Flange system for low temperature gas stream 1

[green1959]

I am involved in a project to design pressure equipment handling either Nitrogen, Hydrogen, Oxygen or a mixture of these - all at very low temperatures. These will all be in gaseous form within the equipment and in the connecting piping. The design temperature of the equipment and piping is -257C/-430F. Design Pressure is 20 barg. The equipment will be made from Stainless Steel.

Regarding the connections to the equipment: Can anyone please suggest an appropriate "flange system" for these conditions. Is there a standard I can refer to? Whats the minimum allowable temp for ASME B15.5 flanges?

Any help pointing me in the right direction would be appreciated

 

[LSThill]

http://www.pip.org

piping class specifications

 

[iainuts]

Use ASME piping codes. They address the low temperature issue. Specifically, look in ASME B31.1 (power) and B31.3 (chemical) depending on your application.

In a nutshell, 300 series stainless steel flanges are good to any low temperature, though I'd suggest checking the code first.

 

[green1959]

Thanks.

But can you provide any advice on the type of sealing face and gasket that can be employed. Is there a flange standard appropriate to these conditions. (Incidentally, 300Lb R/F has been specified but I am hesitant to use a standard raised face flange - I have insufficient evidence to support my feelings other than "it just doesnt seem right").

 

[iainuts]

There's no written standard that specifies what gasket material or style of gasket should be used, nor what style flange should be used. Regarding the flange, we also use conventional raised face flanges. Regarding the gaskets, we typically use Garlock 3200 or Flexitalic gaskets. I'd suggest contacting them directly for recommendations. Of course, as with any gasket, it must be compatible not only with the pressure and temperature involved but with the fluid media as well.

 

[eric2718]

I am currently using ASME B15.5 flanges with oxygen, hydrogen, and nitrogen. At 150 psi, I am using an ASME B15.5 class 150# flange with a pure PTFE gasket (95665K44 by McMasterCarr). At 6000 psi I am using an ASME B15.5 class 2500# flange with a 316SS reinforced PTFE gasket (by Chesterton.

 

[scooter911]

For the last 10 or so years I've been replacing teflon and Garlock gaskets with the 304/teflon Flexitallics. I've even had custom ones made for a valve bonnet when it's applicable. Never had a problem with one Flexitallic. The Teflon and Garlock are good but we have had experiences with a few cracking over the 40 years of thermal cycling. I usually order the gasket with the outer ring to help with centering in the flange. Extra cost for whatever system you use is easily justified when you consider the insulation removal and replacement costs, going cheap will haunt you down the road on a permanent system.

 

[green1959]

Dear Scooter911,

Thanks for sharing the benefit of your experience.

Could you please let me know the minumum temperatures at which you have experience of the 304/Teflon Flexitallic gaskets, the pure Teflon gaskets and Garlock gaskets.

Did you go as low as -257C?

Thanks in advance.