Stresses Due to Sustained Loads (ASME B31.3 - 2010)

Case with Pressure Extension Cases (Default)

For case with pressure extension cases and with Pcase in sustained, the equation to be used for calculating Sustained loads will be

given as follows (as per code case 178 in earlier editions):

Where,

SL = Stresses due to sustained loads

Where,

Ii = sustained in-plane moment index

Io = sustained out-plane moment index

Mi = in-plane moment due to sustained loads

Mo = out-plane moment due to sustained loads

Zcor = sustained section modulus, using thickness of pipe as tnom - corr

Where,

Ia = sustained longitudinal force index, taken as 1.0 in absence of more applicable data

Fa = longitudinal force due to sustained loading, e.g. Gravity and Pressure

Ap = cross-sectional area of pipe, using thickness of pipe as tnom - corr

Note: The Circ. weld factor, Zc, defined using the Xtra Data/User Weld Efficiency Factor menu command will only reduce the

longitudinal force due to pressure, i.e. (P*Do)/(4*tcor*Zc)

Where,

It = sustained torsional moment index, taken as 1.0

Mt = torsional moment due to sustained loads

Note: The sustained SIF is 0.75*I, but >= 1.0

AutoPIPE Reference Information

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Case with No Pressure Extension Case

In this case the equations used for sustained stress are the same as above, except that forces and moments from pressure are not

included. The only pressure force that will be included is the longitudinal pressure force P*Ai, under the term Fa above. In-plane, out-

of-plane and torsional moments would be those of Gravity case alone in the absence of pressure cases.

This condition would violate the code as the pressure forces and moment should be included. A warning message will be shown if

pressure cases are not analyzed.

Code Case 178

The equations detailed in Code Case 178 have been added to B31.3 in the 2010 edition as section 320. Therefore, the Code Case 178

option will not be available for B31.3 when the 2010 edition is selected.

See Also:

Definition of Terms

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