Dear All,
Two days ago I posted some questions here (see below) and first I would
like to thank for all the excellent and helpful answers. Special thanks to
Gareth Morris, Robert D Scott, Rainer Haessner, Mark Davis and William
Padgett for their insight, their full answers are provided below. My
summary is as follows.
1. There seems to be an agreement on the point that magnets do not
significantly "age". Indeed, performance can be kept at its initial level
if the vacuum is kept intact and the magnet is handled correctly (in
particular, no sudden strong mechanical or magnetic impacts). Newer magnets
generally have longer hold times and smaller field drift but these issues
are usually of minor-to-negligible importance/magnitude.
2. To keep the vacuum intact, one may occasionally replace old O-rings and
getter. If one moves an old magnet where these operations are highly
advisable, one just as well can discharge and warm up the magnet and
perform maintenance.
3. There seems to be no complete agreement on the issue of moving the
magnet warm, cold, and cold and charged (sorry for not being sufficiently
specific in my original question). As concerning risks, the safest mode is
probably warm. In that state one, for example, does not have to worry about
"finding the steel" in the surrounding walls. If one chooses to move the
magnet warm, there is a small risk that it cannot be charged up again. The
less the distance and the level of geometric complexity, the less are the
risks with moving the magnet cold and charged which is certainly the
cheapest option (assuming it works).
4. Many of you recommended to let the move be handled by professional
vendors. The main motivation is perhaps the implicit insurance - if
something happens to the magnet they have to replace/fix it.
Sincerely yours
Istvan Furo
>X-Sender: mbdpsgm@nessie.mcc.ac.uk
>Date: Wed, 20 Feb 2002 17:40:51 +0000
>To: Istvan Furo <ifuro@physchem.kth.se>
>From: Gareth Morris <g.a.morris@man.ac.uk>
>Subject: Re: magnet move
>X-Scanner: exiscan *16dajb-0001Eb-00*NHFpIBDY4ts* (Manchester Computing,
> University of Manchester)
>
>
>Dear Dr Furo
>
>These are just personal opinions baed on limited experience, but
>
> >
> >1. What is the approximate lifetime of NMR magnets? What are the most
> >important factors (except keeping the vacuum good and not dropping the
> >magnet during the move!) influencing this lifetime?
> >
>
>Oxford Instruments are probably the best people to ask. The only limits
>of which I am aware are
>(a) vacuum seals: typical advice is to replace every 10-20 years, or
>whenever magnet is warmed up;
>(b) (small) probability of switch damage on quench;
>(c) vacuum deterioration (replace any getter if magnet warmed up);
>(d) mechanical damage: hitting energised magnets with large ferrous metal
>objects can seriously reduce their life expectancies.
>In principle there might be deterioration of materials, e.g magnet
>suspension, but I've never heard of this being a problem.
>
> >2. If there is a lifetime not much longer than 20 years, in which way does
> >the performance of the magnet suffers? Stability, homogeneity, more
> quenches?
> >
>
>Most magnets experience a softening of the vacuum after a period of years,
>but we routinely use a turbomolecular pump when needed, and this restores
>performance. Otherwise I'm not aware of any degradation - I think the main
>reasons for the junking of old magnets are the drive to higher fields and
>the poorer hold times of old cryostats.
>
> >3. Moving a magnet cold is cheaper. On the other hand, one hears that
> >moving a magnet warm is safer. Does this mean (i) safer for the persons
> >moving the magnet or (ii) safer for the magnet as concerning its
> >performance after the move? Can anybody direct us to some written
> >instructions or checklist about moving NMR magnets?
> >
>
>My personal view (and again you should talk to the experts here) is that
>_if_ appropriate precautions are taken there is not much difference in
>safety between a cold and a warm magnet: if it lands on your foot the
>difference is probably imperceptible. The added hazards of a cold magnet
>are (a) to the movers, the risks associated with cryogens (cold liquids,
>oxygen-displacing gases - don't share a lift, as a former colleague once
>did); and (b) to the magnet, slightly increased mass and perhaps slightly
>decreased internal flexibility.
