Correct Gasket material for 96% Sulphuric acid 4

[eski1]

Hello

We have recently had an issue with a supplier who supplied us Viton FKM gaskets to go in an Ambient 96% Sulphuric Acid Line .
After about 12 days the gaskets have started to go Hard & disintegrate causing the pumps to block up .

We have since bought some other gaskets from another supplier made from FKM sheet Viton which seem to be fine, so the thinking is the first lot of gaskets supplied were of a lower quality maybe .
So my question is , are there known to be some grades/types of Viton Rubber that are not suitable for 96% Sulphuric Acid .
The customer won't let us use PTFE as its deemed as a 1 use gasket because it compresses , so we have to look elsewhere & Viton was a suggested option until this happened .

Can anyone also confirm that different types of Viton should smell of different things to distinguish them i.e. Viton A = Cinnamon spice .

Any help with this problem would be appreciated .
Chris

 

[btrueblood]

"are there known to be some grades/types of Viton Rubber that are not suitable for 96% Sulphuric Acid ."

Yes. Visit the DuPont website, they have at least 3 or 4 types of Viton(R) rubber with varying stability in acids, bases, fuels, etc. Furthermore "FKM" is not "Viton"; the latter is a trademark of the DuPont corporation and they very carefully maintain the brand (for example, molders must be certified by DuPont before being allowed to use the Viton brand name). FKM is a generic term, and yes the resistance of FKM rubbers can vary dramatically, even more than they do in the Viton brand line.

"Can anyone also confirm that different types of Viton should smell of different things to distinguish them i.e. Viton A = Cinnamon spice ."

No, the smell/color of your gasket does not have much to do with its ability to resist chemicals. Some mold release chemicals and/or curing agents have different odors, as do some types of plasticizer oils. Colors are whatever you want (within certain limits), I've seen FKM seals in brown, red, black, and a light yellow.

 

[ash9144]

"The customer won't let us use PTFE as its deemed as a 1 use gasket"

Any gasket that is under any pressure, even head pressure, should be considered single use especially in something as dangerous as 96 sulfuric. This is a foolish practice by some to save a few cents on gaskets here and there. This "savings" will be chewed up many times over as soon as one of those reused gaskets fails and burns someone. I've seen this foolish game many times and it always fails. During plant outages I walk around with a knife and cut old gaskets in half then throw them away in separate bins.

 

[johnnymat]

96% sulphuric acid is very aggressive as you have discovered. As chemicals become more aggressive, there tends to be a thought that moving to Viton (FKM) is the answer. This is not the case, as the previuos contributor has stated there are varying grades of Viton(FKM) varying in levels of Fluorine ( the unreactive component) and structure of the polymer backbone, in some cases moving to FKM of the wrong sort is a backward step.

EPDM are pretty good in acid conditions but at 96% I think they would still be unsuitable.

other alternatives are FFKM which have higher levels of the inert Fluorine are a good choice, they are very expensive though

I have some data that shows a vol swell of 3% in 95% H2SO4 after 180 days ( very good !) Aflas (TFEP) is also not bad, Neither material is very elastic if the temp drops below 0 deg C. other than that these are the best grades for this application in terms of chemical resistance. I would also concur with the other contribuor that re- use of a gasket in these conditions is a bad idea

Johhnymat