"Working pressure" is defined as the pressure that a pipe, tubing, or other part is under during standard operating procedures. It is important to know a parts working pressure not not only for safety reasons, but also so that any machinery is equipped with the right parts. Using a part with lower working pressure than required can cause the pipe to burst and cause bodily damage, especially if the substance is harmful.
Things You'll Need
 Calculator
 Working pressure equation: P = (2*S*T)/((O.D.2*T)*SF)

Multiply the material strength, in pounds per square inch, by the wall thickness of the part in inches. Multiply the result by two. Write down this number, as you will need it to finish the rest of the calculation.

Multiply the thickness of the pipe in inches by two. Subtract this figure from the diameter of the pipe to the outside wall, not the inside.

Multiply the resulting figure by the safety factor. This number can range, from 1 through 10. For a basic calculation, use 1.5. Write this second number down so that you can complete the equation.

Take the first number your wrote down and divide it by the second one. The final figure will be the working pressure of the object.
Tips & Warnings
 This equation is to give a general idea of a part's capability. You should always check specifications with the manufacturer, as the manufacturer does extensive testing and know the exact figures. Being off on your math can lead to serious problems.
References
 Photo Credit industrial refinery image by Chad McDermott from Fotolia.com