ASME B31T:2018 pdf free download – Standard Toughness Requirements for Piping
Material T-number groups for each covered material specification are provided in Table 3.2-1. (In addition, a table sorted by material type and T-number group that lists all materials in each T-number group is provided in Mandatory Appendix III.) In determining the applicable T-number group for a material from Table 3.2-1, consid- eration shall be given to the material specification, grade, and any other variables as established in the notes. The table separates the materials into types (carbon steels, low-alloy steels, etc.), and the group number is represen- tative of the low-temperature service limit for the mate- rial; however, the low-temperature service limit may vary based on the design and fabrication requirements. Low- temperature service limits shall be determined from Table 3.1-1. An “(A)” in the T-number group [e.g., CS −20(A)] indicates that materials of that group may not be used at temperatures colder than the group number [e.g., −29°C (−20°F)].
For material T-number groups in which the low- temperature suitability varies significantly according to the thickness, a thickness is listed in column 2 of Table 3.1-1. Note that the thickness is the nominal thickness as defined in the code or specification referencing this Code. The variation based on thickness applies to carbon steel T-number groups CS A, CS B, CS C, and CS D, where Table 3.1-1 lists thickness at each 10°F incre- ment. When it is desired to refine the influence of the thick- ness, Mandatory Appendix I provides the continuous curves and tables that can be used at intermediate values or greater thicknesses. Since the nominal thick- nesses in Table I-1 of Mandatory Appendix I are generally derived based on uniform increments of temperature, the table does not contain uniform increments of thickness. The continuous curves in Figures I-1 and I-1M in 2 Mandatory Appendix I should be consulted for the precise values. For material T-number groups in which the low- temperature suitability is dependent on some other factor, those factors are given in the notes listed in column 3 of Table 3.1-1.
Column 4, the first temperature column in Table 3.1-1, is the low-temperature service limit. If the design minimum temperature is equal to or warmer than this value, then low-temperature requirements do not apply. Materials within a group may be used at this temperature or temperatures warmer than this limit without imposing any of the requirements of this Code. This limit considers material properties and the influence of fabrication processes on the material properties.
Column 5 lists the minimum permitted temperature of the material. When a temperature is listed, this is the design minimum temperature permitted for the material group regardless of impact testing or any other require- ments except as permitted by column 18, where the applied stress is limited to 30% of the allowable. Column 6 contains the minimum temperature without impact testing for the material. If the design minimum temperature is equal to or warmer than this value, the material does not require impact testing. If the design minimum temperature is colder than this value, impact testing of the material in accordance with section 3 is required. For carbon steels, this limit might vary with material thickness (T-number groups CS A, CS B, CS C, and CS D) or with stress levels. Additional rows are provided in Table 3.1-1 for thickness variations. Interpolation between thicknesses is permitted. Figures and a table for the curves of the variation of temperature with thickness are provided in Mandatory Appendix I, and these may be used as an alternative to the values in Table 3.1-1. Permitted temperatures with stress limits are provided for by using columns 10 through 18 instead of column 6 as discussed in para. 3.6.