IEC Electrical Trace Heating Installation in Process Plants

PURPOSE – This technical engineering specification defines the minimum requirements for the installation of electrical trace heating systems.

2.  IEC Electrical Trace Heating Installation in Process Plants

This technical specification applies to electrical trace heating systems on process plants. This article is limited to the use of electrical trace heating systems for the prevention of freezing or coagulation of fluids, or the malfunction of equipment during normal operation, by application of self-limiting type electric trace heating cables to process plant.

2.3      The supply and installation of thermal insulation is not discussed here.

3. RELATED DOCUMENTS

3.1      Air Products Engineering Documents

All equipment covered by this article shall be according to the requirements of the latest edition of the following documents:

Shipment and Packing Specification for Consolidating Warehouses and Direct Export Shipping

4GN90001E                         Winterisation of Piping, Equipment, Vessels, and Instrumentation

VDR                                    Vendor Documentation requirements form

STANDARD ELEC 0002          Electrical Installation Details

3.2      British Standards Institute (BSI)

All equipment for installation in the European Union shall be according to the requirements of the latest edition of the following documents:

BS EN 60079-14    Electrical apparatus for explosive gas atmospheres

Part 14:  Electrical installations in hazardous areas (other than mines)

BS 6351: Part 1     Electrical surface heating: Specification for electric surface heating devices

BS 6351: Part 2     Electrical surface heating: Guide to the design of electric surface heating systems

BS 6351: Part 3     Electrical surface heating: Code of practice for the installation, testing and maintenance of electric surface heating systems

3.3      European Council/Commission Legislative Documents (EC)

All equipment for installation in the European Union shall be according to the requirements of the latest edition of the following documents:

73/23/EEC       Council Directive on the Harmonization of the Laws of Member States Relating to Electrical Equipment Designed for Use within Certain Voltage Limits

2004/108/EC   Council Directive on the Approximation of the Laws of the Member StatesRelating to Electromagnetic Compatibility

3.4      International Electrotechnical Commission (IEC)

All equipment covered by this specification shall be according to the requirements of the latest edition of the following documents:

60079             Electrical apparatus for explosive gas atmospheres

60800             Heating cables with a rated voltage of 300/500 V for comfort heating and prevention of ice formation

3.5      China National Standards (GB)

Equipment for final installation in the People’s Republic of China shall conform to the following standards, where applicable.

GB 1207          Voltage transformers

GB 1208          Current transformers

GB 6995          Markings for electric cables and wires

GB 13539        General requirements for low-voltage fuses

GB 14048        Low-voltage switchgear and controlgear

GB 3836.15     Electrical apparatus for explosive gas atmospheres Part 15: Electrical installation in hazardous areas (other than mines)

GB 16847        Requirements for protective current transformers for transient performance

GB 16916        Residual current operated circuit-breakers without integral overcurrent protection for household and similar uses

GB 16917        Residual current operated circuit-breakers with integral overcurrent protection for household and similar uses (RCBO)

GB/T 7676       Direct acting indicating analogue electrical measuring instruments and their accessories

GB/T 4728.7    Switchgear, controlgear and protective devices

GB/T 14598     Electrical relays

GB/T 17627     High-voltage test techniques for low voltage equipment

4. DEVIATIONS

4.1      No deviations from this specification shall be permitted without the written approval of

Air Products. The supplier may list exceptions in their quotation for Air Products’ consideration and approval. Without an exceptions list, Air Products will assume the supplier fully complies with this specification.

5. GENERAL REQUIREMENTS

5.1      Installation Climatic Conditions

1. Electrical trace heating systems shall be designed to prevent the freezing or coagulation of fluids, or the malfunction of equipment during normal operation under the climatic conditions specified by 4GN90001E, unless specifically stated to the contrary in the project scope report.
2. Unless otherwise specified, the installation shall be designed for operation under the following environmental conditions:

• • Design Ambient Temperature        -15°C (5°F) minimum to +40°C (104°F)
  • Relative Humidity                           90%
  • Altitude                                          Less than 1000 meters above sea level
  • Atmosphere                                   Heavy industrial

Note:   The installation shall guarantee complete protection against the ingress of water when installed in the open without additional protection. This shall include provision to prevent the ingress of moisture during transit of materials/equipment from the contractor’s works and storage before installation on site.

