GB/T 21789-2008 Petroleum products and other liquids — Determination of flash point — Abel closed-cup method

Summary page. This page is a compiled excerpt/summary of the standard — it is not the full standard text and does not replace it. Verify every value against the official standard and the product certificate before use.

GB/T 21789-2008 specifies the Abel closed-cup determination of the flash point of petroleum products and other liquids; this page is historical study material on the superseded 2008 edition, covering its ranges, the low- and high-temperature routes, pressure correction, precision and reference-material verification.

Evidence note: original study material for the historical 2008 edition, which has been wholly replaced by the 2025 edition; it is not the full text of the standard, a controlled operating procedure or a calculator, and independent technical review is pending.

Identity and historical range: Designated 2008 original PDF physical pages 1, 2. GB/T 21789—2008, issued 2008-05-12, implemented 2008-09-01, first issue; the designated 18 physical pages serve only as historical study of this edition. The official record shows withdrawal and wholesale replacement by the 2025 edition on 2026-02-01. This page does not replace the current standard or a controlled technical document.

Scope and precision range: Designated 2008 original PDF physical pages 3, 7. The method covers −30 to 70 °C; original clauses 1 and 13 note that the precision applies only to −5 to 66.5 °C, and the two ranges must be used separately. Water-borne paints are not covered, and halogen-containing samples may behave abnormally. A flash point obtained in a controlled test is not directly equal to the real fire risk. Use | Temperature range °C | Boundary Method | −30 to 70 | not applicable to water-borne paints Precision | −5 to 66.5 | r/R apply only within this range

Principle and references: Designated 2008 original PDF physical pages 2, 3, 5, 6. The closed-cup sample is heated at the specified rate and a test flame is introduced at intervals, and a distinct flash is recorded; a blue halo and enlargement of the ignition flame are not a flash. Sampling per ISO 3170:1988/SY/T 5317—2006, and ISO 3679:1983 as a separate method for water-borne paints; the historical IDT does not imply equivalence with the current version.

Apparatus and arbitration: Designated 2008 original PDF physical page 4. Abel apparatus with the specified thermometer and sleeve; automatic instruments must be verified to agree with manual results and used according to the manufacturer's instructions, and disputes are arbitrated by the manual method. The barometer is accurate to 0.1 kPa, and a barometer pre-corrected to standard atmospheric pressure must not be used. The complete A–C manufacturing dimensions, thermometer specifications and installation still await technical review.

Materials and original wording: Designated 2008 original PDF physical pages 3, 4. The cleaning solvent is chosen according to the nature of the residue; the conflict between the heading of 5.1, "benzene-free", and the TAM benzene–acetone–methanol example in the text is retained, and no formulation is recommended. Ethylene glycol/glycerol are used as bath media and silicone lubricant for the equipment, not as calibration standards or product specifications.

Sampling and preparation: Designated 2008 original PDF physical page 4. Keep the sample sealed after sampling to avoid loss of volatile components; this edition does not use plastic sample containers. A level bench and a draught-free environment/three-sided shield are separate conditions; the original dimensions of about 450 mm wide and 600 mm high locate the equipment shield and are not a storage requirement.

Low-temperature route: Designated 2008 original PDF physical page 5. 10.1 covers −30 to 18.5 °C. The heating bath uses ethylene glycol/water and similar bath media, with an air-gap liquid depth ≥ 38 mm; the bath temperature is −35 °C or at least 9 °C below the expected value, whichever is higher, and the sample/cup cover −35 °C or at least 17 °C below the expected value, whichever is higher; cooling must stay above the crystallisation point and ice adhesion must be prevented, and the complete operation requires controlled safety.

Higher-temperature route: Designated 2008 original PDF physical page 6. 10.2 covers 19 to 70 °C, with a water bath and an air-gap water depth ≥ 38 mm; the bath temperature is 10 °C or the expected value minus 9 °C, whichever is higher, and the sample/cup cover 2 °C or the expected value minus 17 °C, whichever is higher. The transition between the two routes at 18.5–19 °C is not listed separately in the original, and no automatic selection algorithm is added. The reference in 10.2.8, for a flash at the first ignition, to 10.1.2/10.1.3 is retained as a cross-reference awaiting review.

Heating and ignition roles: Designated 2008 original PDF physical pages 4, 5, 6. The unshaken sample is filled to the mark avoiding bubbles, the flame is about 3.8 mm and is compared with the bead; the sample is heated at 1 °C/min with stirring at about 30 r/min or a value appropriate to the viscosity, stirring being stopped at ignition; ignition is applied at each 0.5 °C rise. The metronome at 75–80 beats/min and the electronic timing of 2 s open/1 s closed are separate, and the complete shutter movement is not reconstructed.

Pressure correction and result: Designated 2008 original PDF physical pages 6, 7, 16. Tc = To + 0.25×(101.3 − P), where To is the observed flash point and P is as originally defined in kPa at 0 °C; hPa/mbar × 0.1, mmHg × 0.133322. The note to 11.1, that readings need not be corrected to 0 °C, and the definition of P await review, and are not harmonised on the author's behalf. The routine result is corrected and given to 0.5 °C, while verification records use 0.1 °C. No calculator is published. Original unit | Conversion to kPa hPa | × 0.1 mbar | × 0.1 mmHg | × 0.133322

Use of the precision: Designated 2008 original PDF physical page 7. The original r = 1.0 °C and R = 1.5 °C, with about one exceedance in 20 determinations under correct operation, limited to −5 to 66.5 °C; this is not a guarantee over the whole −30 to 70 °C range, not the uncertainty of a product batch certificate, and the 1.4/3.2 °C of the 2025 edition is not applied. Use | Original value °C Repeatability r | 1.0 Reproducibility R | 1.5 Routine result | 0.5 Verification record | 0.1

Role of verification materials: Designated 2008 original PDF physical pages 15, 16. Annex D is normative, with CRM and SWS listed separately; an SWS may be assigned from a CRM-verified instrument with at least 3 determinations and statistics, or from duplicate determinations in at least 3 laboratories. Avoidance of sunlight and ≤ 10 °C are the SWS conditions of this method, not storage conditions for all products. Table D.1 gives closed-cup approximate values, and −9 °C for isooctane and the like cannot be taken as a certificate value for a particular batch or as an available product. The CRM verification at least once a year and the interim SWS verification are separate.

Verification acceptance limits and reporting: Designated 2008 original PDF physical pages 7, 16. Single result |x−u| ≤ R/√2; multiple results |x̄−u| ≤ R1/√2, with R1 = √[R²−r²(1−1/n)]. The original wording that calls x the mean for a single determination awaits review; the conditions include the assumption that the certificate/assigned-value uncertainty is relatively very small, and the acceptance limit is not certificate uncertainty — the difference must not be used to alter the flash point result. An exceedance is handled by checking the instrument/operation separately from the CRM re-check and the SWS treatment. The report gives the number, sample identification, result, procedure deviations and date.

Evidence and unverified items: Designated 2008 original PDF physical pages 2, 8, 9, 10, 11, 12, 13, 14, 17, 18. Based on the designated 2008 original, the method range, ignition pressure, precision and verification acceptance limits were checked in particular; this content is not a complete technical acceptance. A/B/C/D are all normative; the dense manufacturing dimensions and the full three-column thermometer table, controlled safety/software and historical applicability still await review. No standard scans are provided, and this text cannot replace the current edition or a controlled technical document. Official metadata from the same system is not independent technical review.

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