⛽ Ash content in petroleum products
In short
Determination of ash in petroleum products in which ash-forming constituents are undesirable impurities: a test portion is ignited and burnt to a residue of carbon and ash, and the residue is heated in a muffle furnace at 775 °C and weighed. The test is performed according to PN-EN ISO 6245:2008; Range: 0.001–0.180 % (m/m); excluding products with ash-forming additives (clause 1). The procedure comprises 8 steps; it is used for: Diesel fuel — at most 0.010 % (m/m) (Journal of Laws 2024, item 1018, Annex 3 item 9), B20 diesel fuel and paraffinic diesel fuel — at most 0.010 % (m/m) (Journal of Laws 2025, item 426, Annexes 2 and 3), Distillate and residual fuel oils, crude petroleum, lubricating oils without ash-forming additives, waxes (clause 1).
At a glance
- Standard: PN-EN ISO 6245:2008
- Category: Petrochemistry
- Procedure steps: 8
- Range: 0.001–0.180 % (m/m); excluding products with ash-forming additives (clause 1)
- Ashing temperature: 775 ± 25 °C (5.2, 8.8)
- Test portion mass: up to 100 g, chosen from Table 1 to yield up to 20 mg of ash (8.3)
Overview
STATUS (as of 30.10.2026). PN-EN ISO 6245:2008 — Polish version, published 08.02.2008, implements EN ISO 6245:2002 and ISO 6245:2001 [IDT]; it replaced PN-EN ISO 6245:2003 (English and German versions). The PKN catalogue card has no withdrawal note — the standard is current; Polish title according to the card: “Przetwory naftowe — Oznaczanie pozostałości po spopieleniu” (Petroleum products — Determination of ash). ISO 6245:2001 is the third edition, which replaced ISO 6245:1993.
SCOPE (clause 1). Determination of ash in petroleum products — distillate and residual fuel oils, crude petroleum, lubricating oils, waxes and others — in which ash-forming constituents are normally considered undesirable impurities or contaminants. Ash can result from oil-soluble or water-soluble metallic compounds or from extraneous solids such as dirt and rust. Range: 0.001–0.180 % (m/m). The method does not apply to products containing ash-forming additives, including certain phosphorus compounds: lubricating oils with additives (unused and used), used engine crankcase oils, lubricating oils containing lead and certain non-hydrocarbon diesel fuels are tested according to ISO 3987 (sulfated ash). With some samples the result does not account quantitatively for all metals: in oils with low-molecular-mass metal additives (e.g. sodium, potassium) the metal oxide may sublime below the test temperature (Note 2).
LEGAL REQUIREMENTS. Diesel fuel: ash content at most 0.010 % (m/m) (Journal of Laws 2024, item 1018, Annex 3 item 9). The same requirement applies to diesel fuel containing 20 % methyl ester (B20) and to paraffinic diesel fuel (Journal of Laws 2025, item 426, Annex 2 item 9 and Annex 3 item 8).
PRECISION (clause 11, Table 2). For 0.001–0.079 % (m/m): repeatability 0.003 % (m/m), reproducibility 0.005 % (m/m); for 0.080–0.180 % (m/m): 0.007 % and 0.024 % (m/m).
REFERENCE DOCUMENT. The publicly available text of the standard covers clauses 1–12. The American method ASTM D482 on the same subject states that knowing the amount of ash-forming material in a product can show whether the product is suitable for a given application.
Method principle
A test portion in a suitable vessel is ignited and allowed to burn until only ash and carbon remain. The carbonaceous residue is reduced to ash by heating in a muffle furnace at 775 °C, allowed to cool and weighed (clause 3). The result is the mass of ash as a percentage of the mass of the test portion (clause 9).
Applications
- Diesel fuel — at most 0.010 % (m/m) (Journal of Laws 2024, item 1018, Annex 3 item 9)
- B20 diesel fuel and paraffinic diesel fuel — at most 0.010 % (m/m) (Journal of Laws 2025, item 426, Annexes 2 and 3)
- Distillate and residual fuel oils, crude petroleum, lubricating oils without ash-forming additives, waxes (clause 1)
- Lubricating oils with additives and used engine oils — not by this method but according to ISO 3987 (clause 1)
Key parameters
| Parameter | Value |
|---|---|
| Range | 0.001–0.180 % (m/m); excluding products with ash-forming additives (clause 1) |
| Ashing temperature | 775 ± 25 °C (5.2, 8.8) |
| Test portion mass | up to 100 g, chosen from Table 1 to yield up to 20 mg of ash (8.3) |
| Weighing | to the nearest 0.1 mg; to constant mass — consecutive weighings differ by at most 0.5 mg (8.2, 8.9) |
| Result | to the nearest 0.001 % (m/m) (clause 10) |
| Precision | r 0.003 and R 0.005 % (m/m) for 0.001–0.079 %; r 0.007 and R 0.024 % (m/m) for 0.080–0.180 % (Table 2) |
Standard
- Standard number
- PN-EN ISO 6245:2008
- Title (PL)
- Przetwory naftowe — Oznaczanie pozostałości po spopieleniu
- Title (EN)
- Petroleum products — Determination of ash
Step-by-step procedure
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Homogenizing the sample
Mobile samples are mixed until visually homogeneous — the lowest intensity is 10 min of manual or mechanical shaking, followed by longer mixing and, if needed, the mixer. Viscous and solid samples are heated until mobile (normally about 5 °C above the pour point), taking care above 90 °C that water in the sample may boil. A sample that cannot be homogenized is not tested — a new sample is obtained (clause 7).
