gland design and oring selection for high pressure and high temp

[Rmechanical]

Hi fellow engineers,

I'm designing a tool that will be in an environment of 15000 - 20000 psi and a temp of 450F. So far I've looked at some examples and done some research about the size and shape of the gland, clearance and materials for the o-rings, but I still have a few questions:

Right now I'm debating whether to use AS568-2XX or AS568-3XX o-rings.

If I use 2xx o-rings, they will be 3 consecutive and if I use 3xx, I'll use only 2 due to space restrictions.

Can anyone tell me the difference between using o-rings with a smaller or larger cross section?

I assume bigger o-rings will be more resistant and will provide a better sealing in extreme environments, but I'm still curious.

Thank you.

 

[israelkk]

Static?, dynamic?, reciprocating?, Rotating? Gas?,Fluid?, Leakage?, Type of application?, Housing materials? Surface coatings?

O-ring catalogs usually do not give information for pressures so high, how did you researched about size and shape of glands?

 

[EdDanzer]

At the pressure and temperature you describe o-rings may be a poor choice. In many cases multiple seals can have a shorter life than a single seal because of pressure trapping between them.

The round ring will become almost square causing wear to the gland and the o-ring when going from 0 to 20,000 psi. Few elastomeric materials will handle 20,000 psi at 450°F. Size is relative and since you did not provide any details about the application no suggestions can be made.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[Rmechanical]

thanks for your replies,

The application will be static and the type of sealing is radial. The material for the housing is steel and its finish is smooth.

The idea is to prevent leakage (it is a logging tool, so no mud/sand/dirt and water must come in).

I,ve seen other logging tools and also found information about gland design; that was for more normal pressures, but the dimensions were very close to those found in other tools.

I'm planning to use backup rings as well.

 

[PeterSleet]

For those pressures, temperatures and fluids (I'm assuming the wells you're logging are as unpleasant as the ones I've worked with) and assuming unidirectional sealing (i.e. you only need to keep pressure out) I'd be looking at pressure enrgised metal seals.

 

[btrueblood]

What Emmet said. Spring-loaded U-cup seals, typically with PTFE coating, is what we use.

The "best" O-ring materials for petroleums don't really take that temperature well, and if any gases are present, you can have trouble with explosive decompression when the tool is pulled back up (gas dissolves into the rubber at pressure, esp. CO2, then comes back in a hurry when the pressure is relieved, rupturing the seal material).

 

[GPRnD]

Question.

Does it have to be an O ring or an elastomer type seal ?

Have you considered spiral wound gaskets ?

The conditions you specified are pretty extreme for any O ring type seal

 

[HydraulicsPE]

Based on your radial application parameters you are going to experience seal failure through wear and by the Joule Effect. The only viable solution you have is with a spring energized PTFE based seal.
With radial spring energized PTFE for rotary you have to select a spring with a very flat spring constant or you will have seal failure rather promptly.
Recommend something like this or equivalent:

http://bit.ly/4qypIB

 

[HydraulicsPE]

Application very unfavorable for O-ring. Many possible failure modes including explosive decompression, compression set, nibbling at extrusion gap.

You are going to require a high filled PTFE Variseal PTFE spring energized seal c/w PEEK back-ups or equivalent. Moveover request to have seal contact surface come complete with point loads so that force is acting on points for contact and not across entire seal footprint.

 

[exverto]

I'd would have to agree. PTFE (filled material not virgin) spring energized seal with a backup ring just as HydraullicsPE is saying. I wouldn't go with a peek backup though unless you are positively certain that you won't be on the high range of the temperature that often.

Scott N.
Ex-Verto Engineering

http://www.ex-verto.com

 

[HydraulicsPE]

There is an online O-ring Calculator here:

http://www.tss.trelleborg.com/com/

http://www/en/homepage.jsp

 

[kevindurette]

Does this tool have to handle these pressures, or are these pressures part of your own design? You might want to consider making a larger tool to generate the same force with less pressure over a larger surface area.

When you give this temperature and pressure, how much safety has already been added to this? I find that stories quickly change when people find out how much it costs to have a wide safety margin. (Recommendations usually have a margin built-in anyway.)