1、Designation: D6728 11Standard Test Method forDetermination of Contaminants in Gas Turbine and DieselEngine Fuel by Rotating Disc Electrode Atomic EmissionSpectrometry1This standard is issued under the fixed designation D6728; the number immediately following the designation indicates the year oforig
2、inal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of contami-nants and
3、 materials as a result of corrosion in gas turbine ordiesel engine fuels by rotating disc electrode atomic emissionspectroscopy (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 LowSulfur No. 1-D, Low Sulfur No. 2-D, No. 1-D, No
4、. 2-D, andNo. 4-D diesel fuel oils.1.1.2 This test method provides a rapid at-site determinationof contamination and corrosive elements ranging from frac-tions of mg/kg to hundreds of mg/kg in gas turbine and dieselengine fuels so the fuel quality and level of required treatmentcan be determined.1.1
5、.3 This test method uses oil-soluble metals for calibra-tion and does not purport to quantitatively determine or detectinsoluble particles.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard. The preferred units are mg/kg (ppm b
6、y mass).1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Refe
7、renced Documents2.1 ASTM Standards:2D975 Specification for Diesel Fuel OilsD2880 Specification for Gas Turbine Fuel OilsD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD5854 Practice for Mixing and Handling of Liquid Samplesof Petroleum and Petroleum ProductsD6299 Practice for A
8、pplying Statistical Quality Assuranceand Control Charting Techniques to Evaluate AnalyticalMeasurement System Performance3. Terminology3.1 Definitions:3.1.1 burn, vtin emission spectroscopy, to vaporize andexcite a specimen with sufficient energy to generate spectralradiation.3.1.2 calibration, nthe
9、 determination of the values of thesignificant parameters by comparison with values indicated bya set of reference standards.3.1.3 calibration curve, nthe graphical or mathematicalrepresentation of a relationship between the assigned (known)values of standards and the measured responses from themeas
10、urement system.3.1.4 calibration standard, na standard having an ac-cepted value (reference value) for use in calibrating a measure-ment instrument or system.3.1.5 detection limit, nthe smallest concentration of anelement that can be measured for specific analysis conditionsand data collection perio
11、ds.3.1.6 emission spectroscopy, nmeasurement of energyspectrum emitted by or from an object under some form ofenergetic stimulation; for example, light, electrical discharge,and so forth.3.2 Definitions of Terms Specific to This Standard:3.2.1 arc discharge, na self-sustaining, high current den-sity
12、, high temperature discharge uniquely characterized by acathode fall nearly equal to the ionization potential of the gasor vapor in which it exists.3.2.2 check sample, na reference material usually pre-pared by a single laboratory for its own use as a measurementcontrol standard, or for the qualific
13、ation of a measurementmethod.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.03 on Elemental Analysis.Current edition approved Oct. 1, 2011. Published November 2011. Originallyapproved in 2001.
14、Last previous edition approved in 2006 as D672801(2006).DOI: 10.1520/D6728-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page on
15、the ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.3 contaminant, nmaterial in a fuel sample that maycause ash deposition or high temperature corrosi
16、on.3.2.4 graphite disc electrode, na soft form of the elementcarbon manufactured into the shape of a disc for use as anelectrode in arc/spark spectrometers for oil and fuel analysis.3.2.5 graphite rod electrode, na soft form of the elementcarbon manufactured into the shape of a rod for use as acount
17、er electrode in arc/spark spectrometers for oil and fuelanalysis.3.2.6 profiling, nto set the actual position of the entranceslit to produce optimum measurement intensity.3.2.7 standardization, nthe process of reestablishing andcorrecting a calibration curve through the analysis of at leasttwo known
18、 oil standards.3.2.8 uptake rate, nthe amount of oil or fuel sample thatis physically carried by the rotating disc electrode into the arcfor analysis.4. Summary of Test Method4.1 A fuel test specimen is excited by a controlled arcdischarge using the rotating disk technique. The radiant ener-gies of
19、selected analytical lines and a reference are collectedand stored by way of photomultiplier tubes, charge coupleddevices, or other suitable detectors. A comparison is made ofthe emitted intensities of the elements in the fuel test specimenagainst those measured with calibration standards. The concen
