National foreword

This British Standard is the UK implementation of ISO 540:2025. It supersedes BS ISO 540:2008, which is withdrawn.

The UK participation in its preparation was entrusted to Technical Committee W/-, Miscellaneous Standards.

A list of organizations represented on this committee can be obtained on request to its committee manager.

Contractual and legal considerations

This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

This publication is provided as is, and is to be used at the recipient’s own risk.

The recipient is advised to consider seeking professional guidance with respect to its use of this publication.

This publication is not intended to constitute a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 August 2025.

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

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).

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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 540:2008), which has been technically revised.

The main changes are as follows:

change of the document title;
removal of coke from scope;
increase of the allowance of the pyramid to between 12 mm and 19 mm.

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.

Introduction

The method for determination of the fusibility temperatures of coal ash described in this document provides information about the fusion and melting behaviour of the composite inorganic constituents of the ash at high temperatures. The standard method is based on the “Seger Cone” method, which is well known in the ceramic industry, the use of which predates the year 1900. The conditions of the test, as well as basic studies on the influence of ash chemistry and of gas composition on ash fusibility temperatures (which have led to the standardization of the method), arose from the pioneering work of Fieldner, Hall and Field ^[1^].

In the laboratory, the ash used for the test is a homogeneous mixture prepared from a representative sample of the coal, and the determination is performed at a controlled rate of heating in either a reducing or an oxidizing atmosphere. In contrast, under industrial conditions, the complex processes of combustion and fusion involve heterogeneous mixtures of particles, heating rates (that can be several orders of magnitude greater than those used in the standard test) and variable gas composition.

During the first quarter of the 20th century, laboratory, pilot-scale and field studies were undertaken to establish that the ash fusibility test can provide a reasonable indication of the propensity of ash to form fused deposits (referred to as “clinker”) in stoker and other fuel-bed type furnaces.^[2^] Subsequently, the test has been used as a general indicator of the tendency for ash to fuse on heating and of ash slagging propensity in pulverized coal-fired furnaces.

1 Scope

This document specifies a method of determining the characteristic fusion temperatures of ash from hard coal.

NOTE Descriptors: fossil fuels, ash, ashes, tests, high temperature tests, determination, and fusibility.

2 Normative references

3 Terms and definitions

4 Principle

5 Reagents

5.1

5.2

5.3

5.4

5.5

5.6

5.7

6 Apparatus

6.1

6.2

6.3

6.4

6.5

6.6

6.7

6.8

7 Test conditions

7.1 Test atmosphere

7.2 Shape of test piece

8 Calibration check

9 Preparation of the test piece

10 Procedure

11 Precision of the method

11.1 Repeatability limit

11.2 Reproducibility limit

12 Test report

13 Precision statement

Bibliography

BS ISO 540:2025

Hard coal. Determination of ash fusibility

Current

Published:

31 Aug 2025