Flange Strength Calculation 3

[Aloumina]

I am in a situation investigating if #400 flanges are adequate for 272 Celsius and 57barg. We have the design drawing of the flange. So I am thinking of asking a calculation of it's strength from an engineering consultant company. I am not sure what exactly to ask for. From what I have found on the net the calculations can be done accordingly to:

1. ASME VIII div1 App2
2. ASME VIII div2 par. 4.16
3. ASME VIII div2 par. 5
4. EN 1591:2001
5. EN 13445-3:2002,Sec.11
6. EN 1591/EN 13445 Annex G

Questions
a) Are there any other European or Aamerican (USA) codes that can be used or other divisions of ASME and EN?
b) From what I have understand by using cases 1 and 2 calculations will be done by rules and by case 3 is done by numerical analysis (so less material and thickness). Case 2 has a more restrict way of calculating so les material and thickness than that of case 1.What about the others?
I have more questions but if I won't find any answers to these to no point in going further

 

[MJCronin]

Some questions:

1) Are these flanges part of a pressure vessel design or are they part of a piping system ?

2) By "#400".... do you mean ASME B16.5, Class 400 dimensions ?

3) What is the material of construction ?

4) Are there any imposed external forces on these flanges ? ( say...such as from an attached Relief valve?)

Regards

 

[Aloumina]

Hi and thanks for your time

a)They are part of a piping sytem

b) Yes ASME B16.5, Class 400

c) I think ASTM A105 but must get back to you for that

d) No external forces. I am even thinking of requesting for a new pipe srtess analysis with new pipe supports with all external forces mimimum as possible.

 

[saplanti]

Under B16.5 the flange seems to failing with internal pressure of 5.7 MPa at 272 deg C and no external load. See the attachment.
The flange size does not effect he result without external loading. Class 600# has some reserv for the external loads.

Ibrahim Demir

 

[Aloumina]

Thank you saplanti

Is Pall= Allowable pressure? I have seen that it fails but I think if a more percise calculation will be done the flange has no problem. That is why I want to use cases 1 to 6 and I think case 3 and case 6 produce the bigest allowable stresses on the flange.

Even in your formula it seems that it fails for a 4% of the allowable pressure. Having a look at your formula I can see if forces and moments are implemented that are negative (in the formula) the flange strength is ok? So all I have to ask is the engineer that will perform the the pipe stress analysis is that I want these kind of forces and moments (negative)?

 

[C2it]

You should not rely on the 'Kellogg' formula for decision making, since it is a very conservative check when used only to check equivalent + internal pressure against flange Code allowable.

It is not very sensible to require a piping system design to apply virtually no external loads to a joint, unless it is something like a garden hose.

I would recommend a full calculation in accordance with either:

ASME VIII Div 2 (2007 or later) which allows direct inclusion of external loads to a flange stress calculation, so there is no question about use of 'Kellogg' etc.

Or EN1591 ... this is the mathermatically complex method and needs software. It has the major advantage that it properly considers deformation of the flange, gasket and bolts as an entity.

Review the results in terms of allowed stresses (and for EN1591, displacements) rather than simply comparing the pressure to a Code allowed value.

 

[MJCronin]

I agree with the knowlegable and experienced C2it....

But, in the long run, it may be cheaper and simpler to use Class 600 flanges.

Suggestion: Can the 57 barg design pressure be better defined ?

Is this a "peak pressure" that the system will only see ~1% of the time ?

Is there a lot of "margin" included ?

ASME B31.3 has rules about this

Perhaps a more reasonable design pressure (and peak pressure) could enable the use of the Class 400 Flanges

Regards

 

[StevenHPerry]

But, in the long run, it may be cheaper and simpler to use Class 600 flanges.

Almost certainly it will be unless we're talking about a very large size, very expensive material, or dozens upon dozens of flanges (but none of these were mentioned).

Plus, CL400 is less likely to be stocked than a CL600. You might end up paying more for the CL400 after you get done qualifying it.

The OP said no external forces, but to C2it's point: the Kellogg formula may not be great, but it is conservative. Bump up the pressure class and move on unless you already have the ability to run a more involved check. Is it really worth spending 2 hours to save the marginal cost between CL400 and CL600?



- Steve Perry
This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.

 

[jtseng123]

If it is B16.5 and class 400, why running any calc ? Use pressure-temp rating table and be done with it. No any complicate or fancy calc. If you have external axial and bending loads, just convert them to equivalent pressure by a simple formula and add to your design pressure.
If you really want ot justify, then use Div 1, App 2 that I have done hundreds of times for special large diameter flanges.
The most important, 2-14, Flange Rigidity.
And remember, as long as it complies with pressure-temp rating table even it fails in calc, you do not need to change your flange. Presusre-Temp table take precedence over calc.
Good luck.

 

[Aloumina]

"..........agree with the knowlegable and experienced C2it....

But, in the long run, it may be cheaper and simpler to use Class 600 flanges.

Suggestion: Can the 57 barg design pressure be better defined ?

Is this a "peak pressure" that the system will only see ~1% of the time ?

Is there a lot of "margin" included ?

ASME B31.3 has rules about this

Perhaps a more reasonable design pressure (and peak pressure) could enable the use of the Class 400 Flanges

Regards "

57barg is the pressure the Unit works at. The Unit has many of #400 flanges I am talking about more than 150 of them. Probably I am going to use ASME VIII Div 2 or EN1591

 

[XL83NL]

To answer the OP's initial question, I believe other flange calc methods can be found in ;
- PD 5500 [not sure which part]
- VDI 2230

 

[C2it]

MJC .. thanks for the kind words.

PD5500 (Section 3.8) flange design method is the exactly the same as ASME VIII Div 1 App. 2 and my also be found in the main text of EN13445 ..... not EN13445 App.G though, that is same as EN1591.

Confused ? You will be.

I think the VDI code may be an old East German code .. and if that is true, it may be the fore-runner of EN1591.

I'll get my coat .....

 

[XL83NL]

I think VDI is referenced by AD 2000 (so yes, German).

 

[TGS4]

I'm going to agree with jtseng123 on this one. Why would you even bother doing any analysis on such a thing? The only thing that I would add is that the "equivalent pressure" method is SO conservative, I would be fine with the total of internal pressure + equivalent pressure from external loads be TWICE the rated pressure, provided that sufficient initial bolt load is provided.

A couple of points about using any sort of analysis to evaluate bolted flange joints (this coming from some who has published extensively on the subject and does this for a living):
1) Most flanges don't fail due to overstress - stress checks on flanges are mostly useless
2) Most flanges fail because they leak. Unless your analysis method considers the gasket performance - especially it's leakage performance doing unloading and repeated loadings - you're not going to find much in an analysis.
3) Gasket selection and bolt loading are MUCH more important than the pressure ratings. Any flange with a poor gasket choice and lousy bolting will leak.
4) Spend your time/effort on a procedure for properly bolting these flanges - spending time on analyzing flanges without proper bolting is a waste of time.