combined stresses on pipe clamp 3

[vgengineer66]

I am trying to calculate the combined stresses on a pipe clamp.
2 forces acting on it.
a) the clamp is in 2 halves , the 2 halves connected with 10 hyd cylinders on top (12'o clock) exerting a closing force of 2000 tons
b) another 2 cylinders connected at 9 o clock and 3 o clock exerting axial force on 750 tons.
c) What wold be the collapse pressure of this clamp
The clamp is 50 inch OD, Yield Stress of Pipe is 60,000 psi and wall thickness is 0.7 inch, lenght of clamp is 80 inches

 

[LittleInch]

You need to llok at the units and the equation carefully.

The one in your spreadsheet is for casing pipes which are already a bit bent.

The Clamp will hold the pipe circular and hence is a bit odd compared to water external pressure. You might need to do something a bit more fancy.

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[vgengineer66]

That fancy bit is eluding me
Does the elastic collapse or equation (in my latest post above) hold good?

 

[3DDave]

Since the pipe is constrained against gross changes in form the I think the buckling has to be analyzed as if it is composed of very short elements, possibly analyzed at the gaps in the clamp where there is no support. Even thin shells that are swaged in place rarely seem to buckle except where such gaps are allowed.

 

[LittleInch]

FEA

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[vgengineer66]

Ok.
Thanks

 

[LittleInch]

Or physical testing with instrumented section of pipe / test to destruction.

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Also: If you get a response it's polite to respond to it.

 

[desertfox]

Hi vgengineer66

I have had a look in formula’s for stress and strain fifth edition by J.Roark & Young and all I could find was a thin ring under uniform external pressure see page 556 case 19.

That’s the nearest I have found however has I stated earlier the pressure from the clamp will not be uniform because of the gaps in the clamp pads and also because of the hinge at the base of the clamp, in addition to that the clamping force supplied by the cylinders is based at the top of the clamp also adding to a non uniform clamping pressure.

So I would base my design on uniform pressure and then do some testing to be sure my design worked.




“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[vgengineer66]

Hi desertfox,

thanks for ponting to Roark book. I got the seventh edition

Substituting my clamp values for dia 1270 and w.t. 0f 17.78 mm,
the Q (Stress) = -1316 Mpa (-ve for external stress) for long tube and 7.5 Mpa for short tube.
This must be the value of what this cyl will take max, before yielding.
my clamp stress calculation for 2250 Tons at dia of 1270 mm length of 2 m is coming to 2.5 Mpa

I guess, the short tube clamp length shall be applicable and the allowable stress is acceptable.

But as Littleinch recommended, best way to find out is by destructive testing only.

Regards

 

[LittleInch]

19b though says "ends held circular"

Something wrong with your units as there is far too much difference here and I can't believe the long tube will withstand 13,000 bar....

q to me looks like external pressure, not stress.

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Also: If you get a response it's polite to respond to it.

 

[vgengineer66]

sorry, re checked

E/4 x t3/r3 x 1/(1-v2)
where E if 210000 Mpa
t is 17.78 mm
v is 0.3
r is 638 mm

answer is 1.26 Mpa for long tube.

and 7.57 Mpa for short tube, (if the ends are held circular)
have taken l = 2000 mm (my clamp length)

 

[vgengineer66]

i think the applicable length is short tube as the long tube length comes to be more than 18 m for the eq. to be valid.

 

[LittleInch]

Your ends aren't really being held rigid like having an end cap but the clamp will hold them circular to a certain extent.

So it looks like you have a decent FOS to me, but only a physical test will tell you.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[vgengineer66]

yes. Thanks a lot sir.
Shout out to all for making this valuable.

by the way, I am hoping to use this clamp to do Direct Pipe by substituting the HK thruster with my designed and fabricated thruster.
we have a project of installing 50 inch pipe x 700 meters under a river. I dont have budgets to buy HK and hence am taking the risk to make my own.
Am confident especially since I have made a few of them, but only for smaller pipe and smaller thrust force.

This one is going to be for 750 Tons of Thrust and hence was wanting to ensure that I do not miss and mess!!

if and when this comes to Fruition, I shall share with you all.

Till next time....

 

[desertfox]

Hi vgengineer66

Yes I think the short length is probably more applicable for your case and like Littleinch says the clamp should keep the pipe circular to some extent. Yep agree with Littleinch on a good factor of safety and some physical testing.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[LittleInch]

We look forward to seeing it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.