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Preferred practices for Electrical Pipeline Heat Tracing

Published on 11 Jun 2019 by Lana Hajovsky


The following list of preferred practices is a validated set of recommendations based on industry experience for cost, quality and problem avoidance. The stated references are not absolutes, but are intended to provide a default set of practices. Changes should only be made with a full understanding of the impact.

Design

  • USE Raychem or Thermon to provide design/engineering
  • Provide ground fault equipment protection for all branch circuits as required by NEC Article #427-22. (Use 30ma EPD breaker, a heating controller incorporating this feature or a ground-fault relay.)
  • Use 120 Volts A standard voltage, use 208 or 240 volts for long circuit length. (Limited by manufacturers maximum circuit length for minimum ambient for line switched circuits, or by manufacturers maximum circuit length at 50°F [10°C] for soft-start controllers).
  • Use the site recorded minimum and maximum ambient temperatures, 25-MPH wind as the design basis.
  • Use 50% safety factor for heat loss calculation on all process heating and freeze protection on pipelines 2" and smaller. Use a 30% safety factor for freeze protection on pipelines over 2".
  • Use 40°F (4.4°C) as the pipe maintenance temperature for freeze protection applications.
  • Use 60°F (15.5°C) as the pipe maintenance temperature for all safety shower applications, Provide 95°F (35°C) Hi-limit protection for personnel.

Tracer/Controller Selection

  • Use Raychem or Thermon
  • Use highest temperature rated self-limiting heating cable throughout (Raychem XTV, Thermon TSX).
  • Use low temperature rated self-limiting heating cable on safety showers and non-metallic pipelines and vessels (Raychem BTV, Thermon PSX, use aluminum heat transfer tape on non-metallic application per manufacturers recommendations).
  • Provide all cables with Copper Braid and overall TEFZEL, Fluoropolymer over jacket.
  • Use pre-traced tubing instead of field traced and insulated tubing applications (due to short service life of field traced systems).
  • Use integrated heating control cabinets located in a clean/dry environment, preferably and ECR (Integrated systems consisting of power transformer, branch circuit breakers, controllers, alarm relays, and terminals for field wiring have proven to be overall lowest cost/highest utilization).
  • Provide a common alarm for heating control panels (alarmed to a process control system or continuously manned location. Provide a minimum of loss-of-voltage/ground-fault alarm for all circuits, except those without personnel or business risk).
  • Provide real time controls or auto-cycling timers to provide year-round monitoring of system status.
  • Use resistance inference control to eliminate the cost and maintenance associated with field temperature sensors and use ambient switched control for low end freeze protection such as VTI controllers).

Thermal Insulation

  • Follow the Company specific thermal insulation specification (if applicable otherwise use ASTM Standard).
  • Use Polyisocyanurate rigid oversized thermal insulation on all application with maintenance temperature up to 250°F (121°C) on steel pipe. For unprotected stainless steel pipes, use Polyisocyanurate for maintenance temperature up to 140°F (60°C).
  • Use Perlite expanded Calicum Silicate rigid thermal insulation for all application where the temperature service ratings of Polyisocyanurate are exceeded.
  • Provide draft stops in all vertical sections of the piping system per thermal insulation specification.
  • Use outside of pipe load-bearing pipe supports. Use non-metallic pipe shoes when outside load bearing support cannot be used (Uncompensated heat losses at welded pipe shoes are an industry wide source of system freeze-ups/failures to attain heat).
  • When using Polyisocyanurate insulation indoors, consult a thermal insulation specialist (Generally, Polyisocyanurate should not be used indoors unless a sprinkler system is present, or a steel type jacketing or fire resistant coating is provided).

Installation

  • All installers should be trained and certified in manufacturers methods.
  • Locate all penetrations into the lower 180° quadrant of the thermal insulation (Eliminate all source of water ingress through openings in the upper quadrant of the insulation system).
  • Locate the tracer in the upper air-space of the oversized rigid thermal insulation.
  • Use heat tracing installation details developed from Raychem and Thermon.
  • Do NOT spiral tracer on pipe (Spiraling causes problems during maintenance and is hard to control in installation and maintenance).
  • When project/contracting strategies permit, consider turnkey to provide full service "warm-pipe" warranty.



Tags: pipeline electrical heat tracing

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