GB/T 5096-2017 Copper strip corrosion test for petroleum products

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Card type: Test method

1. Method number / full title / English title / replacement relationship

• Standard number: GB/T 5096—2017
• Chinese title: Petroleum products—Copper strip corrosion test method
• English title: Test method for corrosiveness to copper from petroleum products by copper strip test
• Replacement relationship: replaces GB/T 5096—1985 "Petroleum products—Copper strip corrosion test method"
• Issued/implemented: issued on 2017-07-31, implemented on 2018-02-01
• Proposed and administered by: National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280)
• Drafting organization: Sinopec Research Institute of Petroleum Processing; participating drafting organization: Oil Products Technology Research Institute of Sinopec Sales Co., Ltd.
• Main drafters: Yang Tingting, Zheng Yu, Dong Fang, Chen Jie, Wu Xiaodong, Zhang Fengquan, Liu Xinlu
• Previous versions: GB/T 5096—1985

2. Scope of application and non-applicability

• Applicable to the determination of the corrosiveness to copper of automotive gasoline, aviation gasoline, jet fuel, solvent naphtha, kerosene, diesel, distillate fuel oils, lubricating oils and natural gasoline, or other hydrocarbons whose vapor pressure at 37.8 ℃ is not greater than 124 kPa.
• Not applicable/restrictions: samples with a vapor pressure exceeding 124 kPa can generate very high pressure at 100 ℃, which may cause the pressure vessel to rupture; therefore, for samples with a vapor pressure exceeding 124 kPa, SH/T 0232 shall be used for the determination.
• Warning: do not place pressure vessels containing high-vapor-pressure natural gasoline or other products into the 100 ℃ bath.

3. Method principle

A polished copper strip is immersed in a certain volume of the sample, heated to the specified temperature according to the product category of the sample, and held for a certain time. At the end of the heating period, the copper strip is removed, washed, and compared with the copper strip corrosion standard color plate to evaluate the discoloration of the copper strip and determine the corrosion grade.

4. Reagents and materials (purity / preparation)

• 5.1 Washing solvent: any volatile hydrocarbon solvent with a sulfur content of less than 5 mg/kg that does not discolor the copper strip at 50 ℃ and in the test 3 h may be used. Analytically pure petroleum ether (90 ℃~120 ℃) may also be selected. 2,2,4- trimethylpentane with a purity not lower than 99.75% may be used as the washing solvent for arbitration tests. Warning: isooctane is extremely flammable, see A.1.
• 5.2 Polishing material: 65 μm (P220) silicon carbide or aluminum oxide (corundum) abrasive paper or cloth, 105 μm (P150) silicon carbide or aluminum oxide (corundum) abrasive grains, and pharmaceutical-grade absorbent cotton. Silicon carbide polishing material shall be used as the polishing material for arbitration tests. Note: for particle size P220 and P150, see the provisions of GB/T 9258.1—2000.
• 5.3 Copper strip: electrolytic copper with a purity greater than 99.9%; the T2 copper specified in GB/T 5231—2012 can meet the use requirements. Width 12.5 mm±2 mm, thickness 1.5 mm~3.0 mm, length 75 mm±5 mm. The copper strip may be reused, but if pitting or deep scratches appear on the surface of the copper strip and cannot be removed by the specified polishing procedure, or if the surface of the copper strip is deformed, the copper strip shall be discarded.
• 5.4 Ashless filter paper or disposable gloves: used in the copper strip surface preparation and final polishing steps to protect the copper strip from direct contact with the operator's fingers.
• 5.5 Steel wool (cotton): 00 grade or finer. Used for the initial surface polishing treatment of the test strip.

