Raychem Mineral Insulated (MI) Series Heating Systems

1. General Information

This manual applies to Raychem Mineral Insulated (MI) series resistance heating cable systems installed on thermally insulated pipes and vessels and associated equipment. It provides general information and an overview of common installations and applications. In cases of conflict, project-specific information takes precedence.

Chemelex offers two types of electrical heat-tracing cables: single conductor cables (typically laid in loop configurations) and dual conductor cables (typically laid in single runs).

Figure 1: Typical Cable Construction

A diagram illustrating the construction of single-conductor and dual-conductor MI heating cables, showing the heating conductor(s), insulation (magnesium oxide), and metal sheath.

Types of MI Bulk Heating Cables:

• HCC/HCH: Copper sheathed MI heating cables
• HDC/HDF: Cupro-nickel sheathed MI heating cables
• HSQ: Stainless steel sheathed MI heating cables
• HAx: Alloy 825 sheathed MI heating cables
• HIQ: Inconel sheathed MI heating cables

Figure 2: Typical Heating Unit Designs

Diagrams showing Design type B (Single conductor) and Design type D (Dual conductor) heating units, illustrating the hot/cold joint, cold lead cable, gland, potted seal, and flexible tail length.

Joints can be brazed or laser welded. Refer to Raychem product literature for details.

Note: This manual covers the installation of pre-fabricated MI heating units. Termination and repair of heating cable units are not covered and require qualified personnel. Keep cable ends and kit components dry during installation.

Important: To maintain Chemelex warranty, follow manual instructions. Design, installation, inspection, operation, and maintenance must comply with IEC EN 60079-0, IEC EN 60079-30-1, IEC EN 60079-31, and local electrical codes. Personnel must be trained in special techniques and general electrical work. Supervisors should be experienced in heat-tracing applications. Caution signs or markings should indicate the presence of heating cables.

2. Area Classification

Details are provided for Ordinary Area Classification and Hazardous Area Classification (Zone 1 or Zone 2 for gas, Zone 21 or Zone 22 for dust).

Specific Conditions of Use in Hazardous Areas:

1. MI Cable Seal assembly must be installed in a suitable enclosure to protect from light and impact.
2. Service temperature range: -30°C to +120°C, -30°C to +105°C, or -60°C to +70°C.
3. Maximum withstand temperatures and supply voltages are shown in Table 1.
4. Minimum installation temperature: -60°C.
5. Minimum cable spacing: 25 mm.
6. Minimum bending radius: 6 x cable diameter.
7. Handle MI Electric Heating cables with care to avoid weakening the mechanical strength.
8. Consider environmental exposure when selecting sheath material to prevent stress corrosion cracking (SCC).
9. When PVC sleeving is used, operating temperature must not exceed +85°C.
10. In dust atmospheres, the Compression Ring Type cable Gland must be sealed according to manufacturer's instructions and applicable codes. The enclosure must have a minimum ingress protection of IP6X.
11. The heating element supply circuit must include an electrical protection device per EN 60079-30-1.

Certificates and Codes:

Information on ATEX, IECEx, and EAC certifications and corresponding code numbers for heating units and bulk cable is provided, including ambient temperature ranges and specific conditions for hazardous locations.

3. Heating Cable Selection and Storage

Order Reference Nomenclature:

An explanation of the order reference nomenclature for MI heating units is provided, detailing each component of the reference string.

Table 1: Properties of MI Heating Units

A table summarizing the properties of MI heating units, including Number of conductors, Maximum voltage, Withstand temperatures (brazed and laser welded), Temperature classification, Minimum cable spacing, Minimum installation temperature, Minimum bending radius, and Chemical resistance for various MI Heating Cable Types (HCC/HCH, HDC/HDF, HSQ, HAx1N, HAx2N, HAx2M, HIQ).

Storage and Transportation:

• Store and transport MI heating units in a clean, dry place or container.
• Protect heating cable from moisture and mechanical damage.
• Storage below 10°C may cause condensation and low insulation resistance.
• After extended storage, measure insulation resistance before installation.

4. Heating Cable Installation

WARNING:

Improper installation can lead to electrical tracking, arcing, and fire hazards. Unconnected heating cable ends exposed to the environment must be sealed.

