Overview
ISO 6257:2002 - Carbonaceous materials used in the production of aluminium - Pitch for electrodes - Sampling - specifies standardized methods for sampling and preparing binder pitch used to manufacture electrodes for the electrolytic production of aluminium. The standard covers pitch in liquid or solid form (solids having a softening point > 30 °C as per ISO 5940), and applies at sites of manufacture, storage and delivery, including sampling and sampling plans for large consignments or lots during loading and unloading of ships.
Key topics and technical requirements
- Scope of samples: Applies to bulk shipments and containers, for both liquid and solid (high softening point) pitches.
- Sampling concepts and definitions: Clear definitions for terms such as sampling unit, incremental sample, final sample, laboratory sample and representative sample.
- Sample size and frequency:
- Representative sample masses (examples): 1–10 t → 10 kg; 10–50 t → 15 kg; 50–100 t → 20 kg.
- Mass of laboratory/reference samples: at least three times the amount required for testing and never less than 1 kg (minimum recommended 2 kg).
- Incremental samples: minimum ≈1 kg, preferred 2 kg; larger sample sizes recommended for coarse or heterogeneous material.
- Sampling plans for lots/consignments: Prescribed minimum number of containers/items to sample depending on lot size (e.g., sample all items for 1–10 items; specified fixed counts for larger lots). Specific charts and tables guide sample counts for solids and liquids.
- Preparation and reduction: Methods for reducing sample size to laboratory portions - riffle splitting or coning-and-quartering - after lump breakdown (punners) and avoiding segregation.
- Contamination and storage: Requirements to avoid contamination - dry, clean containers and tools; precautions against surface oxidation (melting and resolidifying powdered samples at ~50 °C above softening point, then sealing airtight).
- Water content: Special spot-sampling and immediate sealing for moisture determination in solid pitch.
- Safety and reporting: Safety measures (see ISO 3165) for sampling hot liquid pitch (tanks, ships); mandatory sampling reports documenting methods, sample masses and conditions.
Applications and users
ISO 6257:2002 is used by:
- Pitch manufacturers and packers ensuring consistent quality and conformity before dispatch.
- Quality control and testing laboratories preparing representative laboratory and reference samples.
- Aluminium smelters and electrode producers verifying incoming binder pitch specifications.
- Logistics and shipping inspectors managing sampling during tank/ship loading and unloading.
- Regulatory bodies and purchasers requiring documented, reproducible sampling for dispute resolution.
Related Standards
- ISO 3165 - Sampling of chemical products for industrial use - Safety in sampling (safety procedures referenced).
- ISO 5940 - Carbonaceous materials - Pitch for electrodes - Determination of softening point by ring-and-ball method (used to classify solid pitches).
Keywords: ISO 6257:2002, pitch for electrodes sampling, binder pitch sampling, aluminium electrode pitch, sampling plan, representative sample, softening point.
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