Electrical Heat Tracing Research Articles

Analysis for arctic valve heat tracing requirements

Since the introduction of electrical heat tracing, a major operations concern has been design considerations for adequately determining the heat loss of valves in piping systems. Analyses have been done on straight pipes and this part of the design is usually well understood and few problems arise with careful design and installation. Valves, supports, instrumentation, and other devices with "extended surfaces" (noted as "thermal features" in this paper), if not characterized properly, may cause problems with plant operations. The surface area of a pipe increases linearly with increase in diameter, but the surface area of a valve increases with the square of the pipe diameter for valves. This causes significantly increased heat loss and a lower maintain temperature. A frozen valve on the North Slope of Alaska instigated this paper, but the issues associated with this situation have wider application. A common valve heat loss factor, independent of pipe diameter, is sometimes recommended. Studies have found this causes small-diameter valves to be overheated and large-diameter pipes to be underheated. This paper investigates real heat loss of valve systems on the North Slope of Alaska. Two years of data (800 MB) were analyzed and interpreted, and dynamic experiments were conducted along with building a finite-element model. Thermal insulation of valves is shown to be an area of critical concern. Valves and other "thermal features" are usually thermally insulated with fabricated blankets with lacing or Velcro used to attach the insulation. This attachment method is used in order to allow access for maintenance. These blankets usually have a lesser thermal insulating capability (larger k factor) than the insulation for the straight pipe. The insulation thickness may also be less. The purpose of this paper is to highlight these parameters and make design recommendations for critical thermal features and large /spl Delta/T heat tracing applications.

Electric heat tracing: using electronic controls to enhance performance and safety

The Mobil Refinery and Lube Oil Blending Plant at Notre Dame de Gravenchon, France is immediately adjacent to the mouth of the Seine River and its environmentally sensitive estuaries. All the processes and equipment in this facility must operate in a mode that is uncompromising with regard to any environmental impact. Most of the additives present no direct hazard as provided, however, some of them are seriously damaged when overheated-the worst consequence being an exothermic reaction with gas released into the atmosphere, resulting in both a safety hazard and environmental effects. Electric heat tracing and the control system operate to insure the temperatures of the process pipes, equipment, and vessels are maintained within very close tolerances. Maintaining the process temperature is an integral part of the operation that ensures viscosity and other process parameters that ultimately determine the quality of the lube oils produced.

Electrical heat tracing: international harmonization-now and in the future

In the past, electrical heat tracing has been thought of as a minor addition to plant utilities. Today, it is recognized as a critical subsystem to be monitored and controlled. A marriage between process, mechanical, and electrical engineers must take place to ensure that optimum economic results are produced. The Internet, expert systems, and falling costs of instrumentation will all contribute to more reliable control systems and improved monitoring systems. There is a harmonization between Europe and North America that should facilitate design and installation using common components. The future holds many opportunities to optimize the design.

IEEE Std 515 takes a step toward harmonization

IEEE Recommended Practice 515 for the "Testing, Design, Installation, and Maintenance of Electrical Resistance Heat Tracing for Industrial Applications" was first published in 1983. During the first five-year review cycle, which took place from 1984 to 1990, a major effort was made to harmonize 515 with other North American and European standards. The Project Authorization Request (PAR) for the second five-year review cycle was approved in June 1993. At this time, changes to the United States National Electrical Code (NEC) were proposed that would have a major impact on heat tracing systems. In Article 427, consideration was given to requiring metallic coverings on all heating cables, and ground-fault equipment protection on all heat tracing circuits, regardless of area classification or application. In addition, expanding the 1996 NEC to include IEC Zone methods of hazardous area classification was proposed. Inclusion of area classification Zone methods provides wide harmonization. IEEE 515 is now a standard which will provide the user with a means to achieve a safe and reliable heat tracing system.

THERMAL STRATIFICATION IN A HORIZONTAL CIRCULAR CYLINDER WITH EXTERNAL HEAT TRACING

Thermal stratification in a horizontal circular cylinder with electrical heat tracing is studied numerically. Two-dimensional unsteady models for the external heat tracing of thermally stratified cylinders are developed. Dimensionless governing equations are numerically solved by using finite control volume techniques and the SIMPLE algorithm. Temperature distributions, streamline profiles, and heat transfer rate of the fluid inside and at the cylinder walls are analyzed. The results obtained indicate that external heating can reduce the effect of thermal stratification and the temperature difference between the upper and lower part of the cylinder inner wall.

