ASME External factor of Safety
ASME External factor of Safety
(OP)
Where can one find information do confirm the factor of safety is 4 for external pressure disign in the ASME Code.
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS Come Join Us!Are you an
Engineering professional? Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting GuidelinesJobs |
ASME External factor of Safety
|
ASME External factor of SafetyASME External factor of Safety(OP)
Where can one find information do confirm the factor of safety is 4 for external pressure disign in the ASME Code.
Red Flag SubmittedThank you for helping keep Eng-Tips Forums free from inappropriate posts. Reply To This ThreadPosting in the Eng-Tips forums is a member-only feature.Click Here to join Eng-Tips and talk with other members! |
ResourcesWhat is rapid injection molding? For engineers working with tight product design timelines, rapid injection molding can be a critical tool for prototyping and testing functional models. Download Now
The world has changed considerably since the 1980s, when CAD first started displacing drafting tables. Download Now
Prototyping has always been a critical part of product development. Download Now
As the cloud is increasingly adopted for product development, questions remain as to just how cloud software tools compare to on-premise solutions. Download Now
|
RE: ASME External factor of Safety
The simple answer is that you won't find any confirmation of a "safety factor" of 4 for external loads. I don't have a reference handy, but you'll find that the safety factor is between 10 and 20. Take a simple drum, design it to Code rules (Div. 1 or Div. 2 - they are the same), and then build a simple FEA model and calculate the Eigenvalues. The lowest Eigenvalue should be between 10 and 20. The difficult part is in evaluating the effect of imperfections on buckling load. This explains the high Eigenvalue. Buckling behavior is highly geometry dependent which relates to fabrication tolerances and things like nozzles. Local load effects (say a platform clip) are also not considered in the Code calculations. In addition, compressive stresses due to radial external pressure are evaluated completely independently from those due to longitudinal compressive stresses (including wind and seismic). Thus the "factor of safety" when the vessel actually arrives in the field is quite a bit less than 10 to 20. Experience shows that this amount of conservatism is adequate.
More detailed external load analysis can result in reduced material requirements for the cost of more engineering and better fabrication. See Code Case 2286 for this option. Look for a paper to be published at the ASME Pressure Vessels and Piping Conference this year which will explore this issue in more detail.
jt
RE: ASME External factor of Safety
jte is correct that the code can give an answer many times lower than the eigenvalue but the fea model does not account for fabrication imperfections. The code charts are based on information from actual test models.
RE: ASME External factor of Safety
For the plastic buckling range a different formula is used, whereas the ASME code curves account for both phenomena in a single approach.
Anyway App.3 to Part D of ASME II gives a complete description (with bibliographic references) of the basis for external pressure charts, and the specified factor of safety is indeed 3 for cylinders in the elastic range (with respect to theoretical critical pressure). The imperfections are limited in such a way that they can't reduce the critical pressure to less than 80% the theoretical value.
prex
http://www.xcalcs.com
Online tools for structural design
RE: ASME External factor of Safety
RE: ASME External factor of Safety