O-ring E515-80 compatibility to N2H4 1

[ohelbig]

Hi,

I'm looking for any kind of evidence, that o-rings made from Parker EPDM compound E515-80 (formerly known as EPR 515-80) can be used as sealing barriers in a space propulsion valve. The operating media is Hydrazine (N2H4).

Eckart Schmidt says in his Hydrazine bible, that it is "one of the most widely used O-ring material" (page 705). I found evidence that both NASA (through JPL) and ESA (ESRO at the time) have considered and maybe even used this very compound in similar applications. But in all cases a definitive conclusion as to if it is ok was never given. One time there were not enough samples to be tested, the other it was just a side test and metallic materials were more important to the authors.

It is not adapted for bladders to be sure, because of the high initial gas generation, but the surface in contact in my application is very small. My customer is actually more worried that his propellant gets degraded by contamination.

A few years ago, in this very forum (

http://www.eng-tips.com/viewthread.cfm?qid=105409&page=10),

btrueblood stated "good old Parker compund E515-80 was bulletproof as a hydrazine seal". If you are reading this, dear btrueblood, please help.

Thanks in advance!

PS: all spelling mistakes should be imputed to my German accent!

 

[sdra2]

Trelleborg chemical compatibility chart says EPDM - Hydrazine - Very Good Suitability. Phone them and see what applications experience they have!

 

[btrueblood]

Eckhardt was very good at citing references for his book - does he cite any for EPDM? He may have published a paper or two on work he did on the subject, though it may or may not specifically refer to EPDM in the paper title. Talk to the folks at Aerojet General, Rocket Research Company (

http://www.rocket.com).

E515-80 was the Parker material of choice for them for static sealing of hydrazines. Eckhardt worked there for a number of years, and had a whole raft of long-term material compatibility tests running, and I'm certain that he generated data for that compound, probably several others as well - but couldn't tell you if the data is published, nor where exactly. I can tell you that the RRC 0.2-lbf thrusters used on the Voyager spacecraft (now at what, 20 years flight time?) used those O-rings.

Initial reaction rates will be the same for virtually any elastomer you pick, and are more due to the surface condition of the rubber, and trace contaminants from the molding process (mold release compounds, e.g.). For some of the more critical tests (long term qualification life tests), I do recall there was a procedure to "passivate" components in hydrazine, i.e. soak them for some period of time to let the gas production rate decline. Dunno if it was ever done on production hardware or not - ask the arcjet people at the Redmond office.

I don't have a current copy of the handbook, but think you might be able to find more references to that compound in there somewhere.

AFE-411 (AFE = Air Force Elastomer) was the compound used on propellant valve seats. I think because it has a slight "creep" compliance that helps the dynamic seal re-form itself to the metal valve seat. It too should have a raft of data developed by Eckhardt from his long term compatibility tests.

 

[flexibox]

Refer to the Parker Handbook per attached. E540-80 compound is recommended.

 

[btrueblood]

That's their newer compound. Basically ANY epdm elastomer will work.

 

[ohelbig]

Thanks all for the swift answers!

@flexibox:

Yes the Parker Handbook recommends E540-80, but as btrueblood pointed out its a newer compound and I would like to stick to our flight heritage. I actually phoned the Parker guys in Lexington and they said both are suitable for Hydrazine, "not much difference between them". Unfortunatly when I asked them what their justification was, the only answer they could give me was: "the chemist said so"... My customer wants a bit more proof than that.

@btrueblood:

Eckart's book is referencing two papers right beside the phrase I was citing. The NASA one, I got, but as it is centered on propellant tanks, it's not fully appplicable to my case. The ESRO (ESA) document I did not find. Don't tell anybody, but I made an inquiry at the ESA library through my technical officer, and it seems they lost that particular paper. It had been written by W. Berry in 1974 (ESRO-CR(P)-676). The other ESRO paper I was mentioning in my initial message, was also by Berry (ESRO-CR-34), but its main concern was propelant tanks again. And you just can't make the same conclusion when considering possible bladder materials and possible o-ring sealing materials.

Nevertheless. I will follow your advice and get in touch again with the folks in Redmond. Now knowing that Eckart did some long term tests when he was at Aerojet, will certainly help to find the right documents.

The "passivation" of o-rings, that you are mentioning, is called for in the NASA compatibility test, but I don't think that you would apply it to any flight hardware, as you would have the risk of technicians mounting the valve getting in contact with rest of the propellant. And if you clean them after an immersion you always have the risk of damaging them.

The AFE-411 is the material of choice for bladders and if I understood correctly the difference to standard EPDM is that it contains no carbon black fillers. I have no idea if anyone sells o-rings in standard sizes made of AFE-411. Anyway, it's under ITAR regulations and therefore hard to get, even if your just living in good ol' Germany.

As said before, thanks a lot for sharing your very in-deep knowledge in this area of expertise. It's a pleasure reading good news when coming into office in the morning.

Cheers, Olivier

 

[monkeydog]

Olivier,

You are correct regading ITAR restrictions and regulations, with the passing of information. Sometimes the best way to get the info you want is to run your own test.

 

[btrueblood]

The NASA report offers no data on o-rings?

Hmm. The RRC data may be considered proprietary to themselves. However, as I said, you might be able to get them to say they use compound E515-80 on flight hardware, and possibly even to say it's on spacecraft x, y, z.