Why train in the use of electrical heat tracing?

Increasing emphasis is being placed on training for electrical equipment in hazardous (classified) areas for many reasons. The focus of this article is to develop training outlines, drawing from background information and references for the various crafts that require training. Adequate safety considerations of electrical heat tracing systems address proper training for the individuals responsible for their design, installation, operation and maintenance. The reliability and safe operation of the systems are dependent on this knowledge.

IEEE recommended practice for the testing, design, installation, and maintenance of electrical resistance heat tracing for commercial applications

Specific test requirements for qualifying electrical resistance heating cables for commercial service and a basis for electrical and thermal design are provided. Heater characteristics are addressed, and installation and maintenance requirements are detailed. Recommendations and requirements for unclassified heating cable applications are provided.

Safety considerations for electrical heat tracing

Since the advent of electrical heat tracing over 50 years ago, many challenges have confronted industry to ensure safe and reliable heat tracing operation. Reliability of heat tracing systems can directly affect safety-related operations, such as fire protection and emergency eyewash and safety showers. As a good practice, the safety of process systems should not be dependent on the performance of a single component of the heat tracing system. The primary purpose of this article is to address the issue of high-impedance, low-current faults that have been reported in electrical heating cables. These faults usually initiate from phase to ground but have currents that are insufficient to trip the circuit protective device. However, the faults can dissipate enough energy to cause fires and other equipment damage.

Electric heat tracing design for impedance and skin effect systems

When a material is transported by pipeline at a temperature above its surroundings, it will lose heat. Insulation will slow the heat loss, but will not prevent it. Temperature can be maintained by adding heat to make up the loss. This can be accomplished in many different ways. Heating stations can be located along the pipeline to make up the loss at discrete points. The problem with this technique is that the product does not stay at a uniform temperature, and if flow stops the product could lose so much heat that it becomes unpumpable. Heat can be added along the entire length of the pipeline by applying a heater to the pipe. This is commonly called heat tracing. Heat tracing can be accomplished using many different techniques. Steam, hot oil, hot water, and electric heaters are all commonly used methods. Electric tracing can be further broken down into parallel heating cables, series heating cables, self-limiting heating cables, mineral insulated cables, impedance heating, and skin effect heating. Each method has advantages and disadvantages. Here, the authors present an overview of the field and then focus on impedance heating and skin effect heating, and attempt to describe the criteria for selection of the best system for a specific application.

Electric heat tracing design from a temperature perspective

Many plant processes involve the transfer and storage of products in piping. Often it is found that the products being transferred and stored can freeze, become extremely viscous, or condense undesirably if allowed to cool to plant ambient temperatures. While it is sometimes possible to prevent excessive cool-down by a combination of insulation and flow maintenance during processing hours, it is usually not practical to do so during nonprocessing periods. Hence, the addition of heat to the insulated piping and equipment is a common plant requirement. Today, one of the more widely used techniques for adding the desired heat is electric heat tracers. This article presents various facets of the design process involved in attaining a functional heat tracing design. In particular, finite element analysis (FEA) is presented to provide new insight into the details of tracing design in three areas: (a) nonuniform heat flux conditions; (b) temperature variation about a traced pipe's circumference; and (c) power output decline of a self-limiting heater on thermally nonconducting pipe.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Update on IEEE Working Group 622-electrical heat tracing systems (IEEE 622) and related standards

IEEE 622 Working Group has produced three recommended practices that are available through IEEE publications. The subject of these practices is electric heat tracing systems. IEEE Std 622-1987 (IEEE Recommended Practice for the Design and Installation of Electric Heat Tracing Systems for Nuclear Power Generating Stations) was originally issued in 1979 as a document specifically for use in nuclear power plants. This document was updated in 1987. The second document. IEEE 622A-1984 (IEEE Recommended Practice for the Design and installation of Electric Pipe Heating Control and Alarm Systems for Power Generation Stations), addresses the control and alarm systems for heat tracing systems, both nuclear and fossil. The third document IEEE 622B-1988 (IEEE Recommended Practice for Testing and Startup Procedures for Electric Heat Tracing Systems for Power Generating Stations) completes the series with the recommendations for commissioning the heat tracing systems. The working group proposes to combine the three documents into one. IEEE 622A and IEEE 622B continually refer to IEEE 622-1987 and the combination is not only justified but necessary in the interests of conciseness and ease of use. Other documents related to electric heat tracing are mentioned, and additional updates are discussed. Future tasks of the group are mentioned.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Use of the personal computer in the design of electrical heat tracing

