[labnetwork] Heat trace issues on DCS gas lines

[Tom Britton]

http://www.obcorp.com/products/tubing-bundle/tracepak-electric.aspx

Hi Vito,

More than likely the way they wrapped the tracing didn't cause any issues. I've represented Thermon, Raychem, Obrien and a host of others and for heat tracing, the way they did it is correct. The key to good heat transfer is continual contact with the tube, followed by the aluminum tape and then insulation. I've attached the link to Obrien's Tube Trace bundles so you can see how this is made in a production environment. The trace lays right on the tube in a continual fashion. I've also attached Thermon's installation guide. 1 strip of heat trace unless you're doing pipe, and then 2. They don't suggest spiraling as you get different distances between the spirals and the heat isn't even.

I spoke to our Operations Manager, Troy at our shop as he was the Gas Systems' manager at ON Semi for 14 years, and his response was:

Based on my experience, I would say they had a soft spot on the insulation of the heat trace itself upon installation. I would highly doubt that the tape caused the issue. I've never installed it with the method of spiral winding around the tubing. We always used fiberglass tape and tape it every 3-5 feet depending on the configuration of the tubing run. The key is inspecting the heat trace for damage during installation if there is any place that it has a scuff or rub on the insulation surrounding the conductor wires and that comes in contact with the tube it will fail.

Over the years I have seen issues where a cable was scuffed, like Troy comments on, as well as incorrect termination of the tracing. I've also seen times where the tracing has an issue when it was manufactured and it shorts out.

Gotta love maintenance issues!

Have a great day Vito and good luck!

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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From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Vito Logiudice
Sent: Wednesday, January 21, 2015 10:23 AM
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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