>
>I'm not aware of anyone committing themselves to advice in print. I've
>moved magnets warm, cold and energised. The orthodox view is to run down
>and warm up before moving; if you have more than a short distance to move
>and if the magnet is more than 10 years old and you can afford it, that is
>the way to go. Warm up, replace the vacuum seals and getter, and all being
>well you should have a long term magnetic field. We have moved (medium
>field) magnets short distances at field with no ill-effects, but this is
>not for the faint-hearted. The furthest I have moved a cold magnet is just
>under a kilometre, again without problems, but I have heard stories of much
>longer moves.
>
> >4. The 400 magnet has been performing extremely well in the past. Any
> >experience concerning the behavior of magnets after warming up, securing,
> >re-pumping, and re-charging? Does one usually get back the same performance
> >on such an old magnet?
> >
>
>We've never had any problems, but there is always the chance of damage to
>switches/connections.
>
>Once again, these are just my personal views based on what we have got away
>with in the past, and are not in any sense authoritative.
>
>
>Good luck!
>
>Gareth Morris
>
>
>
>________________________________________________________________________________
>g.a.morris@man.ac.uk
>Prof. G.A. Morris
>Dept. of Chemistry, University of Manchester,
>Oxford Road, Manchester M13 9PL, UK (0) 161 275 4665
>________________________________________________________________________________
To: Istvan Furo (by way of Rudi Nunlist
<rnunlist@purcell.cchem.berkeley.edu>) <ifuro@physchem.kth.se>
Date: Wed, 20 Feb 2002 12:03:14 CST
From: Robert D Scott <scott@iastate.edu>
Istvan,
I believe that the magnets will probably last longer than an
affordable helium supply. Our 22 year old Oxford wide bore
works as well now as then. We moved down the hall and up an
elevator after discharging the magnet. Didn't want to find
steel beams in the walls. The magnet was cold and rode on a
cart our shop built with rubber pneumatic tires. We would have
warmed it up and replaced O rings if He hold times were decreasing.
List: check out the entire path before your start, discharge,
disconnect, remove rt shims so the bottom is flat, lift magnet, remove
stand, place thin foam sheet or blanket on cart, lower magnet slowly
onto the cart, pull slowly with 3-4 people watching.
hth,
dave scott
iowa state university
>From: Rainer.Haessner@ch.tum.de
>To: Istvan Furo <ifuro@physchem.kth.se> (by way of Rudi Nunlist
> <rnunlist@purcell.cchem.berkeley.edu>)
>Date: Thu, 21 Feb 2002 02:33:27 +0100
>Subject: Re:
>Priority: normal
>X-mailer: Pegasus Mail for Windows (v4.01)
>X-Sender: 08996200185-0001@t-dialin.net
>
>
>Hello, Mr. Furo,
>
> >
> > 1. What is the approximate lifetime of NMR magnets? What are the most
> > important factors (except keeping the vacuum good and not dropping the
> > magnet during the move!) influencing this lifetime?
>
>In principle the lifetime is unlimited. The time between repairs
>depends from the quality of the rubber rings to seal the vacuum
>bottle and the helium content within your laboratory air.
>Please don't laugh about the second fact. The helium content
>in small bad air conditioned rooms is responsible for more
>than 50% magnet repairs during the first years after
>installation.
>
> >
> > 2. If there is a lifetime not much longer than 20 years, in which way does
> > the performance of the magnet suffers? Stability, homogeneity, more
> quenches?
>
>You have to fear nothing with respect to quality. Of course
>depending, whether you keep the rom clean or not, the manets
>collects tiny ferromagnetic particles over the time. But using
>some rolls of adhesive films it is not comlicated to remove these
>particles.
>
> >
> > 3. Moving a magnet cold is cheaper. On the other hand, one hears that
> > moving a magnet warm is safer. Does this mean (i) safer for the persons
> > moving the magnet or (ii) safer for the magnet as concerning its
> > performance after the move? Can anybody direct us to some written
> > instructions or checklist about moving NMR magnets?
>
>It is not clear, whether moving the magnet cold and charged is
>safer than to wam it up. Approximately 1 ... 2% of all magnet warmed
>up never come back to the final field.
>Moving charged and cold magnets is easy, if you have a flat area
>and the doors are high enough. e made it three times meanwhile
>with no problem.
