Good day Gimini55,

The "U" bolt will be in contact with the OD of your hot pipe. When the pipe is new and cold and you tighten the "U" bolt enough (cold) to develop friction how long will it take for the tension in the bolt to creep out at your design temperature? Once the tension has been reduced by creep and the expansion loading axially displaces the pipe, you will have to again tighten the "U" bolt (after repositioning the pipe) to regain the tension (friction). Of course, when the piping system cools to ambient temperature, the permanantly deformed "U" bolt will not return to its original cold (and pipe constraining) configuration. So on the next heat-up it will take a while (perhaps a matter of minutes) for the pipe to "grow" to its hot circumference and in that time the pipe will NOT be axially restrained. So, the pipe will slip through the "U" bolt a little each temperature cycle. Maybe someone will notice that and again tighten the nuts on the "U" bolt. How many years will that scenario be replayed before the "U" bolt "necks down" enough to break?

That is the difference between design and analysis. You can assume all is well at your "U" bolt when you develop your analysis model but in the real world it won't be so for long. Design for the real world and do not count on the friction that is required to "hold" the pipe in position. Find a vertical piece of pipe (upstream or downstream of the horizontal) for the "U" bolt that will "control" the horizontal movement. And as Ricardo says above, ...."never use (it) as the primary piping (weight) support".

Regards, John.