Larger The Tubing OD Less Pressure Can Withstand
Tubing and hose can be thought of as a cylindrical thin-walled pressure vessel.
The strength of thin walled pressure vessels is determined by:
1. The material strength
2. The wall thickness, and
3. The size of the tubing.
The formula is: strength, psi = yield*(wall thickness/radius)
This last item, tubing size, is unusual. One can understand how strength is related to how strong the material is and how thick it is but size (radius)? The relationship between tubing size and strength is inverse; the larger the tube diameter the less strength it has. When you look at pressure ratings for tubing and hose you will notice that for the same hose, maximum recommended operating pressure goes down as the size goes up.
You can use the properties to your advantage. For example, you might have a choice of tubing or hose size for a particular application. Everything else being equal, a smaller diameter line holds more pressure than a larger diameter line. Another advantage is that a smaller size weights less.
Inspection:
When you inspect a hose or line, you are inspecting a pressure vessel. As with all pressure vessels, they should be protected from damage that reduces the wall strength. Inspect for nicks, cuts, chafing, and corrosion. Make sure that the line does not vibrate.
A 1/4 inch (0.025) aluminum tubing can hold 3,500 psi of pressure. The same aluminum tubing, but in 1/2 inch can only hold 1,800 psi. If we made a business jet pressurized fuselage out of the same tubing, it could only handle 182 psi.
When working with large pressure vessels, such as aircraft fuselage, don't be fooled by the low pressures. Because of their large size, these pressure vessels are under a lot of stress.
|
