Unstayed Flat Head Thickness (Metal to Metal Contact Outside the Bolt Circle)

[LawEngineering]

Hello,

I am trying to calculate the required thickness of unstayed flat heads with metal to metal contact outside the bolt circle per ASME Section VIII non-mandatory appendix Y with reference to mandatory appendix 2 as necessary. My main point of focus is on a category 1 class 3 assembly per paragraph Y-6.3 using a self energizing gasket.

I have already calculated all the equations from table 2-7.1 of appendix 2 for the flange factors F, V, and f. I am now trying to calculate the remaining variables in section Y-3 and the 6-3 analysis.

Does anybody have any sample calculations or references to proofs of this full analysis? I am trying to set up an excel spreadsheet to automate this calculation however I have nothing to compare my calculated values to.

Thanks.

 

[LawEngineering]

Is there really nobody with any familiarity in this topic?

 

[TGS4]

Familiar: yes. Willing and able to share proprietary stuff: no.

 

[prex]

Have a look here.

prex
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[doct9960]

LawEngineering,

Get a hold of the literature listed in Appendix Y-10. There might be example problems in those journals.

 

[LawEngineering]

Prex: Thanks for the link. I have come across that web page before and it was a good reference for some points.

doct9960: Those journals look promising however I could not get my hands on any without paying for them through ASME. I searched and searched! Spending some time working the code I believe I have made sense of my initial questions.

TSG4: I have finished my spreadsheet and have proofed the whole thing by hand. What are you using for this calculation? A paid for software or a personally developed tool/spreadsheet?

Would you be willing to compare my calculated stress values to whatever your tool is outputting for a given a set of inputs. I'm not looking for any formulas or setup details. Just a simple comparison of my calculated stresses to those of another.

Thanks to all.

 

[LawEngineering]

Hey Guys,

I wanted to upload a sample PDF calculation of the Appendix Y spreadsheet I have been working on to share my results. All dimensions are in inches and stress values in psi. If anyone sees any errors or has some constructive criticism please let me know!

One question I do have is when g0 equals g1 and the flange hub is actually integral with the pipe, e.g., a casting where the pipe and flange are one, what are you supposed to use for the hub thickness? Playing around with different values of "h" doesn't seem to make much of a difference in this scenario however it would be nice to know if the code mentions it anywhere. For reference, I am referring to something like figure 2-4(5) of appendix 2. Plugging in 0 for the hub length doesn't work out so well with the calculations because of division. It seems safe to me to just use a value of 1 in this situation. What do you guys think?

Thanks.

 

[prex]

You shouldn't have problems when g[sub]0[/sub]=g[sub]1[/sub]: the formulae for flange factors in App.2 do consider this special case, so you don't need to assume any value for h (and BTW if you assume one, the result should be totally independent of it).
Note also that your sheet does not state the design temperature, the materials, the corrosion allowance, and other: how could we check your calculation?

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[LawEngineering]

Prex,

I was assuming people would just use the allowable stress and modulus of elasticity values provided in the input values and therefore eliminate the need to know design temperature and material. The original intent of this calculation was to determine flat head thickness values for hydro testing so the material would be at room temperature and no corrosion allowance is required. The actual materials being used in this calculation are SA-105 for the flange, SA-36 for the flat head, and SA193-B7M bolting.

You are correct that there is no problem when g0 equals g1. The issue is that when G0 equals g1, the hub length disappears. If the hub length is entered as 0, the value for C in the flange factor equations becomes 0. The remaining flange factor equations that divide by C are now undefined and thus values for the flange factors F, f, & V are undefined.

The first equation to divide by 0 is #6 for C4. The last term (1+3A)/C is undefined when C equals 0.

I do agree that the results are independent of h when g0=g1 although the stress values do change insignificantly by a couple degrees psi when altering the values of h significantly. Most likely decimal place rounding issues I would assume.

 

[prex]

For F, f & V you have the limit values for g[sub]1[/sub]=g[sub]0[/sub] in the graphs: you should use: [tt]if(g1/g0<1.00001){f=1;F=0.90892;V=0.550103}else{use_formulae}[/tt]

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[LawEngineering]

Prex: I understand that when g0=g1, f automatically becomes 1 because the calculated value is less than 1.

Lets approach this differently. There are 4 variables you need to know in order to calculate the flange factors. They are (g0,g1,h,h0). When g1=g0, the calculated values should be F=0.908920, V=0.550103, and f=1 because the calculated is less than 1 and one is the minimum. Using the values in my calculation of g0=0.325 and changing g1 to 0.325 the calculated flange factors (F,f,V) should equal those shown above however they do not. They equal F=0.908625, V=0.548588 and f=1. When you change the value of h to 0.325 the factors fall into place at F=0.908920 and V=0.550103.

When g0=g1, what value are you using for h in your flange factor equations?

 

[prex]

Simply take F=0.90892 when g1=g0, otherwise go to the formulae per Table 2-7.1 (the same for f and V, of course). If you do so, h will never be used and you do not need to specify it.
The fact that the formulae do not converge exactly to their limit values is due to the fact that those formulae result from a numerical interpolation of quantities that were formerly known in their graphical representation only, so they cannot be exact. But the code specifies that the graphs are mandatory, and that the formulae may be used in place of them, so there is no doubt on the procedure to follow.
And BTW f is 1, for g1=g0, not because, as you say, the formulae provitde a value less than 1, but simply because that is stated in fig.2-7.6

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[LawEngineering]

Prex:

I believe I understand the logic in this now. The hub length is only required when g1/g0 is greater than 1. When they are equal, the hub length is to be omitted from the calculation rather than to input 0 as its value. If this is right thank you for the clarification.

Any chance you had some time to compare the calculated stress values?