ISO 501:2025

Hard coal - Determination of the crucible swelling number

This document specifies a method for determining the swelling properties of hard coal when heated in a covered crucible. NOTE The "crucible swelling number" (CSN) is also known as the "free swelling index" (FSI).

Houille — Détermination de l'indice de gonflement au creuset

General Information

• Status: Published
• Publication Date: 30-Apr-2025
• ICS: 73.040 - Coals
• ICS: 75.160.10 - Solid fuels
• Technical Committee: ISO/TC 27/SC 5 - Methods of analysis
• Drafting Committee: ISO/TC 27/SC 5 - Methods of analysis
• Current Stage: 6060 - International Standard published
• Start Date: 01-May-2025
• Due Date: 20-May-2025
• Completion Date: 01-May-2025

Relations

• Revises: ISO 501:2012 - Hard coal - Determination of the crucible swelling number
• Effective Date: 27-May-2023

Overview

ISO 501:2025 specifies a standardized laboratory method for determining the crucible swelling number (CSN) - also known as the free swelling index (FSI) - of hard coal. The test quantifies how a ground coal sample behaves (swells and cokes) when heated in a covered silica crucible under controlled heating and atmosphere. The CSN/FSI is a widely used indicator of coal coking properties and is important for coal characterization, quality control and process selection.

Key topics and technical requirements

• Sample preparation

  • Use the general analysis test sample prepared per ISO 13909-4 and ISO 18283.
  • Grind to pass a 212 µm sieve; avoid over-pulverization and ring mills.
  • Perform test within 24 h of grinding to avoid oxidation.
  • Test sample mass: 1,00 g to 1,01 g.

• Apparatus

  • Silica crucible and lid with specified dimensions (e.g., external height 26 mm ± 1 mm, top diameter 41 mm ± 1 mm, capacity 16–17.5 ml, mass 12 g ± 1 g).
  • Pierced lid and thermocouple for temperature monitoring.
  • Burner (Teclu or Meker) or alternative electrical heating if equivalent to gas method (within ±0,5 CSN unit).
  • Draught shield, silica triangle support, 500 g mass and sight tube for profile comparison.

• Heating profile and conditioning

  • Empty crucible base temperature: 800 °C ± 10 °C after 1.5 min, 820 °C ± 5 °C after 2.5 min.
  • Precondition apparatus and check temperature profile regularly.

• Procedure and result classification

  • Heat coal in covered crucible until volatile flame dies out (minimum 2.5 min), cool, and examine residue.
  • Classify results as 0, 0.5, 1, 1.5–9, or >9 based on coke button form and standard profile templates.
  • Perform tests in triplicate (or up to 5/10 depending on spread rules); report mean to nearest 0.5 unit.

• Precision

  • Repeatability: maximum acceptable difference for 3 determinations = 0.5 unit.
  • Reproducibility: for 5 determinations, maximum acceptable difference between labs = 1 unit.

• Safety

  • The standard includes a safety warning; users must establish appropriate health and safety practices.

Applications and users

ISO 501:2025 is used by:

• Coal laboratories and quality control teams for coal characterization, coking potential assessment and blending decisions.
• Coke producers and steelmakers assessing feedstock suitability for coke ovens.
• Researchers and standards bodies comparing coal swelling behavior.
• Regulatory or procurement teams specifying coal quality.

Practical benefits include consistent CSN/FSI measurement for process control, product specification, and comparative testing across laboratories.

Related standards

• ISO 13909-4 - Coal and coke - Mechanical sampling - Part 4: Preparation of test samples of coal
• ISO 18283 - Coal and coke - Manual sampling

Keywords: ISO 501:2025, crucible swelling number, CSN, free swelling index, FSI, hard coal testing, coal coking properties, crucible test, coke button, coal laboratory standard.

Standards Content (Sample)

International
Standard
ISO 501
Fifth edition
Hard coal — Determination of the
2025-05
crucible swelling number
Houille — Détermination de l'indice de gonflement au creuset
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Preparation of the test sample. 1
6 Apparatus . 2
7 Preparation of apparatus . 4
8 Procedure . 5
9 Expression of results . 6
10 Precision of the method . 7
10.1 Repeatability .7
10.2 Reproducibility .7
11 Test report . 7

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
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Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 27, Coal and coke, Subcommittee SC 5, Methods
of analysis.
This fifth edition cancels and replaces the fourth edition (ISO 501:2012), which has been technically revised.
The main changes are as follows:
— replaced the word "should" with "shall" throughout the document;
— corrected dimension expressions e.g. 26 ± 1,0 mm to 26 mm ± 1 mm;
— standardised the reporting of ½ as 0,5.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
International Standard ISO 501:2025(en)
Hard coal — Determination of the crucible swelling number
WARNING — Use of this document can involve hazardous materials, operations and equipment.
This document does not purport to address all of the safety issues associated with its use. It is the
responsibility of the user of this document to establish appropriate safety and health practices and
determine the applicability of regulatory limitations prior to use.
1 Scope
This document specifies a method for determining the swelling properties of hard coal when heated in a
covered crucible.
NOTE The "crucible swelling number" (CSN) is also known as the "free swelling index" (FSI).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 13909-4, Coal and coke — Mechanical sampling — Part 4: Preparation of test samples of coal
ISO 18283, Coal and coke — Manual sampling
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Principle
A sample of coal is heated in a covered crucible under standard conditions of time and temperature. The
shape of the coke button obtained is classified by comparison with the outlines of a set of standard profiles.
5 Preparation of the test sample
The test sample shall be the general analysis test sample prepared in accordance with ISO 13909-4 and
ISO 18283. Ensure that the moisture in the sample is in equilibrium with the laboratory atmosphere,
exposing it, if necessary, in a thin layer for the minimum time required to achieve equilibrium.
The sample used for the crucible swelling number (CSN) test shall be ground to pass a 212 μm sieve. A small
swing hammer crusher with rotary hammers is suitable for grinding samples, a mortar and pestle can be
used to grind samples of low mass, e.g. less than 60 g. Avoid very fine grinding, as CSN can be adversely
affected with pulverization level. Avoid the use of ring mills as the heat generated during very fine grinding
can potentially oxidise the sample and adversely affect the CSN result. Once the sample is prepared to this
size specifi
...