×
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!
  • Students Click Here

*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.

Students Click Here

Jobs

API 579 MAT Problem

API 579 MAT Problem

API 579 MAT Problem

(OP)
I am having a little problem with the API 579 determining the minimum allowable temperatures.  In the example problem #3 in API 579, Section 3.11 the formula for S*E* = P((Rt/Tc)+0.6).  This is for a vessel shell.

In example problem #4, the formual for S*E* = P/2(Rt/Tc)+0.2).  This is for a sphere.

My question is, in example problem #3 where did they get the value 0.6 from for the equation?

Also, for example problem #4 where did they get the value 0.2 for the equation?

Is the value always 0.6 for vessel shells, always 0.2 for spheres, etc.?  If so, where would these values be found?

Thanks


RE: API 579 MAT Problem

I believe the formulas come from ASME Section 8.  Not sure about the derivation.

"Formulas for Stress and Strain" gives a thick-walled stress equation for cylinders, that if some t^2/R terms are neglected, will give you stress = P(r/t + 1).

They give another equation, the "mean diameter formula", which will give stress = P(r/t + 0.5).  About this equation, they say "the expression for bursting pressure, commonly known as the mean diameter formula, is essentially empirical but agrees reasonably well with experiment for both thin and thick cylindrical vessels."

My guess, lacking better information, is that the equations mentioned are committee compromises between these two results.

RE: API 579 MAT Problem

Sharik-

The formulas you are referring to are directly from ASME VIII-1, as stated in API-579 Appendix A.3. In essence, the "nuisance factors" of 0.6P and 0.2P are there to compensate for high pressure / thick wall conditions. For most vessels, they have little effect on the result.

I'm a bit concerned that someone doing an FFS evaluation per API-579 isn't familiar with vessel design per VIII-1. Perhaps you have experience with different codes in which case you have some feel for vessel analysis. If you don't, you really need to get a mentor before playing with FFS evaluations.

jt

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