WRC 107 Stress Summations - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II
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CAESAR II Version
12

Because the stresses computed by WRC 107 are highly localized, they do not fall immediately under the B31 code rules as defined by B31.1 or B31.3. However, Appendix 4-1 of ASME Section VIII, Division 2 “Mandatory Design Based on Stress Analysis” does provide a detailed approach for dealing with these local stresses. The analysis procedure outlined in the aforementioned code is used in CAESAR II to perform the stress evaluation. In order to evaluate the stresses through an elastic analysis, three stress combinations (summations) must be made:

  • Pm

  • Pm + Pl + Pb

  • Pm + Pl + Pb + Q

P is the design pressure of the system. Pm is the general membrane stress due to internal pressure removed from discontinuities and can be estimated for the vessel wall from the expression (PD) / (4t) for the longitudinal component and (PD) / (2t) for the hoop component. The allowable for Pm is kSmh, where Smh is the allowable stress intensity. The value of k can be taken from Table AD-150.1 of the code, which ranges from 1.0 for sustained loads to 1.2 for sustained plus wind loads or sustained plus earthquake loads. Pl is the local membrane stress at the junction due to the sustained piping loads. Pb is the local bending stress (and is zero at the nozzle to vessel connections according to Section VIII, Division 2 of ASME Code). Q is the secondary stress due to thermal expansion piping loads or the bending stress due to internal pressure thrust and sustained piping loads. The allowable stress intensity for the second stress combination is 1.5kSmh, as defined by the Figure 4-130.1 of the Code. Smh is the hot stress intensity allowable at the given design temperature. Both Pl and Q are calculated by WRC 107. The third combination defines the range of the stress intensity, and its allowable is limited to 1.5(Smc+Smh).

A summation is provided automatically following the WRC 107 analysis and displays on the Drawing window within the main WRC 107/297 window. The calculation provides a comparison of the stress intensities to the entered allowables, along with a corresponding Pass/Fail ruling. Failed items display in red.