SH/T 0768-2005 Flash Point Determination Method (Constant Closed Cup Method)

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Card type: Test method

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

• Standard number: SH/T 0768—2005
• Chinese name: Flash Point Determination Method (Constant Closed Cup Method)
• English name: Test method of flash point by continuously closed cup tester
• Replacement relationship: not provided in the available source (the foreword does not mention replacing any old standard)
• Adoption relationship: modified adoption of ASTM D6450-99 "Continuous Closed Cup Flash Point Determination Method", redrafted according to ASTM D6450-99
• Publication/implementation: published on 2005-10-10, implemented on 2006-02-01
• Issuing authority: National Development and Reform Commission of the People's Republic of China
• Custodian: Sinopec Research Institute of Petroleum Processing
• Drafting organization: Sinopec Shanghai Gaoqiao Company
• Main drafters: Ding Yun, Jiang Tong

2. Scope of application and non-applicability

• 1.1 This standard is a dynamic method with a specified heating rate; it is an empirical method. Note: flash point is not an invariable physicochemical property and is related to instrument design, instrument usage, and the test process; it is not guaranteed that results measured by different methods or different test instruments have generally valid correlation.
• 1.2 Applicable to the determination of flash point of fuel oils, lubricating oils, solvent oils, and other liquids by the constant closed cup method; the sample amount required for the determination is 1 mL.
• 1.3 Uses a sample cup that is closed but not sealed and can introduce air into the test chamber.
• 1.4 Applicable to samples with flash point from 10 ℃ to 250 ℃. Note: samples with flash point lower than 10 ℃ or higher than 250 ℃ can be determined, but precision has not been established.
• 1.5 If the flash point test method specified by the user's product specification is not this standard, then neither this standard nor any other standard may replace the specified standard without comparative data and the approval of the specification setter.
• 1.6 Uses SI International System of Units; values in parentheses are for reference only.
• 1.7 Involves hazardous materials, operations, and equipment, but does not address all safety issues associated with them; it is necessary to establish appropriate safety and protective measures and operating procedures before use. For special hazard warnings, see the note in Chapter 7.
• Not applicable: 6 fuel oil (the note to 14.1 points out that its precision is significantly worse than that of other samples, and it must be assumed that the test procedure in Chapter 11 is not applicable to such samples).

3. Method principle

• 4.1 Adjust the temperature of the test chamber lid so that it is at least 18 ℃ lower than the sample cup temperature and the expected flash point. Inject 1.0 mL±0.1 mL of sample into the sample cup. The sample and sample cup ... (the source text is incomplete at source-text extraction) ... must then be able to cool it. Raise the sample cup and lid to form a continuously closed but not sealed test chamber with a total volume of 4.0 mL.
• 4.2 After closing the test chamber, the sample ... (source-text extraction incomplete) ... a fixed amount of energy arc at specified intervals in ... (source-text extraction incomplete) ... the next flash test provides the required ... (source-text extraction incomplete) ... the pressure in the test chamber should be ambient ... (source-text extraction incomplete)
• 4.3 After each arc discharge ... (source-text extraction incomplete) ... recorded, as uncorrected ... (source-text extraction incomplete) ... correction ... (source-text extraction incomplete) ... substance flash point.
• 3.1.1 Flash point definition: under specified test conditions, the lowest temperature at which the application of an ignition source causes the vapor of the sample to ignite momentarily (corrected to 101.3 kPa pressure). Note: in a closed test chamber, when the instantaneous pressure increase caused by the flame is not less than 20 kPa, it is confirmed that the sample has flashed.
• 3.2.1 Dynamic: the state in which the vapor above the sample and the sample have not reached temperature equilibrium when the ignition source is introduced.
• 6.1.7 Note: When the sample contains low-flash-point substances or the sample ... (source-text extraction incomplete) ... is below the initial temperature, supersaturated vapor may be generated in the test chamber; therefore, the instrument should be designed so that the instrument can, in the test chamber ... (source-text extraction incomplete) ... before reaching the initial ignition temperature, every 10 ℃ ... (source-text extraction incomplete) ... once.

