ASTM D7095 Standard Test Method for Rapid Determination of Corrosiveness to Copper from Petroleum Products Using a Disposable Copper Foil Strip
10. Procedure
10.1 General:
10.1.1 There are a variety of test conditions, which are broadly specific to given classes of product, but within certain classes, more than one set of test conditions of time or temperature, or both, may apply. In general, aviation gasoline shall be tested in a pressure vessel at 100 °C (212 °F) and other high vapor pressure fuels, like natural gasoline or winter-grade gasoline at 40 °C (104 °F). Other liquid products shall be tested in a test tube at 50 °C (122 °F), 100 °C (212 °F) or even higher temperatures. The temperature conditions (but not the time durations) given are commonly used and are quoted in the ASTM specifications for these products tested by Test Method D130 where such specifications exist. These are, however, guidelines only. In this procedure, test durations are defined as 45 min +/- 1 min. Other conditions can also be used as and when required by specifications or by agreement between parties. The test conditions of time and temperature shall be recorded as part of the result (see 12.1). (Warning - Some products, particularly natural gasoline, may have a much higher vapor pressure than would normally be characteristic of automotive or aviation gasolines. For this reason, extreme caution must be exercised to ensure that the pressure vessel used in this test method and containing natural gasoline or other products of high vapor pressure, is not placed in the 100 °C (212 °F) bath. Samples having vapor pressures in excess of 124 kPa (18 psi) may develop sufficient pressures at 100 °C (212 °F) to rupture the pressure vessel. For any sample having a vapor pressure above 124 kPa (18 psi), use Test Method D1838.)
10.2 Pressure Vessel Procedure (PVP) - For use with aviation gasoline, aviation turbine fuel, samples with initial boiling points (IBP) at or below test temperature, and highly volatile samples, such as those with vapor pressures >80 kPa at 37.8 °C (100 °F) (see 10.3.1.2).
10.2.1 For aviation gasoline and aviation turbine fuel, place 30 mL of sample, completely clear and free of any suspended or entrained water (see 8.3) into a clean and dry 25 mm by 150 mm (1 in. by 6 in.) test tube. Within 1 min after completing the surface preparation (polishing), slide the copper foil strip into the sample tube. Place the sample tube into the pressure vessel (see Fig. 1) and screw the lid on tightly. Note the time at which the assembly is placed in the bath. If more than one sample is to be analyzed, immerse each pressure vessel in the bath at 100 °C +/- 1 °C (212 °F +/- 2 °F), and note the time at which each specimen is placed in the bath. After 45 min +/- 1 min in the bath, withdraw the pressure vessel and immerse it for a few minutes in cool water (tap water). Open the pressure vessel, withdraw the test tube and examine the copper foil strip as described in 10.4. Discard the copper foil strip after use.
10.2.2 For natural gasoline, samples with initial boiling points (IBP) at or below test temperature, and highly volatile samples, such as those (for example, winter-grade gasoline) with vapor pressures >80 kPa at 37.8 °C (100 °F), carry out the test exactly as described in 10.2.1, but at 40 °C (104 °F) and for 45 min +/- 1 min. Discard the copper foil strip after use. (See warning statement in 1.1.)
10.3 Test Tube Procedure (TTP) - For use with samples with IBP above test temperature (for example, for use with most liquid or middle distillate products).
10.3.1 For diesel fuel, fuel oil, automotive gasoline, place 30 mL of sample, completely clear and free of any suspended or entrained water (see 8.3) into a clean, dry 25 mm by 150 mm (1 in. by 6 in.) test tube, and, within 1 min after completing the surface preparation (polishing), slide the copper foil strip into the sample tube. Stopper the tube with a vented-cork having about 45 mm (1 3/4 in.) length ofa 4 mm (1/8 in.) inside diameter (and about 6 mm (1/4 in. outside diameter)) plastic or glass tubing passing through it. For gasoline samples, place a plastic-cap with a pin-hole in it, over the plastic or glass tubing to reduce evaporation. Place the tube in a bath maintained at 50 °C +/- 1 °C (122 °F +/- 2 °F), and note the time at which the tube is placed in the bath. Protect the contents of the test tube from strong light during the test. If more than one sample is to be analyzed, immerse each test tube in the bath, and note the time at which each specimen is placed in the bath. After 45 min +/- 1 min in the bath, withdraw the test tube and examine the copper foil strip as described in 10.4. Discard the copper foil strip after use.
