Carbon steels are used in the
However, it is important to note that these materials are not necessarily exactly equivalent because there can be minor differences in the chemical composition or mechanical properties requirements for the material. Note that in Table 2-1, these are designated as comparative materials, not equivalent materials. The material specifications of ASME and ASTM International (ASTM), which are listed as comparative, are similar in both chemistry and mechanical properties to those of the international specifications listed. In general, an alloy is considered comparable if the specified mechanical properties are essentially the same despite variation in the compositions. The specifications are not identical, so they cannot be considered equivalent. It is possible that a material meets the requirements of any or all of the comparative specifications. Where available, the Unified Numbering System (UNS)  identification is also given because this identification provides some link between materials with the same chemical composition (and to some extent, with their mechanical properties) and has some significance in the ASME Codes.