4. Reagents and materials (purity / preparation)

• 7.1 Reagent purity: use only chemicals whose purity meets the requirements of Table B.1 in Annex B. When the reagents used ... (source-text extraction incomplete) ... accuracy, reagents of other grades may be used.
• 7.1.1 Anisole. Note: flammable and harmful to health; handle solutions and waste according to relevant regulations.
• 7.1.2 n-Dodecane. Note: flammable and harmful to health; handle solutions and waste according to relevant regulations.
• 7.2 Cleaning solvent: only non-corrosive solvents may be used to clean the sample cup and lid. Toluene and acetone may be used as cleaning solvents. Note: toluene, acetone, and ... (source-text extraction incomplete) ... are especially flammable and harmful to health; handle solutions and waste according to relevant regulations.
• Annex B Table B.1: anisole purity greater than 99.7% (mole fraction), n-dodecane purity greater than 99.5% (mole fraction).
• Annex B Note 3: Since this is the first version of this standard, there are no certified reference materials; the values listed in Table B.1 are anisole and n-dodecane values that meet the precision requirements of the method. If certified reference materials remain unavailable, anisole and n-dodecane of the same purity may be used as reference materials.

5. Instruments and equipment

• 6.1 Flash point tester (constant closed type): has a lid made of brass with temperature control near the lid; the lid contains two temperature sensors for respectively measuring sample temperature and lid temperature, two electrically insulated probes capable of generating a high-voltage arc, and a connecting tube connected to the lid for pressure detection and air introduction, and also ... (source-text extraction incomplete) ... an electronic device for controlling the test chamber temperature, and a digital display capable of displaying the sample temperature. The instrument and its main components are shown in Figures A.1 and A.2.
• 6.1.1 Test chamber: composed of the sample cup and lid, total volume 4.0 mL ... (source-text extraction incomplete) ... 0.2 mL (requires confirmation against the source standard source-text extraction). The metal contact between the lid and sample cup is to ensure good heat conduction, but it is not completely sealed to ensure that during testing the test chamber ... (source-text extraction incomplete) ... ambient atmospheric pressure. Main dimensions are shown in Figure A.2. When the temperature rises, the pressure in the test chamber is detected. Excessive sealing will cause ... (source-text extraction incomplete) ... the sample temperature and vapor pressure cause the pressure increase to be higher than atmospheric pressure. Poor heat conduction will cause a large difference between the sample and lid temperatures.
• 6.1.2 Sample cup: may be made of nickel-plated aluminum or another material with the same thermal conductivity. Total volume 4 mL, capable of holding 1 mL of sample; main dimensions and requirements are shown in Figure A.2.
• 6.1.3 Sample temperature sensor (TS in Figure A.1): a stainless steel thermocouple (NiCr-Ni or similar) with diameter 1 mm and response time t(90)=3 s. Inserted into the sample to a depth of at least 2 mm, with resolution 0.1 ℃ and accuracy ±0.2 ℃; preferably connected to a temperature display.
• 6.1.4 Magnetic stirring: a rotating magnet is installed outside the sample cup and can cause a small stirring magnet placed in the sample cup containing the sample to rotate; the stirring magnet has diameter 3 mm±0.2 mm and length 12 mm±1 mm; the driving magnet rotation speed is 250 r/min to 270 r/min.
• 6.1.5 Air introduction: the instrument must be able to introduce 1.5 mL±0.5 mL of air immediately after each flash test. A short air pulse is generated by a small diaphragm air compressor, introducing air into the pressure sensor through a T-type inlet in the connecting tube.
• 6.1.6 During testing, the test chamber temperature is adjusted by electrical heating and cooling of the lid, with temperature control accuracy of ±0.2 ℃.
• 6.1.7 A high-voltage arc is used to ignite flammable vapor; the energy of each arc should be 3 J±0.5 J (3 Ws±0.5 Ws)/arc, and the arc duration is 43 ms±3 ms.
• 6.1.8 Flash point pressure test sensor: connected to the connecting tube inside the lid, working range 80 kPa to 177 kPa, minimum resolution 0.1 kPa, accuracy ±0.5 kPa, capable of measuring within 100 ms an instantaneous pressure increase of at least 20 kPa above atmospheric pressure. Note 1: detection above atmospheric pressure ... (source-text extraction incomplete) ... one of several methods for detecting flash in the test chamber ... (source-text extraction incomplete) ... 20 kPa pressure increase corresponds to a flame volume of about 1.5 mm. Note 2: an automatic pressure calibrator that performs atmospheric pressure correction according to the procedure described in clause 12.4 may be installed in the tester. The instantaneous pressure of the pressure sensor described in 6.1.8 can be ... (source-text extraction incomplete) ... read ... (source-text extraction incomplete) ... for calibration.
• 6.1.9 A pipette or syringe meeting the accuracy requirements may be used to transfer 1.0 mL±0.1 mL of sample.
• Annex A (normative annex) Instrument specifications: the lid is made of brass and equipped with a temperature sensor; the sample cup is made of nickel-plated aluminum; 1 mL sample; sample temperature sensor (NiCr-Ni thermocouple); the arc needles are made of stainless steel, with a specified length between the arc needles. Note: the spacing between the metal contact surfaces of the lid and sample cup is 30 μm.
• Figure A.2 Design dimensions (mm): A=5±0.2, B=14±0.3, D=5.5±0.2, E=15±0.5, 11.5; F=20, C=21, 30, 50, 45 (some dimensional correspondences require confirmation against the source standard source-text extraction).

