INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

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.

RE: API 650, Annex E, E.6.2.2.3- Allowable Longitudinal Stress

I think it states that the equations have allowance for internal pressure which helps keep the shell from buckling; thus the pressure term. Those are for seismic compression, not general compression, and significant seismic loading requires that the tank have product in it.
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

(OP)
Great tip JStephen. I see the max allowable compressive stress for longitudinal loads only, is 1.8X10^6t/R, and for longitudinal an circumferential compression stress, it's 10^6t/R. Still curious where the large 10^6 coefficient is derived from?

Thanks again!

RE: API 650, Annex E, E.6.2.2.3- Allowable Longitudinal Stress

See Chapter 11 in Timoshenko's Theory of Elastic Stability, Eq. 11-9, for example.
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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close