Collapse Pressure is the pressure which is supplied from the outside of a pipe. When the Collapse Pressure is higher than the rated or designed Collapse Pressure of the pipe, then the pipe crushes or collapses. In other words, when the differential pressure from outside to inside the tube or vessel increases, the tube deforms catastrophically.
For a perfectly round-shaped pipe or tubing, the Collapse Pressure has to be relatively high. In case the tubing is not round but slightly oval, the Collapse Pressure at which pipe will break can be significantly less. It is treated as one of the important factors in finding the operating limits of coiled type tubing strings. This happens because the spooling action of the string hence inducing ovality in the tube. The pipe is subjected to both internal and external pressure and the equation can be written as:
Pe = Po –[1-2/(D/t)]x Pi = Delta P + (2/(D/t))x Pi
Po is equivalent external pressure
Pi is internal pressure
Delta P = Po-Pi
How to Calculate Collapse Pressure
Steel pipes and tubing are used all over the world to build and support construction and building structures. The strength and capability of these items is determined by its ability to withstand pressure in normal or reasonably stable environments. This durability is calculated using proportions known as burst pressure or yield points. The specific point at which the tube will fail cannot be determined as one cannot predict the exact environment or usage in which the device will be placed.
Identify the general formula. Collapse pressure is defined as 2 times the burst pressure times wall thickness times (outer diameter minus wall thickness) divided by outer diameter squared. Recognize there are variants of this formula for different objects, such as screens, PVC (polyvinyl chloride) pipes, and steel casing. For example:
Collapse pressure for 316L material is 2 times 22,200 times 0.25 times 0.035 times 10,400 – 0.25 times 0.035 divided by 10,400 squared equals 16,900.
Use a corrugated factor for screens. Compute the collapse strength of a screen as 24 times 3 times 10 raised to the 7th power times moment of inertia divided by (width of wire on external face – inches plus slot width of screen-inches) times mean diameter of the screen-cubed.
Compute the collapse strength of a PVC pipe using Poisson’s ratio. Use the formula collapse pressure PVC equals (2 times 4 times 10 raised to the 5th power divided by 1 minus 0.33) times 1 divided by (outside diameter of pipe divided by wall thickness) times (outside diameter of pipe divided by wall thickness times minus 1) squared.
Calculate collapse strength of steel casing. Use the formula, (2 times 3 times 10 raised to the 7th power divided by 1 – 0.3 squared) times (1 divided by (outside diameter of pipe divided by wall thickness times minus 1) cubed.