[labnetwork] Heat trace issues on DCS gas lines

[Paolini, Steven]

Hmmm,
   Not knowing the watt/foot rating of the trace, my first guess would be that it got too hot under all that insulation. I have never heard of straight vs. spiral advantages or disadvantages but I would be willing to bet that at the fastener locations, the trace would have cool spots since the heat is being transferred to the tubing more efficiently.
I quit using heat trace for low vapor pressure materials into vacuum systems years ago, I'm assuming your DCS is being used for LPCVD and that would be a perfect candidate for running the gas at sub-atmospheric pressures to lower the boiling point. I use this method with all my prone-to-liquify-high-vapor pressure gases and have never experienced a "flooded" MFC since doing so.
Best of luck

Steve Paolini
Equipment Dood
Harvard University Center for Nanoscale Systems

From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Vito Logiudice
Sent: Wednesday, January 21, 2015 12:23 PM
To: Labnetwork
Subject: [labnetwork] Heat trace issues on DCS gas lines

Dear Colleagues,

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.

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.

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?

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.

Regards,
Vito
--
Vito Logiudice  P.Eng.
Director of Operations, Quantum NanoFab
University of Waterloo
Lazaridis QNC 1207
200 University Avenue West
Waterloo, ON           Canada N2L 3G1
Tel.: (519) 888-4567  ext. 38703
Email: vito.logiudice at uwaterloo.ca<mailto:vito.logiudice at uwaterloo.ca>
Website: https://fab.qnc.uwaterloo.ca

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