Re: AMMRL: The big OOPS
Charles L. Mayne (mayne@chem.utah.edu)
Fri, 4 Jan 2008 18:18:21 -0700
Hi Jerry,
All of your recommendations about how to handle liquid helium
transfers are excellent. However, I have to take exception to your
suggestion that we should protect the neophytes. Knowledge is power. I
resent anyone who would deny me knowledge for my own good. Your
warnings about safety are appropriate and welcome. They should have
been given upfront. But, now that they are out there, I would
encourage any neophyte who doesn't completely understand this
discussion to post questions.
In the meantime, said neophyte might want to get competent assistance
in filling helium the first few times they do it. Otherwise, a magnet
quench is the likely outcome.
I hope it is clear that we have been discussing the possible
consequences of a serious mistake that everyone should avoid.
Charlie
Charles L. Mayne
University of Utah
Department of Chemistry
315 S 1400 E
Salt Lake City, UT 84112-0850
Room b473 HEB
voice: 801-581-7413
FAX: 801-581-8433
On Jan 3, 2008, at 3:13 PM, Jerry Hirschinger wrote:
> Dear all,
> Please don't even consider using another gas to pressurise the LHe
> supply
> dewar, other than helium gas. Any discussion of alternatives is
> unsafe and
> therefore irrelevant. If you all want to debate the subject, please
> do it
> off the list so neophytes don't get any stupid ideas! Grade 4
> helium gas is
> plenty pure enough for pressurizing supply dewars. The contaminants
> from
> the grade 4 gas will likely never reach the magnet. If they do,
> there is
> such a low level that the contamination from exposure to atmosphere
> during
> fills is several orders of magnitude greater than that from the
> pressurising
> gas.
>
> All LHe dewars have 'slush' in the bottom, regardless of whether
> they are
> magnet dewars or supply dewars. The slush consists of any other
> elements
> that are contaminating the LHe. The slush is not harmful because it
> is at
> LHe temperature. That is not to say the slush has no effect. If it
> builds
> up above the minimum LHe level of the magnet dewar, then it can be a
> problem. The slush also has a higher heat capacity than the LHE, so
> in a
> quench the slush should act in your favor.
>
> The slush in a supply dewar cannot be avoided simply by keeping the
> supply
> tip above the bottom of the dewar, because it is necessary to find the
> bottom of the dewar before lifting the tip. Also, many supply
> dewars have a
> small well in the center of the bottom, which serves to concentrate
> the
> slush right at the Xfer line tip where the turbulance of passing
> liquid
> draws the slush out.
>
> To really remove the slush in the supply dewar before Xferring LHe,
> one
> should insert the Xfer line all the way to the bottom during the
> time needed
> to precool the line. Usually the supply dewar must be vented to avoid
> excessive internal pressure while inserting the warm line. This
> will draw
> the slush out the line and waste it to atmosphere. Once the line is
> cooled
> and LHe flows to the magnet, then raise the tip from the bottom to
> avoid
> further contaminants from the pressurizing gas, which are very
> minimal.
>
> Cheers,
> Jerry Hirschinger, NMR Instrumentation Specialist
> Purdue Interdepartmental NMR Facility
> 560 Oval Dr. West Lafayette, IN 47907-2084
> Office: Wetherill 365A
> Phone / Fax: (765) 494-5288 / 494-0239
> Cellular: (765) 427-3034
>
> () ASCII ribbon campaign - against html mail
> /\ - against Microsoft attachments
>
>
>
>> -----Original Message-----
>> From: Charles L. Mayne [mailto:mayne@chem.utah.edu]
>> Sent: Friday, December 28, 2007 9:14 PM
>> To: Silverman, Bob
>> Cc: Charles Mayne; ammrl@ammrl.org
>> Subject: {Spam?} Re: AMMRL: The big OOPS
>>
>> Hi Bob,
>>
>> Do we really know that these materials are insoluble in
>> liquid helium?
>> I have not seen any data on the subject; maybe some of the
>> group knows the answer.
>>
>> Passing warm argon into the storage dewar would undoubtedly
>> evaporate enough liquid helium to pressurize it for the
>> transfer, but is the argon totally insoluble in the liquid
>> helium. If not, argon could be transferred into the magnet
>> and remain there, being less volatile than the helium. As you
>> say, this probably has no bad consequence unless there is a lot of
>> it.
>>
>> Charlie
>>
>> Charles L. Mayne
>> University of Utah
>> Department of Chemistry
>> 315 S 1400 E
>> Salt Lake City, UT 84112-0850
>>
>> Room b473 HEB
>> voice: 801-581-7413
>> FAX: 801-581-8433
>>
>>
>>
>> On Dec 27, 2007, at 1:21 PM, Silverman, Bob wrote:
>>
>>> Dear Jane and Group,
>>>
>>> In giving these issues some thought, I don't believe that there
>>> should be any harm in using a low grade of helium gas to
>> pressurize a
>>> liquid helium dewer. The typical impurities in helium gas are
>>> nitrogen and hydrocarbons. The tiny amount of either of these that
>>> contacts the surface of the liquid helium will solidify. Assuming
>>> that the helium dewer is not emptied in the fill process (I always
>>> arrange for this never to happen.), and knowing that any
>> contaminants
>>> will freeze out of the liquid, then only ultra pure helium will
>>> transfer into the magnet. I guess it is possible that a "spec" of
>>> frozen material could get swept into the liquid stream but
>> this should
>>> sit on the bottom of the magnet helium can and cause no problem.
>>> Most, if not all, of the miniscule amount of oil residue
>> will go back
>>> to the liquid helium supplier.