10.3.1.1 For tests on fuel oil and diesel fuel, using specifications other than Specifications D396 and D975, a temperature of 100 °C (212 °F) for 45 min +/- 1 min may be used as an alternative set of conditions.
10.3.1.2 Some automotive gasolines with vapor pressure above 80 kPa at 37.8 °C (100 °F) have exhibited evaporation losses in excess of 10 % of their volume. If such evaporation losses are apparent, it is recommended that the pressure vessel procedure (see 10.2) be used.
10.3.2 For cleaners (for example, Stoddard solvent) and kerosine, carry out the test exactly as described in 10.3.1 but at 100 °C +/- 1 °C (212 °F +/- 2 °F). Discard the copper foil strip after use.
10.3.3 For lubricating oil, carry out the test exactly as described in 10.3.1, but the tests may be carried out for varying times and at elevated temperatures other than 100 °C (212 °F). For the sake of uniformity, it is suggested that even increments of 5 °C (10 °F), beginning with 150 °C (302 °F), be used. Discard the copper foil strip after use.
10.4 Strip Examination:
10.4.1 Empty the contents of the test tube into a suitably-sized receiver. If a glass receiver is used, such as a 150 mL tall-form beaker, let the copper foil strip slide in gently so as to avoid breaking the glass. Immediately withdraw the copper foil strip with forceps and immerse in wash solvent. Withdraw the copper foil strip at once, dry and inspect for evidence of tarnishing or corrosion by comparison with the Copper Strip Corrosion Standards. Drying of the copper foil strip may be done by blotting with filter paper, air drying, or by other suitable means. Hold both the test copper foil strip and the standard strip plaque in such a manner that light reflected from them at an angle of approximately 45° will be observed.
10.4.2 In handling the test copper foil strip during the inspection and comparison, the danger of marking or staining can be avoided if it is inserted in a flat glass tube (see X1.1), which can be stoppered with absorbent cotton.
11. Interpretation of Results
11.1 Interpret the corrosiveness of the sample in accordance with one of the classifications of the ASTM Copper Strip Corrosion Standard as listed in Table 1.
11.1.1 When a test strip is in the obvious transition state between that indicated by any two adjacent standard strips, rate the sample by the more tarnished standard strip. Should a strip appear to have a darker orange color than Standard Strip 1b, consider the observed strip as still belonging in Classification 1; however, if any evidence of red color is observed, the observed strip belongs in Classification 2.
11.1.2 A claret red strip in Classification 2 can be mistaken for a magenta overcast on a brassy strip in Classification 3 if the brassy underlay of the latter is completely masked by a magenta overtone. To distinguish, immerse the strip in wash solvent; the former will appear as a dark orange strip while the latter will not change.
11.1.3 To distinguish multi-colored strips in Classifications 2 and 3, place a test strip in a 25 mm by 150 mm (1 in. by 6 in.) test tube and bring to a temperature of340 °C +/- 30 °C (644 °F +/- 54 °F) in 4 min to 6 min with the tube lying on a hot plate. Adjust to temperature by observing a high distillation thermometer inserted into a second test tube. If the strip belongs to Classification 2, it will assume the color of a silver and then a gold strip. If in Classification 3, it will take on the appearance of a transparent black, and so forth, as described in Classification 4a.
11.1.4 Repeat the test if blemishes due to fingerprints are observed, or due to spots from any particles or water droplets that may have touched the test strip during the test.
11.1.5 Repeat the test also if the sharp edges along the flat faces ofthe strip appear to be in a classification higher than the greater portion of the strip; in this case, it is likely that the edges were burnished during preparation (polishing).
