Pipeline heating

• Configuration of Heating System
• Parameters of Heating System
• Basic Criteria for Choosing Heating System Parameters

In oil producing and petrochemical industry pipelines of different diameter and purpose very often fail because of clogs, narrowing of flow area and high viscosity of delivered liquids. Teplomag system maintains necessary temperature in accordance with technology, provides liquid low viscosity and estimated line capacity. Water pipelines heating eliminates danger of their breakdown during freezing in winter period and at the system start up. Heated pipelines can be located practically in every environment, and also can be underground and submerged.

Teplomag system uses heating cables, as heat-producing elements, since they in the best way solve the problem of heating branched and long pipelines. Unlike ordinary power cables, which function is delivery of power to the load with minimum losses, heating cables are load by themselves, but a distributed load. All 100 % of voltage, delivered to the heating cable, “falls” in it. Heat emission taking place at that should not cause the cable or heated object overheating. Three main types of heating cables are used: self-regulating tapes, series resistance cables, SKIN-cables..

For products delivered over pipeline networks essential dependence of kinematic viscosity on temperature is quite typical. Besides, at definite temperatures settling out of solid fractions is possible, and also product hardening. It may result in total break of the pipeline, and, as a consequence, considerable expenditures on their restoration. Pipelines heat tracing systems and tank heating is the only solution of these problems. They have been used comparatively long, but became widely spread only after appearance of relatively inexpensive heating cables. The main purpose of these systems is to provide delivered product temperature maintenance.

It allows:

• to keep the value of product kinematic viscosity, not allowing clogs formation and pipeline stoppage;
• to prevent solid fractions settling out from delivered product;
• to increase product delivery speed;
• to start up the pipeline, fully or partially filled with product, after its stop;
• to provide proper drain of viscous products from tanks for shortened time interval.
• Heating systems are used also in pipelines for gas products delivery. In this case their main function is to prevent condensate dropout at gas cooling.

• heating part: heating cables , and accessories for their fastening on the pipeline, local elements for pipeline units heating (flanges, valves, pumps);
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  Typical heating system
  
  
• distribution network in the form of power and data cables, distribution boxes and fastening elements, which supply power to all elements of the heating part and send information signals from sensors to the control system panel.
• control system: control cabinets, thermostats,pipe and air temperature sensors, flow sensors, start-control and protective equipment.

Parameters of heating system

Depending on number of technical features there several types of heat tracing systems can be singled out. Their parameters depend on:

• delivered product characteristics (product maximum temperature, temperature at the pipeline input, temperature of hardening, temperature of solid fractions settling out);
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• pipe characteristics (material, geometrical dimensions, thermal insulation, open or underground location);
• pipeline topology (linear, branched, with small or large number of sections);
• environmental characteristics (minimum and maximum temperature of ambient air, wind speed).

Based on these data the following parameters are defined:

• design value of pipeline maximum heat losses;
• type of heating cable (different cables may be used in one system), its length and location on the pipe (threads number, laying pitch);
• type of accessories for sections powering (distribution boxes, terminations, couplings);
• distribution network structure and parameters (or its absence);
• • control system structure and parameters (thermostats and commutation devices, control cabinets, transformers). Since oil and oil products delivery systems are explosive and fire hazardous objects, only explosion-safe components are used in heating systems (heating cables, thermostats, mounting and distribution boxes). They are also adapted for operation in excessive humidity conditions, in corrosive environments, for underground and submerged pipelines laying certificate ISO 9001-2000 (issued by German certification body TUV 28.09.04).

Basic criteria for choosing heating systems parameters

Pipeline length:

• up to 100 m – all kinds of self-regulating and series resistance heating cables are used; there is no need in distribution network;
• up to 200–300 m – self-regulating and series resistance cables are used; as a rule, distribution network is necessary, but its share in total system cost is small.
• up to 3–6 km – without distribution network, only series resistance cables of big cross-section can be used (“Longline”), and also special composite cables, combining self-regulating and power cables;
• up to 8 km – without distribution network, only series resistance cables “Longline” and SKIN-effect system can be used;
• up to 15 km – SKIN-effect heat tracing system, powering from one end;
• up to 25–30 km – SKIN-effect heating system, powering from both ends or from the pipeline intermediate point.

The vital criterion of changing the heating system design from one to another type is its cost. Beginning with 1–2 km length, cost of distribution network for self-regulating cables highly increases, and at about 3–4 km their use becomes economically non-feasible. At linear pipeline configuration, beginning with 6–8 km, economically feasible, secure and reliable solution is SKIN-effect system.

Operation temperature:

• 60–80 °С – in this case practically all kinds of self-regulation and zonal cables are used; necessary power range up to 80 W/m is easily achieved;
• 100–200 °С – in this case only self-regulating cables with fluoroplastic matrix are used;
• 220–400 °С – special series resistance cables with mineral or fiber glass insulation, as a rule, in stainless steel tube, are used. Typical application – heat tracing of facilities for receiving heavy oil products, bitumen and mazut refinery and storage units. Relating to heating cables it is necessary to distinguish pipeline or product maximum temperature allowable for the cable, and temperature, which owing to cable, is possible to maintain on the pipeline. As a rule, the last is less than the first one at least by 10–20 °С or (often) more. The most typical case of essential difference in these temperatures is pipeline heat tracing, occasionally cleaned with open steam at temperature up to 200 °С. But at operation mode pipeline temperature can be not higher than 60 °С. Nevertheless, in this case only self-regulating cables (REFERENCE) with fluoroplastic matrix or cables with mineral insulation can be used.

The preheated vessels on Harampurskoe field

The pipeline system Eastern Siberia-Pacific Ocean is being expanded

International exhibition” Oil and gas of Turkmenistan” Ashgabad.