5. Apparatus and equipment

• 4.1 Copper strip corrosion test pressure vessel: made of stainless steel, dimensions as shown in Figure 1; the vessel shall be able to withstand a test gauge pressure of 700 kPa. As long as it can be ensured that the internal dimensions of the vessel are the same as those required in Figure 1, other design forms may also be used for the vessel cover and synthetic rubber sealing gasket. The internal dimensions of the pressure vessel shall ensure that a test tube with an outer diameter of 25 mm and a length of 150 mm can be placed inside. Material: stainless steel; welding: maximum test pressure 700 kPa. Note: all dimensions without tolerance are nominal values.
• 4.2 Test tube: made of borosilicate glass, outer diameter 25 mm, length 150 mm, wall thickness 1 mm~2 mm. The internal dimensions shall ensure that the test copper strip can be properly accommodated (see 5.3). When 30 mL of sample liquid and the copper strip immersed therein are placed in the test tube, the surface of the sample liquid shall be at least 5 mm above the upper end face of the copper strip.
• 4.3 Test bath
  • 4.3.1 The test bath includes a pressure vessel liquid bath and a test tube bath. All test baths shall be able to maintain the required test temperature within a controllable range of ±1 ℃.
  • 4.3.2 Pressure vessel liquid bath: the bath shall be deep enough to ensure that one or more pressure vessels can be completely immersed during the test (see 4.1). The bath medium may be water or any liquid that can stably control the test temperature. The bath shall be equipped with a suitable support to support each pressure vessel in a vertical position in the bath.
  • 4.3.3 Test tube bath: the liquid test tube bath shall be equipped with a suitable support to support each test tube (see 4.2) so that it is in a vertical position in the bath and the test tube is immersed to a depth of about 100 mm in the bath liquid (distance from the bottom of the test tube to the surface of the bath liquid). Either water or oil may be used as the medium for the liquid bath. A metal block bath shall also meet the same temperature control requirements and immersion depth conditions, and shall be tested by using a test tube containing 30 mL of sample, a metal test piece of specified dimensions, and a temperature measuring device, to verify the temperature measurement (heat transfer) for each product type. Note: light interferes with test results; therefore, when using the test tube procedure (see 10.3) for testing, a bath made of opaque material can avoid light interference.
• 4.4 Temperature measuring device: capable of stably monitoring the test temperature of the test bath, with a measurement accuracy of ±1 ℃ or better. The GB-48 full-scale thermometer in GB/T 514—2005 meets the requirements for use in this method. When this thermometer is used, the height of its mercury column exposed above the surface of the bath medium at the test temperature shall not be greater than 10 mm.
• 4.5 Polishing fixture: ensures that the copper strip is firmly clamped during polishing without damaging its edges. Any type of fixture may be used as long as it can clamp the copper strip and allow the surface of the copper strip to be polished to protrude above the fixture surface. Detailed dimensions of the fixture are shown in Figure 2.
• 4.6 Observation test tube: flat glass test tube (as shown in Figure 3). At the end of the test, it is used for inspecting the corroded copper strip or for holding the corroded copper strip during storage. The dimensions of the observation test tube shall be suitable for placing the test copper strip (5.3), and the glass material used for its manufacture shall be free of striae or similar defects.
• 4.7 Tweezers: tips made of stainless steel or polytetrafluoroethylene, used for holding the copper strip.
• 4.8 Timer: electronic or manual, capable of accurately recording the time during the test within the allowable error.

