ASTM D6728 Standard Test Method for Determination of Contaminants in Gas Turbine and Diesel Engine Fuel by Rotating Disc Electrode Atomic Emission Spectrometry
1. 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 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.
2. Referenced Documents
2.1 ASTM Standards:
D975 Specification for Diesel Fuel Oils
D2880 Specification for Gas Turbine Fuel Oils
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
D5854 Practice for Mixing and Handling of Liquid Samples of Petroleum and Petroleum Products
D6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measurement System Performance
3. Terminology
3.1 Definitions:
3.1.1 burn, vt - in emission spectroscopy, to vaporize and excite a specimen with sufficient energy to generate spectral radiation.
3.1.2 calibration, n - the determination of the values of the significant parameters by comparison with values indicated by a set of reference standards.
3.1.3 calibration curve, n - the graphical or mathematical representation of a relationship between the assigned (known) values of standards and the measured responses from the measurement system.
3.1.4 calibration standard, n - a standard having an accepted value (reference value) for use in calibrating a measurement instrument or system.
3.1.5 detection limit, n - the smallest concentration of an element that can be measured for specific analysis conditions and data collection periods.
3.1.6 emission spectroscopy, n - measurement of energy spectrum emitted by or from an object under some form of energetic stimulation; for example, light, electrical discharge, and so forth.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 arc discharge, n - a self-sustaining, high current density, high temperature discharge uniquely characterized by a cathode fall nearly equal to the ionization potential of the gas or vapor in which it exists.
3.2.2 check sample, n - a reference material usually prepared by a single laboratory for its own use as a measurement control standard, or for the qualification of a measurement method.
3.2.3 contaminant, n - material in a fuel sample that may cause ash deposition or high temperature corrosion.
3.2.4 graphite disc electrode, n - a soft form of the element carbon manufactured into the shape of a disc for use as an electrode in arc/spark spectrometers for oil and fuel analysis.
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 counter electrode in arc/spark spectrometers for oil and fuel analysis.
3.2.6 profiling, n - to set the actual position of the entrance slit to produce optimum measurement intensity.
3.2.7 standardization, n - the process of reestablishing and correcting a calibration curve through the analysis of at least two known oil standards.
3.2.8 uptake rate, n - the amount of oil or fuel sample that is physically carried by the rotating disc electrode into the arc for analysis.
