ASTM D1838 Test Method for Copper Strip Corrosion by Liquefied Petroleum (LP) Gases
8. Preparation of Strips
8.1 Surface Preparation - Remove all surface blemishes from all six sides of the strip obtained from a previous analysis. 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 grade (220-grit CAMI-grade or P220 FEPA-grade) silicon carbide paper or cloth, removing all marks that could have been made by other grades ofpaper 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from oxidation prior to final preparation, such as by immersing the strip in wash solvent from which it can be withdrawn immediately for finish preparation (polishing) or in which it can be stored for future use.
8.1.1 Only final preparation (8.2) is necessary for commercially purchased pre-polished strips.
8.1.2 As a practical manual procedure for surface preparation, a sheet of silicon carbide paper may be placed on a flat surface and then moisten the paper with wash solvent before rubbing the strip against the silicon carbide paper or cloth with a circular motion. Protect the strip from contact with the fingers, such as by using ashless filter paper. Alternatively, the surface ofthe strip may be prepared by use ofmotor-driven machines using appropriate grades of dry paper or cloth.
8.2 Final Preparation - For strips prepared in 8.1 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. 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 absorbent cotton moistened with wash solvent, making sure that the surface is protected from coming in contact with the fingers, such as by using ashless filter paper. Wipe vigorously with fresh pads ofabsorbent cotton and subsequently handle without touching the surface of the strip with the fingers. Padded forceps (to prevent the scratching of the surface) have been found suitable to use. Secure the copper strip in a vise or suitable holder 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, with minimal delay, attach to the dip tube and lower into the prepared corrosion test cylinder (see Fig. 1).
8.2.1 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 will facilitate uniform polishing.
8.2.2 It is important to follow the order of preparation with the correctly sized silicon carbide material as described in 8.1 and 8.2. The final preparation is with 105-µm (120-grit to 150-grit CAMI-grade or P120 to P150 FEPA-grade) silicon carbide grains. This is a larger grain size than the 65-µm grade (220-grit CAMI-grade or P220 FEPA-grade) 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.
9. Sampling
9.1 Obtain a sample from a point in the LPG system that will give a representative sample of the volume being tested, such as from a dynamic flowing stream or from a well mixed container, as appropriate. Preferably, collect the sample directly into the corrosion test cylinder (6.1) after it has been prepared for testing (10.1). Pay particular attention to safety and warning notes in Practices D1265 and D3700.
9.2 Alternatively, collect a sample in accordance with Practices D1265 and D3700.
9.2.1 If a sample is first collected in a sampling cylinder, ensure that the interior surfaces are inert and will not react with corrosive species. Sampling cylinders with protective (inert) internal coatings or surface treatments (such as fused glass) may be used.
NOTE 2 - Some internal coatings are porous and can adsorb or release contaminants that can affect test results. Also, fresh steel surfaces can react with some corrosive sulfur species and potentially remove them, which could result in a "false pass" in the copper strip corrosion test.
9.3 The time between when the sample is collected and when the test is begun should be held to a minimum (preferably only a few minutes) (see Note 3).
9.4 In case of dispute, a sample shall be collected directly into a corrosion test cylinder.
