The following information outlines many of the problems and concerns that can be encountered during the Maintenance and Operations 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, operation and maintenance should look beyond the electrical boundaries to assure a reliable heat tracing system.
1. General Maintenance Requirements
- Requires good initial installation
- Qualified maintenance personnel are required with a thorough knowledge of the equipment and the ability to locate problems and repair any component
- Good documentation and test and repair records are required
- A preventative maintenance program should be in place
- Require heating circuit to be turned off for all work that will require removal of the thermal insulation
OSHA requirements for plants where highly hazardous chemicals are contained within the process restrict work on electrical circuits to "qualified personnel." Proximity to energized circuits, if the energized electrical tracer were compromised or damaged, non-electrical maintenance personnel could be exposed to possible electrical shock.
2. Visual Inspection
- Periodic visual inspections should consist of carefully observing for damage or defects in the thermal insulation
- The tracers and components should be inspected for signs of overheating, absence of water or moisture, corrosion and foreign matter
The use of checklists provides a good means of assuring that the common problems associated with heating circuits are systematically checked.
With the cultural change taking place in many segments of industry today, the overlapping of craft responsibilities and attaching of maintenance personnel to the business unit, there is a shared commitment and responsibility that extends beyond specific responsibility. For traced systems there should be a shared vision that considers all factors that can cause a system to fail. Maintenance electricians should be just as concerned with missing, damaged or water soaked thermal insulation as with electrical problems.
3. Periodic Operational Check
- Schedule at regular intervals depending on the importance and usage of the heat tracing system to the process or plant
- Check freeze protection systems in the fall, before the heating system
- Check process heating systems on a more frequent basis
- Check each circuit for electrical insulation resistance, continuity or normal current flow and proper voltage
- Check controls for proper settings, indication and operation
- Preventive maintenance of electro-mechanical thermostats per manufacturer's instructions (lubricate moving parts, tighten connections)
The use of checklists also provides a good vehicle for administering a maintenance program. In Industry today, there is a real conflict with the focus on programmed maintenance to provide better utilization of production facilities with the realities of downsized corporations and its impact on available maintenance and technical resources. The use of state-of-the-art control systems can bridge the gap in many areas to provide on-line diagnostics equivalent to that provided for process controls. The use of ground-fault detection, current and temperature alarming and features such as auto-cycling can be integrated into off-the-shelf heating controllers and alarmed into monitored control rooms or process control systems for event recording and visual/audible alarms. The use of real-time or autocycling controllers can provide year-round monitoring of circuits which bridges the gap in seasonal maintenance.
Establish a procedure for re-commissioning the system after repairs are made. Assuming that the heating cable or other repairs have corrected the problem without verification of operation is risky since fault currents in heating circuits can introduce other problems.
Consider the need to calibrate or verify operation of high limit controls that may be needed in processes to prevent excessive temperatures that could result in safety or product quality problems. These could be required per OSHA regulations or ISO-9000 procedures. Applications of electric heat in areas of personnel safety may also be a concern. The periodic testing/calibration of high limit thermostats is needed in emergency safety shower/eye wash applications (refer to ANSI Z358.1, IEEE-515.1).
4. Record Keeping
- Keeping up-to-date records of electric heat-tracing systems is an important aspect of a good preventative maintenance program
- Maintain original installation drawings with up-to-date information on the heater type, length, line size, watts per foot, power source type of controller and location of the power connection
- Use a standard checklist to provide a record of inspections
- Other maintenance records may include cost or repair record, maintenance schedule of inspections and inventory control
A down-side of the increasing use of central rack mounted control system has been the unauthorized change of controller setpoints or switching to manual operation. It is not uncommon to find system provided with sophisticated electronic control systems running flat out at higher setpoints. The wasted energy can be dramatic and most problems tend to get worse without attention. Use system passwords, configuration lockouts as part of the set-up routine to prevent phantom changes.
The use of packaged computerized plant maintenance systems usually contain all the elements to provide printed-out maintenance activities, individual records of each circuit, inventory control and the ability to generate shop-orders for maintenance and repair. Advanced systems can also store drawings, original purchase orders and vendor print files with instruction information.