The following information outlines many of the trends and pitfalls that can be encountered during the Installation and Commissioning of an electrical heating system. The basic structure and numbering system used in the outline have been repeated from IEEE-515, "Recommended Practice for the Testing, Design, Installation and Maintenance of Electrical Resistance heat Tracing in Industrial Applications," an excellent resource covering all phases of these products and systems. Emphasis has been placed on "soft" issues that may not be readily apparent are know to cause down-steam problems.
When reviewing the material, it should be apparent that a "system concept" is the basis for consideration. Instead of viewing the electrical heating system as an assembly of component parts, the electrical heat tracing should be viewed as a piece of an interdependent system that consists of piping, electrical tracer and thermal insulation. It follows that considerations for the design, installation and commissioning should look beyond the electrical boundaries to assure a reliable heat tracing system.
1. Receipt and Storage of Materials
As you receive materials and prepare them for storage, observing the following guidelines will help avert problems at a later date:
- Verify that correct type and quantity of materials were received
- Test cables (both bulk & and individually fabricated circuits) for damage incurred during shipping and handling (megger & continuity)
It is important to determine that received material is ready to use and to benchmark that cable and equipment has not been damaged. Discovery of problems downstream leads to responsibility problems and schedule delays.
1.1 Warehousing & Handling
In the areas of warehousing and handling materials received, follow these general guidelines:
- Store indoors in dry location in original boxes or reels
- Temperature conditioned storage if electronics are involved (may be space heaters in cabinets with temporary power)
For outdoor, site stored equipment is often exposed to weather extremes. It is not uncommon to find bad megger readings due to water in cable that has been stored outdoors. The water can enter from open ends of cable as it is cut off reels or even loose cable ends that have been submerged in puddles. Traced tubing has been found with waterlogged thermal insulation from open ends during storage.
Heat Tracing should be tested before installation, following these guidelines:
- Upon receipt of material for incurred damage during shipping & handling (megger & continuity)
- Individual controls should be bench tested to ensure proper calibration
The IEEE-515 working group is updating testing requirements for the use of a 500Vdc megohmeter as a minimum and recommending the use of a 1000Vdc for mineral insulated cables and 2500Vdc for polymeric cables. Minimum insulation resistance should be 20 megohm.
The move toward increasing use of lump-sum contracting requires that "ownership" be accomplished for receipt of materials, especially if the material is furnished by others. Testing as a condition of transferred ownership ensures that many problems with shipped materials is discovered at time of receipt. This applies not only to testing, but for checking quantities and material type.
2. Scheduling Installation
When scheduling installation of the heat trace system, follow these general guidelines:
- Coordinate schedule with the piping completion schedule. (including any hydrostatic testing that may require devices to be removed for the pipeline or cause rework)
- Coordinate with scaffolding and crane access requirements
- Coordinate delivery of materials
- Coordinate with other crafts, contract packages
- Review the impact that weather may have on the installation procedures
Beginning work too early can result in many problems. Hydrostatic testing may require the removal of instruments and in-line devices in the piping system that will require mechanical work that may impact installed tracer. Piping system that fail the hydrostatic test may require welding process or removal of piping that again can expose the tracer to damage.
Contract packages may provide many challenges, scaffolding and working platforms may not be shared by separate contractors. The tracing installation may be contracted to a mechanical contractor to control scheduling and prevent delayed work charges. This can result in an installer that is a non-electrical craftsperson and make sure that they are trained for the project.
Turnkey contracts are becoming more common. The installation of the tracer and thermal insulation can be performed by companies that are subsidiaries or associated with major manufactures. This service can provide benefits by providing a trained installer who is familiar with the manufacturers products as a system and can prevent problems associated with work delays in completion of the tracer installation and start of the thermal insulation installation.
3. Heating Cable Installation
These general guidelines should be followed for installing heating cable:
- Cables should be installed on a pipeline that is complete, free of rust, mill scale, no sharp edges and has been hydrostatically tested
- All installers should be trained in the manufacturers recommended practices and for any special details or standards
- Installation details that fit the application are a must
- Cables should be attached to the pipe according to the manufacturers specifications. Care should be taken to avoid high-halide content materials on stainless steel pipe
- Cables should applied in a manner to facilitate the removal of valves and small in-line devices and instruments without the cutting or damage to the heating cables
- Do not exceed maximum bending radius of the cables (critical for Constant Wattage, mineral insulated)
- All penetrations should be in the lower 1800 quadrant of the thermal insulation to minimize water entry sources. Outside load bearing pipe supports are preferred over through the insulation hangers and pipe shoes
- Use compatible materials with stainless steel piping or vessels
- Identify approved connection hardware for tracers to be used (BOM, manufacturers information, no substitutions unless written approval)
- Use only fiberglass tape or nylon ties to secure the tracer to the pipe (wire is acceptable for mineral insulated cables)
- Install caution labels per NEC requirements (Article 427-13).
