Effective gasket area 1

[marc400317]

Hi Guys, I am currently trying to calculate Wm1 using the effective gasket area on a Slip-on flange raised face. According to AS1210, Wm1= H + Hp with Hp= 2*b*(pi)*G*m*P.
I got different answer Hp= b*(pi)*G*m*P and dunno why here's what I have done:
Hp= P*m*A where A is the total area of gasket based on effective gasket width b hence, the overall effective width of the gasket is 2b. therefore A= (pi/4) * ((G+b)^2-(G-b)^2)
and that will give A=G*b*(pi) and Hp=b*(pi)*G*m*P.

could anyone clarify this please ?

 

[SnTMan]

marc400317, "overall effective width of the gasket is 2b. therefore A= (pi/4) * ((G+b)^2-(G-b)^2)..."

Where did your 2b go?

Regards,

Mike

 

[marc400317]

Sorry Mike, I guess I am still confused: I am trying to calculate the effective area for Hp ; A= (pi/4) * ((G+2b)^2-(G-2b)^2) and that will lead to A=2*b*(pi)*G and Hp=m*A*P will lead to Hp= 2*b*(pi)*G*m*P which is correct however, When calculating Wm2= A*y will lead to Wm2= 2*b*(pi)*G*y which is not right. I guess what I am trying to say is that if the same area A is used to calculate Hp and Wm2 why am I getting a different answer for Wm2 compared to the standard?

 

[saplanti]

marc400317,

As far as I undertand you have confused with the definitions. I have attached a pdf file you may see the definitions and the formula all together.

In the file Pt = P + Pe
where

P = design pressure

Pe = 4 Fe / ( pi G^2 ) + 16 Me / ( pi G^3 ) , the equivalent pressure for external forces.

Hope it helps,

Ibrahim Demir

 

[marc400317]

saplanti, Thanks for this pdf, though it didn't answer my question I guess. Just as a simple answer why Wm2= b*(pi)*G*y ? does anywone know how it's been derived?
Thanks,
Marc

 

[doct9960]

marc400317,

The seating width in the equation Wm2= b*(pi)*G*y was probably reduced (from 2b to b) to account for flange rotation.

Read the article about flange rotation on the links below...

http://www.mech.uwa.edu.au/DANotes/threads/joints/joints.html

http://www.garlock.eu.com/pdfs/Prod...ng-OK/Graphonic Series of Gaskets GMG1-11.pdf

 

[saplanti]

Unfortunately, it is not possible for us to even find the source of information.

In the older days, the standards used to include the source of information as the reference. Nowadays, there is no such a thing. We always try to educate the engineers and ask them not to use the formula blindly. However, we do not give them the background at all.

I wish there are others can join me to convince the standard committees to include the references.

I know that AS1210 is the mixture of British and ASME codes and Australian Standards are not backed up by any test on the pressure equipment at all. When you ask the committee members they always say they do not have the resource even to write or collect information, and ask for your involvement.

The ASME codes are the same for the reference issue.

I recently have tried to find the background of the flange calculation in accordance with ASME code especially I concentrated on the gaskets. There was nothing available and the responds were not encouraging. I found a link of the background of EN 13445 which includes the flange calculation. It may be useful for you but it is written differently, understanding might be a bit difficult without having EN 1591 or/and EN13445.

http://www.eng-tips.com/viewthread.cfm?qid=204661&page=7

Hope it helps


Ibrahim Demir

 

[marc400317]

Thanks Doc, That answered my question