3.1 Pre-installation Checks:

• Check design recommendations: Verify engineering documents, special instructions (e.g., foil, mesh), and hazardous area information compatibility.
• Check materials received: Inspect for damage, verify heating cable types and components against catalogue numbers, and check identification tags. Measure and record electrical and insulation resistance.
• Check equipment to be traced: Verify identification, length, and diameter of pipework/vessel. Ensure actual temperatures and insulation properties align with design. Confirm pressure testing is complete and coatings are dry. Plan heating cable routing, including heat sinks (valves, flanges, supports, drains). Inspect piping for burrs, rough surfaces, or sharp edges; smooth or cover with aluminum foil. For elevated sheath temperatures, consider stainless steel foil. Clean surfaces with a wire brush and suitable solvent.

3.2 Heating Cable Pulling and Laying and General Installation Guidelines:

Figure 3: Importance of Cable Pulling Direction

Diagrams illustrating correct and incorrect cable pulling directions to avoid distortion and kinking.

When pulling the heating cable, avoid:

• Sharp edges
• Excessive pulling force
• Kinking and crushing
• Running over it with equipment
• Pulling into a spiral
• Pulling the cable by the flexible pig tail wires of the cold lead(s)

The minimum bending radius must be respected.

Figure 4: Minimum Bending Radius of MI Heating Cables

Diagram showing the minimum bending radius (6 x Ø Cable).

• Do not repeatedly bend and straighten the cable.
• Keep heating cable strung loosely but close to the pipe.
• Add heating cable to trace fittings and supports as required.
• Leave appropriate amounts of heating cable at power connection, splice, and tee locations.
• Do not bend the cable within 150 mm of the hot to cold junction or remote terminations.
• Do not bend the cold lead within 150 mm of the termination pot seal.
• Avoid crushing and excessive bending or pulling of cold leads.
• Avoid excessive heat to the epoxy seal termination.
• Keep gland back nut and olive assembled to the body.
• Use thread lubricant for stainless steel glands.
• Ensure MI and other constant wattage heating cables do not overlap or cross to prevent overheating and fire hazards.

Figure 5: Minimal Spacing Must Be Respected

Diagrams illustrating minimum cable spacing requirements. Standard minimum spacing is 25 mm, and 50 mm for hazardous areas unless otherwise specified.

Heating Cable Allowances:

Areas with increased surface area (fittings, supports) require compensation through higher design safety factors or extra cable length. Consult design software and documentation for allowances.

3.3 Heating Cable Attachment:

• Fix cables with metal bandings, tie wire, or wire cloth band at intervals of 300 mm. Avoid tie wire with softer sheath cables (HC, HD) to prevent damage; use wire cloth band.
• Secure hot-cold joints with metal bands 150 mm on either side.
• Install cable to permit movement during heating cycles without free movement.
• Install cables in straight or multiple runs as required.
• On horizontal pipes, fix on the lower quadrant.
• On vertical pipes, fix equally distributed around the circumference.
• Consult design documents for cable allowances and junction box locations before permanent attachment.

Figure 6: Cable Orientation on Pipe

Diagrams showing cable orientation on pipes for one and two heating cables, including temperature sensors.

Figure 7: Typical Cable Layout on Large Surfaces like Tank Walls

Diagram showing cable layout on tank walls using pre-punched strapping and banding.

Figure 8: Fixing Device: Pre-punched Metal Strap

Diagram illustrating a pre-punched metal strap fixing device.

• Verify design documentation for aluminum or stainless steel foil coverage requirements.
• Tank installations may require pre-punched steel strips.
• Avoid sharp edges and properly seal MI cold lead cable penetrations.

3.4 Attachment Materials:

• Stainless steel pipe straps, banding, tie wire, or wire cloth band.
• Tie wire (RMI-TW) is suitable for irregular shapes but should be used with caution on softer sheath cables.

3.5 Typical Installation Details:

• Dual conductor cables follow the same principles as single conductor cables, which typically form a loop. For single conductor configurations, both ends must terminate in the same power supply box.
• Uncoil heating cable and lay alongside the pipe. For short single conductor cables in a hairpin configuration, unroll, loop, and lay alongside the pipe for simultaneous installation.

Figure 9: Uncoiling Heating Cable

Diagram showing uncoiling of heating cable.

Figure 10: Attaching Hot-Cold Joint and End Cap

Diagrams showing the attachment of the hot-cold joint and end cap.

• Attach hot-cold joint to the pipe end nearest the power supply. Attach the other end of the heating cable to the other pipe end.
• Support the hot-cold joint with pipe straps/banding 150 mm on either side. Secure the joint itself to the pipe.
• Fasten the middle of the heating cable to the halfway point of the pipe, leaving equal slack.
• Attach heating cables with pipe straps/banding, tie wire, or wire cloth band at 300-450 mm intervals. Tie wire should be snug but not cut the sheath. Avoid tie wire with softer sheath cables; use wire cloth band.

