Friction Loads during Hydrotest case

I have noticed that the lateral loads appear during Hydrotest case. (ex. FX and FZ). Supposed to be, only FY should have a significant load, and if there are FX and FZ, they should be minimal or negligible.

But why is it that sometimes there are lateral loads that is equivalent to friction loads appearing on Hydrotest case? Can anyone help me understand?

Thank you.

Hi Leo.

I'm really not noticing this when I give loads to Structural Group unless they raise a concern on sizing the support. So far, nobody raise a concern from our structural group regarding this in my experience.

Let me guess it, Friction as we know is resisting any load that tends to have a horizontal component (e.g., thermal expansion load). In hydrotest case, thermal load is not present, what I can guess, is that maybe there is an imbalance in the support system that's trying to cause a horizontal component of load (weight), say an unsupported elbow that is hanging and trying to pull the pipe down and causing it to have a horizontal component of weight which might trigger friction to activate.

Just my guess. Please correct my interpretation of the friction loads.

Those that develop the algorithm for non-linear friction in stress analysis software can explain best since he knows deeply how the software is programmed.

Cheers!!!

Did you have "Bourdon Effect" activated?
Pressure Elongation Effect generates a certain longitudinal movement, and due to that movement friction effects induce horizontal forces.
This is absolutely correct and normal.
As piping/mechanical stress engineers you should be aware of that, although this might raise suspicions to structural engineers, who in general are not aware of pressure and temperature variation effects on pipework.

Best regards,

Thank you Dorin. Turns out it is the bourdon effect. It was my first time dealing with this long pipelines so it got me questioned the loads.

Nice catch Dorin. I'm mostly involved in inplant piping but yes bourdon effect must be considered especially for large diameter thin walled pipe.

Cheers!!