Hi all,
I've had a look in ISO 14692-3/2017, Sect. 7.8 ("Allowable Stresses" - not quite proper title, since it presents actual hoop and axial stresses induced by applicable external loads).
The axial stress-component under discussion, "sigma"_ac = OD/(2*C)*Ea, is defined as "roping curvature" stress. Other details are not provided.
Since this stress does not depend of any external applied loading/strain, I guess Borzki opinion regarding cold forming-bending origin of this stress makes sense and is reasonable. Thus, this stress should be considered for FRP/GRP/GRE bends/elbows only.
In addition, please note that all the other axial and hoop pressure-induced stresses, and axial bending-induced stresses (e.g. SIF x M/Z general formula based stresses) are considered separately from "sigma"_ac "roping curvature" stress.
My opinion is that ISO 14692 based stresses for FRP/GRP/GRE pipework cannot be extended to ASME B31.4 and B31.8 metallic pipeline components. FRP/GRP/GRE materials are un-istropic, with different "load-strain-stress" inter-dependence behavior than that of metallic materials.
I hope these thoughts might help...
Best regards,
_________________________
Dorin Daniel Popescu
Lead Piping Stress Engineer