This International Standard specifies the requirements for the optional continuous character and colour marking of ferritic and austenitic steel tubes that are used in the fabrication of piping systems. The colour coding specified can also be used for the marking of fittings and components (see 6.2.3). It covers specific requirements for definitive material identification by the use of printed characters which are applied repetitively (continuously) along the length of the tube, and for the colour coding of discrete groups of steels. The colour coding may be specified at the option of the purchaser and is intended for use only in conjunction with the definitive character marking requirements given in clause 5. In the absence of a suitable International Standard defining colours suitable for use in colour coding, annex A makes reference to certain equivalent colour codes given in national standards which may be used. It is recognized that this International Standard can only be applied by agreement between the parties concerned.