Target bolt stress for a double gasket flanged joint - ASME PCC1 1

[VFK]

What correction should be applied to the "fraction of gasket load remaining after relaxation" factor when performing target bolt stress calculations per ASME PCC1 App O Combined Component method for a flanged connection that has a sandwiched plate with one gasket on both sides? For example a joint with an orifice plate, spade, spec-blind, or a tubesheet extended for bolting. My interest lies in the latter - its a BEU heater design with kammprofile gasket both sides. I initially used the default 0.7 value as suggested by PCC1, however, I've had feedback from a consultant this is an underestimate because the second gasket will also experience gasket relaxation. So should the PCC1 "fraction of gasket load remaining after relaxation" factor be equal to 1.0 less 0.3*2? Or is the relaxation factor a proportional relationship, such as 1/ϕgtotal = 1/ϕg1 + 1/ϕg2? I'd like to be an "informed buyer" rather than taking the consultants feedback as gospel.

 

[Trestala]

API 660 Sec. 7.8.5. still recommends 0.70 gasket load remaining after relaxation for girth flanges. I would assume that stationary tubesheets was considered as well. But better to contact a gasket supplier such as Flexitallic or Lamons if they can provide some opinion.

 

[BJI]

I would expect the relaxation to increase by some degree when the number of gaskets are increased (most likely below 0.7). Regarding the gasket manufacturers, it depends on whether they have performed this type of advanced testing, worth asking though. There are also independent publications which cover this type of testing, one example is below.

https://www.advseal.com/wp-content/themes/advanced-sealing/pdfs/RAST-Paper-Brown.pdf

The majority of gasket testing that is performed is conducted at room temperature, therefore, doesn't typically address relaxation.

 

[XL83NL]

Could this paper be of help?

https://asmedigitalcollection.asme.org/PVP/proceedings-abstract/PVP2009/43666/933/343090

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