<div dir="ltr"><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">John:</div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">
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.</div>
<div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">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.</div>
<div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">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.</div>
<div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">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.</div>
<div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">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.</div>
<div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">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.</div>
<div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">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.</div>
<div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">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 ...</div>
<div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">I look forward to the comments of others ...</div>
<div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">Thanks John ...</div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">
<br></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Thu, Jun 5, 2014 at 3:08 PM, John Shott <span dir="ltr"><<a href="mailto:shott@stanford.edu" target="_blank">shott@stanford.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Labnetwork Community:<br>
<br>
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.<br>
<br>
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?<br>
<br>
Thanks for sharing your experience and insights,<br>
<br>
John<br>
<br>
<br>
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</blockquote></div><br><br clear="all"><div><br></div>-- <br>Dennis S Grimard, Ph.D<div>Managing Director, Lurie Nanofabrication Facility</div><div><br></div><div>University of Michigan</div><div>1246D EECS Building</div>
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