general primary membrane stress formula in microprotol

[seamantgn]

I´m new using this program (microprotol).

I´m try to understad the report for a horizontal vessel with internal pressure. Various parts are based in a code o general practice.

But in a saddle analisys; when calculate "maximum primary membrane stress verification" for a "maximum longitudinal stress verification":

use the formula: Sigma eq. = max (abs(sigma circunf. - sigma longitudinal) ; abs(sigma longitudinal - 0.5 P))

I don´t understand why use the term: abs(sigma longitudinal - 0.5 P)

I was reading PV books and understood: Sigma eq = max (abs(sigma1 - sigma2) ; abs (sigma2- sigma3) ; abs (sigma3- sigma1))

When: sigma1/2/3 are the principal stresses and then Sigma eq = max of 3 principal stress difference but i have only 2, Why? And It´s 0.5 P a principal stress?


Somebody could give me a hand with this.

Thanks

 

[TGS4]

Not sure if this helps, but if you only have internal pressure on a cylinder, -0.5P is the membrane stress in the through-thickness direction.

 

[seamantgn]

Thanks TGSR!!

Do you know books about this theme? to read more.

 

[TGS4]

I would start with the Design Code - ASME Section VIII, Division 2, particularly Part 5. You should also read ASME PTB-1, for the background on the VIII-2 rules.