Best seal for low pressure steam

[Speedy]

What is the best seal for low pressure(5Bar) steam applications. Temp is approx 170C max.

We have a Viton (don't know grade) O-ring seal failing on these applications after a relatively short time. The seal is between aluminium and steel. The viton is spec'd ok for 220C.

Ideally I would like to use an 0-ring type again.

Any recomendations on suitable material?

Thanks,
Speedy

 

[Metalguy]

Try Kalrez for this.

 

[ApC2Kp]

Speedy,
The grade of Viton would be critical for the upper end of service temperatures. Viton is supposedly good for higher temperatures / chemical exposures than most elastomers. However, the material compounders are known to blend some polyester or fillers with the Viton. The Viton o-rings for FM / CSA approved applications would probably be best grade for obtaining quality Viton o-ring seals. There was a guy in Marsulex Co. working with liquid SO2, that went through a number of seal vendors before finding the pure Viton o-rings that withstood the chemical attack.
If the o-ring is a static seal, then I would suggest the expanded Teflon rope sealant Goretex GR. The joint would need to compress the rope sealant. If the seal needs to work with rotary or axial movement, the typical seal would be flexible graphite rings, or Teflon V-rings. Both would require some compression to seal the joint.

 

[Cockroach]

Open the wallet, Aflas. Otherwise, Metalguy is correct with the suggestion of Kalrez.

Parker-Hannifin has a new material out, rated to 260C (500F) which is called Hifluor. The word on the street is superior chemical and heat resistance. Go to the website and look for V3819-75, which is durometer 75. The technical bulletin lists this as "Highly Fluroinated Flurocarbon", recommended operating range (-25,260)C or (-13,500)F with short term peak temperatures to 280C (536F)

Good luck, steam is just one of those applications!

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[quark]

Have you tried silicon? Not as good as exotic kalrez but fits into the budget at that temperature.

 

[sealguy]

Speedy,

Viton is not recommended for steam applications. Fluoronated elastomers do not like water or steam! Your best choice for an o-ring rubber compound is EPDM for applications under 300F and then Aflas for applications from 300F to 450F. You can get both in 70 and 90 durometer. Aflas is comparable in price to a good quality Viton.

Let me know if you have any questions or need a place to get the rings.

 

[johnchrc]

No Viton.

I think EPDM alone, w/out back-ups, will work due to low pressure. Next step up would be Chemraz or Kalrez w/out Back-up Rings. They are 100 times more expensive than EPDM.

I can check at work tomorrow and see what works in out low pressure steam autoclaves.

Good Luck.

CCJ