Tuesday, October 14, 2008

Carbon Steel Materials

The carbon steel materials used in pressure applications cover a very wide range of mechanical properties. Carbon steel materials are listed in the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code [1] with a room temperature tensile strength range from 40 kips per square inch (ksi) (275 megapascals [MPa]) up to 100 ksi (690 MPa). Most of the higher strength materials have very limited application in power plants; accordingly, the materials covered in this report will be limited to those with a specified minimum tensile strength less than 80 ksi (550 MPa).

Carbon steels are used in the United States and throughout the world for nearly all of the same reasons: their cost, properties, ease of fabrication, availability, welds ability, and so on. Table 2-1 lists some ASME material specifications covered in this report with some comparative European material specifications and with those of the UK, Germany, and Japan (where comparative international specifications are identified) [2].

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) [3] 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.

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