Paulin Research Group Houston, Texas
Missing Stress Calculation at
Intersection
Why is there a missing band of material in the
plotted results on output graphics as shown below?
The non-rendered region is
the zone within one-half the wall thickness of the pressure vessel head or
one-half the wall thickness of the nozzle plus fillet weld lengths. In the case of very thick head, shell or
nozzle, the region is rather wide.
This approach (not using
stresses within the volume of the intersection) has been supported by past
Pressure Vessel Research Council (PVRC) publications and is also supported by
the new ASME Section VIII, Division 2, Annex 5.A. The concept is that the stresses within the
intersection volume do not represent valid membrane or bending stresses. However, the stresses in the shells directly
adjacent to this zone are valid.
Therefore, our reports begin at the edge of the intersection plus any
fillet weld that is specified.
This procedure is good
practice regardless of the type of finite element tool being used. For instance, if you are using a product like
ANSYSŪ, you should be reporting stresses at a similar region. Stresses within the volume of the weld have
no physical meaning and should be discarded.
This is often not done because: 1) analysts do not understand the intent
of the Code, 2) it is too difficult and time consuming to do with general FEA
tools.