Flexibility analysis

ASME B31.3

319.3 Properties for Flexibility Analysis

319.3.2 Modulus of Elasticity. The reference modulus of elasticity at 21°C (70°F), Ea, and the modulus of

elasticity at maximum or minimum temperature, Em, shall be taken as the values shown in Appendix C for the temperatures determined in para. 319.3.1(a) or (b).

For materials not included in Appendix C, reference shall be made to authoritative source data, such as

publications of the National Institute of Standards and Technology.

319.3.5 Dimensions. Nominal thicknesses and outside diameters of pipe and fittings shall be used in flexibility calculations.

320 ANALYSIS OF SUSTAINED LOADS

Sustained conditions may be evaluated by detailed analysis, approximate methods, or simplified means such as span tables. When detailed analysis is performed, the stress due to sustained loads, SL, shall be computed and combined as described in this paragraph and shall not exceed the allowable described in

para. 302.3.5(c). See Appendix S, Example 2 for guidance on loading conditions and support scenarios that result in the greatest SL for each operating condition being considered. The loads due to weight should be based on the nominal thickness of all system components unless otherwise justified in a more rigorous analysis. Section moduli used to compute the stresses in this paragraph shall be based on nominal pipe dimensions less allowances, i.e., the sum of mechanical (thread or groove depth), internal and external corrosion, and erosion allowances. Areas used to compute the stresses in this paragraph assume nominal pipe dimensions less allowances affecting the inside diameter of the pipe, i.e., the sum of mechanical and internal corrosion and erosion allowances. It is the responsibility of the designer to determine sustained stress indices, Ia, Ii, Io, and It, when a piping component is not explicitly addressed in Appendix D, e.g., base-ells, reducing elbows, crosses, close proximity findings, etc., as well as elbows, pipe bends, or miters other than 90 deg or supported by a trunnion. Sustained stress indices shall not be lower than 1.00.