(a) The design pressure for steel pipe is determined in accordance with the following formula:
P = (2 St/D) x F x E x T
P = Design pressure in pounds per square inch (kPa) gauge.
S = Yield strength in pounds per square inch (kPa) determined in accordance with section 255.107 of this Part.
D = Nominal outside diameter of the pipe in inches (millimeters).
t = Nominal wall thickness of the pipe in inches (millimeters). If this is unknown, it is determined in accordance with section 255.109 of this Part. Additional wall thickness required for concurrent external loads in accordance with section 255.103 of this Part may not be included in computing design pressure.
F = Design factor determined in accordance with section 255.111 of this Part.
E = Longitudinal joint factor determined in accordance with section 255.113 of this Part.
T = Temperature derating factor determined in accordance with section 255.115 of this Part..
(b) If steel pipe that has been subjected to cold expansion to meet the SMYS is subsequently heated, other than by welding or stress relieving as a part of welding, the design pressure is limited to 75 percent of the pressure determined under subdivision (a) of this section if the temperature of the pipe exceeds 900 degrees F (482 degrees C) at any time or is held above 600 degrees F (316 degrees C) for more than one hour.