[labnetwork] Anhydrous HCl after it escapes ...

[John Shott]

Labnetwork Community:

First, I'd like to thank Chung Wing Leong, Dennis Grimard, Craig Cheney, 
Tom Britton and John Weaver for taking the time to respond to my query.  
I appreciate your collective expertise and input and am taking a number 
of things you suggested under careful consideration as we move forward.

In the meantime, we have learned a bit more about this leak and I 
thought that I would share with you a bit more about what we have learned:

First, the leak seems to have occurred at the joint between the valve 
body and the tube stub ... not, as we had originally feared and 
suspected at one of the VCR connection points.  Nor did it occur at one 
of the orbital welds between the tube stub on the valve and a VCR gland. 
To me it is unusual to see a leak at that point in a valve ... 
particularly one that has not been in service very long.

Second, this failure occurred downstream (on the tool side) of the 
pneumatically-controlled, low-pressure outlet valve on the panel. 
Certainly on our panel, and in most auto-purge panels of this type, this 
valve is typically closed during bottle changes and similar leak 
checking activities.  To be candid, this has been a bit of a blind spot 
for me:  while I told you that we leak check the panel each time that we 
change a cylinder (which is true), now that I think about it more 
carefully, we don't have a mechanism for leak checking anything on the 
downstream side of this valve on a regular basis.

In fact what we normally leak check is that portion of the panel that is 
upstream of the pneumatically-controlled, low-pressure outlet valve.  
Since this is a manifolded cabinet that has two bottles feeding a single 
output line, there are actually a number of potential failure points 
that we do not regularly check that includes the output side of each 
pneumatically-controlled output valve, the manual quarter-turn valve in 
series with and downstream from the pneumatically-controlled output 
valve and the fittings associated with the tee in the manifold.  As this 
cabinet has not been service for an extended period of time, those 
downstream fittings have likely been checked only twice:  once by the 
cabinet manufacturer at their facility and once by us during the cabinet 
install.  While our cabinet was helium leak checked and certified by a 
third-party to be less than 10^-9 SCCM leakage, is there a chance that 
we missed something then?  I'm certainly wondering ...

My guess is that I am not alone in having thought that we leak check the 
entire panel and all fittings each time we change a gas cylinder ... 
whereas there are likely several fittings and connection points that are 
not actually checked each time.  I will certainly think about this in a 
new light ...

Thanks,

John



On 6/9/2014 5:43 AM, Weaver, John R wrote:
> John -
> I've had experiences (certainly plural :)) with both external and internal leaks. For an internal leak, where moisture has gained access to the piping, I have always replaced the piping components up to the point where the leak was blocked - a valve, etc. I use valves with Hastelloy wetted surfaces (sometimes called Hastelloy trim), which is not impervious to HCl corrosion but certainly holds up better.
> For external leaks, the key is to neutralize the surfaces as quickly as possible. In one instance we had to replace many components because we didn't neutralize the surfaces more quickly. A mild base works well for neutralization - something with a pH in the 9 range. Then a thorough rinse to remove any salts is necessary.
> We run all of the gas cabinet exhausts for chloride gas cabinets through our plastic exhaust system, so we don't have to worry about exhaust. If you use a metal exhaust on the gas cabinet where the leak occurred, I'd carefully inspect the exhaust for a month or two after the incident.
> I hope this helps.
> John
>
> John R. Weaver
> Facility Manager
> Birck Nanotechnology Center
> Purdue University
> jrweaver at purdue.edu
> nano.purdue.edu
> ________________________________________
> From: labnetwork-bounces at mtl.mit.edu [labnetwork-bounces at mtl.mit.edu] on behalf of John Shott [shott at stanford.edu]
> Sent: Thursday, June 05, 2014 3:08 PM
> To: labnetwork at mtl.mit.edu
> Subject: [labnetwork] Anhydrous HCl after it escapes ...
>
> 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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