[labnetwork] Anhydrous HCl after it escapes ...

[Dennis Grimard]

John:

As usual you ask the interesting questions.  Anhydrous HCL is not corrosive
to the typical SS that is used for wetted parts in vacuum and delivery HPM
systems.  However, once it is exposed to air and hydrolyzes with the water
in the air it becomes HCL acid and then is corrosive to the SS and most
everything it touches.

No matter what the quality of the part, they all leak a very small amount.
 That leakage is what causes the eventual failure of the part since the SS
is corroded as the leak occurs.  So, with HCL (an other gasses that act in
the same manner), it is always a matter of time before they fail ... not if
... when.

The time scale is tens of years in my estimation.  That is, if a system is
in service for tens of years you will experience a catastrophic failure of
some component.  In industry, they usually avoid this problem since very
few systems are in use that long before being ripped out for an upgrade or
reconfiguration of a manufacturing floor.  In universities we have this
problem because our systems stay in service much longer and in many cases
without proper oversight and maintenance.

The best defense is to use as much welded components as possible.  That is
avoid mechanical components if a welded component can be used.  At the
points where there are mechanical fittings / components they need to be in
ventilated enclosures so when and if the leak occurs it can be contained.

As for when a part fails, it typically means a significant amount of
hardware needs to be inspected / replaced since the HCL acid is very
corrosive and makes a real mess.

There is not a day that goes by that I am not worried about such components
(HCL, DCS, CL2, HBR ...) and their eventual failure.  I don.t pray but I do
worry ... alot.

My approach at Michigan is to work hard on preparing the staff for the
eventuality that is a failure.  Good hardware, weekly safety meetings,
continues preparation of documentation ... drills.

Not sure that I really added any value to what you already knew ... but I
though that a good conversation on this topic may help us all ... this is
my starting point for that conversation ...

I look forward to the comments of others ...

Thanks John ...



On Thu, Jun 5, 2014 at 3:08 PM, John Shott <shott at stanford.edu> wrote:

> Labnetwork Community:
>
> Sooner or later, it seems, anhydrous hydrogen chloride (or a number of
> equally corrosive materials) is going to escape.  At least that is our
> experience at the Stanford Nanofabrication Facility.  Despite our best
> efforts to use quality components, do proper leak checking, etc., it seems
> as if we end up with a leak either in a gas cabinet or in a tool near a
> mass flow controller.  At that point, anything near the site of the
> original leak has been covered with now moisture-laden hydrogen chloride
> ... which, I believe, is far more corrosive than the original anhydrous
> material.
>
> For those of you who have encountered similar situations, how do you
> recover or what to you replace?  Do you have effective means of
> neutralizing those metal surfaces?  Do your replace VCR gaskets with
> thicker-than-normal or grooved "super gaskets"?  Do you replace the entire
> assembly?  Do you leak check, put back in service, and pray?
>
> Thanks for sharing your experience and insights,
>
> John
>
>
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-- 
Dennis S Grimard, Ph.D
Managing Director, Lurie Nanofabrication Facility

University of Michigan
1246D EECS Building
1301 Beal Avenue
Ann Arbor, MI 48109-2122
(734) 368-7172 (Cell)
(734) 647-1781 (Fax)
http://www.lnf.umich.edu
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