6. Recommended operating conditions

• 9.1 Overview: different test conditions may be used for different product types, and for certain specific categories of products, more than one set of test temperature and/or test time conditions may also be used. Usually, aviation gasoline is tested in a pressure vessel at 100 ℃, while other high-vapor-pressure fuels such as natural gasoline are tested under 40 ℃ conditions, and other liquid products may be tested in test tubes at 50 ℃, 100 ℃ or higher temperatures. The test temperature and test time conditions described below are commonly used and are specified in the specifications for these products (if any). These conditions are only guidance, and other test conditions determined according to product specification requirements or agreed upon by the parties may also be used. The test time and test temperature conditions shall be recorded and reported as part of the test results (see 12.1).
• 9.2 Pressure vessel procedure: applicable to aviation gasoline, jet fuel and high-vapor-pressure samples
  • 9.2.1 Aviation gasoline and jet fuel: 100 ℃±1 ℃, 2 h±5 min.
  • 9.2.2 Natural gasoline: 40 ℃±1 ℃, 3 h±5 min.
  • 9.2.3 Automotive gasoline (optional procedure, see 9.3.1): 50 ℃±1 ℃, 3 h±5 min. If this optional pressure vessel procedure is used to test automotive gasoline samples, it shall be stated in the report (see the provisions of 12.2).
• 9.3 Test tube procedure: applicable to most liquid products
  • 9.3.1 Diesel, fuel oil and automotive gasoline: 50 ℃±1 ℃, 3 h±5 min. For fuel oil and diesel samples, corresponding to product specification requirements other than the relevant product specifications, 100 ℃, 3 h may also usually be used as alternative test conditions. For some automotive gasolines whose vapor pressure at 37.8 ℃ is greater than 80 kPa, the test process shows that their evaporation loss is greater than 10% of their volume; if this evaporation loss is significant, it is recommended to use the pressure vessel procedure (see 9.2 and 9.2.3) for testing. In addition, if the laboratory wishes to minimize or reduce the evaporation loss generated during the testing of automotive gasoline samples as much as possible (even if their corresponding vapor pressure is less than 80 kPa), the laboratory may also choose to use the pressure vessel procedure (see 9.2 and 9.2.3) to test automotive gasoline samples.
  • 9.3.2 Cleaning solvent and kerosene: 100 ℃±1 ℃.
  • 9.3.3 Lubricating oil: proceed according to the procedure described in 9.3.1, with a test temperature of 100 ℃±1 ℃; the test may also be conducted under different time conditions and at higher test temperatures other than 100 ℃. For the sake of uniformity, it is recommended to use 150 ℃ as the initial test temperature and to increase the test temperature in an average increment of 5 ℃.

7. Sampling and sample preparation

• 7.1 Sampling shall be performed according to the method of GB/T 4756 or GB/T 27867. It is particularly important that, for various types of fuel samples that may cause slight discoloration of the copper strip, they should be collected and stored in clean dark glass bottles, plastic bottles, or other suitable containers that will not affect the corrosiveness of the sample. It has been proven that tin-plated containers can affect the corrosiveness of the sample; therefore, tin-plated containers should not be used to store samples.
• 7.2 When placing the collected sample into the sample container, volatilization should be avoided, and the composition of the sample should be retained as completely as possible. After filling, the container lid should be immediately closed. Sufficient headspace should be left at the top of the container to prevent thermal expansion of the sample during transport. For volatile samples, it is recommended to fill the sample to 70%~80% of the sample container capacity. Care should be taken during sampling to prevent the sample from being exposed to direct sunlight or even scattered daylight. After the laboratory receives the sample, testing should be carried out as soon as possible, and testing should be carried out immediately after opening the sample container.
• 7.3 If suspended water (turbidity) is observed in the sample, a sufficient volume of the sample may be filtered and dried using a piece of medium-speed qualitative filter paper and placed in a clean, dry test tube. This operation should be carried out as much as possible in a dark room or under light-avoiding conditions. If the copper strip comes into contact with water before, during, or after the entire test, contamination and discoloration will occur, causing difficulty in evaluating the copper strip.
