Hello Stress guy,

The occurrence number was invented by COADE to keep track of materials in the ASME database that have same name but different material properties. We have to uniquely identify the materials and the occurrence number allows us to do that. Following are most common reasons for multiple instances of same material in ASME database.

[*] Materials may have different UNS number due to different chemical composition, but same name. So, use the material with the UNS number corresponding to your spec.

[*] If it is a pipe then the allowables can be of welded pipe or seamless pipe. The welded pipe properties include the multiplication by the Joint efficiency of the longitudinal weld (taken as 0.85). Remember that this longitudinal seam, so it will affect the circumferential stress.

[*] For some stainless steels the yield stress is very low, so ASME publishes 2 set of allowables, in one set the allowable is strictly less than or equal to 2/3rd of Yield. In the other set the allowable can be up to 90% of yield. The allowables for the second set should not be used for components that fail with deformation, such as flange or end cover.

[*] For some plates there are different allowables based on different thickness ranges. For bolts, there could be different set of allowables based on its size.

The material includes some codes that can help you distinguish these issues.

I hope that helps.