flange gasket for pressure vessel

[offonoff]

hello:

I am designing a pressure vessel and have questions about how to seal the lid, which will be opened and closed frequently.

The vessel will be containing supercritical carbon dioxide and whatever organic substance may be dissolved in it (oils, ethanol) at a pressure of 1500 PSI and a temperature not exceeding 100C (It will be in a water temperature bath, so even under failure the vessel will not be over heated).

Currently, i expect to use a 6" 900# A106 carbon steel flange bolted to a a106 carbon steel lid with a gasket in between. Is this a poor strategy considering the lid is being removed frequently?

If this strategy is alright, then any suggestions on gasket materials?

much thanks

 

[unclesyd]

How many times is frequently?

Part of our process requires that we make and break Class 2500 flanges on the average of every two weeks. There are very few problems. We use a standard spiral wound gasket with an inner ring.

There are several approaches to your problem.

 

[offonoff]

Its a batch process and so the lid needs to be opened every time a new batch is started. So, it will be opened daily. changing the gasket every time is not acceptable. every dozen times (once a week) is not preferable.

you break the actual flange (warping it)? Or you just open it and break the seal?

do you reuse the same gasket or do you replace it every two weeks?

 

[vesselfab]

Use a quick opening closure.

with o-ring seal

 

[vesselfab]

meant to add GD closures make a very nice one

 

[unclesyd]

If you use a standard flange and gasket the gasket is a one time affair. A standard gasket is normally deformed during the tightening process.

Another approach would be to design an Oring type closure where you can use a relative inexpensive Oring for several
times when you make and break the flange.

There are other type closures that use metal to metal to seal that requires special flanges that use a breach lock or
screw threads to seal.

I would give someone like Taper-Lok, for bolted connections or Helicoflex, for quick connects, a call and get their
recommendations.

http://www.taper-lok.com/index.htm

http://www.taper-lok.com/sealintegrity.htm

http://www.helicoflex.com/

 

[unclesyd]

I think vesselfab hit the nail on the head. I didn't realize that they made this type closure in a 6" size.

A note of caution is the Oring selection has to be predicated on it reaction to your process fluid. As you probably know these super critical fluids do strange things to elastomers.

 

[offonoff]

Thank you both for your suggestions (what an excellent forum this is).

I've sent inquiries to companies you recommended. The GD closures product looks excellent.

Ideally, we'd like to avoid proprietary solutions, so I'm talking to some machinists about the o-ring option. those are some tight tolerances but i assume within the capacity of a good machinist.

Those using scCO2 who divulge their gasket material on the internet seem to be using teflon o-rings. From marcorubber's website though looks like Viton is a more compatible option in the same price range as teflon. There will likely need to be some testing on our part before the best option is realized.

 

[HDS]

Be very careful the the flange can not be opened with ANY pressure inside. 4 psi creates 100 pounds of force to push that flange into your face.

Self energizing seals would be the best way to go. They use the pressure in the system to improve the seal.

 

[offonoff]

thanks for the warning. there will be pressure guages at the inlet and outet and the contraption wont be opened until atmospheric equilibrium is reached. promise.

also, for the followability of this thread, please note that it has migrated to thread404-235539

 

[vesselfab]

code requires, on quick opening closures, a safety mechanism that will not allow the closure to be opened if not vented first.

GD offers this

gauges won't do for code acceptance

 

[U076762]

Greetings,
I have made extensive use of PFA/Viton and PFA/Silicone encapsulated o-rings in Tube-Turns quick opening covers and many static o-ring seal applications in various chemical services. The cost is really inexpensive when you order from

http://www.creavey.com

who makes them to order.

 

[racookpe1978]

Wait a minute. You've got to think of your entire operating cost here.

You're (very correctly) worried about the first cost of a specialty product (a quick disconnect/quick opening proprietary nozzle/handhole 6" diameter). You've rejected buying a new 6" flex gaskets each time (every day) for the reload batch process because flex gaskets are too expensive.

Have you considered the hundreds of man-hours you are going to need getting up to the nozzle on the tank, unbolting it - 12 bolts 1" dia bolts take a while to unbolt, remove, store the washers and nuts (so they're not lost), protect the threads, and re-install. (All down on a platform or scaffolding or in the field.) If you don't do each step, the cover WILL leak, you WILL have to regularly shut down production and "fix the cover again."

Simply removing the flange isn't trivial: you'll need a hoist or jib crane to get it moved: a 6" 600 lb flange is 14" dia and 1-7/8 thick. OSHA (and common sense) prohibits that from being hand-lifted by one person. Hand-lifting will also damage the mating surface (leaks and repair time) and damamge the studs/bolts/threads/o-ring surface.

Now, repeat this 1/2 hour process (remove and re-install and re-torque 12 1" bolts - it might be closer to 1 hour in total) every day for a year. Without damaging the studs, threads, bolts, nuts, and flange and mating surfaces.

No. You do NOT want a conventional flange in this case. You can't afford a conventional flange in this case.