engine fuels and the signifi-
wavelengths are listed, they are in the order of preference or
cance of contamination and trace metals are detailed in
desired analytical range.
Specifications D 2880 and D 975.
7.3 Heated Ultrasonic Bath (Recommended)—an ultrasonic
5.1.1 Pre-conditioning of the fuel before it reaches the gas
bath to heat and homogenize fuel samples to bring particles
turbine or diesel engine has become a prerequisite for instal-
into suspension. The ultrasonic bath shall be used on samples
lations that use heavy petroleum fuel, and also for sites that use
containing large amounts of debris, those that have been in
light distillate fuel oils. On-site fuel analysis to determine the
transitorinstorageforatleast48handforheavyresidualfuels
extent of contamination is an integral part of a fuel quality
to reduce viscosity effects.
management program. It is used first to determine the extent of
7.4 Power Mixer—A power mixer should be used before a
the required treatment, and later, the effectiveness of the
sample is transferred from one container to another to ensure
treatment. It starts with the delivery of the fuel, continues
throughout fuel handling and ends only as the fuel is injected
TABLE 1 Elements and Recommended Wavelengths
into the turbine or engine.
Element Wavelength, nm Element Wavelength, nm
5.1.2 Fuel contamination specifications vary among the
different gas turbine manufacturers. However, without excep- Aluminum 308.21 Magnesium 280.20, 518.36
Calcium 393.37 Nickel 341.48
tion, each requires that contaminants must be as low as
Chromium 425.43 Potassium 766.49
possible. In most power generation installations, it is the owner
Copper 324.75 Silicon 251.60
who has the responsibility of verifying fuel cleanliness in Iron 259.94 Sodium 588.99
Lead 283.31 Vanadium 290.88, 437.92
compliance with the turbine manufacturer’s warranty specifi-
Lithium 670.78 Zinc 213.86
cations. This leads to an on-site analytical instrument perfor-
Manganese 403.07
mance requirement of below 1.0 mg/kg for several elements.
D6728–01
thatahomogeneousmixtureiscreatedandmaintaineduntilthe specimen holders must be cleaned after each analysis. All
transfer is complete. Practice D 5854 should be consulted for specimen holders must be free of contamination and shall be
the mixing and handling of liquid samples. stored accordingly. Specimen holder covers shall be used on
those fuel samples that may catch on fire during the analysis.
8. Reagents and Materials
8.1 Base Oil—a75cSt(40°C)baseoil,freeofanalyte,tobe 9. Sampling
used as a calibration blank or for blending calibration stan-
9.1 The fuel sample taken for the analysis must be repre-
dards.
sentative of the entire system. Good sampling procedures are
8.2 Check Sample and Quality Control (QC) Samples—one
key to good analyses and samples must be taken in accordance
or more oil or fuel standards or samples of known concentra-
with Practice D 4057.
tion which are periodically analyzed as go/no-go samples to
confirm the need for standardization based on an allowable
10. Preparation of Test Specimen
accuracy limit as described in Appendix X1.
10.1 Homogenization—Fuel samples may contain particu-
8.3 Cleaning Solution—an environmentally safe, non-
late matter and free water and, in order to be representative,
chlorinated, rapid evaporating, and non-film producing solvent
must always be vigorously shaken prior to pouring a test
to remove spilled or splashed oil or fuel sample in the sample
specimen for analysis.
stand of the spectrometer.
10.2 Ultrasonic Homogenization—Samples that have been
8.4 Counter Electrode—The counter electrode is a rod
in transit for several days, idle in storage or very viscous, shall
electrode. The counter electrode shall be of high-purity graph-
be placed in a heated ultrasonic bath to break up clusters of
ite (spectroscopic grade). Dimensions of new counter elec-
particles and to bring them back into suspension. The samples
trodes shall conform to those shown in Fig. 1.
shall be vigorously shaken with a power mixer after being in
8.5 Disc Electrode—graphite disc electrode of high-purity
the ultrasonic bath and prior to pouring a test specimen for
graphite (spectroscopic grade). Dimensions of the electrodes
analysis. The bath temperature shall be 60°C for very viscous
shall conform to those shown in Fig. 2.
fuels and below the flash point of non viscous fuels. The total
8.6 Glass Cleaning Solution—capable of cleaning and re-
agitation time for a sample should be at least 2 min.
moving splashed oil or fuel sample from the quartz window
10.3 Specimen Holders—Fuel samples and oil standards
that protects the entrance lens and fiber optic.Ammonia based
shallbepouredintoaspecimenholderofatleast1mLcapacity
window cleaner or 70 % isopropyl rubbing alcohol have been
prior to analysis. Exercise care to pour the sample consistently
found to be suitable for this purpose.
to the same level in the specimen holders.
8.7 Organometallic Standards—single or multi-element
10.4 Specimen Table—The specimen table shall be adjusted
blended standards for use as the high concentration standard
so that when it is in the full raised position, at least one-third
for instrument standardization purposes or for use as a check
of the disc electrode diameter is immersed in the oil test
sample to confirm calibration. Multi-element blends are used
specimen.
for fuel analysis applications that contain a 3:1 concentration
ratio of magnesium to all other metals present. The typical
11. Preparation of Apparatus
concentration for the upper calibration point is 10 mg/kg for
light fuels whenASTM No. 0-GT, No. 1-GT, No. 2-GT, Grade 11.1 Warm-up Burns—If the instrument has been idle for
1-D, Grade 2-D and Grade 4-D fuel samples are analyzed. The severalhours,itmaybenecessarytoconductwarm-upburnsto
typical concentration for the upper calibration point is 100 stabilize the excitation source. The warm-up procedure can be
mg/kg for heavy fuels when No. 3-GT and No. 4-GT fuel performed with any fuel sample or standard. Consult the
samples are analyzed. manufacturer’s instructions for specific warm-up requirements.
8.7.1 Standards have a shelf-life and shall not be used to 11.2 Optical Profile—Perform the normal optical profile
standardize an instrument if they have exce
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