ASTM D6728-16(2021)
(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
SIGNIFICANCE AND USE
5.1 Operating experience of gas turbines and diesel engines has shown that some of the ash-forming substances present in a fuel can lead to high temperature corrosion, ash deposition, and fuel system fouling. Ash-forming materials may be in a fuel as oil-soluble metallo-organic compounds as water-soluble salts or as solid foreign contamination. Their presence and concentration varies with the geographical source of a crude oil and they are concentrated in the residual fractions during the refining process. Although distillate fuel oils are typically contaminant free, ash-forming materials may be introduced later in the form of salt-bearing water or by contact with other petroleum products during transportation and storage. Specifications of gas turbine and diesel engine fuels and the significance of contamination and trace metals are detailed in Specifications D2880 and D975.
5.1.1 Pre-conditioning of the fuel before it reaches the gas turbine or diesel engine has become a prerequisite for installations that use heavy petroleum fuel, and also for sites that use light distillate fuel oils. On-site fuel analysis to determine the extent of contamination is an integral part of a fuel quality management program. It is used first to determine the extent of the required treatment, and later, the effectiveness of the treatment. It starts with the delivery of the fuel, continues throughout fuel handling and ends only as the fuel is injected into the turbine or engine.
5.1.2 Fuel contamination specifications vary among the different gas turbine manufacturers. However, without exception, each requires that contaminants must be as low as possible. In most power generation installations, it is the owner who has the responsibility of verifying fuel cleanliness in compliance with the turbine manufacturer's warranty specifications. This leads to an on-site analytical instrument performance requirement of below 1.0 mg/kg for several elements.
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.
1.1.1.1 Trace metal limits of fuel entering turbine combustor(s) are given as 0.5 mg/kg each for vanadium, sodium + potassium, calcium, and lead in Specification D2880 for all GT grades.
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 standard. No other units of measurement are included in this standard. The preferred units for concentration 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.4 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.
General Information
Relations
Standards Content (Sample)
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: D6728 − 16 (Reapproved 2021)
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 D6728; 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 mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.1 This test method covers the determination of contami-
nants and materials as a result of corrosion in gas turbine or
2. Referenced Documents
diesel engine fuels by rotating disc electrode atomic emission
2.1 ASTM Standards:
spectroscopy (RDE-AES).
D975 Specification for Diesel Fuel
1.1.1 The test method is applicable to ASTM Grades 0-GT,
D2880 Specification for Gas Turbine Fuel Oils
1-GT,2-GT,3-GT,and4-GTgasturbinefuelsandGradesLow
D4057 Practice for Manual Sampling of Petroleum and
Sulfur No. 1-D, Low Sulfur No. 2-D, No. 1-D, No. 2-D, and
Petroleum Products
No. 4-D diesel fuel oils.
D4177 Practice for Automatic Sampling of Petroleum and
1.1.1.1 Trace metal limits of fuel entering turbine combus-
Petroleum Products
tor(s) are given as 0.5 mg⁄kg each for vanadium, sodium +
D5854 Practice for Mixing and Handling of Liquid Samples
potassium, calcium, and lead in Specification D2880 for all GT
of Petroleum and Petroleum Products
grades.
D6299 Practice for Applying Statistical Quality Assurance
1.1.2 Thistestmethodprovidesarapidat-sitedetermination
and Control Charting Techniques to Evaluate Analytical
of contamination and corrosive elements ranging from frac-
Measurement System Performance
tions of mg/kg to hundreds of mg/kg in gas turbine and diesel
engine fuels so the fuel quality and level of required treatment
3. Terminology
can be determined.
1.1.3 This test method uses oil-soluble metals for calibra- 3.1 Definitions:
tion and does not purport to quantitatively determine or detect 3.1.1 burn, vt—in emission spectroscopy, to vaporize and
insoluble particles.
excite a specimen with sufficient energy to generate spectral
radiation.
1.2 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this 3.1.2 calibration, n—the determination of the values of the
significant parameters by comparison with values indicated by
standard.The preferred units for concentration are mg/kg (ppm
by mass). a set of reference standards.
3.1.3 calibration curve, n—the graphical or mathematical
1.3 This standard does not purport to address all of the
representation of a relationship between the assigned (known)
safety concerns, if any, associated with its use. It is the
values of standards and the measured responses from the
responsibility of the user of this standard to establish appro-
measurement system.
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
3.1.4 calibration standard, n—a standard having an ac-
1.4 This international standard was developed in accor-
cepted value (reference value) for use in calibrating a measure-
dance with internationally recognized principles on standard-
ment instrument or system.
ization established in the Decision on Principles for the
3.1.5 detection limit, n—the smallest concentration of an
Development of International Standards, Guides and Recom-
element that can be measured for specific analysis conditions
and data collection periods.
