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ID Overlap between the gasket and the raised face flange

C

cheezypuff

Mechanical
Joined
May 13, 2025
Messages
2
I'm using class 150 1 1/2" pipe raised face flange. It has an ID of 1.37" I was looking at the gasket from MMC. For 1 1/2", the gasket ID is 1 29/32". I understand the gasket OD should be between the raised face OD and bolts, but I don't understand why the gasket ID can't be a little bit closer to the pipe ID. In some ways, I'm tempted to get 1 1/4" gasket because the gasket ID is a little closer. Maybe the difference in ID is not that big of a deal after you compress it? Love to hear your thoughts.
 

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The larger diameter gasket is easier to center on the flange by resting it on the studs.
 
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From the figure it appears that the flange is slip-on type. In that case, there is no certainty that the pipe thickness cross-section will make contact with the gasket, in case the gasket is extended up to ID of pipe; this depends on the connection of the flange with the pipe and pipe-end surface quality.

So it is better to limit the gasket ID to the pipe OD, which is maintained here with 1-1/2 in pipe gasket (1.9 in ID gasket, 1.9 in OD pipe).
 
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Your ID is only because you have schd 160 pipe. That's quite high for a class 150 system.

Gaskets are not going to be supplied in multiple different ID. If you had a sch 160 gasket but a sch 80 pipe then it would stick into the pipe and disrupt flow and have no impact.

Width of the gasket is not really an issue. Centering the gasket is much more important and hence why gaskets are designed to sit on the bolts.
 
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Thanks for all your comments. I didn't think about different schds for the pipe. It make sense that they probably want to make one size gasket to cover different pipe schds., as long as the compression area is sufficient for the pressure rating.
 
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