SH/T 0698-2000 Test method for chemical stability of refrigeration oils in refrigerant systems (sealed glass tube method)

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Card type: Test method

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

• Standard number: SH/T 0698-2000
• Chinese full title: Test method for chemical stability of refrigeration oils in refrigerant systems (sealed glass tube method)
• English name: Sealed glass tube method to test chemical stability of refrigerator oils for use within refrigerant systems
• Replacement relationship: not provided in the available source (the foreword only states that it was formulated by equivalently adopting the relevant technical content of ASHRAE 97-1983, and does not mention replacing an old standard number)
• Adoption relationship: equivalently adopts the relevant technical content of ASHRAE 97-1983 "Test for chemical stability of materials used in refrigeration systems (sealed glass tube method)"
• Main differences from ASHRAE 97-1983 (foreword):
  1. The referenced standards adopt the corresponding current standards of our country.
  2. ASHRAE 97-1983 is applicable to evaluating the thermochemical stability of all materials used in refrigeration systems with refrigerants; this standard is only applicable to the evaluation of the chemical stability of refrigeration oils in refrigerant systems.
  3. This standard removes the relevant content of tests for non-refrigeration oils.
  4. Editorial modifications were made to the standard text format in accordance with the requirements for drafting standards in our country.
  5. In light of the specific domestic situation, the description mainly focuses on the glass-type refrigerant charging system.
  6. In addition to using R-12 as the refrigerant, R-134a is also selected.
  7. For ease of operation, this standard uses the volume scale method to charge refrigerant, and does not mention the pressure difference method and related appendix content in the reference standard.
• Approval/implementation: approved by the State Bureau of Petroleum and Chemical Industry 2000-11-27, implemented on 2001-05-01
• Proposed by/under the jurisdiction of/drafted by: proposed by China Petroleum & Chemical Corporation; under the jurisdiction of the Research Institute of Petroleum Processing, China Petroleum & Chemical Corporation; drafted by Chongqing Yiping Lubricant Branch of China Petroleum & Chemical Corporation; main drafters Cheng Ying, Yan Zili

2. Scope of application and non-applicability

• This standard specifies a method for evaluating the chemical stability of refrigeration oils in refrigerant systems.
• This standard is applicable to refrigeration oils using R-12 or R-134a as the refrigerant.
• Not applicable: the available source does not explicitly list non-applicable clauses; the foreword points out that this standard removes the relevant content of tests for non-refrigeration oils, and is only applicable to the evaluation of the chemical stability of refrigeration oils (not applicable to evaluating all materials in refrigeration systems).
• Safety statement: This standard involves certain hazardous materials, operations and equipment, but it is not intended to address all safety issues related to them; users should establish appropriate safety and protective measures before use, and determine applicable management systems.

3. Method principle

Metal materials such as steel and copper are placed as catalysts into a specially made test tube, a certain amount of refrigeration oil and refrigerant are injected in proportion, and then the test tube is sealed. After the sealed test tube is heated at 175℃ for a specified time (14d), the chemical stability of the refrigeration oil with the refrigerant is evaluated based on the appearance, color, etc. of the refrigeration oil and catalyst.

4. Reagents and materials (purity / preparation)

4.1 Materials

• Refrigerant: R-12 or R-134a (4.2.1)
• Catalyst: according to the purpose of the experiment, usually one or more different metals are selected as catalysts (4.2.2)
  • Steel: meets the requirements of GB/T 699, and may be a steel sheet of 3mm×50mm×0.15mm, or a steel wire with a diameter of 1.6mm and a length of 50mm; the steel surface must be uniformly polished, and before shearing and cleaning it must be ensured that there is no rust on the surface (4.2.2.1)
  • Copper: copper meeting the requirements of T2 in GB/T 5231, with a purity of 99.9% or above; diameter 1.6mm, length 10mm (4.2.2.2; the original text "length lo= o" is source-text extraction noise, requires confirmation against the source standard (source-text extraction))
  • Other materials: other materials such as aluminum may be selected as catalysts according to the purpose of the test (4.2.2.3)
• Liquid nitrogen (4.2.3)
• Vacuum rubber tubing (4.2.4)

