[labnetwork] Heat trace issues on DCS gas lines

[John Shott]

Vito:

While I do not profess to be Mr. DCS ... and, some would argue, being in 
California I have no right to weigh in on the topic ... I will share 
what we have done on our DCS lines.  As a qualifier, however, our DCS 
runs in single-walled, rather than double-contained, tubing.  We have 
two DCS lines and each is about 400 feet in length and nearly half of 
that runs outdoors between our gas bunker and the main lab.

We don't run spiral wrap ... we simply run our heat trace along the 
length of the line.  We do, however, use sticky aluminum tape along 
virtually the entire length of the line to try to improve the thermal 
conductivity between the heat trace and the actual gas line.  While we 
believe that is reasonably effective from a thermal standpoint, it's a 
real mess to undo if you ever remove the line. In our case, the 
line/heat trace/tape assembly is encased by inexpensive black foam 
insulation normally used on 1/2" plumbing lines.

Here is a low-quality image of what we have with the foam pulled away:



Good luck,

John

On 1/21/2015 9:23 AM, Vito Logiudice wrote:
> 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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