[3dem] liquid nitrogen supply lines

[Thomas Cleveland]

Hi David,

I'm not an expert at cryo engineering so take this with a grain of salt,
but I looked into this a while back for our facility and can share what I
remember (we still haven't implemented anything, so I can't say from
experience).

>From information I found online, it seems that copper piping is OK for
liquid nitrogen, and has actually been used that way for a long time. There
are a few special points, e.g. the joints need to be silver brazed, not
soldered, to deal with temperature contraction. Traditionally, closed-cell
urethane foam with a PVC outer jacket (as a vapor shield) was used to
insulate cryogenic copper pipes. However, supposedly the repeated chill
cycles cause this insulation to break down somewhat and lose performance
over a few years. Whether this is a huge problem for you probably depends
on how long your pipes are and how expensive your nitrogen supply is. A
more modern and lower-maintenance (but more expensive) insulation method is
to use vacuum-insulated lines, but I think this goes back to the stainless
steel you were trying to avoid...

Best,
Tom




On Wed, Oct 6, 2021 at 1:56 PM Morgan, David Gene <dagmorga at indiana.edu>
wrote:

> Hi,
>
> Does anyone have a good reason for not using copper pipes to supply liquid
> nitrogen to cryo-microscopes?
>
> We are looking to move our liquid nitrogen tank further away from our
> Arctica.  We want to run an insulated line from the new location to where
> the tank stood and then use a flexible hose to connect from there to the
> instrument itself.  We can make this happen almost immediately if we use
> copper, but it will take months and months if we ask for stainless steel.
>
> Thanks in advance for any advice.
>
> --
>     politics is more difficult than physics.
>                                              A. Einstein
>
>             David Gene Morgan
>         Electron Microscopy Center
>              047E Simon Hall
>              IU Bloomington
>           812 856 1457 (office)
>           812 856 3221 (3200)
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