Once pressure within a pipe reaches its yield strength, the pipe will deform and fail. It may even burst, which is why the value is also known as the pipe's "burst pressure." A pipe's yield strength depends primarily the yield strength of its material. Beyond that, the pipe's configuration further defines the value. The pipe's size and the thickness of its wall increase the pressure that it can withstand. Additional pipe variables contribute to a fixed "safety factor," which further affects the yield strength.
Multiply the pipe material's yield strength, measured in pounds per square inch, by the wall thickness, measured in inches. Yield strength equals approximately one third of the material's hardness, measured in pounds per square inch, but your manufacturer will provide an exact figure. If the material yield strength equals 30,000 pounds per square feet and the wall thickness is 3 inches: 30,000 x 3 = 90,000.
Multiply your answer by 2. Using the example in Step 1: 90,000 x 2 = 180,000.
Multiply the pipe's outside diameter by the pipe's safety factor. The manufacturer provides data on the safety factor, which is a ratio relating the pipe's burst pressure and working pressure. If the outside diameter equals 10 inches, and the safety factor equals 1.4: 10 x 1.4 = 14.
Divide the answer to Step 2 by the answer to Step 3: 180,000 / 14 = 12,857 pounds per square inch.
If your result is negative, multiply by -1: -56,104 x -1 = 56,104. This answer is the pipe's yield strength, measured in pounds per square inch.