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Preparing the vessel
A vessel of suitable capacity for the test portion is heated in the muffle furnace at 700–800 °C for at least 10 min, cooled to ambient temperature in the cooling vessel and weighed to the nearest 0.1 mg; heating and weighing are repeated until consecutive results differ by at most 0.5 mg (8.1–8.2).
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Test portion
The test portion mass (up to 100 g) is selected from Table 1 according to the expected ash content so as to yield up to 20 mg of ash; for portions requiring more than one firing, the mass is obtained from the difference in mass of the container with homogenized sample (8.3).
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Burning
The vessel with the test portion is heated until the contents can be ignited with a flame applied externally near the liquid surface, and the temperature is maintained so that the portion burns at a uniform, moderate rate until only carbon and ash remain. A platinum vessel must not contact the reducing part of the flame. Neither the portion nor the vessel may be heated to red heat, and the flame must not rise above the rim of the dish (8.4, 8.7).
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Samples containing water
If water causes foaming or spattering, the test is discontinued; 1–2 ml of propan-2-ol is added to a second portion before heating, and if that is not enough, 10 ml of an equivolume toluene/propan-2-ol mixture and strips of ashless filter paper are added to a third, or the mixture is added in 2–3 ml increments with heating between additions (8.5).
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Crust on the residue
When heavy samples form a crust over unburnt material, it is broken with a glass rod, and material adhering to the rod is returned to the vessel with a strip of ashless filter paper and burning continued until only carbon and ash remain (8.6).
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Ashing
The residue is heated in the muffle furnace at 775 ± 25 °C until the carbonaceous material has disappeared, cooled in the cooling vessel to ambient temperature and weighed to the nearest 0.1 mg; it is then reheated for 20–30 min, cooled and weighed until consecutive weighings differ by at most 0.5 mg (8.8–8.9).
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Calculation and result
Ash content A = m₁ / m₀ × 100 %, where m₁ is the mass of ash, g, and m₀ the mass of the test portion, g. The result is reported to the nearest 0.001 % (m/m) (clauses 9–10).
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Evaporating vessel | dish or crucible of 50–150 ml made of platinum, silica or porcelain (alumina where appropriate); vessels not made of platinum may contaminate the ash (5.1) | — |
| Muffle furnace | electric, maintaining 775 ± 25 °C; with manual temperature control and front and rear apertures for a slow natural draught of air, or programmable, controlling both temperature and air flow (5.2) | — |
| Cooling vessel | closed, of adequate capacity, without a desiccating agent (5.3) | — |
| Analytical balance | weighing to the nearest 0.1 mg (5.4) | — |
| Mixer | high-speed shear type, non-aerating — for homogenizing the sample (5.5) | — |
| Burner | Meker or Bunsen gas burner or equivalent (5.6) | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Propan-2-ol | 67-63-0 | minimum purity 99 % — for test portions containing water (4.1, 8.5) |
| Toluene (methylbenzene) | 108-88-3 | according to ISO 5272, grade B — in an equivolume mixture with propan-2-ol for test portions containing water (4.2, 8.5) |
| Ashless filter paper | — | strips for removing water from the test portion and for transferring residue from the rod (4.3, 8.5–8.6) |
Health and safety (OHS)
- The standard warns that its use may involve hazardous materials, operations and equipment, and that the user establishes the safety and health practices (warning before clause 1)
- Burning samples are not left unattended (8.5)
- When samples are heated above 90 °C, water in the sample may boil, causing spattering or foaming — safety goggles and gloves (7.3)
- Toluene and propan-2-ol are flammable — according to their safety data sheets; the muffle furnace and hot vessels are a burn hazard
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 6245:2008 — “Petroleum products — Determination of ash”.
How does this method work?
A test portion in a suitable vessel is ignited and allowed to burn until only ash and carbon remain. The carbonaceous residue is reduced to ash by heating in a muffle furnace at 775 °C, allowed to cool and weighed (clause 3).
What is the measuring range and accuracy?
Range: 0.001–0.180 % (m/m); excluding products with ash-forming additives (clause 1); Ashing temperature: 775 ± 25 °C (5.2, 8.8); Test portion mass: up to 100 g, chosen from Table 1 to yield up to 20 mg of ash (8.3); Weighing: to the nearest 0.1 mg; to constant mass — consecutive weighings differ by at most 0.5 mg (8.2, 8.9).
How long does the test take?
The procedure comprises 8 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Evaporating vessel, Muffle furnace, Cooling vessel, Analytical balance, Mixer, Burner.
Where is this test used?
Diesel fuel — at most 0.010 % (m/m) (Journal of Laws 2024, item 1018, Annex 3 item 9); B20 diesel fuel and paraffinic diesel fuel — at most 0.010 % (m/m) (Journal of Laws 2025, item 426, Annexes 2 and 3); Distillate and residual fuel oils, crude petroleum, lubricating oils without ash-forming additives, waxes (clause 1); Lubricating oils with additives and used engine oils — not by this method but according to ISO 3987 (clause 1).
What safety precautions apply?
The standard warns that its use may involve hazardous materials, operations and equipment, and that the user establishes the safety and health practices (warning before clause 1); Burning samples are not left unattended (8.5); When samples are heated above 90 °C, water in the sample may boil, causing spattering or foaming — safety goggles and gloves (7.3); Toluene and propan-2-ol are flammable — according to their safety data sheets; the muffle furnace and hot vessels are a burn hazard.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 6245.