Pressure Vessel Hatch

[moerdogg]

I am designing an access hatch on a pressure vessel that needs to be able to withstand 2.5 bar. The issue I am running into is properly sizing the gasket used to seal the hatch. The information I have dug up covers the calculation of the required gasket width and bolt preload, but no information on how to determine the required thickness. Most of the responses I have seen to questions like these involve a "rule of thumb" approach.

The equations that give the gasket stress neglect the gasket thickness, where it seems like the gasket would act as a relatively weak spring and reduce the stress when thickness is increased. Can anyone clarify this concept? If it wasn't obvious, this isn't exactly my area of expertise.

 

[vesselfab]

why not use a prefabricated/designed closure

so much easier and not near the risk involved

 

[gr2vessels]

The gasket thickness is not a code requirement, hence it was left to the manufacturers to define the thickness requirements.
Generically, the gasket require some 15-50% compression of thickness to achieve the sealing requirements, whilst preserving their mechanical strength. However, it depends on the type of gasket, as the metallic ones will not compress any near 15%.
For example, there is a cleaver gasket with a layer of 0.5 mm graphite on both sides of a grooved stainless steel ring, that will compress down to the thickness of the grooved plate ring, by squeezing the graphite into the grooves. This gasket can take huge pressure at elevated temperatures in aggressive environment, without huge bolting lods (m=2, y=17.2).
I would suggest to contact your local gasket supplier and ask him for literature usually provided free by the gasket manufacturer.
Cheers,
gr2vessels

 

[MJCronin]

I agree w-vesselfab...

Pressure Vessel manways/manholes designs are typically developed by the fabricator (or specified by the purchaser) and are standard designs rated by pressure.

I also suggest that you do not use the term "hatch", unless you are on a marine vessel.

So, unless you are a newbie working for a fabrication shop, don't invent your own designs

My opinion only....


-MJC

 

[moerdogg]

Thanks for the replies, everyone! I agree about using a standard flange, unfortunately I am working with a legacy design, so I'm constrained to the existing shape. I'm going to look up some gasket manufacturers and see what they have to say...

It is indeed a marine vessel, so I believe the term was used correctly.