SMYS is an engineering term that stands for Specified Minimum Yield Strength, the stress value used to determine how much pressure a pipe can handle before it weakens and deforms permanently. The SMYS value gives an engineer confidence that a pipe will function safely, especially under high pressures. With a little arithmetic, you can determine a pipe’s SMYS if you know its internal pressure, wall thickness and outside diameter. The equation for finding SMYS is simply, P OD / (2 T), where P is pressure, OD is the pipe’s outside diameter, and T is its wall thickness.
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Multiply the internal pipe pressure in pounds per square inch by the pipe outside diameter in inches. For example, a pipe whose diameter is 10 inches and has a pressure of 2,400 psi, 2,400 x 10 = 24,000.

Multiply the pipe wall thickness in inches by 2. In this example, the pipe’s wall is 0.75 inches thick, so 0.75 x 2 = 1.5.

Divide the value from Step 1 by the number obtained in Step 2 to calculate SMYS.
In our example, SMYS is 24,000 / 1.5 = 16,000 psi.
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References
 Gas Pipeline Hydraulics; E. Shashi Menon; 2005
 Pipeline and Hazardous Materials Safety Administration: Barlow’s Formula