Appendix 13 examples - differences with rules?

[tigny]

Hi,

following my thread "failure mode for criteria 3Sm",
I'm into appendix 13 of ASME VIII div 1.

Following rules of chap. 13-13 (vessel of circular cross section having a single diametral staying member), I'm trying to compare my excel sheet with example 13(i) but I find discrepancies.

The example is for unequal pressures;
I find the same membrane stresses for formulas (6) and (7) (13-17(i)(1).

But as for bending stresses in diametral plate I find a big difference (99975psi<>25020 psi).

It seems the parameter L1 which permits the choice of formula (9) or (10) is the source of this trouble.

For a circular cross section, I thought L1 would be 0.

Does anyone know what value should be assigned to L1? (it seems L1 = Lv gives the good result)

Second point (sorry!); the coefficent c appears in formulas both for shell and plate.
Should it be adapted (c value for shell in shell formula; c value for plate in diametral plate in plate formula?)

yours,

tigny

 

[SnTMan]

tigny, on page 427 for eqns (9) & (10), I wonder if that is a misprint and should read:

Lv <= 2R and

Lv > 2R

rather than L1?

I'm looking at the example 13-17(i), but it still doesn't look quite right, like where did the 4 in the 4R^2 term go?

As for your second question I would say yes, c is per shell or plate, whichever is under consideration.

Code gurus?

Regards,

Mike

 

[prex]

I agree with SnTMan, the choice between formulae (9) and (10) in 13-13 should be based on L_v, not L₁ (L₁ has no place in a circular section).
And tigny, your result appears incorrect to me by a factor of 4, you probably used R=12 in, but R=6 in in the example.
And c is simply half the thickness for an unreinforced vessel, and of course you should take the thickness of the element under consideration.

prex

http://www.xcalcs.com

Online tools for structural design

 

[tigny]

Thank you SnTMan and prex,

SnTMan, the 12² in example 13-17 is 4*R²; R = 6; it's ok.

tigny

 

[SnTMan]

tigny, agreed, thanks.

Mike

 

[tigny]

btw,

another comment to the chap. 13-13 formulas,

when using I₁ and I₃ with lentgh units in mm, in equations (3), (8), (9) and (10), don't forget to divide them by 25.4

for example, replace I₁ by I₁/25.4

yours,

tigny

 

[tigny]

Hi,

I'm coming back with chapter 13-13 formula's questioning.

For diametral plate bending stress calculation, formula J1c/I3.[(P1-P2)Lv²] (9), we are stuck with Lv parameter

Since we are talking plate, should'nt be Lp parameter instead? This would be coherent with the use of (4R) in the (10) formula, wouldn't it?

Also, instead of L1 in the tests, shouldn't this be "for Lp =< 2R" instead of "for (Lv) L1 =< 2R"?

If anybody 's got a clue...

 

[prex]

Can't follow you. L_p is not defined in the code, and L_v has its place in those formulae. These tell you to take the shorter span (length of vessel or vessel diameter) to calculate the bending stress in the diametral plate. Didn't check the formula in detail, but I guess it comes from supported rectangular plate analysis.

prex

http://www.xcalcs.com

Online tools for structural design

 

[lopezon]

Hello tigny,

It is very interesting your post and I have a new one.

Can we use UG-34 instead of Ap. 13 for calculation of rectangular vessel like headers of aerorrefrigerants?
What do you think?

Please tigny, is it possible to obtain a copy of your excel sheet you are refering above?.

Best regards.
lopezon