Use of FEA in Pressure Vessel Design 1

[yehlo1972]

Hi

I want to know till what extent ASME code covers the design of pressure vessels. From extent i mean in which cases we have to use FEA (Finite Element Analysis)in designing Pr. Vessel.

 

[corus]

Certain calculations in design standards for pressure vessels will be dependent/applicable on say the distance between nozzles or the thickness of shell. When these guidelines are not applicable then you have to use FE to justify the design.

corus

 

[jte]

yehlo-

Simply put, FEA is never required for an ASME VIII pressure vessel. Well, never for Div. 1 or 2, I don't know 'bout Div. 3. Instead, FEA is, in some situations, an optional analysis method. Sometimes, in competent hands, FEA is the best approach. But even then, you need to discuss and decide on shells vs solids vs axisymmetric, static or transient, linear or nonlinear... The new Div. 2 has been written to be a bit more "FEA friendly" but its still never a requirement.

And, of course, the obligatory "If ya gotta ask, you should hire competent help" comment. Really.

jt

 

[LSThill]

jte (Mechanical)

Please review PART 5 ASME SECTION VIII DIVISION 2 2007.

L S THILL

 

[jte]

Leonard-

I have reviewed Part 5. Are you implying that FEA is mandatory? And if so, can you please state exactly where it says so?

 

[jte]

Got interrupted by a phone call...

So, if I'm designing a drum in accordance with the Design by Rules basis, what part of 5.1.1 applies besides the clause about overpressure protection. In particular, with the above exception, none of 5.1.1.2 applies.

Further, 5.1.1.3 explicitly limits the application of Design by Analysis.

And finally, Design by Analysis does not require FEA. Although I will grant that most folks, myself included, will choose FEA as their analysis method, the Division is very careful to not specify any particular numerical analysis method.

jt

 

[pingmi]

jte,

I was under impression that FEA is normally used in the designs where vessel / part geometry is very complicated and should be used if design calculation / justification as per ASME section VIII Div I/II or any other code is difficult.
Pls correct me if I'm wrong.
I'm eager to know if any guidelines have been set up by ASME for performing FEA on pressure parts.

 

[jte]

pingmi-

As I stated above,

...most folks, myself included, will choose FEA as their analysis method

My point is that although FEA is one often used analysis tool, others exist and are acceptable. For example, when evaluating nozzle or other external attachment loadings, lots of people use the WRC-107 method. This is a commonly used method (and yes, FEA is playing a larger role here over time) and perfectly acceptable. Others may write and solve differential equations or take a series solution type of approach. Some may prefer a finite difference approach, in particular with buckling evaluations. And finally, one day some may use a numerical analysis approach which does not yet exist. Section VIII Div. 1 and Div. 2 do not restrict the method of evaluating a design which is not directly dealt with in the design rules. Any rational method may be used - provided that the AI (and, to keep 'em happy, the customer) agree with the design approach.

As for your "guidelines" question - I'd suggest that you take a long, hard look at Part 5 of the 2007 edition of Div. 2. If you're just getting into vessel FEA you might as well start with the latest, and the new Div. 2 was written to be much more "numerical analysis friendly" than the various variants of the 1968 version. The Div. 1 rules are along the same lines as the old (and parts of the new) Div. 2 with S (primary), 1.5*S (primary membrane & bending), and 3*S (primary & secondary) limits.

jt