4.2 Reagents

• Water: distilled water or deionized water (5.1)
• Acetone: analytical reagent (5.2)
• Ethanol: analytical reagent (5.3)
• n-Heptane: reagent grade (5.4)

5. Apparatus and equipment

• Test tube: made of borosilicate glass tubing, outer diameter 9mm, inner diameter 7mm, with a spherical closed bottom at one end; after loading the refrigerant and the material to be tested, the other end is sealed with a pointed-tip welding torch; after sealing, the total length of the test tube is about 180mm (4.1.1)
• Refrigerant charging device: evacuates the test tube loaded with the sample, injects refrigerant, and then seals by melting (4.1.2)
  • Glass-type charging system (Figure 1): includes suitable glass tubing and stopcocks, and is connected to a refrigerant cylinder, vacuum pump, dry nitrogen, filter dryer, vacuum gauge, mercury manometer, and the test tube to be charged (4.1.2.1)
  • Metal-type charging system (Figure 2): includes metal tubing, vacuum pump, vacuum pressure gauge, vacuum gauge, open capillary mercury manometer, refrigerant cylinder, filter dryer, valves, and copper charging port, etc. (4.1.2.2)
• Aluminum block bath (Figure 3): used for aging test tubes at high temperature; cylindrical holes are used to place test tubes, serving to prevent mutual influence when test tubes burst and to maintain constant temperature; the holes should be drilled completely through, and the separable movable bottom facilitates cleaning; the hole depth must be sufficient to accommodate the test tube; the bottom of the holes is filled with glass wool to support the test tubes (4.1.3)
• Sleeve: may be used instead of the aluminum block bath when the number of samples is small; made of aluminum or steel tubing, with both ends fastened by nuts (4.1.4)
• Oven: temperature control range ±1℃, with sufficient space to place the aluminum block bath and ensure air circulation (4.1.5)
• Tube opener: Figure 4; another type of tube opener is shown in Figure 5 (4.1.6)
• Syringe: 5mL, with a needle of length 150mm (4.1.7)
• Desiccator: sufficient to hold test tubes (4.1.8)
• Metal Dewar flask (4.1.9)
• Vacuum desiccator (4.1.10)
• Glass tube: diameter 2mm, length 140mm (4.1.11)
• Safety shield (4.1.12)

6. Recommended operating conditions

• Aging temperature: 175℃ (3, 7.6)
• Aging time: 14d (3, 7.6)
• Oven temperature control: ±1℃ (4.1.5)
• Absolute pressure for refrigerant charging: about 93.3kPa(700mmHg), then evacuate, with the evacuation pressure at least 66.7Pa(500μmHg) (7.4.1)
• Charge refrigerant to absolute pressure 93.3～100kPa(700～750mmHg) (7.4.2)
• System evacuation requirements: the sealed system should be able to be evacuated to 2.0Pa(15μmHg), and the rise of the mercury column within 1h should not be greater than 26.7Pa(200μmHg); before refrigerant charging, the system should be evacuated for 15～20min (7.2)
• Degassing endpoint: when the test tube is tapped, the sample no longer generates bubbles or the system pressure is lower than 6.7Pa(50μmHg) (7.3.3)
• Sealing by melting speed: 20～30s (7.5.1)
• At 25℃, the recommended maximum safe charging amount of liquid refrigerant is 0.7mL (6.2.3 note)
• Sample charging amount: 0.7mL (7.1)

