The paragraph UG-23 (b) mentions the use of external pressure chart for the determination of one value of max allowable longitudinal compressive stress,

these charts are also called as stress-strain charts?

What is the basis of using these charts for determination of max allowable longitudinal compressive stress?

as per Jawad and farr in their Guidebook for the design of ASME pressure vessels,(Page 38 hard copy)

" if the point A is to the left of the curve then B = (AE) / 2.

E = modulus of elasticity (if we measure E using the slope between 2 points on elastic portion of a curve for a material in external pressure chart, its value comes to be half of the actual value of E under tensile loading conditions)"


Please explain.
Regards
ASD23789

For compressive stress (UG-23(b), UG-28 ) the consideration is failure due to buckling .The Buckling strain decides the allowable stress .

The charts provide a simpler method for estimation of buckling stress . A careful reading of Jawad will make the point clear.