Stress Concentrations and Intensification - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II
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CAESAR II Version
12

Designates the stress intensification calculation for bends with trunnions. It is based on the relationship between the ASME NB stress indices C2, K2, and the B31 code i factor or stress intensification factor. That relationship has long been taken to be

(m)(i) = (C2)(K2)

Where:

m = multiplier, usually either 1.7 or 2.

i = B31 stress intensification factor

C2 = ASME NB secondary stress index

K2 = ASME NB peak stress index

The peak stress index (K2) is commonly known as the “stress concentration factor.” This factor is the ratio of the highest point stress at an intensification (or an elbow) and the nominal local computed stress at the same point. Peak stresses typically only exist in a very small volume of material, on the order of fractions of the wall thickness of the part.

Because most piping components are formed without crude notches, gross imperfections or other anomalies, the peak stress index is kept well in control. Where a smooth transition radius is provided which is at least t/2, and where (t) is the characteristic thickness of the part, the peak stress index is typically taken as 1.0. At unfinished welds, sockets, and where no transition radius is provided, the peak stress index approaches values of 2.0.

If you enter a trunnion (where there will be a weld between the trunnion and the elbow), and you do not enter a stress concentration factor, CAESAR II assumes a stress concentration factor of 2.0.