API 650, Annex E, E.6.2.2.3- Allowable Longitudinal Stress
API 650, Annex E, E.6.2.2.3- Allowable Longitudinal Stress
(OP)
I'm trying to better understand the equations in E.6.2.2.3.
Can someone help me understand what's in the coefficient 10^6 of the allowable stress equation 10^6*t/D? I think it must be some derivation possibly including 1.33FY/(12D/t) (1.33 for ASD times yield stress, all divided by D/t).
Also, the equation GHD^2/t^2 is a limit to determine thin vs thick wall stress criteria (I think), but how does it relate to the common limit of R/t? GHD^2/t^2 appears to have pressure in the equation.
Thanks in advance for your insight.
Can someone help me understand what's in the coefficient 10^6 of the allowable stress equation 10^6*t/D? I think it must be some derivation possibly including 1.33FY/(12D/t) (1.33 for ASD times yield stress, all divided by D/t).
Also, the equation GHD^2/t^2 is a limit to determine thin vs thick wall stress criteria (I think), but how does it relate to the common limit of R/t? GHD^2/t^2 appears to have pressure in the equation.
Thanks in advance for your insight.





RE: API 650, Annex E, E.6.2.2.3- Allowable Longitudinal Stress
There's a similar general-purpose equation for compression stress in thin-wall cylinders in API-620, in the allowable stress section of the standard.
RE: API 650, Annex E, E.6.2.2.3- Allowable Longitudinal Stress
Thanks again!
RE: API 650, Annex E, E.6.2.2.3- Allowable Longitudinal Stress
He comes up with critical buckling stress = E*t/R * sqrt(3*(1-nu^2)), where nu = Poisson's ratio. I'm not sure how that compares numerically. There's probably a factor in there to adjust from theoretical to reality, plus a factor of safety. Some of these theoretical buckling-strength derivations can be 50% off.
There's been no end of work on problems like this and external pressure buckling of shells, the latter problem being motivated largely by submarine design issues.