Figure 11: Allowances for Valves, Flanges, and Pipe Supports

Diagram showing allowances for valves, flanges, and pipe supports, using various attachment materials.

• Use tie wire or wire cloth band for irregularly shaped objects like valves or pipe supports.

Figure 12: Installing Cable on Valves and Pipe Supports

Diagrams showing cable installation on valves and pipe supports.

• Allow cable to wave along the pipe (approx. 2% of total length) for expansion and contraction. Distribute excess cable equally.

Figure 13: Completed MI Heating Cable Installation

Diagram showing a completed MI heating cable installation.

Figure 14: Pipe Strap Spacing

Diagram illustrating pipe strap spacing for hot-cold joints and junction boxes.

Figure 15: Fastening Several Runs of Cable

Diagram showing fastening of multiple runs of cable using banding and strapping.

• Wave cables with a minimum spacing of 25 mm to 50 mm, unless specified otherwise.
• Pre-punched metal strapping can aid installation and consistent spacing.

Figure 16a & 16b: Valves

Diagrams showing cable attachment to valves of different sizes.

Figure 17: Installation at 90° Elbow

Diagram showing cable installation on a 90° elbow.

Figure 18: Flanges

Diagram showing cable attachment to flanges.

• Heating cable must maintain contact with the flange when bending.
• In hazardous areas, secure the cable to the pipe on either side of the flange.

Figure 19: Cable Layout Over Clamps and Straps

Diagram showing cable layout over clamps and straps.

Figure 20: Shoe and Sleeve Type Support

Diagram showing cable attachment to shoe and sleeve type supports.

Figure 21: Dummy Supports

Diagram showing cable attachment to dummy supports.

• Check drawings for dummy leg insulation.
• Pumps require their own heating cable, separate from the connection box.

Figure 22: Pumps

Diagram showing cable attachment to pumps.

• Use stainless steel tie wire or wire cloth band on both sides to hold cable.
• Cover cable with metal foil or equivalent before applying insulation.
• Trace pipe fittings as shown to allow easy maintenance; metal wire mesh cages are an alternative.

Figure 23: Cable Applied on Metal Wire Mesh

Diagram showing cable applied on metal wire mesh.

• Consult design specification for heat-tracing requirements of fittings and supports.
• Respect minimum bend radius (refer to Table 1).
• Respect minimum spacing (refer to page 12, Figure 5).
• Push mesh firmly against valve body to optimize contact.

3.6 Heating Cable Allowances:

Increased heat loss areas require compensation. Refer to Raychem design specification for details.

5. Components Selection and Installation

4.1 General Notes:

Use the Design Specification to select components. Raychem components are required for warranty and compliance.

4.2 Component Installation Hints:

• Locate junction boxes below horizontal pipes, for easy access, and protected from mechanical abuse.
• Position junction boxes so power and heating cable entries point downwards to prevent water ingress.
• Confirm junction box glands and stopping plugs are appropriate and firmly fixed. Ensure sealing washer is installed.
• Route heating cable to minimize mechanical damage risk.
• Do not strain cold lead cable at entries.
• Fix heating cable over pipe straps to avoid mechanical damage.
• Locate cable joints (splices) where cable is not bent or stressed.
• Do not bend cold lead within 150 mm of the termination pot seal.
• Inspect glands for scratches or damage.
• Ensure cable surface is clean where the gland seals. Clean contaminated parts.
• In Ex d hazardous applications, glands must have a minimum of 5 threads engaged.
• Perform visual inspection of gland after tightening.
• Tighten back nut to approximately 25 ft-lb (34 N-m).
• Tighten lock nut wrench tight.
• Enclosures with unthreaded gland entries must comply with IEC 60079-31.
• Optional fiber or PTFE sealing washers may be used for IP66 rating.

Important: Tighten compression nut to the torque setting indicated on the tag to ensure proper grounding and prevent moisture entry.

6. Temperature Control and Limitation

5.1 General Rules:

Raychem MI heating cables typically require temperature control. Independent temperature limitation devices may be required based on local regulations and environmental conditions.

