ASTM D7667 Standard Test Method for Determination of Corrosiveness to Silver by Automotive Spark-Ignition Engine Fuel - Thin Silver Strip Method
11. Procedure
11.1 Procedure A - Using a Pressure Vessel (PVP):
NOTE 3 - The pressure vessel is used to prevent evaporation of volatile samples such as gasoline during the test procedure, therefore, ensure that the O-ring of the PV is also in a good, usable condition to prevent leakage.
11.1.1 Wearing disposable gloves or other finger protection, insert the polished silver strip taken from the wash solvent, under the clip of the SSCD, up to the ridge (about 4 mm to 6 mm (5/32 in. to 7/32 in.)).
11.1.2 Place 30 mL of sample, completely clear and free of any suspended or entrained water (see 9.5) into a clean and dry 25 mm by 150 mm (1 in. by 6 in.) graduated test tube (see 6.2) and, within 1 min, place the SSCD into the test tube. Note that the lower edge of the assembled silver strip is about 22 mm (7/8 in.) from the bottom of the test tube.
11.1.3 Carefully place the test tube in the pressure vessel, and screw the lid on tightly.
11.1.4 Place the pressure vessel in a bath maintained at 50 °C +/- 1 °C (122 °F +/- 2 °F), and note the time at which this is done.
11.1.5 If more than one sample is to be analyzed at essentially the same time, it is permissible to prepare each pressure vessel in the batch before immersing each one in the bath maintained at 50 °C +/- 1 °C (122 °F +/- 2 °F), provided the elapsed time between the first and last samples is kept to a minimum. Note the time at which this is done.
11.1.6 After 120 min +/- 2 min for the automotive spark-ignition engine fuels, withdraw the pressure vessel from the bath and immerse in cool water for a few minutes.
11.1.7 Open the pressure vessel carefully in a well-ventilated area, such as a fume-hood, to safely vent any residual pressure that may have built up during the test (Warning - Contents may be under pressure.)
11.1.8 Forceps (see 6.7) may be used to grip the bar of the SSCD and remove it from the test tube. Remove test tube and dispose of contents appropriately.
11.1.9 Wearing disposable gloves or using alternate finger protection, lower the SSCD into wash-solvent such that silver strip is completely immersed. Remove immediately, give a few moments for the solvent to evaporate, then, within 15 min, inspect the strip for evidence of tarnishing or corrosion, with reference to Section 12 and Table 1.
11.2 Procedure B - Using a Vented Test Tube (VTTP):
11.2.1 Wearing disposable gloves, or other finger protection, insert the polished silver strip taken from the wash solvent, under the clip of the SSCD, up to the ridge (about 4 mm to 6 mm (5/32 in. to 7/32 in.))
11.2.2 Place 30 mL of sample, completely clear and free of any suspended or entrained water (see 9.5) into a clean and dry 25 mm by 150 mm (1 in. by 6 in.) graduated test tube (see 6.2) and, within 1 min, place the SSCD assembly into the test tube. Note that the lower edge of the assembled silver strip is about 22 mm (7/8 in.) from the bottom of the test tube.
11.2.3 Now place the test tube in a bath maintained at 50 °C +/- 1 °C (122 °F +/- 2 °F), and note the time at which this is done.
11.2.4 If more than one sample is to be analyzed at essentially the same time, it is permissible to prepare each sample in the batch before immersing each one in the bath maintained at 50 °C +/- 1 °C (122 °F +/- 2 °F), and note the time at which this is done. Protect the contents of the test tube from strong light during the test (see Note 4).
11.2.5 After 120 min +/- 2 min for the automotive spark-ignition engine fuels, wearing disposable gloves or other finger protection, withdraw the test tube from the bath. Allow test tube to cool slightly. Forceps (see 6.7) may be used to grip the bar of the SSCD, and remove it from the test tube. Dispose of contents of test tube appropriately.
11.2.6 Wearing disposable gloves or using alternate finger protection, lower the SSCD into wash-solvent such that silver strip is completely immersed. Remove immediately, give a few moments for the solvent to evaporate, then, within 15 min, inspect the strip for evidence of tarnishing or corrosion, with reference to Section 12 and Table 1.
NOTE 4 - Use of a dry block bath would prevent light penetration to a great extent.
12. Interpretation of Results
12.1 Interpret the corrosiveness of the sample, under normal daylight conditions, by comparing the appearance of the test strip with a freshly polished one (preserved in iso-octane) to give a classification based on that given in Table 1. Both larger surfaces shall be rated, but not the thin edges.
12.2 The Color Standard for Tube Deposit Rating (referenced in Test Method D3241) shall be used to differentiate between the brown colorations mentioned in Classifications 1 and 2. Any brown coloration less than No. 4 on the Color Standard shall be rated as Classification 1. Any coloration equal to or darker than No. 4 on the Color Standard shall be rated as Classification 2 or higher.
