Longline Heating

LongLine-Heating-Industrial.jpg Industrial longline heating is necessary to heat long pipelines, like transfer lines between processing plants or between storage or transportation facilities, for pipe freeze protection, condensation prevention, viscosity control, or temperature maintenance.

The complexity of this pipe heat trace system comes from the need for long electrical circuit lengths, usually with a single electrical power point.

Longline Heating – A Complete Heat Management System Approach

nVent Thermal Management offers a wide range of industry-proven longline heating solutions as a complete heat management system which includes the selection of appropriate pipe heat trace technologies, advanced control system technologies, in addition to turnkey services, such as engineering design services and site services.

Heat-Tracing System
  • Electric heat trace cables – heat trace cables that maintain the temperature of non-flowing fluids by replacing the heat lost through the thermal insulation on pipes, vessels and associated equipment.
  • Control and monitoring solutions – devices such as thermostats, controllers, and electric panels that monitor and/or control heat trace cables to help maintain the temperature of the fluid through a heat traced pipe.
  • Components and accessories – items for making electrical connections and properly completing the installation, such as end terminations, glass tape and warning labels.

We can supply the individual components, provide engineering design services and will even install and maintain the entire system.

When our advanced heat trace products are combined with our services, you get an integrated solution that is strategically planned and executed for an optimum heat management system (HMS). By managing and executing all aspects of the heat trace system design and installation, we provide a single interface to your project team.

Longline heating is required to ensure that liquids are transported cost-effectively and safely over long distances. In the absence of longline heating, the following problems could result in significant environmental and property losses:

  • Liquids becoming too viscous
  • Gases condensing
  • Liquids freezing resulting in catastrophic pipe failures

Longline heating applications have several challenges, such as:

  • Large pipe diameters
  • Elevation changes along the length
  • Remote locations
  • Lack of power availability along the length

For pre-insulated pipes, additional challenges include:

  • Alignment of channels
  • Lack of insulation at the pipe joints
  • Pulling long lengths of cable through the channels
  • Lack of accessibility of connection kits

Reliable Engineered Solutions

nVent Thermal Management designed longline heating technologies keeping these challenges in mind.

  • Our nVent RAYCHEM, nVent PYROTENAX, and nVent TRACER heat trace cable technologies allow single circuit lengths from 1000 ft to 15 miles from a single power source. We have:
    • RAYCHEM self-regulating, cut-to-length heat trace cables for temperature sensitive fluids
    • RAYCHEM polymer-insulated series resistance heat trace cables for medium to high temperature applications
    • RAYCHEM STS Skin-Effect Heat-Tracing cables for very long pipelines
  • These heat trace products typically come in long lengths minimizing the installation costs of the system

In addition, we meet longline challenges by offering:

  • Customized pipe supports, customized power distribution systems, optimized insulation systems and pre-fabricated/ pre-insulated piping systems to minimize the total costs of the longline heating system.
  • Advanced control systems with multiple temperature inputs to adequately monitor and control longline heat tracing.
  • Fiber optic temperature sensing to measure the temperature of the pipe along its length with 1 meter resolution and 1ºC sensitivity for some specialized applications. This helps to precisely locate temperature variations during commissioning and troubleshooting of the lines.
Premiere Heat Management System Services

A properly designed heat management system is complicated. Let our heat trace experts provide you with turnkey solutions and project management through all phases of your pipe heat tracing project to ensure that you stay on schedule and have an optimal heat trace system that will provide you with many worry-free hours of operation

  • nVent Thermal Management is a global organization with a complete line of heat tracing systems, superior technical support, proven project execution strategies, and high safety standards, making us an ideal partner for our customers worldwide who benefit from our expertise, products, and services to meet their heat management system needs.

Longline heating systems can be complex to design and install. For this reason nVent Thermal Management offers several technologies to choose from, thus providing the best cost optimization for your longline heating project. The longline heating technologies are:

Self-Regulating Technology

Self regulating

nVent RAYCHEM self-regulating electric heat trace cables are ideal for applications such as freeze protection and process temperature maintenance on longline heating systems.

  • Depending on cable choice, self-regulating electric heating cables can withstand continuous exposure temperatures to 300°F (150°C), intermittent exposures to 420°F (215°C) and maximum circuit lengths of to 12,000 feet (3660 m).

Mineral Insulated (MI) Technology

RAYCHEM mineral insulated electric heat trace cables are ideal for longline applications that require high temperature maintenance and/or have high temperature exposures, or require high power output. RAYCHEM mineral insulated heat trace cables:


  • Are used in many applications, including transfer lines
  • Are rugged and economical and can be used for lines up to 5000 + feet (1500 + m)
  • Use a 600 Vac Delta or Wye electrical configuration that balances the electrical load
  • Require an engineered design that must be done on a case-by-case basis because the total resistance must be matched to the transformer characteristics

Series-Resistance Technology

RAYCHEM flexible series-resistance electric heat trace cables are ideal when circuit lengths exceed the ratings of conventional parallel-resistance heat trace cables and you need a single power source.

