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Overheating of pre-insulated instrument tubing and freeze protection lesson learned in supporting the use of ground-fault equipment protection

Published on 04 Oct 2019 by ES Staff


Overheating of pre-insulated instrument tubing exceeded the service temperature of the tracer materials (Polyolefin) which set up conditions for an arcing ground fault as the energized bus contacted the instrument tubing. The uninterrupted arcing fault resulted in a 1/16" x 2" long hole in the tubing which caused a dowtherm leak. The result was a total shutdown of the manufacturing unit. This was a new installation that did not have ground-fault protection.

The following incident consisted of a self-limiting tracer protected by a 120 VAC/20 amp circuit breaker. The application was to provide freeze protection on the impulse lines to an instrument on a metal piping system in a petrochemical facility.

Some strands of the stainless steel braid over the self-limiting tracer penetrated the dielectric sheath of the energized heating cable. Although the exact events in the failure were not determined, the overheating and/or arcing burned a pin-hole in the instrument tubing, allowing the flammable gas to escape and ignite. The gas flame was detected by operating personnel and extinguished before major damage could occur.



Tags: overheating of pre-insulated instrument tubing