Primary plus secondary stress intensity

Guideline 4 establishes the global locations for assessment of stresses, and states that the general primary membrane stress intensity, should be evaluated remote from a discontinuity whereas the primary membrane plus bending stress intensity, Pl + Pb, and primary plus secondary stress intensity, P + Q, should be evaluated at a discontinuity. 

The MlTl Code apparently recognizes this feature and provides a strain enhancement factor for stress ranges, S in the neighborhood of 3Sm, where values of exceed unity and progressively increase with increasing ratios of Sp/Sn, where Sp is the peak. Equation (11.3b), valid for primary-plus-secondary stress intensity ranges between 35 and 3mSm, is modified in the MITI Code as... 

Primary plus secondary stress intensity. The maximum stress intensity S as based on the primary or local membrane stresses plus the primary bending stress plus the secondary stress (cr m or ctl + (7b -f X) 2) cannot exceed the... 

The Cm and (Cm+cfb) values for the first three load cases, as indicated in the Table 1, are the primary membrane (Pm) and primary membrane plus bending stress intensity (Pm+Pb)-(Cm+Cb) for case 4 is primary plus secondary stress intensity (Pm+Pb+Q)-... 

A 3D beam element finite element model (FEM) was analyzed using the commercial code ABACUS to obtain beam section moments at each point in the hot leg piping. These section moments have been used in spreadsheet calculations to determine the primary stress intensity and primary plus secondary stress intensity range values using the ASME NB pipe stress equations. 

The stress state used for the evaluation of the primary plus secondary stress intensity range limit is Stress State at steady state normal operation) - Stress State at ambient /emperafure (293 K) and zero gage pressure)... 

Primary plus Secondary Stress intensity Range Limit... 

A number of sensitivity studies have been performed which investigate the effects of changing piping wall thickness, secondary support stiffness, and structure material and temperature on the ASME primary and primary plus secondary stress limits discussed above. A summary of the cases run is listed In Table 9-32. The primary stresses are only evaluated for the wall thickness study, because the primary stresses are not dependent on the other parameters studied. For all of the results tables, the minimum, average, and maximum stress values refer to the minimum, average, and maximum stress Intensity values at all of the element nodes evaluated in the model. It is presented in this form to better comprehend the distribution of stress values. 

The SMI, SM2, and SMS output parameters are section bending moments in the piping about the. three local element axes (x, y, z). These three output parameters are taken from the ABACUS output and used in ASME B PV Code Section III Div I - NB piping limit equations. The primary and the primary plus secondary stress range limits are evaluated for this anaiysis. The primary stress limit is evaluated for the pressure only load case for the cases listed in Table 9-32. The primary plus secondary stress limit is a limit on the stress intensity range. This requires a stress state at each end of the range. The range used to evaluate the limit is ... 

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