5.2          Electric Trace Heating – Materials/Contractors:   

The following types of equipment/materials shall be provided by the contractor for the installation of the electric trace heating system.

5.2.1      Cables

1. Cables shall be of the self-limiting, parallel circuit, semiconductive resistance type with the heating element extruded in a continuous strip between parallel copper conductors, or Teflon covered parallel resistance type cable with Teflon-insulated, stranded copper bus wires.
2. In hazardous areas, the self-limiting type cables shall be provided with a metallic braid and protective sheath, and each circuit equipped with an earth leakage protection device.
3. In nonhazardous areas, a metallic braided cable shall be used in applications where a plastic pipe, stainless steel pipe, or painted surfaces are to be electrically traced.
4. Cables shall be suitable for frost protection or process temperature maintenance.
5. Self-limiting heating cables shall be supplied from the following manufacturers:
   • Raychem type BTV, QTVR
   • Thermon type BSX, TSX
   • Note:   Other contractors may be considered, subject to the approval of Air Products Electrical Design Department.
6. For external heating of metallic tanks, electric heating “pads” or “blankets” may be specified based on technical/economical selection, as an alternative to heating cables. Air Products will supply full technical details, including an approved subcontractor’s list, to enable the contractor to supply and install according to the technical specification.

5.2.2      Junction Boxes

1. Normally, a maximum of three heaters may be connected to a heat tracing box. For trace heating boxes associated with an instrument housing, three outgoing ways may be used; two of which will be used for the heaters of the instrument lines while the third way shall be reserved for the instrument housing heater.
2. Junction boxes shall be of the polycarbonate type, with a minimum IP 65 enclosure rating. For hazardous area applications, shall be certified by a European Committee for  Electrotechnical Standardization (CENELEC) approval authority.

5.2.3      Thermostats

Frost protection circuit thermostats shall be supplied by the contractor for automatic control of the trace heating distribution board. In addition, all other types of process control thermostats or thermocouples shall be supplied by the contractor.

5.2.4      Distribution Boards

Distribution boards shall be supplied by Air Products unless stated to the contrary.

5.2.5      Power Cables – Circuit Design Considerations

Minimum Cable Size:  The minimum size of power cable to be used shall be 2.5 mm2. Cable shall be 600/1000 V grade polyvinyl chloride (PVC) or cross-linked polyethylene (XLPE) insulated, stranded copper conductors, wire or tape armored, and PVC sheathed to IEC standards.

5.3         Installation Practice

1. Detailed installation procedures and guidelines are provided by the electrical trace heating cable contractors. Air Products has the following minimum requirements for installation.
   1. Before installation of the electrical trace heating cable, the contractor shall verify with the Air Products site representative that:
      • All pipe pressure testing has been completed and flanges tightened.
      • All burrs, rough surfaces, and sharp edges have been removed from the pipework to be traced.
      • All paint/pipe coatings have been touch dry for a minimum of six hours.
      • Installation of the electric trace heating cable has been coordinated with the insulation contractor to minimize the risk of damage to the electrical trace heating cable after installation.
   2. Heating Tapes – Cable Installation
      • Electrical trace heating cable to be installed shall be free from damage to the insulation, kinks, bends, or excessive force during pulling.
      • Electrical trace heating cable shall be fixed securely into position using fiberglass cloth tape or aluminum tape, as required by the design calculation method.
      • Unless otherwise stated, the cables shall be installed in a straight run along the pipe to be traced at 45 degrees from the bottom of the pipe.
      • When cables need to be spiraled along the length of the pipe, the installation shall be according to the manufacturer’s detailed installation procedure.
      • When possible, electrical trace heating cable shall be looped at flange joints and valve bodies, to enable the electrical trace heating cable to be removed without damage if the removable spools to a flange or valve need to be disturbed.
2. To prevent cable damage, external thermal insulation shall be applied without delay after the electrical trace heating cables have been properly installed.
3. All entry and exit points for power, controls, and thermostat capillaries shall be enclosed in seamless tubes and shall be located 60 degrees or more below the horizontal centerline to avoid water entry into the thermal insulation. The entry and exit points shall be sealed with a suitable epoxy compound.
4. Cable manufacturer’s standard cable entries may be used instead of seamless tubes. All junction boxes mounted directly onto heat-traced pipes shall be located underneath pipes to avoid water entry into the thermal insulation.
5. Signs shall be permanently fixed to the outside of the finished external thermal insulation for visibility from ground level. The sign shall read “Electric Tracing,” and shall be spaced at a maximum of 3 m and at any change of direction.
6. Thermostat sensing elements in process temperature maintenance service shall be located in the vicinity of the downstream end of the pipe being monitored.
7. The contractor shall be responsible for the supply of all materials necessary to complete the installation, including all trace heating materials and fixings, power cabling from sub- distribution boards including all supports, brackets, cable trays, cable ladders, and fixings, as required to complete the installation.
8. For typical installation details, refer to STANDARD ELEC 0002 Electrical Installation Details T01 through T13.