- Consider Quality Assurance of all systems (especially, medium to large systems)
It is a good idea to develop a specification for installation on large projects to define all aspects of the installation and control of material. The practice of specifying the amount of extra cable to be applied at valves, devices and heat sinks works well but can cause problems if a device is missed on the heat trace circuit drawings. This problem can be mitigated by requiring the contractor to trace all heat sinks such as drains, high point vents, pipe supports, etc. even if they do not appear on the drawings but exist in the field. The contractor will have to assume other costs of rework if missed.
Since the initial installation will set the long-term operability and utilization of the system, a good installation is essential with attention to the details that if not done per design will "re-qualify" the system with each new low temperature experienced. If the system is not turnkey nor installed by a contractor with specialized heat tracing experience, consider Company or third-party quality assurance of the system. This service is also available from several manufacturers and can be combined with on-site follow-up of field problems and completing "as-built" drawings.
Anticipate what findings the QA effort will produce. Common problems are tracer not installed per design, insufficient tracing at valves, pipe supports and other devices that represent heat losses greater that of the pipeline. Other easily answered problems are where the wrong type cable has been installed or the circuiting in the field does not match design. There will also be gray area non-conformance issues where the tracer may be slightly less than design. Timely discovery and resolution of field problems is critical to avoid schedule delays.
Have ground rules been established for locating power connection, TEEs and end-seals during installation. What makes sense to the installing contractor may not be what the Company desires to support long-term maintenance. If there are concerns, they need to be identified by the Company during the design phase. The ground rules can be as simple as requiring all connections be visible from the ground and accessible by ladder. For complex multi-story processes this is an important issue.
Responsibility for approval to start work can vary with the type and size of the heating project. A walk-down of the pipelines can identify mechanical interference/problems that can impact the finished installation.
The continued improvement of tracers and components by the manufacturers has continued to improve. The products available today are easy to install but, training has proven to be an essential component of a successful installation.
3.2 Tagging and Identification
To properly identify heating circuits, use these guidelines:
- It is recommended that all heating circuits be permanently identified so that electrical components can be quickly identified or located.
4. Controls & Sensors
- Use rain tight or watertight enclosures for outdoor installations (or appropriate enclosure to meet the electrical area classification or environmental exposure)
- Design and install outdoor control enclosures to prevent water entry to from conduit and cable
Water intrusion into control enclosures is a common cause of premature failures. The water can contribute to corrosion problems within thermostats and electronic controllers and result in ground-fault current. Water and excessive moisture in control devices and power connection kits is the most common cause of "Nuisance" alarms with ground-fault protected circuits.
Provide "Tee" condulets in vertical piping before entering the boxes allowing any water entering the conduit system from above to drain-off before entering the enclosure. Entering the enclosure from the bottom is another method of preventing water entry into enclosures.
4.2 Ambient Sensing Temperature Controls
Temperature control sensors should be located in areas with representative ambient temperature. The sensor location should see a representative ambient temperature and should not be exposed to direct sunlight, process or building heat.
For ambient switched heating controllers or contactor switched panels, the failure of a single sensor can render an entire system inoperative. Consider the use of redundant ambient thermostats.
4.3 Pipe Sensing Temperature Controls
Follow these general recommendations to install pipe temperature-sensing controls:
- Attach the sensor securely to the pipe, spacing it 90° away from the cable. (Installing high-limit thermostats on non-metallic pipe is an exception to this recommendation)
- Be careful not to damage capillaries of filled tube systems, resistance temperature detectors (RTDs), or thermocouples (T/Cs) during installation
Pipe mounted temperature sensors (RTDs & T/Cs) for use in electrical tracing systems must be carefully selected. Such sensors can be a chronic maintenance problem unless the sensor mounting to the pipe, sensor leads, and transition to extension cable or termination are weather-tight and durable for the service.
The location of temperature sensors can have a big impact on temperature control since there are always temperature variations within a traced system that result from piping geometry, adjacent heat sources, sunlight, indoor vs. outdoor, rain, wind, etc. The use of sensors like RTDs affords the opportunity of installing multiple sensors or changing locations where required.
