Pipe Stress Due to Sustained Loads Formulae and Calculator

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Pipe Stress Due to Sustained Loads Formulae and Calculator

Pipe Stress Due to Sustained Loads Calculator and Equations per. ASME B31.3 - 2020

The equation for the stress due to sustained loads, such as pressure and weight, S_L is given in Eq. 1. Equations for the stress due to sustained bending moments S_b, is given in Eq. 2.

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Eq. 1
S_L = [ ( | S_a | + S_b )² + ( 2 · S_t )² ]^0.5

Eq. 2
S_b = [ ( I_i · M_i )² + ( I_o · M_o )² ]^0.5 / Z

Eq. 3
S_t = ( I_t · M_t ) / ( 2 · Z )

Eq. 4
S_a = ( I_a · F_a ) / A_p

Where:

S_L = stress due to sustained loads
S_a = axial stress range due to displacement strains
S_b = bending stress range due to displacement strains
S_t = torsional stress-range due to displacement strains
I_i = sustained in-plane moment index. In the absence of more-applicable data, I_i is taken as the greater of 0.75I_i or 1.00.
I_o = sustained out-plane moment index.In the absence of more-applicable data, I_o mistaken as the greater of 0.75I_o or 1.00.
I_t = sustained torsional moment index. In the absence of more applicable data, I_t is taken as 1.00.
I_a = sustained longitudinal force index. in the adsence of more applicable data, I_a is taken as 1.00.
M_i = in-plane moment due to sustained loads,e.g., pressure and weight
M_o = out-plane moment due to sustained loads,e.g., pressure and weight
M_t = torsional moment due to sustained loads, e.g. pressure and weight
Z = sustained section modulus of pipe.
A_p = cross sectional area of the pipe, considering pipe dimensions less allowance
F_a = longitudinal force due to sustained loads, e.g. pressure and weight

Reference:

ASME B31.1-2020, Paragraph 320.2