7. Sampling and sample preparation

• Take a refrigeration oil sample from the container; the oil must be degassed before refrigerant charging (6.2.1)
• Select one or several metal materials as catalysts according to the purpose of the experiment (6.2.2)
  • Steel: clean the steel sheet with n-heptane and wipe dry with soft gauze; clean the scissors with n-heptane and cut into pieces of 3mm×50mm; if steel wire is used, polish it with abrasive cloth to expose a new surface, then cut into 50mm segments with clean wire cutters; hold the cut steel wire with clean tweezers, clean with n-heptane, and dry on clean filter paper; place in a small vacuum desiccator for vacuum drying at room temperature, then fill with dry nitrogen to break the vacuum, and store in a desiccator until use (6.2.2.1)
  • Copper: prepare copper wire according to the procedure for preparing steel wire in 6.2.2.1, cut into 10mm segments, place in the desiccator in 6.2.2.1 for storage (6.2.2.2)
  • Other materials should also be carefully prepared (6.2.2.3)
• Marking the scale: inject into the test tube ethanol equivalent to the total volume of sample, refrigerant and catalyst, and mark the scale on the test tube with a glass pen; then dry and cool the test tube according to 6.1.2, and store in a desiccator (6.2.3)
• Test tube preparation: blown from borosilicate glass by a skilled glassblower, outer diameter 9mm, inner diameter 7mm, each length 240mm, with one end closed with a spherical bottom and the other end fire-polished (6.1.1); must be thoroughly cleaned and placed in a closed container to avoid contamination; after closing the bottom, clean with distilled water or deionized water, then clean with acetone, then dry at 125℃, and cool in a desiccator; if necessary, calcine at 580℃ for further cleaning; after drying, store in a desiccator (6.1.2); before use, check cleanliness and for cracks, severe scratches or other defects; defective ones should be discarded (6.1.3); prepare at least four test tubes for each sample, three for aging and one for comparison (6.1.4)

8. Analytical procedure

8.1 Sample loading (7.1)

Use clean tweezers to place the catalyst into the test tube, and use a 5mL syringe with a 150mm needle to inject 0.7mL sample. Then purge the test tube with a fine dry nitrogen stream, cover with aluminum foil, and place in a desiccator until use. To avoid oil contaminating the upper wall of the test tube, a glass tube of length 140mm and diameter 2mm may first be inserted into the test tube, with one end of the glass tube clamped to prevent it from slipping into the test tube; insert the needle along the inner tube of the glass tube into the test tube and then inject the sample.

8.2 Inspection of refrigerant charging device (7.2)

The interior of the refrigerant charging device should be clean, dry, and free of leaks; the sealed system should be able to be evacuated to 2.0Pa(15μmHg), and the rise of the mercury column within 1h should not be greater than 26.7Pa(200μmHg). Before refrigerant charging, the system should be evacuated for 15～20min.

8.3 Degassing of test tube (7.3)

• Take the test tube out of the desiccator, remove the aluminum foil, fit a vacuum rubber hose of length 30mm onto the open end of the test tube to a depth of about 15mm, and at about 60mm from the open end, draw the test tube thin by hand with a torch; there must be no oil at the heated location, and the operation must be performed by a skilled glassblower (7.3.1)
• Carefully hold the sleeve portion to connect the test tube to the charging port on the refrigerant charging device (7.3.2)
• Slowly open the filling port valve to evacuate the test tube. At the beginning, the sample will generate many bubbles; avoid bubbles rising to the part to be sealed. A hair dryer with hot air can be used to eliminate bubbles, and tapping the test tube wall with a pencil can also accelerate degassing. When tapping the test tube no longer produces bubbles in the sample or the system pressure is lower than 6.7Pa(50μmHg), refrigerant (7.3.3) may be added.
• If a metal filling system is used, repeat the steps from 7.3.1 to 7.3.3 until all branch ports are connected to test tubes (7.3.4).

8.4 Adding refrigerant (7.4)

• Open the needle valve on the steel cylinder to fill with refrigerant; the absolute pressure of the refrigerant is about 93.3kPa(700mmHg), then evacuate; the evacuation pressure is at least 66.7Pa(500μmHg). Repeat filling and evacuation so that the air in the test tube is completely replaced by refrigerant gas. Close the filling port valve while the system is under evacuation (7.4.1).
• Place the test tube in liquid nitrogen so that the marked line on the test tube is about 20mm below the liquid surface, fill with refrigerant until the absolute pressure reaches 93.3～100kPa(700～750mmHg), slowly open the valve on the filling port to condense the refrigerant to the marked line on the test tube, and close the filling port valve. When using a metal filling line, repeat 7.4.2 so that all test tubes are filled with refrigerant (7.4.2).
• Leave the test tube in liquid nitrogen for a few minutes to ensure that the substance inside the tube is completely solidified. Evacuate the system to below 6.7Pa(50μmHg) and open the filling port valve (7.4.3).

