Corrosiveness to copper from petroleum products by Copper Strip test
10. Preparation of Test Strips
10.1 Surface Preparation - Remove all surface blemishes from all six sides of the strip obtained from a previous analysis (see Note 1). One way to accomplish this is to use 00 grade or finer steel wool or silicon carbide paper or cloth of such degrees of fineness as are needed to accomplish the desired results efficiently. Finish with 65-µm (220-grit CAMI-grade or P220 FEPA-grade) silicon carbide paper or cloth, removing all marks that may have been made by other grades of paper used previously. Ensure the prepared copper strip is protected from oxidation prior to final preparation, such as by immersing the strip in wash solvent from which it can be withdrawn immediately for final preparation (polishing) or in which it can be stored for future use.
NOTE 1 - Only final preparation (10.2) is necessary for commercially purchased pre-polished strips, although if gasoline samples are being analyzed, pre-polished strips may be used "as is" (that is, without going through the final polishing procedure), based on the results of a 2008 interlaboratory study versus manually prepared copper strips. No statistical evaluation involving pre-polished copper strips has been performed using sample types other than gasoline at this time. See Section 14 for more details.
10.1.1 As a practical manual procedure for surface preparation, place a sheet of silicon carbide paper or cloth on a flat surface and moisten it with kerosine or wash solvent. Rub the strip against the silicon carbide paper or cloth with a circular motion, protecting the strip from contact with the fingers by using ashless filter paper or wearing disposable gloves. Alternatively, the surface of the strip can be prepared by use of motor-driven machines using appropriate grades of dry paper or cloth.
10.2 Final Preparation - For strips prepared in 10.1 or new strips being used for the first time, remove a strip from its protected location, such as by removing it from the wash solvent. To prevent possible surface contamination during final preparation, do not allow fingers to come in direct contact with the copper strips, such as by wearing disposable gloves or holding the strips in the fingers protected with ashless filter paper. Polish first the ends and then the sides with the 105-µm (120-grit to 150-grit CAMI-grade or P120 to P150 FEPA-grade) silicon carbide grains picked up with a pad of cotton (cotton wool) moistened with wash solvent. Wipe vigorously with fresh pads of cotton (cotton wool) and subsequently handle without touching the surface of the strip with the fingers. Forceps have been found suitable to use. Clamp in a vise and polish the main surfaces with silicon-carbide grains on absorbent cotton. Do not polish in a circular motion. Rub in the direction of the long axis of the strip, carrying the stroke beyond the end of the strip before reversing the direction. Clean all metal dust from the strip by rubbing vigorously with clean pads of absorbent cotton until a fresh pad remains unsoiled. When the strip is clean, immediately immerse it in the prepared sample.
10.2.1 It is important to polish the whole surface of the strip uniformly to obtain a uniformly stained strip. If the edges show wear (surface elliptical), they will likely show more corrosion than the center. The use of a vise (see Appendix X1) will facilitate uniform polishing.
10.2.2 It is important to follow the order of preparation with the correctly sized silicon carbide material as described in 10.1 and 10.2. The final preparation is with 105-µm silicon carbide powder. This is a larger grain size than the 65-µm paper used in the surface preparation stage. The reason for this use of larger silicon carbide grains in the final preparation is to produce asperities (controlled roughness) on the surface of the copper, which act as sites for the initiation of corrosion reactions.
