Hello all,
I am modeling GRE piping to ISO 14692-2017.
When a Tvar% tolerance is entered and I manually calculate the hoop stress, I do not get the same value calculated by Caesar II. (Caesar 2019 SP2 and Caesar V12)
The code formula for hoop stress (14692-3-2017, section 7.8, eq 10) is (P x Dr,min)/(2x tr,min) where
tr,min is the minimum reinforced wall thickness and
Dr,min is the mean diameter of the minimum reinforced wall.

However, it appears that Caesar is using the mean diameter of the maximum reinforced wall to calculate the hoop stress.
Using the maximum reinforced wall thickness results in a slightly smaller mean diameter and in turn a lower hoop stress than what I think the code intends.
Can any FRP experts confirm if there is a code formula error in Caesar or if I am misinterpreting the code? The question applies to Caesar 2019 and Caesar V12.

The parameters for the calculation are:
Pipe OD = 110 mm. (OD of the structural wall only)
Wt/sch = 2.5 mm (structural thickness only)
Tvar% = 1%
Pressure = 870 kPa.

Calculated minimum wall, tr,min = 2.5x(1-1%) = 2.5x0.99 =2.475 mm.
Mean Diameter, Dr,min = OD-tr,min = 110-2.475 = 107.525 mm
Hoop stress = (P x Dr,rmin) / (2* tr.min) = 870x107.525/(2*2.475) = 18898.3 kPa
Hoop stress reported by Caesar = 18889.5 kPa. (8.8 kPa lower)

If the mean diameter of the maximum reinforced wall is used, then I calculate the same hoop stress as Caesar:
tmax = 2.5x(1+1%) = 2.5x1.01 =2.525 mm
Mean Diameter, Dr,max = 110 - 2.525 = 107.475 mm (note that r,max is my subscript, not a code subscript)
Hoop stress = (P x Dr,max) / (2* tr,min) = 870x107.475/(2*2.475) = 18889.5 kPa

Furthermore, the formula listed in the quick reference guide is also incorrect. It lists the Hoop stress as PDm/2tn. Where tn is nominal wall?

DM