Curve Fitting/ Digitalising of ASME VIII external pressure charts

[jehan17718]

Can anybody give me any WEB BASED FREE references for curve fitting of factors "A" and "B" used in ASME Sec VIII external pressure calculations?

Any type of reference used to "digitalise" the curves by curve fitting or any other methods would be helpful.

From ASME Sec II-D Appendix 3, para 3-800, I have obtained a reference to "Michalopoulos, E., A New Method for the Development of External Pressure Charts, ASME PVP-Vol.312-2, pp. 293–301, 1995". However, I have not been able to obtain the same online. Any idea if the same is available online?

Thanks in advance.

-jehan17718

 

[vesselguy]

You can download freeware for curve fitting. Goggle "curve fitting software" or something like that and you'll come up with a few hits. I did this 10 years ago by using a free curve fitting program I down loaded from the net to fit several equations for WRC curves and others with no problem. Be ready to do a lot of typing to enter the points. Good luck.

 

[arto]

You can't really fit these - they're constructed from different sets of equations for different L/D & D/t "regimes".
There's an old ASME paper that gives the method (which I saw lately, but can't put my finger on - might it be Saunders & Winderberg "Strength of Thin Cylindrical Shells under External Pressure" Trans ASME vol53#15 p.207? - that's the reference in Roark's Elastic Stability chapter)

 

[jehan17718]

Thanks guys for your responses.

I already have prepared a spreadsheet (about 3 yrs back) which does interpolation based on the equivalent tabular values of Fig G and the Fig B charts. I have run SOME cases and compared it with software outputs and the results are fairly comparable.

Using a curve fitting software, one can arrive at the best fit curve for each curve. As vesselguy pointed out, it obviously involves sonme very tedious typing.

 

[psafety]

It can be done, and very accurately as previous posters have indicated. May I add it is very time consuming.