5. Cable Testing During/After Installation
5.1 Prior to Installation of Thermal Insulation
Follow these general recommendations for testing after cable is installed and before thermal insulation is installed:
- Test at receipt of material
- Test each circuit after it is installed on the pipeline and before the thermal insulation is installed
- Use an Installation Checklist form to document testing and installation progress
- Only "trained" installers should be permitted to install cables
This test is important for two reasons: first, to prevent the rework that would result if the thermal insulation was installed over a damaged tracer; second, with separate contractor responsibility for cable and thermal insulation, the test establishes ownership points.
5.2 Completed Circuit
Follow these general recommendations for testing the completed circuit:
- Test the completed circuit after the thermal insulation is complete.
- Use the Installation Checklist to verify completed work by tracing installer (components, connections, caution labels on thermal insulation, etc.)
This test assures that the tracer was not damaged during the installation of the thermal insulation. Depending on contract splits such as where the tracer is installed by a mechanical contractor and the branch circuit wiring is handled b an electrical contractor, becomes a hand-off point where the branch circuit cables are not connected to the heating cable leads until after the test is completed.
6. Thermal Insulation Recommendations
The following guidelines are recommended for the installation of the thermal insulation:
- Verify that the type, inside diameter and thickness agree with the system design basis.
- Protect against water intrusion during storage, handling and installation. Use temporary protection or other means to assure that water will not enter the thermal insulation system before the weather barrier is completely installed.
- Apply insulation to exposed heat sinks such as pipe shoes, supports and appurtenances, and seal with an appropriate weather barrier.
- Select a thermal insulation material that is the best insulator within the operating temperature of the system.
- Select an insulation system that is not hygroscopic, or is a respirable fiber.
- Install draft stops on long vertical lines to prevent chimney effect loss of heat from the lower portions of the pipeline.
- Do not "route-out" rigid thermal insulation, especially for self regulating cables.
- Identify where "soft" or removable insulation will be used.
The importance of the thermal insulation and its relationship with heating system cannot be understated. The successful operation of an electric heating system is dependent on a properly selected, installed and maintained thermal insulation system. It is important for the designer and Company/operator understand this fact-of-life and consider the thermal insulation system as an essential part of a "heated system."
Establish procedures to be followed during installation to assure that water cannot enter the insulation system. The open ends of the thermal insulation can allow water to enter the insulation to become trapped in low points introducing early failure. Solutions such as sealing openings with mastic at flanges or temporary covers can prevent down-stream problems.
Know what types of fasteners will be used to secure any metal outer weather barriers. It is not uncommon to use sheet metal screws for covers used at straight sections and at preformed fittings. Long screws can damage the heating cable.
Early failure of piping systems can result from water trapped inside the insulation or entering during operation. The corrosion under wet insulation is a common problem in industry that results in millions of dollars of losses per year. While the corrosion problem is more common in steam and high temperature electric systems that are periodically cycled on and off, it stresses the importance in selection of proper thermal insulating materials and maintaining a weather tight system.
If "Soft" or removable insulation will be used and has not been accounted for in the design, there may be big differences between the insulating efficiency of the pipe insulation and what is used at valves and in-line devices. The process for identifying where "soft" insulation at valves and devices should include considerations for other major equipment (such as pumps) that are likely to require frequent maintenance. Solutions to high maintenance equipment may be removable insulation, self-contained heated enclosures, castings with enclosed heaters, etc.
7. Commissioning & As-Built Changes
Commissioning and as-built changes should be documented according to the following guidelines:
- Establish procedures for checkout and commissioning of each circuit.
- Verify the qualification of those performing the checkout procedures.
- Utilize Commissioning Checklists forms for documenting testing and start-up data (turn over to Operations owner).
- Require "As-Built" drawings (has system been checked to drawings).
- Verify that each branch heating circuit is "pad lockable."
7.1 Processing Field Changes that Affect Design
Follow these guidelines for processing changes in the field that will affect system design:
- Anticipate that there will be field changes, and the need to have a process to respond quickly with design, procurement and/or installation.
- Do not allow any changes that affect system without design (does not include minor changes for length of cable for field routed piping).
- Special emphasis on Class 1 - Division 1 heaters, alert design problem to heat tracing engineer (or manufacturer as appropriate). Change design accordingly and verify conformance to project requirements. Maintain documentation file on record for life cycle of system.