ASTM D2624-22 Standard Test Methods for Electrical Conductivity of Aviation and Distillate Fuels

The standard "ASTM D2624-22 Standard Test Methods for Electrical Conductivity of Aviation and Distillate Fuels" published by the American Society for Testing and Materials (ASTM) describes test methods for determining the electrical conductivity of aviation and distillate fuels with and without static dissipative additives. These test methods normally provide a measurement of the conductivity when the fuel is uncharged, i.e. electrically at rest (known as quiescent conductivity).

Two test methods are defined for field testing of fuel conductivity:

• Portable measuring instruments for direct measurement in tanks or field or laboratory measurement of fuel samples
• In-line meters for continuous measurement of fuel conductivities in a fuel distribution system

When using portable meters, care should be taken to allow residual electrical charges to relax prior to measurement and to prevent fuel contamination.

For the purposes of this standard, the following definitions apply:

• Picosiemens/meter is the unit of electrical conductivity.
• The static conductance is the reciprocal of the resistivity of an uncharged fuel in the absence of ionic depletion or polarization. It is a measure of the electrical conductance at the first instant of current measurement after a direct current voltage is applied between the electrodes, or the average current when an alternating current (AC) voltage is applied.

In performing the tests, a voltage is applied to two electrodes in the fuel and the resulting current is expressed as a conductance value. In portable meters, the current measurement is made almost instantaneously when the voltage is applied to avoid errors due to ion depletion. Ion depletion or polarization is eliminated in dynamic monitoring systems by continuously changing the sample in the measuring cell or by using an alternating voltage. With the correct choice of electrode size and current measuring device, this procedure can be used to measure conductivities of 1 picosiemens/meter or greater. The commercially available equipment discussed in these methods covers a conductivity range up to 2000 picosiemens/meter with good accuracy.

The ability of a fuel to dissipate the charge generated during pumping and filtering is controlled by its electrical conductivity, which depends on the content of ionic species. If the conductivity is high enough, the charges will dissipate rapidly enough to prevent their accumulation and to prevent dangerously high potentials in the receiver tank.

Equipment used in the portable meter testing method includes:

• Conductivity cell and current measuring apparatus: Since hydrocarbon conductivities are extremely low compared to aqueous solutions, special equipment is needed that can respond almost instantaneously when voltage is applied.
• Thermometer with appropriate range for measuring fuel temperature in the field: Fuel in bulk storage, rail tankers and trucks should be equipped with a thermometer holder to directly determine the temperature. Some types of thermometers measure and store the sample temperature during the test cycle. Other types measure and display the sample temperature at the completion of the test cycle.
• Measuring vessel: Any suitable container that can hold enough fuel to cover the electrodes of the conductivity cell.

Equipment used in the continuous in-line conductivity testing method includes:

• Emcee staticon system: Capable of measuring and recording the conductivity and temperature of a fuel stream.
• Continuous measurements can be made when appropriate precautions are taken to remove static charges before the representative fuel flow passes through the in-line measuring cell. A controlled, continuous flow through the cell prevents ion depletion and thus provides a value equivalent to stationary conductivity as a continuous measurement. Additionally, measuring conductivity using a constant-flow sidestream sensor makes conductivity insensitive to the actual flow rate of the sampled fuel flow.

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