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Long Distance Pipe Lines

Applications > Industrial Applications > Long Distance Pipe Lines
The Problem

Electric Heat Tracing is commonly used around plants for temperature maintenance or freeze protection of pipework and vessels. Heat Trace Limited manufacture parallel resistance constant wattage and self-regulating cables which are convenient for in-plant applications where pipe runs are usually relatively short, perhaps a few hundred metres or less.

In refineries, chemical plants, power plants, etc., offsite pipework can often involve longer pipe runs of a kilometre or more. Heat Trace developed its LONGLINE heating system for this application where the importance is often to be able to heat the pipeline from a single electrical supply, or supplies at pipe ends only. The LONGLINE 3 phase system is capable of single circuits of upto a few kilometres, and is a highly efficient system of proven reliability over many years.

Cross-country pipes are often used to transport oils and other fluids cost effectively. These long distance pipelines sometimes require even greater heating circuit lengths, with the provision of power supplies often having the greatest expense.

For these very long pipelines, Heat Trace has introduced SKIN-TRACE, a heating system for ultra long distance pipelines. The system comprises basic components of an insulated cable contained within an envelope, fed from a power supply and having a control system.

Heat Trace's expertise in specialised cable manufacture and controls development, combined with the skin effect concept, proven over 30 years, resulted in SKIN-TRACE, a heating system capable of circuit runs of many kilometres.

SKIN-TRACE skin effect heat tracing will usually provide the most cost effective overall heating system, both in capital and operating terms, where long distance pipelines require to be heated, whilst providing the lifetime reliability essential when the pipeline is buried below the ground.

The Solution - SkinTrace

The Concept

Heat is produced by the combination of a ferromagnetic envelope (usually in the form of a carbon steel heat tube) and an insulated copper conductor that passes through the envelope. At the remote end, the two components are connected to each other, whilst at the opposite end, the two are connected to an AC supply.

Current flows through the insulated conductor and into the heat tube where, by skin and proximity effects, the return current passes through and is concentrated towards the inner surface so that the outer surface of the heat tube is virtually potential-free.

Therefore. the heat tube may be directly welded, or fixed to the product line, which remains electrically insulated from the SKIN-TRACE system. The product pipeline may be grounded without affecting the SKIN-TRACE system, therefore ensuring electrical safety.

The current flowing in the heat tube is converted to heat that is supplemented by heat generated in the insulated conductor. The heat is transferred by conduction through the coupling from the heat tube to the product line. This coupling may take the form of a weld, or heat transfer may be improved by the addition of KONDUCT heat transfer cement where necessary.

In addition to buried pipeline installations, SKIN-TRACE may be provided for above ground, or underwater applications. 

System Components

The SKIN-TRACE system comprises four basic components:-

  • the heat tube and its accessories
  • the insulated cable
  • the power supply
  • the control / monitoring panel

The Heat Tube

 The SKIN-TRACE heat tube is carbon steel and is provided complete with all accessories - tube couplings, pull / splice boxes, power feed and termination boxes, and cable change of direction or turn boxes.

The Skin-Trace Cable

The SKIN-TRACE cable is a copper or plated copper conductor having high temperature insulation. Heat Trace manufacture SKIN-TRACE cable in silicone rubber and fluoropolymer insulations combining excellent temperature resistance and electrical properties with good mechanical strength and resistance to corrosive effects or abrasion damage during cable pulling.

The Power Supply

The power supply would usually comprise an incoming HV control cubicle and a power distribution balancing transformer.

The transformer is connected as a three to two phase, balanced load step down. Heat Trace Ltd have specialised in the development of control and monitoring equipment specific to heat tracing.

The Control / Monitoring Panel

A SKIN-TRACE output power, control and monitoring panel would usually include all necessary power control components, Heat Trace's DURASTAT electronic line temperature controller and circuit monitoring and alarms systems.

System Design

Heat Trace are able to provide System Design often within the framework of a turnkey contract.

Design will include heat loss computations and sizing of the heat tubes and the SKIN-TRACE cable. The method of heat tube attachment is specified. The transformer will be rated and specified, together with the control system.

The system will usually be designed to provide an output in the range of 15 to 100 watts per metre.

Systems may be designed for freeze protection, temperature maintenance, or for product temperature raising duties. Pipelines may be above or below ground with thermal insulation, either as factory pre-insulated pipes, or field applied using pre-formed sections.

System documentation will normally include isometric and schematic drawings, bill of materials and components, together with provision of operating manuals.

Heat Trace can install, or supervise the installation of the SKIN-TRACE heating system.

The heat tubes are welded into position onto the pipework together with accessories such as tube couplings, pull / splice boxes, junction boxes, etc, and the SKIN-TRACE cable is pulled into the tubes. The heat tube system is sealed, electrical connections made back to the power supply, and the system commissioned.

Where pre-insulated pipework is used, e.g. buried lines, Heat Trace may also be responsible for making good insulation at pipe joints along the pipeline in completing a turnkey project.

Product and Application Datasheets
Industrial EHT Handbook

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