20、-tration of the elements present in the fuel test specimen arecalculated and displayed.5. Significance and Use5.1 Operating experience of gas turbines and diesel engineshas shown that some of the ash-forming substances present ina fuel can lead to high temperature corrosion, ash deposition,and fuel
21、system fouling. Ash-forming materials may be in afuel as oil-soluble metallo-organic compounds as water-solublesalts or as solid foreign contamination. Their presence andconcentration varies with the geographical source of a crude oiland they are concentrated in the residual fractions during therefi
22、ning process. Although distillate fuel oils are typicallycontaminant free, ash-forming materials may be introducedlater in the form of salt-bearing water or by contact with otherpetroleum products during transportation and storage. Specifi-cations of gas turbine and diesel engine fuels and the signi
23、fi-cance of contamination and trace metals are detailed inSpecifications D2880 and D975.5.1.1 Pre-conditioning of the fuel before it reaches the gasturbine or diesel engine has become a prerequisite for instal-lations that use heavy petroleum fuel, and also for sites that uselight distillate fuel oi
24、ls. On-site fuel analysis to determine theextent of contamination is an integral part of a fuel qualitymanagement program. It is used first to determine the extent ofthe required treatment, and later, the effectiveness of thetreatment. It starts with the delivery of the fuel, continuesthroughout fue
25、l handling and ends only as the fuel is injectedinto the turbine or engine.5.1.2 Fuel contamination specifications vary among thedifferent gas turbine manufacturers. However, without excep-tion, each requires that contaminants must be as low aspossible. In most power generation installations, it is
26、the ownerwho has the responsibility of verifying fuel cleanliness incompliance with the turbine manufacturers warranty specifi-cations. This leads to an on-site analytical instrument perfor-mance requirement of below 1.0 mg/kg for several elements.6. Interferences6.1 SpectralMost spectral interferen
27、ces can be avoided byjudicious choice of spectral lines. High concentrations of someelements can have an interfering influence on the spectral linesused for determining trace levels of contaminants. Instrumentmanufacturers usually compensate for spectral interferencesduring factory calibration. A ba
28、ckground correction system,which subtracts unwanted intensities on the side of the spectralline, shall also be used for this purpose. When spectralinterferences cannot be avoided with spectral line selection andbackground correction, the necessary corrections shall be madeusing the computer software
29、 supplied by the instrument manu-facturer.6.2 Viscosity EffectsDifferences in viscosity of fuelsamples will cause differences in uptake rates. Internal refer-ences of the instrument will compensate for a portion of thedifferences. Without a reference, the analysis will be adverselyaffected if the te
30、st specimen has a different viscosity from thecalibration samples. The hydrogen 486.10 nm spectral lineshall be used for light fuels, and the CN 387.10 nm spectral lineshall be used for heavy fuels as an internal reference tocompensate for viscosity effects.6.3 ParticulateWhen large particles over 1
31、0 m in sizeare present, the analytical results will be lower than the actualconcentration they represent. Large particles may not beeffectively transported by the rotating disk electrode sampleintroduction system into the arc, nor will they be fullyvaporized.7. Apparatus7.1 Electrode SharpenerAn ele
32、ctrode sharpener to re-move the contaminated portion of the rod electrode remainingfrom the previous determination. It also forms a new 160angle on the end of the electrode.7.2 Rotating Disc Electrode Atomic EmissionSpectrometerA simultaneous spectrometer consisting of ex-citation source, polychroma
33、tor optics, and readout system.Suggested wavelengths are listed in Table 1. When multiplewavelengths are listed, they are in the order of preference ordesired analytical range.7.3 Heated Ultrasonic Bath (Recommended)An ultra-sonic bath to heat and homogenize fuel samples to bringparticles into suspe
34、nsion. The ultrasonic bath shall be used onTABLE 1 Elements and Recommended WavelengthsElement Wavelength, nm Element Wavelength, nmAluminum 308.21 Magnesium 280.20, 518.36Calcium 393.37 Nickel 341.48Chromium 425.43 Potassium 766.49Copper 324.75 Silicon 251.60Iron 259.94 Sodium 588.99Lead 283.31 Van