6. Recommended operating conditions

• 11.3 Heating rate: 5.5 ℃/min±0.5 ℃/min.
• 11.4 Ignition frequency: 1 ℃ (introduce arc ignition every liter 1 ℃).
• 11.5 Air introduction amount: 1.5 mL.
• 11.6 Critical value of flash point detection pressure: 20 kPa.
• 11.2 Expected flash point: The initial ignition temperature should be set at least 18 ℃ lower than the expected flash point, and the final temperature should be higher than the expected flash point.
• 11.2.1 Unknown expected flash point: Set the initial ignition temperature to 10 ℃, test according to the described method, and the resulting flash point is an approximate value; when a fresh sample is tested again by the standard method, this value can be used as the expected flash point of the sample.
• 11.7 Adjust the lid temperature to the initial ignition temperature; when the instrument indicates that the initial ignition temperature has been reached, prepare to inject 1 mL±0.1 mL sample.
• 11.10 When the sample cup temperature and the lid temperature are the same, introduce a set electric arc every 10 ℃; if a flash is detected, end the test, discard the result, and retest with a fresh sample, with the initial ignition temperature at least 18 ℃ lower than the detected flash temperature.
• 11.11 When the temperature difference between the lid and the sample does not exceed 1 ℃, begin the actual flash point test; heat the lid at the heating rate specified in the procedure, introduce arc ignition every rise of 1 ℃, and detect the instantaneous pressure increase within 100 ms.
• 11.12 When the temperature at which a flash is detected is more than 26 ℃ above the initial ignition temperature or does not exceed the initial ignition temperature by more than 10 ℃, the result is considered approximate; retest with a fresh sample, and the initial ignition temperature should be 18 ℃ lower than the approximate flash point temperature obtained.
• 11.14 After the test is completed, wait for the sample cup to cool below 50 ℃, then remove it safely.

