[labnetwork] Anhydrous HCl after it escapes ...

Wed Jun 11 12:20:27 EDT 2014

Hi John,

I'm glad that you found the source of the leak. Any time a system is compromised it causes huge issues with down time and cost of repair. As you are probably aware, your gas line is most likely trashed to the tool and needs to be replaced to the tool. Don't just replace the panel and run the gas again, as corrosion spreads once it starts. Your gas cabinet vendor should be able to get you a new panel, hopefully quickly, so you're not down for an excessive time.

In reading what you wrote about leak checking after install, this shouldn't be necessary. The major Fabs don't do this as the downtime and cost would be enormous. The initial installation by your mechanical contactor includes a helium leak check through the cabinet to the tool, and if you're performing a cylinder leak check after every bottle change, you should be fine from a leak check perspective. Instead focus on keeping the gas dry. It is well documented that HCL, and most other corrosives, in the gaseous form, can run for years in stainless steel lines with no issues, but as soon as there is the slightest trace of moisture, game over. It's my guess, that when you send this panel back to the gas cabinet supplier, you're probably going to hear that the valve corroded through where you found the leak.

The major points for using any corrosive gas are:

1.      Helium leak check the connection after every cylinder change prior to the introduction of process gas. We advise using a "He/Inert Gas" blend for your purge gas, as you can use the purge gas to helium leak test the connection.

2.      Always use DISS fittings for both the process gas and the purge gas. Not only do they provide a higher level of leak integrity and purity over a CGA, but one is less likely to introduce a lower purity purge gas by mistake than if the connection has a standard 580 CGA on it.

3.      Purge Gas Purifier - We highly recommend a purge gas purifier for all mineral acid gases. Granted, your cylinder costs $1200, but it's cheap insurance and it will last a very long time.

4.      Trickle Purge Valve - check to make you have a Trickle Purge Valve in your purge line and that it's open during bottle changes. This does a good job of keeping atmosphere from getting into the gas line during the physical changing of the bottle.

5.      Cycle Purges - 30 is not enough. Set your purge cycles at 60 for both pre and post purge. The pre-purge is for the safety of the operators, and does a better job of scrubbing the inside of the tubing and components of the HCl, so any atmospheric moisture that gets past the trickle purge doesn't react. The post purge is to dry the inside of the gas line of the tube and components before the HCl is reintroduced into the system. Any less and there is a chance that residual moisture will remain, and once the HCl gas hits it, the corrosion will start and it's a matter of time before you see the effects.

I was talking with Troy on this and he ran his HCl at ON Semi for over 10 years using the above practice, and some of their systems sat idle for quite some time between quartz cleaning steps on seldom used tools. I also talk with a lot of gas systems managers in my travels and this is a fairly common way that the production Fabs keep their corrosive systems running and the problems at bay.

Hope this helps. See you on Sunday.

Tom

Tom Britton
Director of Sales
Critical Systems, Inc.
Direct: 208-890-1417
Office: 877-572-5515
www.CriticalSystemsInc.com<http://www.criticalsystemsinc.com/>

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-----Original Message-----
From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of John Shott
Sent: Tuesday, June 10, 2014 2:20 PM
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<mailto:jrweaver at purdue.edu>

> nano.purdue.edu

> ________________________________________

> From: labnetwork-bounces at mtl.mit.edu<mailto: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<mailto: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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> labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>

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