I have read this article and I think maybe this is one of the reason why a very detailed stress analysis is usually not undertaken from piping point of view due to some practical reasons. The use of the Code plus a competent stress engineer is I think is sufficient enough based on years of experience in the piping industry.

"First, pressure vessels for typically represent a large investment and an extensive stress analysis thereof represents a relatively small portion of the total cost of the vessel. In contrast, a typical piping system will include many different piping components, each of which individually represents a relatively small investment. The detailed stress analysis of these piping components, however, can be quite costly."

Any other opinion is highly appreciated.

Cheers!!!