Do air compressor tanks grow

Steel is both a strong and stiff material. Mild steel has a yield point (limit of the elastic region) of about 60000 pounds per square inch. The linear relationship between stress and strain is given by Young's Modulus, which for steel is about 30 Million pounds per square inch.

It would be reasonable to design a compressed air tank to have a safety factor of about 6. So for a mild steel tank at maximum working pressure, assume a maximum stress within the steel shell of the tank of 10000 PSI. (Don't confuse this with the air pressure within the tank).

(Up to about twice this max stress is plausible -- I am sure there are regulatory constraints as well as standards bodies involved).

Dividing the max working stress by Young's Modulus gives us the amount of elongation.

10000/300000 0 = .000333 (inches per inch)

For a two foot diameter tank, we get a circumference of 24 inches * PI = 75 inches

Applying the strain determined above, the circumference would grow by 0.025 inches, or about 1/32 of an inch. (The diameter grows by only 1/100 of an inch).

It would be difficult, though perhaps barely possible to measure this change.

Typical hydrostatic testing is done by loading the cylinder to 5/3 of its max working pressure, and measuring the change in volume of the cylinder, not the change in diameter or circumference. The volume change is proportional to the cube of the dimension change, making it more tractable to measure.

A one foot diameter tank (from your "small compressor"), should have a thickness of about 0.12 inches to have a max stress in the steel of 10000 PSI with 200 PSI in the tank. So your "10 guage" steel is just about right for this application.

Thermal expansion growth:

Coef Iron 0.0000058 Steel 0.0000063

DeltaT x Distance x Coef. = Thermal Growth.

Example:
Comparing crankshaft height for an item made of cast iron from ambient temp of 70F to it's operating temp of 180 F. Mounting feet to crank centerline = 24"

DeltaT = 110
Distance = 24"
Coef = 0.0000058

110 x 24 x .0000058 = .015" growth in height between cold and hot.

We use this all the time to align couplings between two peices of machinery. Now since I'm behind a desk, I don't get a chance to use it often.

Richard Skinner

Typical no, that is not enough for you measure with a tape measure. You will be able to measure the expansion from heat tho.

To put it perspective we put on a metal roofs in hot climates during the highest temperatures and in the coldest time in cold climates to allow for metal thermo expansion to keep the roofs from leaking as they expand and contract.

A typical metal roof will grow/shrink 1/4" very easy as it changes temperature.

In pressure piping or vessels, the higher the internal pressure is, the thicker the wall. This is a primarely safety factor for external damage that can cause a rupture.

Most inert gases are stable at a known temperature so it can be predicted what the pressure will be at a certian temperature and does not require a cylinder rupture disc.

Refrigerant on the other hand is not a stable gas. Refrigerant changes pressure as the temperature changes with NO upper limit, meaning the hotter the cylinder becomes the more the internal pressure is. This is why all refrigerant cylinders have a rupture disc.

A while back, the wife and I were taking at the table when we heard a loud explosion outside. We looked around and couldn't find out what it was.

About a week latter I was driving by my tri-axle flatbed trailer and noticed a tire sidewall had blown out. About a 1/3 of the sidewall was in shreads on the sun side. I've never had a tire blow out while sitting in the yard. It was the first week of hot weather, 95*F.

T_Bone

Back to your original question - normal shop air compressor tanks are not subject to this inspection, but yes they can grow and become dangerous due to corrosion. The high pressure bottles are different - they are affected by fatigue from the cycling of pressures.