Modeling Hygienic Unions

I want to model hygienic unions (tri-clamp type, bolted clamp joint) in a stress analysis program (Algor) during the line sterilization process (185 deg. F). Code is ASME BPE & B31.3. The system is mostly 4 and 6 inch size stainless steel tubing.

The major manufacturers say that there is no available data, or that they will not release any available data, for allowable forces and moments resolved to the center of the union. Being a gasketed joint, they argue that the joint can not remain leak-tight with moment loads because "the design of the joint relies on the clamp creating equal force against the angled sides of the ferrules". However, these joints are commonly installed in food and pharmaceutical facilities in which the lines are sterilized, at temperatures higher than this application, I might add. I understand that the joints do leak at times from the piping loads, but for the most part, they work. So, there are obviously some loads which the unions will accept without leakage.

I can model the union as a valve block to examine system flexibility and system stresses, but I don't know if the moments and forces at the union are too high. I could model the unions as flanges and run a flange report, but since the unions are not rated like flanges, the results, though indicative of the load on the union, are open to interpretation. B31.3 paragraph 319.1.1 requires the system to have sufficient flexibility to prevent leakage. I don't see any way to demonstrate that the piping system complies with B31.3 with the use of hygienic unions. Any comments or suggestions?

Ken A. Nisly-Nagele, P.E.

Project Engineer, Mechanical

Applied Engineering Services, Inc.

7999 Knue Road

Indianapolis, IN 46250

317-585-8920

[Non-text portions of this message have been removed] Received on Thu May 20 08:51:00 2004