The design pressure for plastic pipe is determined in accordance with the following formula, subject to the limitations of section 6-77-38:
P = Design pressure, gage, kPa (psi).
S = For thermoplastic pipe the long-term hydrostatic strength determined in accordance with the listed specification at a temperature equal to 23E C (73E F), 38E C (100E F), 49E C (120E F), or 60E C (140E F) for reinforced thermosetting plastic pipe, 75,800 kPa (11,000 p.s.i.).
t = Specified wall thickness, mm (in.).
D = Specified outside diameter, mm (in.).
Haw. Code R. § 6-77-37