>>>
>>> The same could probaly be said about using gases other than
>> helium for
>>> the transfer although I don't feel that this should
>> knowingly be done
>>> since this might produce a significant amount of solids at
>> the bottom
>>> of the delivery dewer. In all instances the liquid helium
>> dewer acts
>>> like a big cold trap!
>>>
>>> Happy New Year to all,
>>> Bob Silverman
>>> UCLA
>>>
>>> -----Original Message-----
>>> From: Jane Strouse [mailto:strousej@chem.ucla.edu]
>>> Sent: Wed 12/26/2007 12:43 PM
>>> To: ammrl@ammrl.org
>>> Cc:
>>> Subject: AMMRL: The big OOPS
>>> Dear AMMRLers,
>>>
>>>
>>>
>>> I indirectly received the message below from someone who was
>>> pretty embarrassed about having used the wrong gas to
>> pressurize the
>>> storage dewar for helium fills. I thought I would relate my
>>> experience with this sort of thing. Quite a number of years ago, I
>>> found that the people working for me had been using
>> nitrogen gas. I
>>> have no idea how long this had been going on or how it
>> happened that
>>> we ended up with
>>> nitrogen rather than helium on the cart we use for fills.
>>> Amazingly, we
>>> seemed to have not observed any ill effects from this. I thought
>>> about it and decided that if you really did your fills
>> correctly, you
>>> could get away with this, because none of the gas should enter the
>>> transfer line, and if the line is sufficiently above the
>> bottom of the
>>> storage dewar, any condensed nitrogen would not be pushed into the
>>> transfer line. At any rate, we did later de-energize a
>> couple of the
>>> solenoids to move them to a new building. There was no problem
>>> whatsoever with putting in the charging rods, so if there was icing
>>> from the nitrogen, it was not substantial. (Of course, it
>> is possible
>>> that the tank had just been put on the cart when I noticed
>> it and was
>>> never used, but I always presumed it had been used.)
>>>
>>>
>>>
>>> This leads me to another question. I once had a mass
>> spec service
>>> person tell us that we should use ultra-high purity helium (UHP,
>>> 99.999%) for the liquid helium transfer into an FT-MS solenoid. I
>>> thought he was crazy, but I supppose it is possible that it
>> would be
>>> better for that particular magnet. Do any of you use UHP
>> helium gas
>>> for transfers? We certainly do not.
>>>
>>>
>>>
>>> Jane Strouse
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> Message received:
>>>
>>>
>> ______________________________________________________________________
>>> __
>>> _______
>>>
>>> Dear Spinners,
>>>
>>>
>>>
>>> First of all, happy holiday season!!!
>>>
>>>
>>>
>>> I have been a passive observer and certainly taking
>> advantages of the
>>> fruitful discussions at AMMRL. Here is a story that I feel
>> I can use
>>> to contribute to the community. I am very much embarrassed
>> in making
>>> such mistake, as you can see I am even hiding my name, but I still
>>> want to post it, so everyone could learn something from it.
>>>
>>>
>>>
>>> I have been filling liquid helium to my 400 MHz magnet by
>> myself and
>>> for the past two years I thought that I have been using
>> helium gas to
>>> pressurize the tank (well, read the label before using it). Just a
>>> few days ago, I found that it had been argon gas all along. Before
>>> using this gas cylinder, there had been no problem doing it
>> and after
>>> switching to the tank, I started experiencing technical
>> problems and I
>>> blamed the liquid helium supplier and moisture in the air.
>> Here were
>>> the problems: (1) the liquid helium inlet (on the magnet
>> side) seemed
>>> to be "ice" blocked, (2) it took from one to two hours to
>> fill it, and
>>> (3)
>>> at the end of the filling process, it was extremely
>> difficult to pull
>>> out the transfer tube (somehow the tube got stuck somewhere in the
>>> system on the magnet side and especially on the liquid helium tank
>>> side
>>> - I even destroyed one of my transfer tubes to pull it out). Of
>>> course the root of the problems is that the argon gas solidified in
>>> the system.
>>> Just last week, I found the mistake and switched to helium gas;
>>> everything goes back to normal now.
>>>
>>>
>>>
>>> So, what can we benefit from such odd experience? Although
>> some might
>>> think that there are other factors to consider, from the
>> experience I
>>> believe that we don't need ultra high purity helium gas at
>> all for the
>>> refilling. A regular grade helium gas will do the job just
>> fine. The
>>> gas I used is almost 100% purity argon and it has been two years.
>>> If it
>>> doesn't hurt the magnet this way (in terms of building up alarming
>>> level of solids in the magnet or clogging the system
>> permanently), why
>>> we need to use ultra high purity helium gas? By the way,
>> the boiling
>>> point of argon is about -186 C, oxygen is about -183, and
>> nitrogen is
>>> about
>>> -195
>>> C.
>>>
>>>
>>>
>>> Anyone cares to shed some more opinions?
>>>
>>>
>>>
>>>> From someone too embarrassed to show his/her name.
>>>
>>>
>>>
>>>
>> ______________________________________________________________________
>>> __
>>> _______
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>> ----------------------------------------------------------------------
>>>
>>> Dr. Jane Strouse
>>>
>>> Director, UCLA Molecular Instrumentation Center
>>>
>>> 1410 Molecular Sciences Building
>>>
>>> Los Angeles, CA 90095-1569
>>>
>>> (310)-825-9841 - voice
>>>
>>> (310)-825-2280 - fax
>>>
>>> strousej@chem.ucla.edu
>>>
>>> http://www.mic.ucla.edu
>>>
>>>
>> ----------------------------------------------------------------------
>>>
>>>
>>>
>>>
>>>
>>>
>>>
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