Coefficient of Friction Between Cured Epoxy and Steel Pipe

[JAX91]

I am designing the pipe supports for 24" diameter schedule 80 pipe full of liquid. The pipes are long, and will experience a decent amount of thermal growth. The client has requested placing the pipe on Tulsa Pipe Supports, which are wedge blocks made of cured Chockfast Red Epoxy Grout. I need to verify that the pipe supports can handle the forces from thermal load. In order to check these forces, I need to know both the static and dynamic coefficient of friction between the steel pipe and the pipe supports. I contacted the manufacturer of the supports, and they were unable to provide me with this information. Does anyone know what the coefficient of friction may be between cured Chockfast Red Epoxy Grout and steel?

 

[Ron]

I would use roller supports or a pipe shoe with a slide plate. Seems like the Tulsa Pipe Supports would have a tendency to bind.

 

[TLHS]

It looks like that's actually the point. They seem to be for vibration sensitive situations and they're trying to get them good and stuck.

It seems like a counterproductive idea though... It's like anchoring the pipe at every support. Normally everyone's trying to release the pipe as much as possible except where absolutely necessary.

If the pipe support guys don't know (which seems a little bushleague, since coefficient of friction is important for any piping related structural design and for a piping stress analysis) maybe the epoxy guys do? Try talking to them, but make it clear that the epoxy is pre-set so it's not a bond strength.

 

[dhengr]

JAX91:
And then, the next question to the manufacture should have been... ‘So, how do you handle thermal expansion and contraction of the pipe with your supports?’ Do they have some sort of light steel bearing skin on them or some other better defined frictional surface btwn. them and the steel pipe, so you would have a well (better) defined friction number. I suspect they are fairly soft in compression so they do not induce sharp line loads on the pipe, due to the gravity loads, and so that they do not induce two point loads due to pipe deflection. This type of support deformation might almost cause a bonding rather than a frictional contact btwn. the supports and the pipe. Then they are even softer in shear resistance internally, so that longitudinal movement of the pipe just causes the support to deform in a shearing action long the axis of the pipe. So, what you really want is an internal shear stiffness, measured in lbs./inch of movement btwn. the top and bottom surfaces of the support, under a shearing action.

 

[TomDOT]

I was looking at a variety of epoxy paints tested for faying surfaces on steel bridges, most of the static friction values were in the .20 to .40 range. Unfortunately for you, this was paint-to-paint, not paint-to-steel.

Of course, the friction of the steel will depend on the surface. In the bridge world, rolled steel with mill scale intact is assumed to be .33, while abrasive blasted is assumed to be .50

 

[TLHS]

If you happen to work out a bit more about these things, report back. While they look a little annoying from the structural design standpoint, they actually seem pretty neat from a soft bearing on the pipe standpoint.