pipe clamp design

[Shafty1]

Hello.

I have a pipe to clamp and am copying an existing design. It is an 'arch' design with 2 bolts. either side. see picture.

I'm checkign section for bending. at the smallest part of the arch (middle) . i am treating the arch as a beam with max moment as PL/4 (where P is 2 x the bolt force).

The current design is checked as failing (2000+ MPa) but i know it has been in use for AGES.

I am using the clamp load from tables for stainless bolts (lurbricated at about 56 kN). i suspect this high load is making the section fail. The pipe clamp is re-used, and hand tightened. over and over. What would be a reasonable bolt force? Or am i oversimplifying my asessment (or making fundamental error!!)?.



sketch below:

 

[Doug Hunter]

Shafty, don't use the rated load for the screws, but rather convert it from the installation torque that's been used. Use T = 0.2dF, where d is the nominal screw thread diameter. The 0.2 is friction dependent.

 

[Stress_Eng]

If you’re copying an existing design, do you have a copy of the stress calculations for it? Sounds like you’re doing a new set of stress calculations. Can you show a picture of your free body diagram (FBD)? I’m assuming there’s another clamp block on the underside. If there is, is there a gap between them once assembled (so you can see the bolt) or are the clamps in contact. I’m interested to see how you are including the pipe contact reaction forces in your FBD.

 

[dvd]

What beam equation are you using? It seems like this will act like a beam on an interrupted elastic foundation.

 

[3DDave]

When you say "fail" is that because the stress exceeds the elastic limit? If so, so what? The stress gets better distributed as a plastic hinge and the conformance to the pipe gets better, unless this is a material with very little elongation before fracture.