ASTM D7157 Standard Test Method for Determination of Intrinsic Stability of Asphaltene-Containing Residues, Heavy Fuel Oils, and Crude Oils (n-Heptane Phase Separation; Optical Detection)
9. Sampling and Test Specimens
9.1 Sampling:
9.1.1 Obtain representative samples in accordance with recognized sampling procedures such as Practices D4057 or D4177.
9.1.2 Samples of very viscous materials may be warmed until they are reasonably fluid before they are sampled.
9.1.3 Store samples prior to taking test specimens at ambient temperatures.
9.2 Test Specimen Preparation:
9.2.1 Sample Temperature - If necessary, warm viscous samples until they can be mixed readily before opening the storage container. For fuels with a high wax content (high pour point) the temperature must be at least 15 °C above the pour point.
9.2.2 Manually shake the sample thoroughly. If the sample contains high content of insoluble inorganic matter, filter the sample through a 47 mm diameter glass fiber filter medium (such as Whatman Grade GF/A), using the Test Method D4870 filtration apparatus. Specimen should be representative of the whole sample.
9.3 Preparation ofSpecimen Dilutions - Prepare three dilutions of specimen in toluene in different ratios (see Table 1) as follows:
9.3.1 Place a magnetic stirrer bar into a clean titration cell.
9.3.2 Add the required amount of specimen to the titration cell and obtain the mass of the specimen to the nearest 0.001 g(Moil).
9.3.3 Add the appropriate volume of toluene to the nearest 0.1 mL to the titration cell.
9.3.4 Stir dilutions of sample Type 1, without heating, for at least two minutes. Obtain the mass of the specimen plus toluene to the nearest 0.001 g (M1). Proceed with Section 12.
9.3.5 For specimen dilutions of Type 2 and 3, place a condenser on the titration cell, place on the hot plate, and boil under reflux, while stirring, for a minimum of 10 min for specimens of Type 2 and for a minimum of 15 min for specimens of Type 3.
9.3.6 Discontinue heating and while stirring, allow the dilutions to cool to ambient temperature. Disconnect the condenser and obtain the mass of specimen plus toluene to the nearest 0.001 g (M1). Proceed with Section 12.
NOTE 1 - In this context, "liquid" means the minimum temperature at which the product has sufficient fluidity to be handled as a liquid.
10. Preparation of Apparatus
10.1 Prepare and set up the instrument for operation according to the manufacturer's manual. (Refer to Fig. 1.)
10.2 Plug the optical probes into their connectors and place them in their stand by position.
10.3 Ensure that the reagent vessel contains sufficient n-heptane to run the tests (minimum 200 mL).
10.4 Cleaning Instructions - Perform the following cleaning procedure after the test procedure (see 12.1.8).
10.4.1 Carefully remove the dosing tube and the optical probe from the titration cell. Clean the optical probe with an appropriate solvent (toluene) (see 8.1.1).
10.4.2 Remove the stirrer bar. Empty the titration cell. Clean the reactor cell and stirrer bar with an appropriate solvent (toluene) (see 8.1.1).
11. Quality Control Monitoring
11.1 Confirm the performance of the instrument and test procedure by analyzing quality control (QC) samples.
11.1.1 When quality control/quality assurance (QC/QA) protocols are already established in the testing facility, these can be used when they confirm the reliability of the test result.
11.1.2 When there is no QC/QA protocol established in the testing facility, Guide D6792 can be used for guidance.