• 8 Preparation of test strips
  • 8.1 Surface preparation
    • 8.1.1 First, use steel wool (cotton) of 00 grade or finer, or silicon carbide (alumina corundum) abrasive paper or cloth of appropriate grit that can effectively achieve the desired effect, to remove corrosion stains left on all six surfaces of the copper strip from the previous test (see Note); then treat with 65 μm (P220) silicon carbide abrasive paper or cloth to remove grinding marks left by other grades of abrasive paper used previously. Before final polishing, ensure that the copper strip that has completed surface preparation no longer undergoes oxidation. After wiping off metal filings on the copper strip with quantitative filter paper, immerse the copper strip in washing solvent. The copper strip can then be removed for immediate final polishing, or can be stored in washing solvent for later use. Note: For commercially purchased pre-polished copper strips, only the final polishing step (8.2) is required, although for gasoline samples, according to the results of comparative tests between commercially pre-polished copper strips and manually polished copper strips conducted in relevant interlaboratory collaborative research, commercially pre-polished copper strips can also be directly used for testing (i.e., without the final polishing step). This statistical test evaluation of pre-polished copper strips does not include samples other than gasoline. See Chapter 11 for details.
    • 8.1.2 Manual procedure for surface preparation: Place a piece of silicon carbide or alumina (corundum) abrasive paper or cloth on a flat surface, and wet the abrasive paper or cloth with kerosene or washing solvent. Rub the copper strip against the abrasive paper or cloth in a rotating manner. When handling the copper strip, use ashless filter paper for protection or wear disposable gloves to prevent the copper strip from contacting fingers. Alternatively, mount dry abrasive paper or cloth of appropriate grit on a motor-driven machine and use the machine to treat the copper strip surface.
  • 8.2 Final polishing
    • 8.2.1 For a new copper strip prepared according to 8.1 or used for the first time, remove it from storage (e.g., from washing solvent); to prevent contamination of the copper strip surface during the final polishing stage, direct contact with fingers is not allowed; instead, wear disposable gloves or use ashless filter paper for protection. Using a piece of absorbent cotton moistened with washing solvent, pick up some 105 μm (P150) silicon carbide or alumina (corundum) abrasive grains, first grind each end edge of the copper strip, then grind its side edges, then wipe vigorously with a new absorbent cotton ball. During subsequent handling, fingers must not touch the surface of the copper strip; the copper strip may be held with tweezers. Clamp the copper strip in the polishing fixture, and polish the main surface of the copper strip with absorbent cotton dipped in silicon carbide or alumina (corundum) abrasive grains. Do not use a rotating motion when polishing; instead, polish back and forth along the long axis direction of the copper strip, and before reversing direction, the polishing stroke should extend beyond the end of the copper strip. Rub the copper strip vigorously with clean absorbent cotton to remove all metal filings until no traces remain when wiped with a new piece of absorbent cotton. After the copper strip is wiped clean, immediately immerse it in the prepared sample.
    • 8.2.2 In order to obtain a uniformly discolored copper strip, it is important to uniformly polish all surfaces of the copper strip. If the edges of the copper strip show wear (surface appears elliptical), corrosion at these locations will mostly be much more severe than at the central part. Using a polishing fixture will help achieve uniform polishing of the copper strip surface.
    • 8.2.3 It is very important to prepare the test strip by polishing with abrasives of different specific grits in the order specified in 8.1 and 8.2. The final polishing stage uses 105 μm silicon carbide or alumina (corundum) abrasive grains, whose grit is larger than the 65 μm silicon carbide or alumina (corundum) grit used in the surface preparation step. The reason for using a larger grit abrasive in the final polishing stage is to produce micro-asperities (controlled roughness) on the copper strip surface as initiation sites for the corrosion reaction.

