Overview
ISO 7087:1984 - Ferroalloys - Experimental methods for the evaluation of the quality variation and methods for checking the precision of sampling - defines laboratory and field procedures to quantify heterogeneity (quality variation) of ferroalloys and to verify the precision of sampling procedures. The standard supports the determination of sampling parameters used in relevant ISO delivery standards and includes an annex with calculation examples.
Key topics and requirements
- Scope: Methods for estimating quality variation for random sampling (bulk consignments) and two‑stage sampling (packed units), and procedures for checking sampling precision.
- Types of experiment:
- Type I - Random sampling for bulk ferroalloys (crushable and uncrushable). Increments are taken (e.g., shovels or drilling chips).
- Type II - Two‑stage sampling for consignments delivered in packed units; selection of m packed units then increments within units.
- Experimental design:
- Experiments are normally repeated at least 10 times on a single consignment.
- Duplicate test samples are prepared from increments; chemical determinations are performed in random order.
- Data must be recorded on a standard data log (examples provided).
- Statistical analysis:
- Quality variation is expressed as a standard deviation between increments (random sampling) or between‑unit and within‑unit standard deviations (two‑stage sampling).
- Procedures include calculation of paired measurement ranges, mean ranges, unbiased variance estimates, and separation of within‑ and between‑unit variance components.
- Practical notes: negative computed variances are treated as zero if no experimental defect is found. The standard provides factors (e.g., d2 = 1.128 for paired measurements) and worked examples.
Practical applications and users
- Quality control and metallurgical laboratories assessing heterogeneity of ferroalloys (ferrosilicon, ferromanganese, ferrochromium, etc.).
- Producers and purchasers validating sampling schemes and ensuring compliance with ISO delivery specifications.
- Inspection bodies and testing laboratories checking the precision of sampling and sample preparation methods.
- Technical committees and R&D groups developing sampling plans or comparing bulk vs packed‑unit variability.
Related standards
ISO 7087 references and complements other ferroalloy standards, for example:
- ISO 3713 - Ferroalloys: sampling and sample preparation - general rules
- ISO 4552 (parts) - Sampling and sample preparation for chemical analysis
- ISO 7347, ISO 7373 - Experimental methods for checking bias and precision of sampling
- Various ISO specifications for individual ferroalloys (ISO 5443–5454 series)
Keywords: ISO 7087:1984, ferroalloys sampling, quality variation, sampling precision, two‑stage sampling, random sampling, standard deviation, experimental methods.
