Dear Sir,

During the checking of one nozzle element,I have got one WARNNING meassage in output i.e. Beta value not within the Curve range .

I increased the Reinforcement pad width then nozzle passed in the combined stress with the above comments. For that s/w take Beta at the curve end value.

If I increased the shell thk. and take shorter pad then the warnning message didn't come and whole design passed.

In view of the above, I want to know whether the First case will be accepted? or we have to go for the second case ie. increased the shell thk.

Dear Pradip,

Generally, in my opinion when the curve parameters such as Beta are out of range, much care should be taken when reviewing the results. Also as you may realize, the 107 bulletin did not address the issue of pad reinforcement. Software programs that perform these calculations must make some general assumptions and then recompute the geometry factors based on the pad thickness, shell thickness and pad diameter. In theory, distributing the same load over a larger area should reduce the stress, but as you noted in 107 this is true up to the point when one of the curve values is exceeded.

Preferably only geometries that fall entirely within the scope of the bulletin should be analyzed using this technique, but that rarely happens. Another issue is one of internal pressure, commonly the highest stress contributor of all the various stresses. Again, 107 did not address this topic.

As the designer, it is your responsibilty to review the cases carefully and make the best decision with the available information. Hopefully you have some experience with this particular design. It should also be pointed out that there is special purpose FEA software for this application.