ISO INTERNATIONAL STANDARD 6618 Second edition 1997-02-01 Petroleum products and lubricants Determination of acid or base number - Colour-indicator titration method Produits pétroliers et lubrifiants - Détermination de I'indice d'acide ou de I'indice de base - Méthode par titrage en presence d'un indicateur coloré ISO Reference number ISO 6618:1997(E) Copyright In No reproduction or networking permited without license from IHS Not for Resale ISO 6618:1997(E) Foreword preparing International Standards is normally carried out through IsO which a technical committee has been establishedhas the right to be and non-governmental, in liaison with iSO, also take part in the work. IsO collaborates closely with the International Electrotechnical Commission (lEC)onallmattersofelectrotechnicalstandardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting avote. International Standard isO 6618 was prepared by Technical Committee ISO/Tc 28, Petroleum products and lubricants. This second edition cancels and replaces the first edition (isO 6618:1987) whichhasbeentechnicallyrevised. Annexes A and B form an integral part of this International Standard. @ISO1997 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International OrganizationforStandardization CasePostale56.CH-1211Geneve20·Switzerland Printed in Switzerland ie from IHS Not for Resale ISO 6618:1997(E) INTERNATIONALSTANDARD ISO Petroleum products and lubricants -- Determination of acid or base number -- Colour-indicator titration method WARNING - The use of this International Standard may involve hazardous materials, operations and is the responsibility of the user of this International Standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 1 Scope This International Standard specifies a colour-indicator titration method for the determination of acidic or basic constituents in petroleum products and lubricants soluble in mixtures of toluene and propan-2-ol. It is applicable for the determination of acids or bases whose dissociation constants in water are greater than 10-9; extremely weak acids or bases whose dissociation constants are less than 10-9 do not interfere. Salts react if their hydrolysis constants are greater than 10-9. NOTE 1 In new and used oils, the constituents considered to have acidic characteristics include organic and inorganic acids, esters, phenolic compounds, lactones, resins, salts of heavy metals, and additives such as inhibitors and detergents. Similarly. constituents considered to have basic properties include organic and inorganic bases, amino compounds, salts of weak acids (soaps), basic salts of polyacidic bases, salts of heavy metals, and additives such as inhibitors and detergents. which ISO 3771 can be used. This International Standard indicates relative changes that occur in an oil during use under oxidizing conditions NOTES 2 No general relationship between bearing corrosion and acid or base number is known. 3 Oils, such as many cutting oils, rustproofing oils, and similar compounded oils, or excessively dark-coloured oils, that cannot be analysed by this method owing to obscurity of the colour-indicator end-point, can be analysed in accordance with Iso 6619. The acid or base numbers obtained by this colour-indicator method may or may not be numerically the same as those obtained by IsO 6619, but they are generally of the same order of magnitude. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At th