8.5 Sealing of test tube (7.5)

• Remove the test tube from liquid nitrogen, hold it with a hand (cotton or thin leather gloves should be worn) at 30mm below the sealing part, and seal the test tube with a handheld torch. After removing the Dewar flask, in order to prevent refrigerant evaporation and pressure increase inside the tube, the sealing speed must be rapid (20～30s). After sealing, the sealed part must be annealed. When using a metal filling line, repeat step 7.5 until all test tubes are filled and sealed. Place the sealed test tubes in an aluminum block bath or sleeve. After standing overnight at room temperature, carefully take them out for observation, wipe each test tube with silk cloth and inspect: a) catalyst and liquid appearance; b) liquid volume; c) appearance of the inner surface of the test tube, especially near the sealed part; d) presence of foreign interfering substances, such as fine metal powder, etc. If the test tube cannot pass visual inspection, open the test tube in the manner described in Figure 4 or Figure 5 and 7.7 (7.5.1).
• After filling and sealing all test tubes, turn off the vacuum pump and disconnect the steel cylinder and filling line (7.5.2).

8.6 Heating aging (7.6)

Place the sealed test tubes sealed according to 7.5 into an aluminum block bath or sleeve, and heat in an oven at 175℃ for 14d. Observe the test tubes several times at the same time intervals as needed and record the phenomena. After observation or testing is completed, remove the aluminum block bath or sleeve from the oven and cool thoroughly.

8.7 Opening of test tube (7.7)

• The best method for opening the tube is shown in Figure 4: immerse half of the test tube in liquid nitrogen until the substance inside the test tube solidifies; take it out briefly and make a scratch near the top with a file, then put it back into liquid nitrogen to cool; take out the test tube and insert it into the fixture shown in Figure 4 so that the top of the test tube is caught by the "ears" at the end of the copper tube, then break the test tube laterally from the top; if gas analysis is required, the fixture can be connected to a pre-evacuated gas sampling system to collect the gas inside the tube.
• Another method of opening the tube is shown in Figure 5: first place the test tube in liquid nitrogen to cool, then place it in the device shown in Figure 5, after evacuating under 6.7Pa(50μmHg), clamp the center of the copper tube with pliers to open the test tube.

8.8 Analysis of test tube (7.8)

Different analytical methods may be selected according to the purpose of the experiment. Generally, after the test, the state of the substance in the tube is visually inspected, including checking the liquid phase and the metal in the tube, and the test result is judged by comparing its state with a reference substance of known stable state.

9. Qualitative and quantitative and calculation formulas

• Calculation formulas are not provided in the available source.
• Result determination method: evaluate the chemical stability of the refrigeration oil and refrigerant according to the appearance, color, etc. of the refrigeration oil and catalyst (3); generally, after the test, visually inspect the state of the substance in the tube, including checking the liquid phase and the metal in the tube, and judge the test result by comparing its state with a reference substance of known stable state (7.8).

10. Precision

Not provided in the available source.

11. Report

Report the color of the mixture of sample and refrigerant, formation of precipitate, discoloration and corrosion state of the catalyst (9).

12. Referenced documents

• GB/T 699 Technical conditions for high-quality carbon structural steel
• GB/T 5231 Wrought copper—Chemical composition and product forms
• GB/T 7372 Industrial dichlorodifluoromethane (F-12)
• Reference note: The provisions included in the following standards constitute a part of this standard by reference. Unless otherwise clearly specified in the standard, the following referenced standards are all currently effective standards (Chapter 2).

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 reference