Section modulus is a structural engineering term that focuses on the strength of an object as compared to the other objects it is connected with. The section modulus of a pipe measures the point at which the pipe will begin to yield. The section modulus is calculated using the outer and inner diameters of the pipe, and uses the mathematical constant pi, or Ļ, which is a non-repeating and non-terminating number that functions heavily in circular areas and volume. Calculating a pipe's section modulus is important to maintain the integrity of the structure.

Calculate the outer diameter of the pipe to the fourth power. For example, if the outer diameter equals 2 inches, then the diameter raised to the fourth power, or 2^4, equals 16.

Calculate the inner diameter of the pipe to the fourth power. For example, if the inner diameter equals 1 inch, then the diameter raised to the fourth power, or 1^4, equals 1.

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Subtract the outer diameter to the fourth power by the inner diameter of the fourth power. For the example, 16 subtracted by 1 equals 15.

Multiply that number by Ļ. For the example, 15 multiplied by Ļ equals 47.124.

Divide that number by the outer diameter multiplied by 32. For the example, the outer diameter multiplied by 32 equals 64. Dividing 47.124 by 64 results in 0.763. The section modulus of the pipe is 0.763.