  • Ohmic heating of the conductor provides the heat in this series circuit heating cable
  • For this type of technology, you must use nVent Thermal Management’ Engineering design services, since the wattage output depends on the total circuit length and the voltage applied

RAYCHEM SC electric heat trace cables are available in single-, double- and triple-conductor configurations for single- or three phase system design.

  • The resistance conductors are electrically isolated with high-temperature, heavy-wall fluoropolymer; a grounding braid; and a fluoropolymer outer jacket.
  • Maximum maintain temperatures to 250°F (121°C) and exposure temperatures to 482°F (250°C) are available.
  • SC electric heat trace cables are capable of circuit lengths to 12,000 feet (3658 m) with one power supply point, and voltages to 600 Vac.

Skin-Effect Heat-Tracing Systems Technology

Skin-Effect Heat-Tracing Systems Technology Graphic-Thumbnail.jpg

RAYCHEM STS Skin-Effect Heat-Tracing System is a versatile engineered heat management system that is designed to deliver heat for medium to long pipelines.

Applications include:

  • Material transfer lines
  • Snow and ice melting
  • Tank foundation heating
  • Subsea transfer lines
  • Prefabricated, pre-insulated lines
  • Longline pipe heating

As the industry leader in offering single source responsibility for heat management systems, we offer Skin-Effect Heat-Tracing systems that combine system engineering expertise with proven procurement / construction capabilities.

Advanced Control Systems

nVent Thermal Management offers a number of RAYCHEM advanced control systems designed specifically for longline heating applications. The RAYCHEM control and monitoring products:

  • Allow for  customized power distribution systems, three-phase current monitoring and high current switching capabilities all of which result in a more reliable and optimized heating system
  • Are capable of sensing up to eight process temperatures for each individual control circuit
  • Allow the circuit to be controlled on minimum, average or designated temperature input
  • Include sophisticated control methods that provide monitoring of circuit integrity, performance and ground-fault current, and ground-fault protection

For certain specialized applications, nVent Thermal Management also offers fiber optic temperature sensing solutions to measure the temperature of the pipe along its length with 1 meter resolution and 1ºC sensitivity.

Optimized Heat Management System Ensures Safe Sulfur Transport at Large LNG Plant
Qatar_safe sulfur.jpg
Key Challenges

The Qatargas Sulfur Transfer Line project consisted of a 35-km, dual, 12-inch sulfur pipeline constructed to transfer molten sulfur from 11 producers to a sulfur pelletizer facility. Heat management system challenges include:

  • Tight range of allowable temperature from 125ºC to 145ºC for molten sulfur with a set point of 135ºC along the entire length of pipeline.
  • An outdoor large sulfur pipeline with significant weight, multiple flow paths, and vertical expansion loops every 150 m.
  • Capability to re-melt and re-heat solidified sulfur without causing overheating or overexpansion.
  • A 100% redundant heat management system for the pipeline.

To meet the needs of this challenging longline heating application, nVent Thermal Management employed the following heat management system:

  • Inherently safe nVent TRACER skin-effect heat tracing system which has high exposure temperatures and efficient heat transfer to the pipe.
  • State-of-the-art nVent RAYCHEM control and monitoring system with vacuum contactors.
  • Finite element analysis to determine the temperature profile of sulfur across the cross section of the pipe.
  • Fiber-optic based distributed temperature sensing system that provides dynamic pipeline temperature profile at each meter with 1ºC accuracy for the entire length.
  • Multi-power heat delivery mechanism with 70% of installed power for normal operating conditions and 100% of installed power for heat-up/re-melt conditions.
  • Multi-layer thermal insulation system with high temperature expanded perlite inner layer, load bearing closed cell foam outer layer and UV resistant jacket.
  • Full service procurement of materials, project management, construction and commissioning of the pipeline.

TRACER skin-effect heat tracing system, RAYCHEM control and monitoring system.


nVent Thermal Management’ ability to engineer and integrate multiple technologies with its expertise in construction and commissioning heat management systems resulted in a world-class, safe, reliable, and efficient heat trace sulfur pipeline with the following benefits:

  • The TRACER skin-effect heat tracing system not only minimized the number of circuits, but also resulted in better heat transfer and low temperature differential between the pipe and cable sheath, thus leading to a safer longline heating design.
  • The finite element analysis and RAYCHEM control and monitoring solutions ensured that the sulfur temperatures did not go outside the tight control temperature range under normal operating conditions.
  • The fiber-optic distributed temperature sensing system provided continuous monitoring of the temperature along the entire length of the pipe. This helped to locate hotspots along the length of pipe during the re-melting process and in turn avoided excessive pressure generated by melting sulfur.
  • Multi-power heat delivery mechanism and multi-layer insulation systems not only optimized the total operating costs of the longline heating system but also contributed to shorter re-melt duration.
  • By assuming total responsibility of the heat management system, nVent Thermal Management ensured that the project was completed on time, safely and to the satisfaction of the customer.

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