Sealing material for Valve Cryo-Test 1

[NGiLuzzu]

Dear All,
we need to seal two test caps against the buttweld ends of a 12" class 300 cryogenic valve and cannot use our usual Spiral Wound Gaskets: the slot for the gasket is 5.5 mm deep, 8.0 mm wide and inclined respect to the flange flat-face plane of about 40°; the relevant mean diameter is about 315 mm.

Now we are using a 8.5 mm square cross-section graphite braid as a seal, but it leaks at ambient temperature and relatively low pressures. It should be tight up to 30 bar of internal helium pressure and down to -196°C temperature.

What kind of sealing material and cross section would you suggest?

Some websites give Virgin PTFE, for example, as appropriate for low temperatures down to -160°C, others give it as appropriate for cryogenic temperatures down to -196°C or -268°C... what do you think about it? And what about fiber reinforced or filled PTFE?

Thanks to all, 'NGL

 

[19831017]

Cixi Weilite sealing material Co.,Ltd. is specializes in manufacturing sheet gasket material, Non-asbestos jointing sheet and reinforced composite sheet sealing material. And we have won good reputation in domestic and foreign market by excellent employees, superior equipment and first-class technology.
Reinforced composite sheet made of expanded graphite and non-asbestos by Weilite has excellent performance in temperature resisting sealing, tensile strength and sealing equality, which has provided various types of sealing gasket materials and products for domestic manufacturer in industries of automobile, motorcycle, power machine and sealing products.
Our main products: Flexible (expanded) graphite sheet (rolls). Reinforced graphite composite sheet, Reinforced asbestos sheet, Reinforced non-asbestos sheet, asbestos rubber sheet, non-asbestos rubber sheet, Flexible graphite packing ring. Reinforced graphite gasket. Spiral wound gasket, gland packing etc.. The all products are extensively applied in petroleum, chemical industry, electrical power, metallurgy, automobiles, ship building, food, paper, mining, steel and pharmacy etc.
Our product have been sold far to Europe. America and Southeast, Japan, Singapore, Germany, Taiwan etc.

 

[scooter911]

Sounds like you might have a ring joint flange. If so you can buy a coated ring in a soft metalic material to go in the groove. if not I've seen people use a sheet of material jammed into a flange like that to seal. We use a sheet material(green in color) from Garlock in cryo service and it seems to hold up well.

Good Luck

 

[CVD]

I would not recommend Virgin PTFE on cryogenic applications due to problems with creep. Any filled PTFE product would do the job such as Durabla's Durlon 9000 series or Garlock Gylon series. Durabla may also be able to provide you with speacially machined gaskets as you require. Though I agree, it does sound like you might have a ring joint flange and scooter911's advice is good.

In the USA, contact GRI Inc for Durlon gaskets at

http://www.durlon.com

 

[cryopumps]

Use a Teflon energized seal. We use these for cryogenic applications for LNG which is down to -260 F and they will not leak. We test these with the same applications that you do but it is a flange to flange connection and we have gotten as high as 3000 PSI and been succesful. Information on these energized seals can be found at

http://www.pressureseal.com

Look for the TF888 Series seals. These are the ones that you want to use. They do not creep and can be reused. I recommend tochoose these with a jacket material of Eligoy but you can use 17-7 as well.

 

[NGiLuzzu]

Thanks to all for the interesting answers!!


Just for your information, the above mentioned experimental activity was momentary interrupted.

In the meantime, for a Customer in the Areo-Space Motors business (testing facility), we've choosen PTFE energized gasket, simil to the ones suggested by CRYOPUMPS.
The application is on liquid oxygen and/or hydrogen down to -427°F =-254°C at 350 psi = 24.1 bar.
The gaskets' Supplier is "Saint-Gobain Performance Plastics" ( see

http://www.omniseal.com/

).
Metallic materials are Inconel 718, Elgiloy and 17-7 PH.


Regards, 'NGL

 

[Aliani]

Dear ANegri

I would reccomend you to approach a company located in San Nicolò - Piacenza (I forgot the name). They perform cryogenic test on TRI-X Butt Welding Top Entry valves, may be they have solved your problem.

 

[NGiLuzzu]

Dear Aliani,
thanks for the suggestion. (In fact, I was wondering about how Top Entry valves Manufacturer could have solved the problem...).

But, by the way, what do you mean for "TRI-X" valves? (Maybe better to submit this question in the "Valve Engineering Forum": forum408?)

Please take also a look at thread774-127182: it's just an idea... but one never can tell ;-)

Regards, 'NGL