Flange as per ASME code VIII, div 1, appendix 2 2

[xufeng]

hi,

could someone tell me how to determine the bolt number and size for the flanges to be designed as per the subject code? especially for larger flange, e.g. above 72" since they are non-standard flanges. thanks.

I have received a calculation for the flange, however, the bolt numbers and size given in the calculation do not match the numbers of the valves which will be connected with the flange.

Feng

 

[TGS4]

There are minimum bolt-spacing requirements. Also, there are total bolt area requirements from Appendix 2. There is no "right" answer, but a set of answers depending on these parameters. Of course, if you are mating to something's that already built, for obvious reasons you should match that...

 

[xufeng]

thanks.

nothing is built yet.

the problem is: we received calculation for flanges (i.e. vounter flange of valves) of station piping, we received also valve drawings (draft version). They do not match with each other.

 

[prex]

So seems the first thing you have to do is to require that calcs and drawings match?

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[xufeng]

yes I did.

I would like just to know how are the bolts numbers defined as per the code.

As per Client Contract, teh non-standard flanges shall be designed per ASME code.

we have more than 50 subcontractors for flanged equipment. We have also general contractor who is doing calculation for flanges of station piping i.e. counter flanges to the equipment. It has to ensured that the calculation to be prepared by piping designer and equipment supplier is same.

I have also checked many other flange calculation made by piping designer and valve supplier for other projects. The flanges match together, although the calculation was made by different company.

I am not familiar with appendix 2. For this reason I asked the question.

 

[dlmeteng]

As TGS4 stated, there in no one right answer. App 2 requires a minimum bolting area which is a product of the number of bolts and the root cross sectional area of one bolt. As one can see, if the bolt size is increased, the number of bolts required could decrease. This works in the opposite direction as well.

That being said, App 2 does list a maximum bolt spacing to ensure gasket seating. The largest center to center distance allowed is given by (2*bolt size) + flange thickness. The minimum spacing is not a code requirement but a design issue. Enough room must be left between the bolts to allow wrench clearance when installing or removing bolts.

 

[marty007]

The code does not tell the designer how many or what size bolts are required for any flange size. It provides a series of formulas that depend on vessel pressure, gasket material, geometry. Two different designers can easily produce two different flange designs that meet the code rules.

The way I normally think about the results of bolt diameter selection with ASME VIII-1 App.2 is as follows:

Smaller bolt size leads to the following:
[ul]
[li]More bolts (higher cost of machining and assembly)[/li]
[li]Smaller bolt circle diameter[/li]
[li]Smaller outer diameter (less material)[/li]
[li]Thinner flange (less material)[/li]
[/ul]

Which flange design will be most economical depends on how the shop operates and the materials of construction. If the raw material is inexepensive (carbon steel), but labor and machining costs are expensive, then it may make sense to use larger diameter bolts, which could reduce machining and drilling costs. However if you're using a high-alloy steel, material costs may be more important than labor costs, making a small-bolt design more economical.

Aside from this, there are other factors to consider such as bolt spacing, minimum bolt size (very strong assembly crews could shear a 1/2" bolt, but would have a hard time shearing a 1" bolt), etc.

Cheers,
Marty

 

[racookpe1978]

BUT ABOVE ALL!!!!!!!!

Thou shalt match the number and sizes of bolt holes on side of the gasket with the number and size of bolt holes on the other side of the gasket!

 

[SnTMan]

Is the valve a custom design as well, or is it perhaps designed to a recognized standard?

Either way, mating flanges will have to be the same bolt pattern etc, as already noted.

Regards

 

[xufeng]

Thank you all.

the valves are designed based on valve standards e.g, API 6D as guideline, but the flanges of the valves have to be designed as per ASME code since the valves are very large , up to 96".

I know that the flanges have to match each other.

As I checked the issue for many previous projects, I was surprised since the flange parameters calculated as per Appendix 2 by various sub contractor(station piping designer, valve suppliers etc) are exactly same.

Only for the current project there are inconsistencies between the calculations made by the subcontractors.

Of course, as Client, I can always request the general contractor to check the issue. I would like just to make clear if any other rules may be applicable for determination of the flange parameters.

I can take an example:
as input data, I can give 48 bolts, with 2.5 inch diamter for a 72" flange. I can ofcourse also give 49 bolts for the flange. Both the flanges are satisfying the requirements in App.2. However, we choose always 48" bolts but never 49 bolts. Why?

I hope you can understand what I mean.

 

[prex]

No.of bolts will always be multiple of 4, and bolt holes will straddle main equipment axes (horizontal and vertical): this is standard practice, not code rules.
For large flanges it is normally more economical to provide many bolts with smaller diameter, as the outer diameter of flange gets smaller and the flange thinner.
However once again this is not ruled by codes, as a client you should provide standard specifications determining how valve and pipe suppliers will find a common basis for flange dimensions.
And TEMA standard has some additional rules on bolt minimum spacings that you, as a client, could require your suppliers to adopt.

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[saplanti]

If you cannot find them anywhere else check AWWA flange dimensions and number of bolts for guidance.

 

[davefitz]

As per the original post, you are trying to mate the pipe to a supplied valve's flange connection. It would seem to be obvious that you must to match the bolt pattern to that of the valve, as racookpe1978 indicated. Gasket or seal ring type also needs to match.

There are also commercial computer programs to design flanges per ASME sect VIII div 1 app 2, such as K-flange by Bill Koves. Some of the other pipe design programs have optional subroutines for flange design.

The older standard flanges were orignally designed by-eye around 1927 and their pressure ratings were originally based on proof testing and not by calculation- if you input their geometry into the asme sect VIII div app 2 calculations you may find that many are not stricly suitable for their historic P-T ratings, but that suggests the newer sect VIII calcs are overly conservative as much as it suggests that the 1927 style flanges are not optimal .

The newer "compact flanges" with a larger number of smaller bolts are much lighter than the 1927 style and would be expected to have less thermal stress near the weld line than the older designs.

"Whom the gods would destroy, they first make mad "