t1 = nominal wall thickness (mm)
t0 = strength thickness (mm)
t = minimum required wall thickness (mm)
c = corrosion allowance (mm)
b = bending allowance (mm)
σt= permissible stress (N/mm2)
σb = specified minimum tensile strength of the material
at 20°C (N/mm2)
σ ft = specified minimum yield stress or 0.2% proof
stress of the material at design material temperature
(N/mm2)
p = design pressure (bar)
D = outer diameter of pipe (mm)
σb 100 000 = average value for stress to rupture after 100 000
hours at design material temperature (N/mm2)
a = percentage negative manufacturing tolerance
e = strength ratio.