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of
Subcommittee D02.03 on Elemental Analysis. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved July 1, 2021. Published August 2021. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2001. Last previous edition approved in 2016 as D6728 – 16. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D6728-16R21. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6728 − 16 (2021)
3.1.6 emission spectroscopy, n—measurement of energy cance of contamination and trace metals are detailed in
spectrum emitted by or from an object under some form of Specifications D2880 and D975.
energetic stimulation; for example, light, electrical discharge, 5.1.1 Pre-conditioning of the fuel before it reaches the gas
and so forth. turbine or diesel engine has become a prerequisite for instal-
lations that use heavy petroleum fuel, and also for sites that use
3.2 Definitions of Terms Specific to This Standard:
light distillate fuel oils. On-site fuel analysis to determine the
3.2.1 arc discharge, n—a self-sustaining, high current
extent of contamination is an integral part of a fuel quality
density, high temperature discharge uniquely characterized by
management program. It is used first to determine the extent of
a cathode fall nearly equal to the ionization potential of the gas
the required treatment, and later, the effectiveness of the
or vapor in which it exists.
treatment. It starts with the delivery of the fuel, continues
3.2.2 check sample, n—a reference material usually pre-
throughout fuel handling and ends only as the fuel is injected
pared by a single laboratory for its own use as a measurement
into the turbine or engine.
control standard, or for the qualification of a measurement
5.1.2 Fuel contamination specifications vary among the
method.
different gas turbine manufacturers. However, without
3.2.3 contaminant, n—material in a fuel sample that may
exception, each requires that contaminants must be as low as
cause ash deposition or high temperature corrosion.
possible. In most power generation installations, it is the owner
who has the responsibility of verifying fuel cleanliness in
3.2.4 graphite disc electrode, n—a soft form of the element
compliance with the turbine manufacturer’s warranty specifi-
carbon manufactured into the shape of a disc for use as an
cations. This leads to an on-site analytical instrument perfor-
electrode in arc/spark spectrometers for oil and fuel analysis.
mance requirement of below 1.0 mg⁄kg for several elements.
3.2.5 graphite rod electrode, n—a soft form of the element
carbon manufactured into the shape of a rod for use as a
6. Interferences
counter electrode in arc/spark spectrometers for oil and fuel
6.1 Spectral—Most spectral interferences can be avoided by
analysis.
judicious choice of spectral lines. High concentrations of some
3.2.6 profiling, n—to set the actual position of the entrance
elements can have an interfering influence on the spectral lines
slit to produce optimum measurement intensity.
used for determining trace levels of contaminants. Instrument
3.2.7 standardization, n—the process of reestablishing and manufacturers usually compensate for spectral interferences
correcting a calibration curve through the analysis of at least during factory calibration. A background correction system,
two known oil standards. which subtracts unwanted intensities on the side of the spectral
line, shall also be used for this purpose. When spectral
3.2.8 uptake rate, n—theamountofoilorfuelsamplethatis
interferencescannotbeavoidedwithspectrallineselectionand
physically carried by the rotating disc electrode into the arc for
backgroundcorrection,thenecessarycorrectionsshallbemade
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
4.1 A fuel test specimen is excited by a controlled arc
samples will cause differences in uptake rates. Internal refer-
discharge using the rotating disk technique. The radiant ener-
ences of the instrument will compensate for a portion of the
gies of selected analytical lines and a reference are collected
differences. Without a reference, the analysis will be adversely
and stored by way of photomultiplier tubes, charge coupled
affected if the test specimen has a different viscosity from the
devices, or other suitable detectors. A comparison is made of
calibration samples. The hydrogen 486.10 nm spectral line
the emitted intensities of the elements in the fuel test specimen
shall be used for light fuels, and the CN 387.10 nm spectral
againstthosemeasuredwithcalibrationstandards.Theconcen-
line shall be used for heavy fuels as an internal reference to
tration of the elements present in the fuel test specimen are
compensate for viscosity effects.
calculated and displayed.
6.3 Particulate—When large particles over 10 µm in size
5. Significance and Use
are present, the analytical results will be lower than the actual
concentration they represent. Large particles may not be
5.1 Operating experience of gas turbines and diesel engines
effectively transported by the rotating disk electrode sample
has shown that some of the ash-forming substances present in
introduction system into the arc, nor will they be fully
a fuel can lead to high temperature corrosion, ash deposition,
vaporized.
and fuel system fouling. Ash-forming materials may be in a
fuelasoil-solublemetallo-organiccompoundsaswater-soluble
7. Apparatus
salts or as solid foreign contamination. Their presence and
7.1 Electrode Sharpener—An electrode sharpener to re-
concentrationvarieswiththegeographicalsourceofacrudeoil
move the contaminated portion of the rod electrode remaining
and they are concentrated in the residual fractions during the
from the previous determination. It also forms a new 160°
refining process. Although distillate fuel oils are typically
angle on the end of the electrode.
contaminant free, ash-forming materials may be introduced
later in the form of salt-bearing water or by contact with other 7.2 Rotating Disc Electrode Atomic Emission
petroleum products during transportation and storage. Specifi- Spectrometer—A simultaneous spectrometer consisting of ex-
cations of gas turbine and diesel engine fuels and the signifi- citation source, polychromator optics, and readout system.
