[labnetwork] Anhydrous HCl after it escapes ...

Tue Jun 10 22:21:34 EDT 2014

Dear John,

To add to this story, in Western Australia procedurally we check the complete line before every use and process according to:

1. pump the line to vacuum and check for leaks
2. open cylinder and process
3. when done processing, pump the line to vacuum and fill it with nitrogen
4. line is filled with nitrogen when Cl is not in use.

It is a pain processing like this, but we are able to get away with it as we are not using Cl on everyday basis. In addition, we do not leave dangerous gasses in the line over extended periods of time.

This is a draconian approach and users have a tendency to rebel against it, but it has worked well for us with no leaks since it was adopted about 6 years ago.

Cheers,
Marius 

Mariusz Martyniuk
-----------------------------
Research Professor, ANFF-WA Managing Director
Microelectronics Research Group
School of Electrical, Electronic & Computer Engineering, Rm 4.17, M018
The University of Western Australia
35 Stirling Highway, Crawley WA 6009, Australia
Tel: +61 8 6488 1905, Fax: +61 8 6488 1095
Secretary Tel: +61 8 6488 3801, Rm 1.73, http://mrg.ee.uwa.edu.au

-----Original Message-----
From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of John Shott
Sent: Wednesday, 11 June 2014 4:20 AM
To: Weaver, John R; labnetwork at mtl.mit.edu
Subject: Re: [labnetwork] Anhydrous HCl after it escapes ...

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
>
>
> _______________________________________________
> labnetwork mailing list
> labnetwork at mtl.mit.edu
> https://www-mtl.mit.edu/mailman/listinfo.cgi/labnetwork

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