Use of Viton (FKM/FPM) with hot water or steam service

[lambda]

Viton is often used as elastomeric seat in butterfly valves. Viton is know to be restistant to 'difficult' chemical media.

However, in many chemical resistance lists the use of Viton is not recommended for hot water applications or steam service.

What is the specific danger of hot water ? Of steam to Viton ? Does it restart the curing process ? Does it attack the cross linked polymers ?

What is the fysical result ? Does it increase hardness ? Does the viton become more brittle ?

 

[Demon3]

I recommend you contact the Corrosion Institute in Stockholm Sweden. They specialise in questions like that. Or ask the manufacturer of Viton.

 

[btrueblood]

The manufacturer of the particular seal you are intending to purchase is also who to ask, and to find out if they have a clue: ask them "what is hydrolysis?", and also ask if they manufacture seals using Dupont trademark Viton rubber.

Viton is a trademark of Dupont, and they claim to have formulations that can resist attack by hot water and steam. I have no direct experience with these. I do have experience with "generic" fluorocarbon seals, and they do deteriorate due to hydrolysis attack in hot water and/or steam. Spoke at length with a gentleman from Greene/Tweed about the subject. The hot water has a relatively high concentration of OH- radicals, which tend to attack crosslinks both between and along the polymer chain. In general, a peroxide or platinum(?) cured Viton will be more hydrolysis resistant, and Dupont has some newer formulations for side chain polymers that also help.

 

[berti]

Hi lambda and all,

most is said, let me make two more remarks:

- "Usual" (cheaper) FKM (Viton is brand name of one of the 4 big producers) is cured by bisphenols and has calcium hydroxide and magnesium oxide as acid acceptors. This type of polymer is affected (typically softening)by hot water and steam (not very easy, it takes high temperatures and somewhat longer times !) You can improve water/steam resistance of bisphenolic type by exchanging the mag oxide by lead oxide ( as far as you are not working for European car industry, they banned any lead in any rubber !)

- There are also peroxide cured FKM available, which are much more resisting against steam and hot water.

Hope to help

Berti

"Chemistry: what the chemist does after hours and on weekends." ;-)