ASTM D6728-01(2006)
(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
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 D 2880 and D 975.
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’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.
1.1.2 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).
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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Designation:D6728–01 (Reapproved 2006)
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 D4057 Practice for Manual Sampling of Petroleum and
Petroleum Products
1.1 This test method covers the determination of contami-
D5854 PracticeforMixingandHandlingofLiquidSamples
nants and materials as a result of corrosion in gas turbine or
of Petroleum and Petroleum Products
diesel engine fuels by rotating disc electrode atomic emission
D6299 Practice for Applying Statistical Quality Assurance
spectroscopy (RDE-AES).
and Control Charting Techniques to Evaluate Analytical
1.1.1 The test method is applicable to ASTM Grades 0-GT,
Measurement System Performance
1-GT,2-GT,3-GT,and4-GTgasturbinefuelsandGradesLow
Sulfur No. 1-D, Low Sulfur No. 2-D, No. 1-D, No. 2-D, and
3. Terminology
No. 4-D diesel fuel oils.
3.1 Definitions:
1.1.2 Thistestmethodprovidesarapidat-sitedetermination
3.1.1 burn, vt—in emission spectroscopy, to vaporize and
of contamination and corrosive elements ranging from frac-
excite a specimen with sufficient energy to generate spectral
tions of mg/kg to hundreds of mg/kg in gas turbine and diesel
radiation.
engine fuels so the fuel quality and level of required treatment
3.1.2 calibration, n—the determination of the values of the
can be determined.
significant parameters by comparison with values indicated by
1.1.3 This test method uses oil-soluble metals for calibra-
a set of reference standards.
tion and does not purport to quantitatively determine or detect
3.1.3 calibration curve, n—the graphical or mathematical
insoluble particles.
representation of a relationship between the assigned (known)
1.2 The values stated in SI units are to be regarded as the
values of standards and the measured responses from the
standard. The values given in parentheses are for information
measurement system.
only. The preferred units are mg/kg (ppm by mass).
3.1.4 calibration standard, n—a standard having an ac-
1.3 This standard does not purport to address all of the
cepted value (reference value) for use in calibrating a measure-
safety concerns, if any, associated with its use. It is the
ment instrument or system.
responsibility of the user of this standard to establish appro-
3.1.5 detection limit, n—the smallest concentration of an
priate safety and health practices and determine the applica-
element that can be measured for specific analysis conditions
bility of regulatory limitations prior to use.
and data collection periods.
2. Referenced Documents 3.1.6 emission spectroscopy, n—measurement of energy
2 spectrum emitted by or from an object under some form of
2.1 ASTM Standards:
energetic stimulation; for example, light, electrical discharge,
D975 Specification for Diesel Fuel Oils
and so forth.
D2880 Specification for Gas Turbine Fuel Oils
3.2 Description of Terms Specific to This Standard:
3.2.1 arc discharge, n—a self-sustaining, high current den-
This test method is under the jurisdiction of ASTM Committee D02 on
sity, high temperature discharge uniquely characterized by a
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
cathode fall nearly equal to the ionization potential of the gas
D02.03 on Elemental Analysis.
or vapor in which it exists.
Current edition approved May 1, 2006. Published June 2006. Originally
approved in 2001. Last previous edition approved in 2001 as D6728 – 01. DOI:
3.2.2 check sample, n—a reference material usually pre-
10.1520/D6728-01R06.
pared by a single laboratory for its own use as a measurement
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
control standard, or for the qualification of a measurement
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
method.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6728–01 (2006)
3.2.3 contaminant, n—material in a fuel sample that may who has the responsibility of verifying fuel cleanliness in
cause ash deposition or high temperature corrosion. compliance with the turbine manufacturer’s warranty specifi-
3.2.4 graphite disc electrode, n—a soft form of the element cations. This leads to an on-site analytical instrument perfor-
carbon manufactured into the shape of a disc for use as an mance requirement of below 1.0 mg/kg for several elements.
electrode in arc/spark spectrometers for oil and fuel analysis.
6. Interferences
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
6.1 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
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 carbon 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
are present, the analytical results will be lower than the actual
5. Significance and Use
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 remove
concentrationvarieswiththegeographicalsourceofacrudeoil
the contaminated portion of the rod electrode remaining from
and they are concentrated in the residual fractions during the
the previous determination. It also forms a new 160° angle on
refining process. Although distillate fuel oils are typically
the end of the electrode.
contaminant free, ash-forming materials may be introduced
7.2 Rotating Disc Electrode Atomic Emission
later in the form of salt-bearing water or by contact with other
Spectrometer—a simultaneous spectrometer consisting of ex-
petroleum products during transportation and storage. Specifi-
citation source, polychromator optics, and readout system.
cations of gas turbine and diesel engine fuels and the signifi-
Suggested wavelengths are listed in Table 1. When multiple
cance of contamination and trace metals are detailed in
wavelengths are listed, they are in the order of preference or
Specifications D2880 and D975.
desired analytical range.
5.1.1 Pre-conditioning of the fuel before it reaches the gas
7.3 Heated Ultrasonic Bath (Recommended)—an ultrasonic
turbine or diesel engine has become a prerequisite for instal-
bath to heat and homogenize fuel samples to bring particles
lations that use heavy petroleum fuel, and also for sites that use
into suspension. The ultrasonic bath shall be used on samples
light distillate fuel oils. On-site fuel analysis to determine the
extent of contamination is an integral part of a fuel quality
TABLE 1 Elements and Recommended Wavelengths
management program. It is used first to determine the extent of
Element Wavelength, nm Element Wavelength, nm
the required treatment, and later, the effectiveness of the
treatment. It starts with the delivery of the fuel, continues Aluminum 308.21 Magnesium 280.20, 518.36
Calcium 393.37 Nickel 341.48
throughout fuel handling and ends only as the fuel is injected
Chromium 425.43 Potassium 766.49
into the turbine or engine.
Copper 324.75 Silicon 251.60
5.1.2 Fuel contamination specifications vary among the Iron 259.94 Sodium 588.99
Lead 283.31 Vanadium 290.88, 437.92
different gas turbine manufacturers. However, without excep-
Lithium 670.78 Zinc 213.86
tion, each requires that contaminants must be as low as
Manganese 403.07
possible. In most power generation installations, it is the owner
D6728–01 (2006)
containing large amounts of debris, those that have been in 8.7.1 Standards have a shelf-life and shall not be used to
transitorinstorageforatleast48handforheavyresidualfuels standardize an instrument if they have exceeded the expiration
to reduce viscosity effects. date.
7.4 Power Mixer—A power mixer should be used before a 8.8 Specimen Holders—A variety of specimen holders can
sample is transferred from one container to another to ensure be used for the analysis of fuel samples. Disposable specimen
thatahomogeneousmixtureiscreatedandmaintaineduntilthe holders must be discarded after each analysis and reusable
transfer is complete. Practice D5854 should be consulted for specimen holders must be cleaned after each analysis. All
the mixing and handling of liquid samples. specimen holders must be free of contamination and shall be
stored accordingly. Specimen holder covers shall be used on
8. Reagents and Materials those fuel samples that may catch on fire during the analysis.
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 D4057.
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,Grade2-D,andGrade4-Dfuelsamplesareanalyzed.The severalhours,itmaybenecessarytoconductwarm-upburnsto
typical concen
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