I had a high-pressure reactor (200 bar) that required regularly removing the catalyst bed section, and I noticed that the Swagelok connections for the bed tended to develop leaks quickly. The rest of the reactor also uses Swagelok connections, but these are fine as the connections are more or less permanent.
Does anyone have experience with flange connections and would be willing to advise on this connection type? Also, what, in your experience, is the consequence for heat transfer/loss?
The consequence of heat transfer/loss of any system is that the system will be operating below the designed heat supply capacity. Inefficiency of the system may be as a result of heat losses through openings by convection and or because of inadequate insulation causing heat loss by conduction through the walls.. Economically you spend much in order to find solution of the insufficient heat supply to the system so as to maintain the system at a comfort operation level.
If temperature is not higher than 300 deg.C you can try with O-Ring Face Seal Tube Fittings with appropriate O-ring material (markez, kalrez,.simrez.). Look at http://www.marcorubber.com/orings.htm. Maybe you can also consider Autoclave Engineers fittings.
Swagelok fittings always fail if over tightened. Swagelok's recommended procedure is to tighten them 1-1/4 turns past finger tight. I have never had a leak when I tighten them 3/4 turns past finger tight. That means that when I disassemble and reassemble, I can tighten them a little more each time until they no longer seal. I typically tighten them by an extra flat (1/6 turn) each time I reassemble them. That means I can usually get at least 6 reassembles without them leaking. The only problem is you have to keep track of where the fitting was assembled last. You can mark the fitting and one flat to do this. To get even more use, use a feeler gage. (Feeler gages are used by machinists. They consist of a package of thin metal leaves of various thicknesses used to measure small gaps.) Use the feeler gage to measure the distance between the nut and the body before you disassemble the fitting and then make the gap smaller by about 2 mils (50 microns) each time you remake the fitting. For a 50 mil pitch (20 threads per inch) you can reassemble the fitting 25 times before it may start to leak.
Swagelok VCR fittings are very useful for frequent reassembly of high pressure systems - particularly if the fitting is exposed to temperature cycles between maintanance. I use them in the hot zones of a pilot hydrotreater reactor where i need to replace catalyst frequently.
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