8. Analysis procedure

• 9.2 Pressure vessel procedure (applicable to aviation gasoline, jet fuel, and high vapor pressure samples)
  • 9.2.1 For aviation gasoline and jet fuel: Pour 30 mL of a completely clear sample free of suspended water or entrained water (see 7.3) into a clean, dry test tube. Within 1 min after completing the final polishing step of the copper strip, slide the copper strip into the test tube and immerse it in the sample. Place the test tube into the pressure vessel (see Figure 1), and tighten the pressure vessel cover. If more than one sample is to be tested at the same time, as long as the interval between handling the first and last sample is kept to a minimum, it is permitted to first prepare each pressure vessel individually and then completely immerse each pressure vessel in a liquid bath at 100 ℃±1 ℃. After placing in the bath for 2 h±5 min, remove the pressure vessel and soak it in cold water (tap water) for a few minutes. Open the pressure vessel cover, remove the test tube, and inspect the copper strip as described in 9.4.
  • 9.2.2 For natural gasoline: Carry out the test exactly as described in 9.2.1, but the test temperature is 40 ℃±1 ℃, and the test time is 3 h±5 min.
  • 9.2.3 For automotive gasoline (this is an optional step, see 9.3.1): Carry out the test exactly as described in 9.2.1, but the test temperature is 50 ℃±1 ℃, and the test time is 3 h±5 min. If this optional pressure vessel step is used to test automotive gasoline samples, it must be stated in the report (see 12.2 provisions) to indicate the difference from testing using the test tube procedure specified in 9.3.1.
• 9.3 Test tube procedure (applicable to most liquid products)
  • 9.3.1 For diesel fuel, fuel oil, and automotive gasoline: Pour 30 mL of a completely clear sample free of suspended water or entrained water (see 7.3) into a clean, dry test tube. Within 1 min after completing the final polishing step of the copper strip, slide the copper strip into the test tube and immerse it in the sample. Stopper the test tube with a cork having a vent hole. If more than one sample is to be tested at the same time, as long as the interval between preparing the first and last sample is kept to a minimum, it is permitted to prepare each sample individually. After first stoppering each test tube with a perforated stopper individually, immerse each test tube in a bath at 50 ℃±1 ℃. During the test, prevent strong light from illuminating the contents of the test tube. After placing the test tube in the bath for 3 h±5 min, remove the test tube and inspect the copper strip as described in 9.4.
  • 9.3.2 For cleaning solvents and kerosene: Carry out the test exactly as described in 9.3.1, but the test temperature is 100 ℃±1 ℃.
  • 9.3.3 For lubricating oils: Carry out the procedure as described in 9.3.1, with a test temperature of 100 ℃±1 ℃; the test may also be conducted under different time conditions and at higher test temperatures other than 100 ℃. For uniformity, it is recommended to use 150 ℃ as the starting test temperature and to increase the test temperature in average increments of 5 ℃.
• 9.4 Inspection of copper strip
  • 9.4.1 Pour the contents of the test tube into a receiving container of appropriate capacity. If a glass receiving container is used, such as a 150 mL tall beaker, the copper strip should be allowed to slide in gently during pouring to avoid breaking the glass beaker. Immediately remove the copper strip with tweezers and immerse it in washing solvent to wash off the sample. After cleaning, immediately remove the copper strip from the washing solvent and dry it; the copper strip may be dried by blotting with filter paper, air drying, or other suitable methods. Inspect the copper strip for discoloration or corrosion by comparing it with the corrosion standard color plate. When comparing, hold the copper strip and the corrosion standard color plate at a 45° angle to the light for observation.
  • 9.4.2 If the copper strip is placed in a flat observation test tube, spots and contamination on the copper strip during inspection and comparison can be avoided. The observation test tube should be stoppered with absorbent cotton.

9. Qualitative and quantitative determination and calculation formula

• 10.1 The degree of corrosion of the sample shall be judged according to one of the grades of the copper strip corrosion standard color plate listed in Table 1.
• 10.2 When the copper strip shows an obvious transition state between two adjacent standard color plates, it shall be judged according to the corrosion grade of the more severely discolored plate. If the copper strip shows an orange color darker than 1b in the standard color plates, the copper strip is still considered to be grade 1; however, if red color is observed, the observed copper strip shall be judged as grade 2.
• 10.3 A purple-red copper strip of grade 2a may be mistaken for a grade 3a copper strip in which the brass background is completely covered by magenta. To distinguish these two grades, the copper strip may be immersed in washing solvent; a grade 2a copper strip will show a dark orange color of 1b, while a grade 3a copper strip will not change color.
• 10.4 To distinguish a grade 2c copper strip from a grade 3b copper strip, place the test strip in a test tube and lay this test tube flat on a hot plate at 340 ℃±30 ℃ for 4 min~6 min. Separately, use another test tube, place a high-temperature distillation thermometer in it, and observe the temperature of this thermometer to adjust the temperature of the hot plate. In this way, a grade 2c copper strip will assume the color of a grade 2d copper strip and continue to darken; while a grade 3b copper strip will assume the appearance of a grade 4a copper strip.
• 10.5 If finger marks or contamination are found on the copper strip, or if the copper strip becomes stained due to contact with any particles or water droplets during the heated immersion process, the test must be repeated.
• 10.6 If the corrosion grade exhibited along the edges of the flat surface of the copper strip is higher than the corrosion grade of most of the copper strip surface, the test must also be repeated; this situation is mostly caused by wear of the edges during the copper strip polishing stage.
• 10.7 If the results of two replicate tests are not the same, re-test; if the two results of the re-test are still not the same, the sample shall be judged according to the more severely discolored corrosion rating; for the two replicate test results of gasoline samples tested using the test tube procedure, they shall comply with the precision requirements of the method (see Chapter 11).
• Table 1 Classification and rating descriptions of the copper strip corrosion standard color plates
  • Classification 1 (slight tarnish): a light orange, almost the same as a freshly polished copper strip; b dark orange
  • Classification 2 (moderate tarnish): a claret red; b lavender; c multicolor with lavender-blue or (and) silver, overlaid on claret red; d silver; e brass or gold
  • Classification 3 (deep tarnish): a multicolor with magenta overlaid on brass; b multicolor with red and green (peacock green), but no gray
  • Classification 4 (corrosion): a transparent black, dark gray, or brown with only peacock green; b graphite black or matte black; c glossy black or jet black
  • Note: The copper strip corrosion standard color plates are composed of the color plates represented by these descriptions in the table. The freshly polished copper strip included in this series serves only as a visual reference for the appearance of the copper strip before testing. Even a completely non-corrosive sample cannot reproduce this appearance after testing.