>Have a look to this URL:
>http://www.spectroscopynow.com/Spy/basehtml/SpyH/1,1556,5-1-1-0-278-news_detail-
>0-278,00.html
>These wheels work great. I am not sure whether you can rent them
>from that specialist or not (phone +49 721 5161 154)
>
>Another magnet became moved using a crane:
>
>http://www.org.chemie.tu-muenchen.de/nmr/nmrdateien/900mhz/200300e.jpg
>
>Cold and charged!
>
> >
> > 4. The 400 magnet has been performing extremely well in the past. Any
> > experience concerning the behavior of magnets after warming up, securing,
> > re-pumping, and re-charging? Does one usually get back the same
> performance
> > on such an old magnet?
>
>During this whole procedure the magnet by no means becomes better.
>It is by no means recommendable to warm up a magnet without
>necessity.
>
>Rainer Haessner
From: "Davis, Mark" <Mark_Davis@nrel.gov>
To: 'Istvan Furo' <ifuro@physchem.kth.se>
Subject: RE: RE:
Date: Wed, 20 Feb 2002 11:49:41 -0700
X-Mailer: Internet Mail Service (5.5.2653.19)
Istvan,
I give you some answers to a couple of your questions based on my
experiences.
1. As long as you can keep the vacuum, an NMR magnet should be good for a
long period of time. I did my graduate work in Maciel's lab and I know that
he has superconducting magnets that are ~ 20 years old (maybe even older).
Several of them have been moved several times with no ill effects. As near
as I can tell, the only reason a magnet should fail is if the o-rings go
bad. We are replacing the o-rings in a R2D2 Varian magnet because the
o-ring seals have started to slowly fail after ~12 years and we are tired of
repumping the magnet every year or so.
3. We just moved a Bruker 200 wide bore cold and energized last month to a
new lab. It was more nerve racking than hard. I don't know of anyone that
has actually written instructions. In my opinion (take it for what it is
worth) , you should be able to move the magnet safely. We were just very
careful and did everything very slowly. Our magnet is performing just as
well now as before the move. Other than having to reshim, nothing else has
changed. The one thing you should be aware of, is that after 10 years, your
magnet may be stuck to the floor (the magnet has a tendency to bounce a
little bit after it pulls away from the floor!).
To move our magnet, we picked it up using an engine hoist (rated to 2000
lbs), 2 nylon moving straps (rated 5000 lbs) and 4 clevis pins rated to 1000
lbs(u-shaped gizmos to attach the straps to the magnet at the magnet lifting
points). You should be able to find out the weight of your magnet in your
magnet manual. Since we had to take the legs of to clear some doors, and
also to satisfy our safety folks, we decided to set the magnet down on a
platform with 4 large castors attached. We had just installed a new 400 so
we used the base that the 400 magnet was shipped on. The advantage of using
the shipping base was 1) the hole for the vacuum valve was already cut out
and 2) we could use the shipping restraints supplied with the magnet. We
felt that this was a more stable configuration for moving to the new lab
than using the engine hoist. The disadvantage is that you have to lift and
set down the magnet twice. Make sure you walk the path ahead of time to
move or secure any magnet objects that might get near the magnet(in our
case, a couple of fire extinguishers and several small metal doors on
electrical panels). We also decide to fill He before the move to prevent
the coil from being exposed during the move. We debated about blowing out
the N2 to lighten the load and then decided against it. Since we were
moving the magnet down some fairly large open spaces, we were not worried
about confined spaces in the event of a quench. But you should also plan
for what you are going to do in case of a quench. Practice a bit with
whatever ever you are going to use to lift the magnet to make sure you are
very comfortable lifting and setting heavy objects down slowly.
In the next couple of weeks, we are going to move the old 300 MHz R2D2
magnet cold and energized to the same lab. So the experience of moving the
200 couldn't have been too bad.
Good luck,
Mark
Mark Davis, PhD
NREL
1617 Cole Blvd
Golden, CO 80020
303-384-6140
mark_davis@nrel.gov
Date: Wed, 20 Feb 2002 16:26:34 -0500
From: Padgett.William@epamail.epa.gov
Subject: Re:
To: Istvan Furo <ifuro@physchem.kth.se> (by way of Rudi Nunlist
<<ifuro@physchem.kth.se<ifuro>)
X-Mailer: Lotus Notes Release 5.0.3 March 21, 2000
X-MIMETrack: Serialize by Router on EPAHUB11/USEPA/US(Release 5.0.6a |January
17, 2001) at 02/20/2002 04:26:35 PM
Hi Istvan.