6. DRAWING AND DATA

6.1       Electrical Trace Heating Design:   Air Products will design the complete electrical trace heating system up to and including the distribution boards. All necessary information to complete the installation work shall be obtained by the contractor from the drawings and documents attached to the technical specification.

6.2      Isometric Drawings

1. For each trace heating circuit, the contractor shall make a simplified “as built” isometric drawing, showing the position of the trace heating cable junction box, and the type and run of the electrical trace heating cable used.
2. The contractor may use the piping isometric drawings supplied by Air Products. However, isometric shall be stamped “For Electrical Trace Heating Only.”

6.3      Detail Drawings

6.3.1   Company will provide standard drawings showing the typical installation of electrical trace heating cables for the following:

• Pipelines including elbows, flanges, tee connections, valves, and pipe supports
• Instruments including pressure indicators, level gauges, and level controllers
• Equipment including pumps and vessels

6.3.2   In addition, Air Products will provide standard drawings showing the installation details of junction boxes and termination requirements of electrical trace heating cables.

6.4      One Line Diagrams

6.4.1   Air Products will supply project-specific, one line diagrams of each distribution board showing the following:

• Rating of incoming load switch
• Number of circuits
• Rating of Molded Case Circuit Breaker (MCCB)
• Circuit loading (W)

6.5      Cable Layout Drawings

6.5.1   Air Products will supply a simplified layout identifying the location of the trace heating distribution board and the power cable route to the first electrical trace heating box for each power circuit. The contractor shall be responsible for determining the cable routes from this point on a “site run” principle.

6.5.2   The contractor shall mark up the Air Products layout drawings, showing the “As-Built” location of the junction boxes and an interconnection diagram of the junction boxes.

7. FIELD TESTING AND INSPECTION

1. The contractor shall perform all tests listed in Appendix A. The test results shall be completed and approved by the contractor’s Quality Assurance (QA) department, then handed to the Air Products construction supervisor for acceptance.
2. Field testing of insulation resistance and continuity shall be performed with a 500 V megger.
3. Insulation resistance from one conductor to shield shall not be less than 10 Megohms, irrespective of the heating cable length.
4. The Air Products construction supervisor shall verify that the heating system is being installed according to the required installation specifications, project specifications, and cable manufacturer’s instructions. If there is a conflict, Air Products shall require the contractor to obtain approval of the installation from the trace heating cable manufacturer at the contractor’s expense.
5. The contractor may provide their own quality control and test/inspection sheets as an alternative to those identified in paragraph 7.1 above, subject to the approval of Air Products Electrical Design Department.

8. EMC AND LOW VOLTAGE DIRECTIVES

All equipment for final installation in the European Union shall be CE marked for compliance with 73/23/EEC, 2004/108/EC and the Supplier shall provide a Declaration of Conformance or Certificate of Incorporation as applicable for the equipment supplied.

Appendix A

Electrical Trace Heating Installation Test Certificate

Circuit No.

 

INSTALLATION RECORDS FOR
Circuit breaker number:
Drawing reference number:
Megger test before                     Reading insulating (bypass thermostat     Initial if applicable                               Date
Megger test after                       Reading insulating (bypass thermostat     Initial if applicable).                            Date
Circuit voltage                           Panel Connection Terminals
Insulation completed                  Initial and sealed                                Date
Locations of under insulation       Initial components are marked on        Date the insulating lagging