The status of computing power, in the design area and plant area, available for heat tracing tasks is reviewed. The use of computers in heat tracing design is discussed. and supplementary programs are listed. CAD (computer-aided design,) programs are being used for isometric and electrical schematic drawings of heat tracing. An example of a setup for CAD using preformatted details is given. Some of these details follow the illustration. Computer program compatibility is discussed, and examples of program operation failures are given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Recommended practice for electrical resistance heat tracing

RP515, IEEE Recommended Practice for the Testing Design, Installation, and Maintenance of Electrical Resistance Heat Tracing for Industrial Applications, was published in 1983. Compared to other US and worldwide standards, RP515 provided a comprehensive set of guidelines for heat tracing in industrial applications. However, during the first year after publication, it was requested that RP515 be revised in order to include recommendations for Class I, Division 1 (CID1) applications and to update product testing in view of new technologies and constructions. The IEEE Standards Board granted its approval for the revised RP515 in August 1989. Publication was completed in early 1990. Revised RP515 provides a basis for the successful application of heat tracing in unclassified, Class I, Division 2 (CID2) and CiD1 areas. Background to and an overview of RP515 are provided, with special emphasis on the revised portions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Control of self-regulating heating cable for use in pipeline heating applications

Self-regulating heating cable is an effective method of electrical heat tracing. The control of temperature without conventional sensors such as resistance temperature detectors (RTDs) and thermocouples is described. The theory of temperature control using variable self-regulating cable is discussed. Characteristics unique to this method of heat tracing are detailed, as is a controller specified to meet these requirements. A cost-effective control system is described, and laboratory results are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design, commissioning, and operational experience of heat tracing system with extensive electronics monitoring

One of the most extensive heat tracing monitoring systems ever installed is examined. Over 400 circuits in a crude oil separation facility are independently and individually monitored. The results of the initial construction commissioning and the first six months of operation are reported. Analysis of cost-effectiveness and engineering lessons learned about electrical heat tracing systems operations are examined in detail. The results of an operational system are examined. The general philosophy and the physical hardware and software of the heat tracing monitoring system are discussed. An analysis of the operational logs of the first six months of operation of the system is included. Various topics related to successful heat tracing projects are addressed. >

Technological advancement in self-limiting electric heat tracing cables

Self-limiting heating cable design utilizing polycrystalline power disk technology are presented. These cables are capable of delivering a wide range of wattages for process applications and limiting their output with an increase in temperature. They are unique in that the output is not substantially affected by applied voltage and that they are unaffected by exposure to temperatures up to the temperature rating of the electrical insulation. The construction characteristics, qualifications, installation, and operating characteristics of the polycrystalline power disk cables are examined.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electric heat tracing systems-standards development (IEEE Power Generation Comm. Report)

Standards development activities at IEEE in the area of electric heat tracing systems is reviewed, and the pertinent standards are summarized. They are: IEEE Std 622-1979, recommended practice for the design and installation of electric pipe heating systems for nuclear power generating stations; IEEE Std 515-1983, Recommended practice for the testing, design, installation and maintenance of electrical resistance heat tracing for industrial applications; and two standards in the development process, IEEE Std 622-198(6), Recommended practice for the design and installation of electric heat tracing systems for nuclear power generating stations, and Project 622B, Recommended practice for testing and startup procedures for electric heat tracing systems for power generating stations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Power line carrier systems for electric heat tracing control and monitoring

Addressable power line carrier (ADPLC) is the latest technology for electric heat-tracing systems. ADPLC systems are unique in that dedicated instrument wiring is not required for centralized temperature control and monitoring. The applications and value of ADPLC systems are examined. >

Electric Heat Tracing Requirements for Post-Accident Sampling Systems in Nuclear Power Generating Stations

Where hydrogen analyzers and remote radiation monitors are used to meet the NRC post-accident sampling requirements, electric heat tracing may be required on the sample lines to prevent condensation of moisture in the lines which would affect the accuracy of the monitoring equipment.

Electric Heat Tracing Requirements for Post-Accident Sampling Systems in Nuclear Power Generating Stations

Electric Heat Tracing Requirements for Post-Accident Sampling Systems in Nuclear Power Generating Stations