Does AutoPIPE count pipe insulation thickness towards the effective diameter for wind/wave force calculations?
Yes, Force coefficients (Cf) are given in Tables 6-10 for "Chimneys, Tanks and Similar Structures" in the ASCE 7-98 code. In Table 6-10, the force coefficient is a function of the h/D (= height/diameter) ratio and D*sqrt(qz). The default value "Automatic" will calculate Cf for each point based on D*sqrt(qz) as per Table 6-10 assuming round smooth pipes and a conservative h/D value of 25. The outside diameter D includes the pipe insulation thickness. The height h of chimneys and tanks in Table 6-10 would correspond to the pipe length facing the wind, not the pipe height. The pipe length is not considered in determining the Cf factor in AutoPIPE and instead a conservative value of h/D=25 is assumed. For most common pipe sizes, the shape factor is typically 0.7 when using "Automatic" option. Only very small diameters will have a shape factor of 1.2. The load summary will list calculated Kz, Cf and qz values as a function of height h. The Cf values in the load summary assume D = 1 ft.
Modeling "Wind" - Load Case
Bentley AutoPIPE