The B31.3 Chapter IX 2020 edition (and later) removes Appendix D and requires direct use of B31J, which provides flexibility factors on tees and branch connections in addition to the stress intensification factors (SIFs). Because Appendix D required the flexibility factors on tees to be 1.0, similar to the flexibility factors of pipe, B31J’s flexibility factors on tees have a large impact on the flexibility of the entire system and produces more realistic results, including the results for displacements and restraint loads.
Flanged End Modifications
B31.3 Chapter IX-2018
Modifications resulting from flanged ends are permitted for smooth bends.
B31.3 Chapter IX-2020
Modifications resulting from flanged ends are permitted for smooth bends and tee fittings. B31.3 Chapter IX, Clause K304.2.3 does not allow mitered bends.
Miter Bends
Clause K304.2.3 does not allow mitered bends.
Stress Intensification Factors (Sifs) For Intersections
B31.3 Chapter IX adds the longitudinal stress components and torsion to the code stress component for all stress categories. The software ignores the value selected for Add F/A in Stresses in the Configuration Editor.
B31.3 Chapter IX-2018
In-plane SIFs and out-of-plane SIFs for intersections are separate and unique. The code uses the effective section modulus, Ze, to calculate bending stresses for the branch pipe of reducing intersections.
B31.3 Chapter IX-2020
The code uses B31J for intersection SIFs and flexibilities. In-plane, out-of-plane, and torsional SIFs and flexibilities are separate and unique. For reduced branch intersections, the actual branch section modulus is used to calculate bending stresses at the branch for both reducing and non-reducing intersections.
If you do not manually define SIFs, then the axial SIF is 1.0 for bends and equals the calculated out-of-plane SIF for other components.
Girth Butt Welds Default Value
B31.3 Chapter IX-2018
The default SIF value for a girth butt weld is 1.0. This is Markl’s original basis for SIFs.
B31.3 Chapter IX-2020
B31J calculates the default SIFs for all weld types using the pipe wall thickness and the maximum and average mismatch values. The default flexibility factor value is 1.0.
Socket Weld Default Value
For a socket weld without undercut (joint type 8 - Socket (4.3)), B31.3 Chapter IX uses a default SIF value of 1.3. For thin wall pipes and unfinished fillet welds (joint type 9 - Socket/Unfin (4.3)), Chapter IX uses a default SIF value of 2.1.
Stress Allowables
Use the equations below to calculate the stress allowables.
Expansion Allowable = 1.25Sc+0.25Sh
Sustained Allowable = Sh
Occasional Allowable = Sh * (Occ)
Where:
Sc = Cold Allowable Stress
Sh = Hot Allowable Stress (as selected)
SL = Sustained Stress
Occ = Occasional Load Factor. Default is 1.33
Corroded Stress
By default, the code applies corrosion to section modulus calculations for sustained and occasional stress calculations. Specify All Cases Corroded in the Configuration Editor to perform the corroded stress calculations for all stress calculations.
Reducer Default Values
B31.3 Chapter IX-2018
The default SIF value is 1.0. The default flexibility factor value is 1.0.
B31.3 Chapter IX-2020
The default SIF values are calculated and unique. The default flexibility factor value is 1.0.