I have had ours moved twice, and am about to have it moved again to a
new facility. Here's my advice on moving magnets, and answers to your
questions.
1 Magnet lifetime
No reason for it to continue to perform. You must keep the vacuum in
tact(until de-energized of course), but during the move it should not be
exposed to any shock. Physical that is. It should not be bumped into
walls or doors, nor should it be tipped. We always apply shock sensors
and tip sensors to the sides of the magnet to indicate if the movers
have done either. They are small crystalline patches applied directly
to the magnet. Any gas vendor can tell you where to get them and they
are very inexpensive.
2) O-ring failure releasing the vacuum and thereby quenching the magnet
would be my main concern. With a fresh start the homogeneity and
stability should remain.
3) Moving cold vs warm.
Definitely move it warm! We have seen no problems with discharging,
warming and breaking the vacuum, other than it taking about two weeks.
In fact we've spec'ed it out each time prior to the move and have been
able to achieve better spec's after setting it back up. This is
probably due to field bleed, since the field over time begins to
dimenish. I got a check list and procedure for moving a magnet from
Bruker, but had them do it for me. As far as safety moving it cold, I
would imagine they mean it is safer to move it warm for the magnet's
sake, since the supports can be reinstalled. It would be very easy to
get the coils misaligned moving it cold. Better to warm it, and put the
moving supports back in it. One advantage to moving the magnet
de-energized and warm, is that you can replace all of the o-rings, and
start with a new vacuum at the maximum. My guess is faulty o-rings
could easily lead to vacuum failure, thus a quench. Also you will
remove any ice that may have formed over time in the helium dewar. If
you have been deligent in your filling, this really isn't a problem.
4) Again, we have had no shortcomings in moving a magnet. We met the
spec's from the original set up, and in fact bettered most of them.
Hope this helps.
William Padgett
Chemist
U.S. Environmental Protection Agency
Environmental Carcinogenesis Division
Biology and Pathobiology Branch
86 T.W. Alexander Drive, MD-68
Research Triangle Park, North Carolina 27711, USA
telephone: 1-919-541-7518
FAX: 1-919-541-0694
Email: padgett.william@epa.gov
>Date: Wed, 20 Feb 2002 13:16:07 +0100
>To: bruker-users-mail@purcell.cchem.berkeley.edu
>From: Istvan Furo <ifuro@physchem.kth.se>
>Cc: UllaJ
>
>Dear All,
>
>We have a 400 MHz spectrometer consisting of a new console and an older
>(20 years) narrow-bore magnet. Next year we are supposed to move the
>spectrometer to a new location and thereby some questions have arisen.
>
>1. What is the approximate lifetime of NMR magnets? What are the most
>important factors (except keeping the vacuum good and not dropping the
>magnet during the move!) influencing this lifetime?
>
>2. If there is a lifetime not much longer than 20 years, in which way does
>the performance of the magnet suffers? Stability, homogeneity, more quenches?
>
>3. Moving a magnet cold is cheaper. On the other hand, one hears that
>moving a magnet warm is safer. Does this mean (i) safer for the persons
>moving the magnet or (ii) safer for the magnet as concerning its
>performance after the move? Can anybody direct us to some written
>instructions or checklist about moving NMR magnets?
>
>4. The 400 magnet has been performing extremely well in the past. Any
>experience concerning the behavior of magnets after warming up, securing,
>re-pumping, and re-charging? Does one usually get back the same
>performance on such an old magnet?
>
>Answers and suggestions will be compiled and distributed. The eventual
>first prize for the best suggestion (in case we do not follow it and
>thereby render the magnet broken) is a shiny cylindrical object that
>cannot be magnetized any more but it is still sufficient to use as garden
>pond or as a pot for larger till medium-size palm trees...
>
>Sincerely
>
>Istvan Furo
>
>************************
>Dr. Istvan Furo
>Division of Physical Chemistry
>Department of Chemistry
>Royal Institute of Technology / KTH
>Teknikringen 30/36
>SE-10044 Stockholm Sweden
>Tel: +46 8 7908592
>Fax: +46 8 7908207
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