Calculating Breakaway Torque for a 16 Pipe: A Simple Explanation

[ljh34481]

Hi, I am not an engineer nor a physicist but said I would try researching for a friend.

The question is - how do you calculate the breakaway torque for a 16" diameter pipe weighing 1350 pounds?

We are trying to determine what HP engine would be required assuming that the motor shaft would be centered in the pipe and there would be zero friction.

I have found WK² or WR² but am totally confused with the radius of gyration.

Is there a "simple" way of making this determination?

Thanks - hope this question was clear

 

[brewnog]

Tough one if you want a real number, rather than a theoretical (probably wrong) one.

Any chance to measure motor current draw?

 

[timthereaper]

To understand the radius of gyration, you have to think about what's actually happening. Here's a quick explanation:

In order to rotate a very thin piece of pipe about its axis, you have to apply a force on the outside of pipe to move it. For the same amount of pipe material, the wider the pipe is, the easier it is to rotate. Imagine your pipe as a lot of really thin (like infinitesimally thin) pieces of pipe whose diameters are getting bigger as you move from the inside to the outside. If you want to rotate all of them, the inside pieces will require more force to rotate than the outside pieces. Now, instead of trying to calculate the force required to rotate each individual piece of really thin pipe and then add it all up together to get one number, it would just be easier to imagine all the material bunched up into one thin piece of pipe with a certain radius that requires exactly the same amount of torque to rotate as all those sections of pipe. That radius is the radius of gyration.

There are equations to solve for the radius of gyration for pipe. You'll need to know the inside and outside radii of the pipe.

Hope this helped clear up some confusion.