>Btw is "40,000 psi strength for the wall material" the common strenght for steel.

Steels can range over an order of magnitude based on alloy and heat treatment. 40,000 psi yield strength is a middle of the road value for cheap aluminum (6061) or stainless steel. Mild steel will be lower, high tensile heat treated steels can be several times higher. Yield is when they will start to permanently stretch. The ultimate strength is when it will actually break, which can be quite a different range for different materials. For instance, 316 stainless steel will start yielding around 35,000 psi, but not completely fail until around 80,000 psi, while 6061 aluminum will yield at 40,000 psi and fail completely at 45,000 psi.

>And does this mean that a steel pipe 36" in diameter which had .312 inches thick wall
>would have burst pressure at 110.3 psi? [The circumference (113.1") divided into 40,000
>times .312]

The hoop stress (which is dominant in cylinders) is equal to the internal pressure times the diameter divided by the wall thickness on both sides.

stress = ( pressure * diameter ) / ( 2 * wall thickness )

For a 36" diameter, .312 wall tube, of 40,000 psi yield strength, that would be 693 psi internal pressure to start yielding.

Think of the tube sliced along the diameter, making two C sections. The internal pressure is trying to push the two sections apart with a force proportional to the pressure and the length of the diameter. The walls are trying to hold it together.

This completely neglects safety factors, tolerances, etc.

It is worth browsing your local library for basic engineering texts, there is a ton of interesting stuff to learn...

John Carmack