ASME 8 - MANDATORY APPENDIX 13 VESSELS OF NONCIRCULAR CROSS SECTION

[flare9x]

I have an existing in-service header box (rectangle, corner joints). The design code is ASME 8 1992.

In observing appendix 13 (ASME 8 2017) - the box in question resembles that of Figure 13-2(a) (1).

There are stress calculations within the code. However my U1A provides:

MAWP: 900psig @ 350F.
Hydro: 1350psig

This has already been designed and MAWP provided. As its in-service I would like to determine the minimum required thickness needed for pressure containment.

Is there a particular section in the code or else where that I can reference too?

Best
Andrew

 

[SnTMan]

Why would it not be per Appendix 13? Question for further study: 1992 allowables or current?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[flare9x]

Well the design of rectangle vessels (header box example) per current code is appendix 13. So current.

I was looking for a pressure design thickness calculation. The calculations I see calculate stresses acting on the long / short side etc..

So a question would be - knowing the stresses - how does one then pick the necessary plate thickness that will contain the pressure in the rectangle box?

1. Know the stress induced on the box
2. size the plate thickness

So really want to know how to arrive at the plate thickness needed for pressure containment, this is simply needed for our corrosion rate calculations (time to tmin).

Thanks
Andrew

 

[Geoff13]

As noted in 13-4(a):

Since, in a rectangular or obround vessel, the walls can have different thicknesses, many of the formulas contained herein require solution by assuming a thickness, or thicknesses, and solving for stress which is then compared with the allowable stress value.

Thus it will likely be a trial-and-error solution. Keep picking thicknesses until you find a suitable solution. Using formulas in Excel and the Goalseek tool may help, or may not.

Geoff

 

[SnTMan]

Like Geoff13 says, you have to decrement the thickness, check the stresses against allowables. I am not convinced it is proper to use current allowables however or for that matter, current
Apx 13 rules. It was designed and stamped to 1992 rules and allowables. They may or may not be different to the current ones.

Regards

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[flare9x]

Ok I see it now and that S values are detailed in 13-4 (1) (2)

(1) for plate section of rectangular cross section, 1.5
times the allowable design stress SE;
(2) for other cross sections (such as composite reinforced
bar or shapes and plate sections, etc.), the lesser of:
(-a) 1.5 times the design stress SE; or
(-b) two‐thirds times the yield strength Sy of the
material at the design temperature (see 13-5 for Sy) except..........

S is found in Section II, Part D, Subpart 1. Section II, Part D.

S = 21,600
E = 1.0
Sy = 38,000
St = 70,000

S per (1) = 1.5 * 21,600 * 1.0 = 32400

That allowable S = 32400 / 38,000 = 85% of the yield.

 

[flare9x]

Ok so in understanding the c term in relation to the neutral axis for: N, M and Q as below:

The definition of neutral axis:

c = distance from neutral axis of cross section to
extreme fibers (see ci and co). The appropriate
ci or co value shall be substituted for the c
term in the stress equations.

ci = distance from neutral axis of cross section of
plate, composite section, or section with multidiameter
holes (see 2-12) to the inside surface
of the vessel. Sign is always positive ( + ).
co = distance from neutral axis of cross section of
plate, composite section, or section with multidiameter
holes (see 2-12) to the extreme
outside surface of the section. Sign is always
negative ( − ).

From what I understand - these terms will be - / + depending on if its long or short side?

My dimensions:
long: 125.875"
short = 10.625"

Would the neutral axis and Ci, Co terms be relative to stressed imposed on N,M and Q?

 

[SnTMan]

flare9x, ci, co terms are as stated, distance from neutral axis to the inside & outside surfaces. As used in Mc / I. If the member under consideration is a plain plate, i.e. no multi-diameter holes, reinforcement bars or so forth, c is just equal to 1/2t. Because of the sign conventions used, c is positive to the inside surface, negative to the outside surface. Proper carrying of the signs is important in these calculations.

Now, I don't know what you've got there but I am guessing the original design calculations were run with the other side dimension (not 10 5/8) substituted for the 125 7/8 dimension, i.e probably off the end view of your header. I'd guess then that one side plate will have the tube holes, the opposite will likely have plug (multi-diameter) holes, in which case the neutral axis will not be at 1/2t.

I hope you have the example manual or another worked-out problem to check your calculations against.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[SnTMan]

BTW it is VIII, not 8.



The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[flare9x]

No example manual - wish i did at this point. I wrote all the equations using the R language.

Ok then that helps clarify. To get the signs correct for c.

The sign convention necessary to establish the proper
algebraic sign of the stresses for combining membrane
and bending stresses to obtain the total stresses is as
follows:
(-a) for both membrane and bending stresses:
(-1) plus ( + ) signifies tension stress; and
(-2) minus ( − ) signifies compression stress.
(-b) for bending stress:
(-1) co = term is always negative;
(-2) ci = term is always positive.
A positive bending moment produces compression in
the outermost fibers of the cross section. The bending moment
at the midpoint of the long side of vessels without
stays will always be negative.
At each cross section, the membrane stress is added
algebraically to the bending stress at both the outermost
surface of the shell plate or reinforcement (when used)
and the innermost surface of the shell plate to obtain
two values of total stress. The total stresses at the section
shall be compared to the allowable design stress calculated
as specified in (b).

For bending stress for the long and short side there are equations 3 to 6.

How do i know which ones are for outermost and innermost?

 

[flare9x]

Ok got the manual here:

ASME PTB-4-2013_Section VIII-Division 1 Example Problem Manual

 

[dig1]

flarex9,

I would purchase a copy of PTB-4; Techstreet (this is not an endorsement/advertisement of them)has it available for immediate PDF download.
They have a worked example of Figure 13-2(a) Sketch 1 which you state is your configuration.

Work through the example and understand it. You could then write a spreadsheet verify the example w/ your spreadsheet and then perform the analysis for tmin.

Use the S values for the edition the vessel was constructed not the current S value. When you perform your analysis make sure you understand where any weld joints were made and any degree of RT; I've seen sections of these broke and then butt welded on the short sides.

BR,

Patrick

 

[flare9x]

Ok thanks for the information so far. I should be good now - just one last clarification then I can get this going:

In determination of the long and short side (L,S annotated)

Do I need the orange or red?

 

[SnTMan]

You can run it either way, but you're not gonna like red

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[flare9x]

Ha

 

[flare9x]

I managed to track down original stress analysis report.

This has evolved since I now found the construction drawings. It has a stay plate. So using the calculation for the Stay plate. I can replicate the outputs for the short plates. However the long plates I can not - this is because my c value is not correct. This has ligaments in the plate.

Is there guidance anywhere where I can learn how to calculate c value for the tube/plug side?

The short side c value: c = t / 2

Thanks

 

[SnTMan]

See 13-6.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[flare9x]

ok there is (eb) to account for in long plate membrane stress.