10. Precision

• 11.1 For pass/fail test results, except for gasoline samples tested using the test tube procedure specified in 9.3.1 (see 11.2 and 11.3), there is no acceptable test method to determine precision.
• 11.2 Based on the results of an interlaboratory cooperative test study conducted by 18 laboratories on 12 gasoline samples, it was determined that the test results obtained using commercially pre-polished copper strips and manually polished copper strips are statistically "equivalent", that is, there is no statistically significant difference in the foreseeable degree of inconsistency between the test results using commercially pre-polished copper strips and manually polished copper strips. In addition, this study also determined the precision described in 11.3.
• 11.3 Since the test results of this method are non-numerical and include multiple rating classifications (e.g., 1, 2, 3, and 4 ratings) as well as rating descriptions (e.g., a, b, c, etc.), conventional statistical methods are not suitable for determining precision. A statistical simulation method was used in the study to mathematically evaluate the interlaboratory cooperative test results under repeatability and reproducibility conditions. According to the statistical method used, for 1 rating, 2 rating, and 3 rating, there is no statistically significant difference in the degree of inconsistency between the results obtained under repeatability and reproducibility conditions. However, for 4 rating, the test results show more within-rating differences. Accordingly, the precision of this method for gasoline samples (including repeatability and reproducibility) was determined, and at the 95% confidence level, the difference between any two ratings shall not exceed the criteria specified in Table 2.
• Table 2 Precision (repeatability and reproducibility) of the copper strip corrosion test tube procedure for gasoline samples
  • Classification 1, 2, 3: two ratings within the same classification (one letter rating within the same classification / two letter ratings within the same classification); rating difference of two results (repeatability and reproducibility): two ratings at the boundary of a classification (e.g., 1b and 2a)
  • Classification 4: one letter rating within the same classification or the closest one letter rating in an adjacent classification; two letter ratings within the same classification or the closest one letter rating in an adjacent classification
  • Note: The specific values in the column "rating difference of two results (repeatability and reproducibility)" in Table 2 are not fully presented in the original text source-text extraction, requires confirmation against the source standard (source-text extraction).

11. Report

• 12.1 Report the corrosiveness of the sample according to one corrosion rating listed in Table 1. Report the test time and test temperature in the following format: Corroded copper strip (X h/Y ℃), rating Zp Where: X—— test time, in hours (h); Y—— test temperature, in degrees Celsius (℃); Z—— rating (e.g., 1, 2, 3, or 4); p—— specific rating description corresponding to Z rating (e.g., a, b).
• 12.2 If the pressure vessel procedure is used when testing automotive gasoline samples (see 9.2.3), report the results obtained in 12.1 and state that the pressure vessel test procedure was used.

12. Normative references

• GB/T 514—2005 Specification for liquid-in-glass thermometers for testing petroleum products
• GB/T 4756 Manual sampling of petroleum liquids
• GB/T 5231—2012 Designations and chemical composition of wrought copper and copper alloys
• GB/T 9258.1—2000 Abrasives for coated abrasives - Particle size analysis - Part 1: Particle size composition
• GB/T 27867 Automatic sampling of petroleum liquids in pipelines
• SH/T 0232 Copper strip corrosion test method for liquefied petroleum gas
• Appendix A (Normative appendix) Safety warning

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Q&A