ASME Sec.VIII Div 1 App.2 Gasket Design 1

[ENG2194]

Can someone help me understand the following points regarding gasket/bolt design according to ASME Sec.VIII Div.1 App.2? Im dealing with a gasket manufacture that claims to follow this portion of the code when sizing gaskets/bolts but they seem to have some extra design criteria that I am trying to understand.

I just recently discover that for the Wm2 case the "effective gasket area" (3.14*b*G) is much different than the actual gasket area (PI/4*(Do^2-Di^2)). The gasket manufacturer seems to be using the actual area of the gasket to determine seating stress which leaves my bolts undersized. What justifies the codes use of "effective gasket area" over actual gasket area, and what does the actual piping industry recommend?

I also need a little help understanding the reality of a bolt tightening procedure. If Wm2 is higher than Wm1 and my ASME allowable stresses at ambient are much different than operating (Sa=23300 psi & Sb=2300 psi), would I tighten my bolts enough to seat the gasket at ambient then loosen them loosen them to meet Wm1 before operation as to not exceed Sb at operating.

I also see references everywhere to tighten the bolts to the yield stress in order to properly stretch them. Im not sure how to correlate this to an ASME project where i believe i should only take the bolt to the allowable stress.

 

[SnTMan]

ENG2194, Apx 2 contains mandatory rules for flange design. They are minimum requirements and are useful for design only of the flange or flanged joint. Assembly and service of the flange may be addressed by other provisions such as Non-Mandatory Apx S or Post-Construction Codes as a ASME PCC-1.

The gasket properties contained in Apx 2 are non-mandatory. To assure a reliable seal gasket manufacturers often recommend applied gasket stresses that are higher than Apx 2 design values, and as you note are based on gross gasket area. They are achieved by assembly bolt stress higher than the allowables used in Apx 2.

The usual process is to design the flange per Apx 2, check the applied gasket stress using bolt stress of 40%, 60%, 80% of yield or some other rational value. If the applied gasket stress meets the manufacturers recommendations you are good to go, if not, add bolting and repeat. To be clear this is simply the P/A assembly stress on the gross gasket area and with no pressure effects applied.

would I tighten my bolts enough to seat the gasket at ambient then loosen them loosen them

NO! Either case Wm1 or case Wm2 will govern the required bolt area. They are not to be mixed.

Suggest you study Apx S, PCC-1 and search the site for this subject, it is discussed endlessly.

Regards,

Mike


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

 

[Christine74]

The reason the Effective Gasket Area doesn't match the Actual Gasket Area is because the code is attempting to account for the effects of flange rotation. See page 26 for a description of Flange Rotation here:

https://www.mp-sealing.com/wp-content/uploads/2015/04/CORR-A-SEAL-Handbook.pdf

-Christine

 

[ENG2194]

I assume that all references to bolt yield throughout PCC-1 means the yield at the operating temperature. ie I should get the bolt yield value from table Sec.II Pt.D Table Y-1 at the operating temp. Correct?

 

[XL83NL]

I think it refers to ambient. It’s in PCC-1, you should be able to find it (Crtl +F on ‘yield)’

Huub
- You never get what you expect, you only get what you inspect.

 

[SnTMan]

As the subject of PCC-1 is Assembly, it is almost certainly at ambient.

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