30 Nov Why is there a missing band of material in the plotted results on output graphics?
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 ANSYS®, 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.