35、adium 290.88, 437.92Lithium 670.78 Zinc 213.86Manganese 403.07D6728 112samples containing large amounts of debris, those that havebeen in transit or in storage for at least 48 h and for heavyresidual fuels to reduce viscosity effects.7.4 Power MixerA power mixer should be used before asample is tran
36、sferred from one container to another to ensurethat a homogeneous mixture is created and maintained until thetransfer is complete. Practice D5854 should be consulted forthe mixing and handling of liquid samples.8. Reagents and Materials8.1 Base OilA 75 cSt (40C) base oil, free of analyte, tobe used
37、as a calibration blank or for blending calibrationstandards.8.2 Check Sample and Quality Control (QC) SamplesOneor more oil or fuel standards or samples of known concentra-tion which are periodically analyzed as go/no-go samples toconfirm the need for standardization based on an allowableaccuracy li
38、mit as described in Appendix X1.8.3 Cleaning SolutionAn environmentally safe, non-chlorinated, rapid evaporating, and non-film producing solventto remove spilled or splashed oil or fuel sample in the samplestand of the spectrometer.8.4 Counter ElectrodeThe counter electrode is a rodelectrode. The co
39、unter electrode shall be of high-purity graph-ite (spectroscopic grade). Dimensions of new counter elec-trodes shall conform to those shown in Fig. 1.8.5 Disc ElectrodeGraphite disc electrode of high-puritygraphite (spectroscopic grade). Dimensions of the electrodesshall conform to those shown in Fi
40、g. 2.8.6 Glass Cleaning SolutionCapable of cleaning andremoving splashed oil or fuel sample from the quartz windowthat protects the entrance lens and fiber optic. Ammonia basedwindow cleaner or 70 % isopropyl rubbing alcohol have beenfound to be suitable for this purpose.8.7 Organometallic Standards
41、Single or multi-elementblended standards for use as the high concentration standardfor instrument standardization purposes or for use as a checksample to confirm calibration. Multi-element blends are usedfor fuel analysis applications that contain a 3:1 concentrationratio of magnesium to all other m
42、etals present. The typicalconcentration for the upper calibration point is 10 mg/kg forlight fuels when ASTM No. 0-GT, No. 1-GT, No. 2-GT, Grade1-D, Grade 2-D, and Grade 4-D fuel samples are analyzed. Thetypical concentration for the upper calibration point is 100mg/kg for heavy fuels when No. 3-GT
43、and No. 4-GT fuelsamples are analyzed.8.7.1 Standards have a shelf-life and shall not be used tostandardize an instrument if they have exceeded the expirationdate.8.8 Specimen HoldersA variety of specimen holders canbe used for the analysis of fuel samples. Disposable specimenholders must be discard
44、ed after each analysis and reusablespecimen holders must be cleaned after each analysis. Allspecimen holders must be free of contamination and shall bestored accordingly. Specimen holder covers shall be used onthose fuel samples that may catch on fire during the analysis.9. Sampling9.1 The fuel samp
45、le taken for the analysis must be repre-sentative of the entire system. Good sampling procedures arekey to good analyses and samples must be taken in accordancewith Practice D4057.10. Preparation of Test Specimen10.1 HomogenizationFuel samples may contain particu-late matter and free water and, in o
46、rder to be representative,must always be vigorously shaken prior to pouring a testspecimen for analysis.10.2 Ultrasonic HomogenizationSamples that have beenin transit for several days, idle in storage or very viscous, shallbe placed in a heated ultrasonic bath to break up clusters ofparticles and to
47、 bring them back into suspension. The samplesshall be vigorously shaken with a power mixer after being inthe ultrasonic bath and prior to pouring a test specimen foranalysis. The bath temperature shall be 60C for very viscousfuels and below the flash point of non viscous fuels. The totalagitation ti
48、me for a sample should be at least 2 min.10.3 Specimen HoldersFuel samples and oil standardsshall be poured into a specimen holder of at least 1 mLcapacityprior to analysis. Exercise care to pour the sample consistentlyto the same level in the specimen holders.10.4 Specimen TableThe specimen table s
49、hall be adjustedso that when it is in the full raised position, at least one-thirdof the disc electrode diameter is immersed in the oil testspecimen.11. Preparation of Apparatus11.1 Warm-up BurnsIf the instrument has been idle forseveral hours, it may be necessary to conduct warm-up burns tostabilize the excitation source. The warm-up procedure can beFIG. 1 Graphite Counter ElectrodeFIG. 2 Graphite Disc ElectrodeD6728 113performed with any fuel sample or standard. Consult themanufacturers instructions for specific warm-up requirements.11.2 Op
