ASME B31T-2021 pdf download.Standard Toughness Requirements for Piping.
3.3 ð21Þ Governing Thickness and Notes (Columns 2 and 3 of Table 3.1-1) For T-number groups in which the low-temperature suitability varies significantly according to the material thickness, a governing thickness is listed in column 2 of Table 3.1-1 at various low-temperature service limit increments. When it is desired to refine the influence of the governing thickness, Mandatory Appendix I provides the continuous curves and tables that can be used at intermediate values or greater governing thick- nesses. Since the governing thicknesses 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 governing thickness. The continuous curves in Figures I-1 and I-1M in 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.
3.6 Design Requirements for Low-Temperature Service (Columns 10 Through 18ofTable 3.1-1) 3.6.1 Minimum Material Temperature Without Impact Testing. Columns 10 through 17 list the minimum material temperature without impact testing based on design stresses and may be used for carbon steels provided (a) the piping system is subjected to a hydrostatic test at no less than 1.5 times the design pressure (b) the piping system is not subjected to unevaluated external loads such as maintenance loads, impact loads, and thermal shock The curve used to generate columns 10 through 17 in Table 3.1-1 is provided in MandatoryAppendixII andmay be used as an alternative to columns 10 through 17. Column 18 lists the minimum low-temperature service limitachievablebylimitingstressestolessthan10%ofthe tensilestrength[i.e.,thestressratio (SR) ≤ 0.3] andmaybe used without any additional low-temperature service re- quirements. At these stress levels, the design margin is considered adequate to prevent a brittle fracture failure mode. The low-temperature service limit listed in column 18 may be used in lieu of that listed in column 4 when SR ≤ 0.3.
3.6.2 Stress Ratio. The stress ratio is defined as the maximum of the following: (a) nominal pressure stress (based on minimum pipe wall thickness less allowances) divided by the allowable stress at the design minimum temperature. (b) for piping components with pressure ratings, the pressure for the condition under consideration divided by the pressure rating at the design minimum tempera- ture. (c) combined longitudinal stress due to pressure, dead weight, and displacement strain (stress intensification factors are not included in this calculation) divided by the allowable stress at the design minimum temperature. In calculating longitudinal stress, the forces and moments in the piping system shall be calculated using nominal dimensions, and the stresses shall be calculated using section properties based on the nominal dimensions less corrosion, erosion, and mechanical allowances. In determining the stress ratio, the loadings coincident with the metal temperature under consideration may be used in lieu of maximum design values. Where there are several low-temperature design conditions, each shall be evaluated to determine the stress ratio.ASME B31T pdf download.