D6728 − 16 (2021)
TABLE 1 Elements and Recommended Wavelengths
Element Wavelength, Element Wavelength, nm
nm
Aluminum 308.21 Magnesium 280.20, 518.36
Calcium 393.37 Nickel 341.48
Chromium 425.43 Potassium 766.49
Copper 324.75 Silicon 251.60
Iron 259.94 Sodium 588.99
Lead 283.31 Vanadium 290.88, 437.92
Lithium 670.78 Zinc 213.86
Manganese 403.07
FIG. 1 Graphite Counter Electrode
Suggested wavelengths are listed in Table 1. When multiple
wavelengths are listed, they are in the order of preference or
desired analytical range.
7.3 HeatedUltrasonicBath(Recommended)—Anultrasonic
bath to heat and homogenize fuel samples to bring particles
into suspension. The ultrasonic bath shall be used on samples
containing large amounts of debris, those that have been in
transit or in storage for at least 48 h and for heavy residual
fuels to reduce viscosity effects.
7.4 Power Mixer—A power mixer should be used before a
sample is transferred from one container to another to ensure
FIG. 2 Graphite Disc Electrode
thatahomogeneousmixtureiscreatedandmaintaineduntilthe
transfer is complete. Practice D5854 should be consulted for
the mixing and handling of liquid samples.
ratio of magnesium to all other metals present. The typical
concentration for the upper calibration point is 10 mg⁄kg for
8. Reagents and Materials
light fuels whenASTM No. 0-GT, No. 1-GT, No. 2-GT, Grade
8.1 Base Oil—A 75 cSt (40 °C) base oil, free of analyte, to
1-D, Grade 2-D, and Grade 4-D fuel samples are analyzed.The
be used as a calibration blank or for blending calibration
typical concentration for the upper calibration point is
standards.
100 mg⁄kg for heavy fuels when No. 3-GT and No. 4-GT fuel
samples are analyzed.
8.2 Check Sample and Quality Control (QC) Samples—One
8.7.1 Standards have a shelf-life and shall not be used to
or more oil or fuel standards or samples of known concentra-
standardize an instrument if they have exceeded the expiration
tion which are periodically analyzed as go/no-go samples to
date.
confirm the need for standardization based on an allowable
accuracy limit as described in Appendix X1.
8.8 Specimen Holders—A variety of specimen holders can
be used for the analysis of fuel samples. Disposable specimen
8.3 Cleaning Solution—An environmentally safe, non-
holders must be discarded after each analysis and reusable
chlorinated, rapid evaporating, and non-film producing solvent
specimen holders must be cleaned after each analysis. All
to remove spilled or splashed oil or fuel sample in the sample
specimen holders must be free of contamination and shall be
stand of the spectrometer.
stored accordingly. Specimen holder covers shall be used on
8.4 Counter Electrode—The counter electrode is a rod
those fuel samples that may catch on fire during the analysis.
electrode. The counter electrode shall be of high-purity graph-
ite (spectroscopic grade). Dimensions of new counter elec-
9. Sampling
trodes shall conform to those shown in Fig. 1.
9.1 The fuel sample taken for the analysis must be repre-
8.5 Disc Electrode—Graphite disc electrode of high-purity
sentative of the entire system. Good sampling procedures are
graphite (spectroscopic grade). Dimensions of the electrodes
key to good analyses and samples must be taken in accordance
shall conform to those shown in Fig. 2.
with Practices D4057 or D4177.
8.6 Glass Cleaning Solution—Capable of cleaning and re-
10. Preparation of Test Specimen
moving splashed oil or fuel sample from the quartz window
that protects the entrance lens and fiber optic.Ammonia based 10.1 Homogenization—Fuel samples may contain particu-
window cleaner or 70 % isopropyl rubbing alcohol have been late matter and free water and, in order to be representative,
found to be suitable for this purpose. must always be vigorously shaken prior to pouring a test
specimen for analysis.
8.7 Organometallic Standards—Single or multi-element
blended standards for use as the high concentration standard 10.2 Ultrasonic Homogenization—Samples that have been
for instrument standardization purposes or for use as a check in transit for several days, idle in storage or very viscous, shall
sample to confirm calibration. Multi-element blends are used be placed i
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