Radiation Effect on Gasket Materials
Radiation Effect on Gasket Materials
(OP)
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: Is there a list of acceptable materials for LL radiation? & thread466-10343: Radiation exposure of materials 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
Question is whether this dosage will degrade the gasket materials. I found and read the two threads thread466-18635: Is there a list of acceptable materials for LL radiation? & thread466-10343: Radiation exposure of materials 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





RE: Radiation Effect on Gasket Materials
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:
In the other thread, Bob167 noted:
(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
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RE: Radiation Effect on Gasket Materials
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.
RE: Radiation Effect on Gasket Materials
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
RE: Radiation Effect on Gasket Materials
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: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.