Raised Face Diameter Basis - Ratio or Rule of Thumb

[takiyasamsama]

I tried looking into B16.5 and ASME VIII Div.1 Appendix 2 and there are no mentioned what are the basis to determine the raised face diameter.

Is there any general rule of thumb to determine the basis of the raised face diameter?

The only close thing I found on ASME VIII Div.1 Appendix 2 is gasket contact width but that's too general.

Please if anyone have any guideline or rule of thumb, kindly share with us.

Thanks

 

[LittleInch]

ASME B 16.5

Figure 6 - Defines dimension R
Table 4 - Defines R as a number for Raised face ( first column)

6.4 Flange Facings
6.4.1 General. Figure 6 (Figure II-6 of Mandatory
Appendix II) shows dimensional relationships for
various flange types and pipe lap facings to be used
with lap joints. Table 4 (Table II-4 of Mandatory
Appendix II) lists dimensions for facings other than
ring joint

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[racookpe1978]

It is a fixed diameter for each nominal diameter pipe flange.

Don't change it, the pressure across the gaskets for each properly-torqued flange are set based on that dia. Gaskets are standardized as well.

Just use the value for the pressure rating of the std flange category you chose.

 

[takiyasamsama]

I'm trying to find the ratio because I'm designing a custom sizes flanges, some says just use gasket seating width for the diameter of the raised face or just add 2 mm.

Just wondering if there are any practical rule I could use

 

[racookpe1978]

NO.

Use the exact size for EACH different flange. They are in the ASME tables for pipe flanges in each rating level.
Do NOT guess, do NOT alter the sizes, and do NOT alter raised face heights.

 

[LittleInch]

"Custom size flanges"

Why?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[takiyasamsama]

When designing a pressure vessel for heat exchanger you may never know what size you'd ended up with. If the size is within that in B16.5 then we could use the nearest size flanges but when the size exceed 24" (DN 600) then definitely B16.5 is out of the picture.

Yes I may go for 16.47 Series A or B, but in terms of pricing, B16.47 flanges is pretty damn expensive! The only solution is to custom design the flanges and meeting ASME VIII Div.1 Appendix 2 requirement, although in that appendix does not mentioned any raised face diameter, the only thing close to it is gasket seating width.

Buying a blank forged thick plate is much more quicker and cheaper than buying a ready-made big sizes flanges

 

[KernOily]

I don't get that. You have to machine the flange blank, plus you are expending engineering $$ to design a flange. And Now you have to design and make special gaskets. And now the owner is saddled with an oddball gasket for which he has to keep spares in his storeroom. Major hassle for the owner.

There are Code rules in ASME Sec VIII for design of flanges and gaskets. You will need to pick a raised face size and iterate that through the Code gasket design and bolted flange design procedures until you find something that works. Unless you have experience with this, and have an experienced person who can check your work, I wouldn't do it.

Did you ask your question over on the pressure vessel forum?

 

[takiyasamsama]

KernOily, we did a cost evaluation and inclusive of the overhead and all other costings and in where I am now, manufacturing custom flange by ourselves if much more cheaper and as for the gaskets we know it had to be custom gaskets and that's one of our business that end-user/customer had to buy from us the custom gaskets or they could duplicate the gaskets themselves which is up to them.

I've seen ASME Sec VIII Appendix-2 and there had nothing mentioned on the raised face diameter other than Table 2-4 for minimum gasket width and Table 2-5.2 for effective gasket width. I've seek few pressure vessel and piping engineers, they all said that just ensure that Table 2-4 is met and confirm that effective gasket seating width is met, it doesn't matter how you design the raised face diameter.

 

[BJI]

Most heat exchangers have custom flanges and gaskets, nothing unusual about this. Typically the raised face is just inside the bolt holes, about 1/8", this will minimize the flange moment.