7. Sampling and Sample Preparation

• 8.1 According to the requirements of GB/T 4756, take at least 50 mL sample from the container, place it in a clean, sealed container, and store at low temperature.
• 8.2 The sample should not be stored for a long time in permeable containers such as plastic bottles, because volatile substances will diffuse through the bottle wall. Samples stored in containers with poor sealing should be discarded and resampled.
• 8.3 Measures should be taken to avoid loss of volatile substances, so as to prevent the flash point obtained from being too high. Do not open the container unless necessary. Do not transfer the sample unless the sample temperature is at least 18 ℃ lower than the expected flash point. If possible... (source-text extraction incomplete)
• 8.4 Very viscous samples may be slowly heated before testing or... (source-text extraction incomplete)... suitable fluid, and its temperature after heating should be at least 18 ℃ lower than the expected flash point.
• 8.5 When the sample contains dissolved water or free water, it may be dehydrated with calcium chloride,... (source-text extraction incomplete)... filtered through absorbent cotton, and the sample may be slowly heated, but not overheated, and its temperature should be at least... (source-text extraction incomplete)... lower than the expected flash point by 18 ℃. Note: If the sample is suspected to contain volatile components, the procedures described in 8.4 and 8.5 should... (source-text extraction incomplete)... filter paper filtration, or through loose dry... (source-text extraction incomplete)... omitted.
• 11.8 The temperature of the sealed sample and sample cup should be at least 18 ℃ lower than the expected flash point, and cooling should be carried out if necessary. Shake the sample well before opening the container. Draw 1 mL sample with a pipette or syringe, and seal the container. Transfer 1 mL±0.1 mL sample into the sample cup.
• 11.9 Place a stirring magnet to ensure the sample is mixed uniformly.
• 11.1 Before testing, thoroughly clean the lid, arc probe, and sample cup, and dry them to ensure that any solvent used for instrument cleaning is completely removed. If the expected flash point of the sample is 15 ℃ higher than the flash point of the previous sample, heat the empty dry sample cup together with the lid to a temperature at least 30 ℃ higher than the expected flash point of the new sample. Note: The drying and heating process of the sample cup can eliminate possible cross-contamination from residual vapor.

8. Analytical Procedure

• 11.1 Clean and dry the lid, arc probe, and sample cup (see Section 7).
• 11.2 Set the initial ignition temperature (at least 18 ℃ lower than the expected flash point) and the final temperature (higher than the expected flash point); for an unknown expected flash point, set the initial ignition temperature to 10 ℃ according to 11.2.1.
• 11.3 Set the heating rate 5.5 ℃/min±0.5 ℃/min.
• 11.4 Set the ignition frequency 1 ℃.
• 11.5 Set the air introduction amount 1.5 mL.
• 11.6 Set the critical value of flash point detection pressure 20 kPa.
• 11.7 Start the test according to the test procedure, adjust the lid temperature to the initial ignition temperature, and when reached, prepare to inject 1 mL±0.1 mL sample.
• 11.8 The temperature of the sample and sample cup should be at least 18 ℃ lower than the expected flash point, and cool if necessary; shake well before opening the container; draw 1 mL sample, and seal the container; transfer 1 mL±0.1 mL sample into the sample cup.
• 11.9 Place a stirring magnet.
• 11.10 Place the sample cup on the sample cup holder and start the test program; raise the sample cup tightly against the lid; when the sample cup temperature and the lid temperature are the same, introduce a set electric arc every 10 ℃; if a flash is detected, end the test, discard the result, and retest with a fresh sample.
• 11.11 When the temperature difference between the lid and the sample does not exceed 1 ℃, begin the actual flash point test; heat the lid at the specified heating rate, introduce arc ignition every rise of 1 ℃, and detect the instantaneous pressure increase within 100 ms; stop the test when a flash is detected or when the final temperature is reached with no flash; when a flash occurs causing the instantaneous pressure increase to exceed 20 kPa, the sample temperature at this time is the flash point temperature.
• 11.12 Result determination and retesting (see Section 6).
• 11.13 Record the detected sample flash point temperature as the uncorrected flash point temperature; if no flash point is detected within the test temperature range, report that the flash point is higher than the final temperature.
• 11.14 After the test is completed, wait for the sample cup to cool below 50 ℃ and remove it safely.
• Chapter 9 Quality Control Check: 9.1 The instrument shall be calibrated at least once a year with the specified certified reference material (CRM); the reference materials are given in Appendix B, and their flash points should be close to the predicted flash point range of the sample being tested; determine according to Chapter 11, and the flash point observed according to clause 11.11 shall be corrected for atmospheric pressure according to Chapter 12; for the listed certified reference materials, the measured flash point should be within the range listed in Table B.1. 9.2 After the instrument calibration is completed, the flash point of the working reference material (SWS) may be determined, and its flash point value should be within the allowable range; thereafter, the working reference material may often be used to calibrate the instrument (see Appendix B.2); on the day of use, the instrument should be checked with the working reference material. 9.3 When the obtained flash point exceeds the limits listed in clause 9.1 or clause 9.2, clean and maintain the instrument according to the instrument manual, and check the instrument calibration, with special attention to the detailed test procedure described in Chapter 10; after completing the adjustment, repeat clause 9.1 or clause 9.2 with a fresh sample. Note: As listed in Appendix B Table B.1, single-component verification materials are only used for instrument verification and cannot verify the precision of the entire test method and sampling, because for single-component substances, losses caused by evaporation will not affect the flash point as do the evaporation losses of light components in multi-component mixtures.
• Chapter 10 Instrument Calibration: 10.1 Pressure sensor—10.1.1 After completing the quality control check in Chapter 9, the pressure sensor may be calibrated if necessary, using ambient atmospheric pressure as a reference. 10.1.2 If the displayed atmospheric pressure differs from the ambient atmospheric pressure, adjust the sensor control until an appropriate reading is observed; the ambient atmospheric pressure is the pressure at the actual local position of the tester at the time of testing. Note: Many metal barometers used in weather stations and airports have been pre-corrected to sea level readings, and these barometers cannot be used for instrument calibration. 10.2 Temperature sensor—After completing the quality control check in Chapter 9, the temperature sensor may be calibrated if necessary by checking the sample temperature; a traceable standard thermometer or sensor may be used to calibrate the temperature sensor.

