modelling a pipe hold down clamp

What is the best way, -and common practice-, to model a pipe hold down clamp for vibrating lines?.

Case: 12 inch steel pipe, ASTM A106-B. anchored with a pipe hold down clamp, 6 inches wide, with gusset plates, 1/4 inch fabreeka pads for vibration isolation, 4 bolts.

This would configuration would require two restraints. A "Y" restraint to prevent vertical motion, and either an "X" or a "Z" restraint to prevent motion transverse to the longitudinal axis of the pipe.

Hello Richrad,

and do we should enter friction factor 0.3 (carbon steel - carbon steel) in restraints dialog box; as pipe can move in "X" or "Z" direction.

Next, what i think is that this 0.3 friction factor is sliding of CS plate to a CS plate in normal conditions. If we press the two CS plates plates by force and then try to slide; in this case we generate more friction, and so i think in this case the friction factor should not be 0.3 and it should be more.

Similar is the case of U Clamp/bolt. If U clamp is tight enough with the pipe then when pipe tries to move the frictional effect on the pipe will be more (because of U bolt which is tightly bolted with the pipe); and so 0.3 friction factor is not valid.

Am i right?

If so how to cater this increased frictional force on pipe in stress analysis.

Thanks

Hello Bajwa,

a suitable model of such a U-bolt clamp can be for a pipe in X-direction as follows:

1. variant - input at an location: restraint Y without friction + restraint Z (or guide) without friction + restraint X2 (K2=1, Fy=resistance force from tightly bolting = additional friction);

2. variant - input at 2 locations: restraint Y with friction + restraint Z (or guide) with friction - at 1st node and restraint X2 (K2=1, Fy=resistance force from tightly bolting = additional friction) at 2nd node near to the 1st

regards

Do a "search" on the word "friction" in this Forum. Read all the posts.

A. Soto

I presume your line is probably connected to reciprocating compressor.
The common and simplest practice is to simply model "Y" and "guide" with friction.
The Best practice depends on what data you can get from the vendor/supplier. If you get the stiffness values of lining material(fabrekka) you can model it as a blinear restraint with K1=stiffness of lining material and K2=default stiffness for steel provided your support is rigid enough.

If you can get the value of bolt tightning forces, then the same should be applied in above restraints.

Generally there are two types of hold down clamps. One which is described above packs the pipe in top half circumference. The other type is like just touches the pipe on the top and have large gaps in both sides(guiding directions). When thermal movements needs to be allowed e.g. near some bends, such type of clamps can be used. There will not be guide restraint in this type of clamps.