# Torque needed to rotate shaft in pipe?

• iokast
In summary: The question specifies all horizontal, so that is not a concern here.In summary, the conversation discusses the need to determine the torque required to begin rotating a shaft within a pipe. The relevant equations for calculating torque and friction force are provided, along with the assumption of a coefficient of static friction of 0.3. However, the complexity of the problem is acknowledged, as the length and clearance of the shaft and pipe make it difficult to accurately predict the required torque. The use of oil well drilling technology is suggested as a reference for dealing with similar situations.
iokast
I have a shaft within a pipe, all horizontal. Shaft diameter is 2.875" and pipe inner diameter is 5". Shaft and pipe length is 650 ft. Shaft weight is 2500 lb.

I need to determine the torque needed to begin rotating the shaft. The coefficient of static friction between the shaft and the pipe is 0.3

T = I * a
T = F * Rs
Fr = Cf * Fn

T = torque
I = moment of inertia
a = angular acceleration
F = force
Fr = force of friction
Rs = radius of shaft = 2.875/2/12 = 1.4375/12 = 0.12 ft
Rp = radius of pipe = 5/2/12 = 2.5/12 = 0.208 ft
Cf = coefficient of friction = 0.3
Fn = force normal to shaft = 2500 lbf
L = length of shaft and pipe = 650 ft

What I have so far is:

Fr = 0.3 * 2500 = 750 lbf
T = 750 * 0.12 = 90 ft-lbf

So 90 ft-lb is what needs to be overcome according to this.

This is bothering me because it does not take into account the inertia equation or the surface area of contact between the shaft and pipe. Wouldn't a greater surface area result in a greater amount of friction acting against motion. What do I use for angular acceleration in the inertia equation?

Can someone please get me on the right track here?

Last edited by a moderator:
This is a very difficult calculation to do .

You can't do a simple friction torque sum on a shaft that long and with that amount of running clearance .

Would take pages to explain why but basic problem is that the shaft is very unlikely to simply sit at the lowest point in the tube and rotate true about it's own axis .

Appreciate the response. I knew there must be more to it.

Making a lot of assumptions do you know of a way to get a general ballpark solution? I know the maximum amount of torque I can generate on the shaft so if it's order(s) of magnitude off I will know whether it is feasible to do.

(2) Have a look at oil well drilling technology - this commonly involves very long shafts running in tubes .

Nidum said:
This is a very difficult calculation to do .

You can't do a simple friction torque sum on a shaft that long and with that amount of running clearance .

Would take pages to explain why but basic problem is that the shaft is very unlikely to simply sit at the lowest point in the tube and rotate true about it's own axis .
I suspect the problem is not intended to be that difficult. It does not matter that it will not sit at the lowest point. I would interpret the question in terms of applying a gradually increasing torque until sliding starts. We can calculate where the shaft will be in the pipe at that time.
Nidum said:
(2) Have a look at oil well drilling technology - this commonly involves very long shafts running in tubes .
I would have thought that involved much smaller clearances, which would indeed raise complications, particularly for a horizontal shaft subject to bending under its own weight.

## 1. What is torque needed to rotate a shaft in a pipe?

The torque needed to rotate a shaft in a pipe is the amount of force required to turn the shaft within the pipe. It is a measure of the twisting or rotational force needed to overcome the resistance or friction in the pipe.

## 2. How is torque calculated for rotating a shaft in a pipe?

To calculate the torque needed to rotate a shaft in a pipe, you need to know the diameter of the pipe, the length of the shaft, and the coefficient of friction between the shaft and the pipe. The formula for torque is T = F x r, where T is torque, F is the force applied, and r is the distance from the center of rotation to the point where force is applied.

## 3. What factors affect the torque needed to rotate a shaft in a pipe?

The torque needed to rotate a shaft in a pipe is affected by several factors, including the diameter and length of the shaft, the coefficient of friction between the shaft and the pipe, and the speed of rotation. Additionally, the type and thickness of the lubricant used, as well as the temperature and pressure inside the pipe, can also impact the torque required.

## 4. How can the torque needed to rotate a shaft in a pipe be reduced?

The torque needed to rotate a shaft in a pipe can be reduced by using a lubricant with a lower coefficient of friction, increasing the diameter and length of the shaft, or decreasing the speed of rotation. Additionally, using a smoother and more polished surface for the shaft and pipe can also reduce the torque required.

## 5. What are some common applications for calculating the torque needed to rotate a shaft in a pipe?

Calculating the torque needed to rotate a shaft in a pipe is important in many engineering and industrial applications. It is commonly used in the design and operation of rotating machinery, such as pumps, turbines, and engines, as well as in the transportation industry for calculating the torque needed to turn vehicle axles and wheels. It is also essential in the oil and gas industry for determining the torque required to rotate drilling equipment and pipes.

• Mechanical Engineering
Replies
5
Views
3K
• Introductory Physics Homework Help
Replies
2
Views
1K
• Mechanical Engineering
Replies
3
Views
3K
• Introductory Physics Homework Help
Replies
15
Views
2K
• Introductory Physics Homework Help
Replies
9
Views
2K
• Introductory Physics Homework Help
Replies
10
Views
2K
• Introductory Physics Homework Help
Replies
7
Views
1K
• Introductory Physics Homework Help
Replies
1
Views
2K
• General Engineering
Replies
3
Views
4K
• Engineering and Comp Sci Homework Help
Replies
11
Views
4K