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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Dennis –<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Great points. We use heat trace, but do not use VMBs for these gases – for the reasons you listed.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">John<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> labnetwork-bounces@mtl.mit.edu [mailto:labnetwork-bounces@mtl.mit.edu]
<b>On Behalf Of </b>Dennis Grimard<br>
<b>Sent:</b> Tuesday, February 10, 2015 10:32 PM<br>
<b>To:</b> Vito Logiudice<br>
<b>Cc:</b> Labnetwork<br>
<b>Subject:</b> Re: [labnetwork] Conclusion: Heat trace issues on DCS gas lines<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">Vito:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">I have watched with great pleasure the discussion on this topic. I too agree that much good info has been discussed ... Great feedback from some very knowledgable people indeed.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">I need to throw a wrench in the discussion (or prove my ignorance). I have always resisted heat taping for the following reasons: 1) when the tube enters a VMB or any ventilated enclosure there is a significant
temperature drop due to the large purging flow rate within the enclosure ... Tending to cool the line at the worst possible point, 2) the VMB type enclosures tend to have many right angle welds and valves which promote condensation .... Rather than long graceful
bends typically used external to the enclosure, 3) SS is a horrible heat conductor ... As is n2 gas ... So if I heat trace a double wall tube how much heat actually gets to the inner tube? how consistent is that heat? What is the temperature gradient?, and
4) the actual cold to hot temperature gradient (desired) is difficult to institute along the length of line ... A good feedback loop is required. Also, heat tape gives me the district impression that it can contribute to an out of control heating failure
with a possible fire as a result.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">So, not that it solves your problem but here is what I have tried to always implement: 1) short runs (home runs not a distribution), 2) minimum short radius right angles, 3) minimize VMB's ... Mini gas cabinets
with multiple outputs in the cabinet, 4) chilled bottles, 5) vacuum delivery, and 6) large radius bends.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">Just food for thought ...<br>
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Dennis S Grimard, Ph.D.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">Associate Director of Operations, MIT.nano<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">Massachusetts Institute of Technology<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">60 Vassor Street, Bldg 39-556<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">Cambridge, MA 02149<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">C: (734) 368-7172<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">EM: <a href="mailto:dgrimard@mit.edu">dgrimard@mit.edu</a><o:p></o:p></p>
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On Feb 10, 2015, at 1:30 PM, Vito Logiudice <<a href="mailto:vito.logiudice@uwaterloo.ca">vito.logiudice@uwaterloo.ca</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">Dear Colleagues,<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">Thank you very much to everyone whom took the time to write in with their insights on this issue. Special thanks to John Shott and Tom Britton for the photos and reference documents provided.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">So that others may perhaps benefit from our experience, we've concluded that the cause of the premature failure appears to have been the presence of several "voids" where the heat trace was not in intimate contact
with the SS tubing. This occurred even though the trace had been taped every 12 inches per the manufacturer's recommendations. We also noted voids at some elbows where maintaining contact was/is difficult. <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">To keep the issue from repeating itself in the future, our plan is to reinstall two new heat traces along the length of the tubing, one on the bottom and one on the top. One of these will remain active while the
backup trace will be kept off and act as an insurance policy should the primary unit fail in the future. If anyone sees a problem with this particular approach, I would be glad to hear from you.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">In the new installation, conductive putty will be used to fill any voids before aluminum tape is applied along the entire length of the line much like John showed in his attached photo. The entire assembly will
then be re-insulated per the original design specification. Fortunately, the problem occurred under warranty so our only out-of-pocket cost will be limited to the cost of the backup heat trace (a few hundred dollars).<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">Regards,<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">Vito<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><b><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">From:
</span></b><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">Vito Logiudice <<a href="mailto:vito.logiudice@uwaterloo.ca">vito.logiudice@uwaterloo.ca</a>><br>
<b>Date: </b>Wednesday, 21 January, 2015 12:23 PM<br>
<b>To: </b>Labnetwork <<a href="mailto:labnetwork@mtl.mit.edu">labnetwork@mtl.mit.edu</a>><br>
<b>Subject: </b>[labnetwork] Heat trace issues on DCS gas lines<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black">Dear Colleagues,<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black">We are experiencing an issue with the heat trace on our Dichlorosilane gas line. The all-welded 1/4" SS line is encapsulated with a 1/2"
SS outer containment line which is itself heat traced with a single strand of heat trace that runs the entire length of the coax assembly. The 120 foot line is insulated as shown in the attached photo. A portion of the heat-trace appears to have failed prematurely
(it was installed less than one year ago) and we are wondering if the method of installation may be the cause.<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black">The heat trace was not installed in a spiral fashion around the outer 1/2" tube. Rather it was installed in a straight fashion along
its entire length with "heat trace fastening tape" located every four feet or so. A member of my team has suggested that such a straight rather than spiral installation may have caused hot spots (at the fastening locations) which may have in turn caused the
failure.<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black">I would appreciate hearing from the community on this point: Are the heat traces around your low pressure gas lines spiral-wound around
the lines or are they installed in a straight fashion and somehow fastened along the entire length?<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black">Other insights/suggestions on the proper heat tracing of gas lines by experts in the field as well as comments on possible causes of
premature heat trace failure are very much welcome and appreciated. Thank you.<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black">Regards,<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black">Vito<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">--</span><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Vito Logiudice P.Eng.</span><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Director of Operations, Quantum NanoFab</span><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">University of Waterloo</span><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Lazaridis QNC 1207</span><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">200 University Avenue West</span><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Waterloo, ON Canada N2L 3G1</span><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Tel.: (519) 888-4567 ext. 38703</span><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Email: <a href="mailto:vito.logiudice@uwaterloo.ca">vito.logiudice@uwaterloo.ca</a></span><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Website: </span><span style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><a href="https://fab.qnc.uwaterloo.ca">https://fab.qnc.uwaterloo.ca</a><o:p></o:p></span></p>
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