Radiation Effect on Gasket Materials 1

[SnTMan]

OK, I'm defintely over my head here. Customer spec for a small shell & tube HX specifies radiation level of "100 rad/hr, principally gamma radiation with a 40 year cumulative dosage of 3.5 x 10^7 rads." I cannot even say whether this is a little radiation or a lot.

Question is whether this dosage will degrade the gasket materials. I found and read the two threads thread466-18635 & thread466-10343 before posting without reaching any conclusions.

The gasket materials in question are a couple of sheet gasket materials, Garlock 9800-HTC (carbon fiber, SBR binder) and JM Clipper NA-60 (aramid fiber, NBR binder).

While we are following this up with the manufacturers as well, I wanted to see if I could get any educated opinions [or even wild guesses] from this forum, thanks in advance.

Regards,

Mike

 

[vpl]

I cannot even say whether this is a little radiation or a lot.

100 rads/hour with a lifetime dose of 3.5E7 rads is a fairly hefty dose rate/ total dose and a lot of gasket materials will not stand up to it. Components exposed to this dose rate and total dose would need to be environmentally qualified as required by 10 CFR 50.49.

As TStead noted in thread 466-10343:

Generally speaking, neutrons knock atoms out of their interstitial sites causing defects, shifting the S-T curve to the left thus decreasing the ductile to brittle transition temperature and making the material more brittle.

In the other thread, Bob167 noted:

Recommended Materials (with 'good' stability at ambient temperatures in air with irradiation levels of 100,000 Grays):

Polyurethane, SBR Butadiene styrene, Ethylene propylene, copolymer EPDM, Polychloroprene, Polystyrene, Polyethylene, Hypalon, ABS, PVA, Polyamide, Nylon, Polycarbonate, Polyester (mineral or glass filled), Mylar (Melinex),
Epoxy and Phenolic Adhesives, Mineral Oils (aromatics are more resistant than aliphatics)

(Note: 10,0000 Grays is equal to 1 E7 Rads)

It's been a long while since I've looked at gasket materials, so I don't want to say whether one manufacturer is better than another. Follow the recommendation of BigAl in thread 466-18635 and make sure the manufacturers have a nuclear grade testing program.

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[racookpe1978]

Congratulate the owner (specification writers) for knowing that they need to require an exposure qualification.

VPL's comments are a good starting point - it's been too long since I've spec'ed material against radiation to agree (or disagree!) with any of them.

 

[SnTMan]

vpl, racookpe1978, thank you for your replies.

I have heard back from the two manufacturers now and can say that Garlock has test reports showing no significant effect up to 10^7 rad, as measured by the usual gasket material tests. Garlock apparently has data for a lot of their materials.

Cilpper, well, not so lucky, they have no test data.

As an aside, the spec requirement is for a 40 yr exposure. Surely nobody expects a 40 yr service life from a sheet gasket. At least I hope not.

Regards,

Mike

 

[vpl]

40 years is the standard period for which an operating license is issued. This can now be extended for additional 20 year periods.

While I doubt that gaskets would be expected to last 40 years, some of them may need to last a long time if they're on a component in a high radiation field that isn't accessed frequently. How long is long -- obviously "that dependends," but I wouldn't be surprised by a minimum 10 year expected life.

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.