9. Qualitative and Quantitative Determination and Calculation Formulas

• Flash point determination: When a flash occurs causing the instantaneous pressure increase to exceed 20 kPa, the sample temperature at this time is the flash point temperature (11.11).
• 12.1 Atmospheric pressure correction: Observe and record the ambient atmospheric pressure during the test; when the ambient atmospheric pressure is not 101.3 kPa, correct the flash point according to the following formula: Corrected flash point = C + 0.25(101.3 − P) Where: C—— observed flash point, ℃; P—— ambient atmospheric pressure, kPa. The corrected flash point is rounded to 0.5 ℃. Note: The atmospheric pressure used in this correction should be the ambient atmospheric pressure of the laboratory at the time of testing; many metal barometers used in weather stations and airports have been pre-corrected to sea level readings and cannot be used here.
• 13 Report: Report the corrected flash point as the flash point of the tested sample, accurate to 0.5 ℃.
• 11.13 Record the uncorrected flash point; if no flash point is detected within the test temperature range, report that the flash point is higher than the final temperature.

10. Precision

• 14.1 The precision data were obtained from 10 laboratories in the 1996 cooperative test program using three pure chemical substances, one pure hydrocarbon, three fuel oils, and three lubricating oils. Applicable to samples with flash points from 10 ℃ to 250 ℃, but excluding 6 fuel oil. Note: The precision of 6 fuel oil is significantly worse than that of other samples, and it must be assumed that the test procedure described in Chapter 11 is not applicable to such samples.
• 14.2 Precision (95% confidence level):
  • 14.2.1 Repeatability r = 1.9 ℃ (the difference between two results obtained by the same operator, in the same laboratory, with the same instrument, following the procedure specified in the method, on the same sample).
  • 14.2.2 Reproducibility R = 3.1 ℃ (the difference between two independent test results obtained by different operators, in different laboratories, following the procedure specified in the method, on the same sample).
• 14.3 Deviation: because there is no acceptable reference material, the deviation was not determined.
• Appendix B Table B.1 Limits: anisole ±1.5 ℃; n-dodecane ±2.1 ℃.

11. Report

• 13 Report: take the corrected flash point as the flash point of the test specimen, to the nearest 0.5 ℃.
• 11.13 Record the detected specimen flash point temperature as the uncorrected flash point temperature; if no flash point is detected within the test temperature range, report that the flash point is higher than the final temperature.
• 12.1 The corrected flash point is rounded to 0.5 ℃.

12. Normative references

• GB/T 4756 Petroleum liquids—Manual sampling (GB/T 4756—1998, eqv ISO 3170:1988)
• GB/T 15000.3 Directives for the work of reference materials (3) General principles and statistical methods for the certification of reference materials (GB/T 15000.3—1994, neq ISO Guide 35:1989)
• GB/T 15000.7 Directives for the work of reference materials (7) General requirements for the competence of reference material producers (GB/T 15000.7—2001, idt ISO Guide 34:2000)
• Adoption source: ASTM D6450-99 "Determination of flash point by continuously closed cup method"

13. Source and verification

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14. Quick-reference Q&A