Hygienic Union Loads

[KANN]

I’m wanting to model hygienic unions (bolted clamp joint) in a stress analysis program (Algor) during the line sterilization process (185 deg. F). Code is ASME BPE & B31.3. Mostly 4 and 6 inch size. The major manufacturers say that there is no available data for allowable forces and moments resolved to the center of the union. 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. It could be that the joint will accept any loads that the piping can, but the manufacturers have not made that statement. Any comments or suggestions?

 

[dicksewerrat]

what are the pipes rated at? 150 psi? The unoins should be rated the same as the pipe. that does not mean that the union will not blow off the pipes. But it should be able to resist the internal forces as well as the pipe.

 

[KANN]

The system is rated for 185 deg. F at 125 psig. I am not concerned about the union failing by pressure. Since this system is being sterialized, it is a system with thermal growth and requires flexibility to accomodate that growth. I am concerned with the moments and forces that will be exerted on the union during thermal growth and sustained operation.

 

[mgp]

It is very unlikely that you will find anybody who will provide you with allowable forces and moments for hygienic low pressure clamp connections. For the same reason I believe it is not uncommon to ignore leakage check of clamp connections in systems like these, even though fluid may sometimes be harmful (but not flammable/explosive) like hot NaOH. Very often the clamps have to be retightened already during hydrotest because most of them have soft gaskets and will leak even with small misalignments in the hydrotest case.

If you really want to check for flange moments it is possible to use the equivalent pressure method (the Kellogg method) similar to that used for flanges but with gasket data and diameter as for the clamp. The resultant pressure can then be compared with the rating table of ASME BPE.

regards
Mogens