Explosive Decompression concerns with Flexible Graphite 1

[ginsoakedboy]

Can anyone advise on the susceptibility of flexible graphite (trade names "Grafoil", "Papyex" etc.) to explosive decompression (ED) or rapid gas decompression (RGD) in a multi-phase hydrocarbon production environment?

The application I am considering does not involve sealing with flexible graphite, rather, the flexible graphite is only being used as a compliant spacer between 2 parts. Thank you in advance.

 

[dsheets05]

What is the temp of your application? Can you use PEEK? or PTFE. I have successfully used flexible graphite as backup rings or fire safe seals behind primary seals which experienced ED, however I did not examine the grafoil rings thoroughly. However, no obvious ED damage occurred in any of these applications which you might typical see on a non EDR O-Ring.

 

[ginsoakedboy]

dsheet05, thank you for the response. The temperature is 450°F.

Can flexible graphite "collapse" from hydrostatic pressure? In other words, is there a possibility that flexible graphite exhibits a "shrinkage" in volume when exposed to high ambient pressure (from, say 15 to 30 ksi)?

This does happen in case of "closed cell" materials like Styrofoam. Technicians in my company often throw some Styrofoam cups in equipment being hydrotested to "shrink" them.

"The engineer's first problem in any design situation is to discover what the problem really is."

"A good scientist is a person with original ideas. A good engineer is a person who makes a design that works with as few original ideas as possible."

 

[13392017]

Guys,
Please give me a shed of light. What is the Explosive Decompression ?

Regards,
RK

 

[PVPguy]

The full name for flexible graphite used in gaskets, packing and the like is "Exfoliated Flexible Graphite". In other words they chemically expand the graphite structure (add voids) in order to get a product with some "squish". So in answer to your question, yes it does compress under hydrostatic pressure. The amount of compression would depend on the state of the graphite when the pressure is applied (initial density and amount of compression during assembly sets how many voids still remain). However there are many grades and densities of the product available, so you might find one that will work. You might try the graphite manufacturers in the US (Graftec and SGL Carbon), they have excellent technical departments and lots of experience with different applications.

 

[valvit]

Explosive Decompression, or ED, is a phenomenon that occurs when a system under high pressure experiences a rapid depressurization. Elastomeric seals in high-pressure vessels used to seal pressurized pipelines tend to become saturated with high-pressure gases. If the pressure inside the vessel is suddenly released, then the gases within the elastomer may expand violently, causing blistering or explosion of the seal.

Graphite seals are not susceptible to ED because the diffusion rate of the gas into, and back out of the graphite is fast enough that upon rapid pressure drop, the gas exits the graphite before it has time to expand.

Thermoplastics (such as PTFE, RPTFE, Nylon and PEEK) are not susceptible to ED because the gas doesn't permeate into the material.

 

[grockj]

valvit pretty much hit the nail on the head

one addition however - I've used many thermoplastics & elastomers in hydrogen gas sealing applications, and even the thermoplasic/elastomeric seals become succeptible to explosive decompression due to the nature of the tiny molecules (or the ioinc constituents especailly) to ingress the seal. As with most things, it comes down to application (media/pressure/tempeature/decomp. rate vs diff. rate)

So, 450°F, max 30ksig, what media?