• For hazardous areas, use stabilized design or a thermostat control with temperature limiter complying with IEC 62086 and IEC/EN 60079-30-1.
• If stabilized design is not applicable, a control thermostat must switch off the system when the maintain temperature is reached.
• An independent temperature limiter prevents exceeding the maximum allowed temperature.
• A lockout function keeps the cable switched off until failure is eliminated.
• Lockout function is manually re-armed.
• Setpoint must be secured against unintended change.
• Limiter must permanently switch off in case of sensor malfunction.
• Follow installation instructions for thermostats and limiters.
• Use a proper wiring diagram.
• Set limiter to ensure maximum cable surface temperature does not exceed T-class or maximum working temperature.
• Warning: Temperature measurement errors can occur due to heat loss. Adjust setpoints accordingly.
• Contact Chemelex for information on offsetting limitation devices.

5.2 Sensor Placement: Temperature Control Device:

Sensor placement depends on fluid flow direction, heat sinks, chimney effect, accessibility, and other heat sources.

5.3 Sensor Placement: Temperature Limiter Device:

Sensor placement for limiter devices depends on similar factors, with specific considerations for upstream/downstream placement and proximity to heat sinks.

7. Thermal Insulation and Marking

6.1 Pre-insulation Checks:

• Visually inspect heating cable and components for correct installation and damage.
• Insulation resistance testing is recommended before covering with thermal insulation.
• Discharge cable immediately after insulation test.

6.2 Insulation Related Requirements:

• Properly installed and dry thermal insulation is required for temperature maintenance.
• Verify that the maximum sheath temperature of the MI heating cable is compatible with the insulation materials.
• Ensure all pipes, fittings, and penetrations are completely insulated.
• Thermally insulate and weatherproof to design specification.
• Ensure heating cable is not damaged during cladding installation.
• Insulation material and thickness must comply with design requirements for stabilized designs.
• Do not place insulation material between the heated surface and the cable.
• Wrap the heating system with appropriate metal foil before installing thermal insulation, especially at difficult-to-access areas.

6.3 Marking:

• Install "Electric Traced" signs on insulation cladding at intervals of 3-5 m.
• Mark the location of heating cable components (connections, splices) on the outside of the insulation.

MI-Heating Unit Identification:

• Each MI heating unit has an identification tag with type and operation details.
• Cable tags are mandatory in hazardous areas.
• Tags contain area classification and other design information.

Figure 24: Typical MI Identification Tag (for use in hazardous areas)

An example of a typical MI identification tag, showing catalogue number, serial number, output power, circuit ID, maximum sheath temperature, design method, hazardous location certifications, and other relevant data.

• Catalogue No. is the order reference.
• Serial No. provides factory traceability; the first two digits indicate the year of manufacture.
• Zone/T*(Class)/AIT states the T-class or Auto Ignition Temperature and Zone classification.
• Design method indicates the temperature control method used.

8. Power Supply and Electrical Protection

• Do not energize cable when coiled or on the reel.
• De-energize circuits before installation or servicing.

7.1 Earth Connection:

• Bond the metal sheath of the heating cable to a suitable earth terminal.
• Optional earth lugs can facilitate earthing of the metal cable sheath.

7.2 Electrical Loading:

Size overcurrent protective devices according to design specification and local practices.

7.3 Residual Current (Earth Fault) Protection:

• Chemelex requires a 30 mA residual current device for safety.
• For higher leakage current, preferred trip level is 30 mA above inherent capacitive leakage, or the next common available trip level up to 100 mA or 300 mA.
• Safety aspects must be proven. Refer to local standards.
• RCD use is restricted in IT power networks.
• Residual current devices are mandatory in hazardous areas.
• Earth fault equipment protection is required for each circuit.

7.4 Isolation from Power Supply:

Means of isolation from the supply is mandatory for heating circuits in hazardous areas.

7.5 Circuit Marking:

System must be properly marked with a heating cable tag in hazardous area installations.

9. System Testing and Commissioning

WARNING:

Megger tests can produce sparks. Ensure no flammable vapors are present before testing.

8.1 Testing of Insulation Resistance and Conductor Resistance:

• Recommend insulation resistance test:
• Before installing heating cable (on reel).
• Before installing thermal insulation.
• Prior to initial start-up/after thermal insulation.
• As part of periodic maintenance.
• Measure and compare heating circuit electrical resistance to design documentation before initial startup.

8.2 Test Method for Insulation Resistance Testing:

• After installation, test insulation resistance between conductor and outer sheath.
• Use a minimum testing voltage of 500 V and not more than 1000 V DC.
• Minimum readings should be ≥20 MΩ for new heating units.
• Record values for each circuit on the installation record sheet.

8.3 Commissioning:

• Verify all system documentation is complete.
• Record and retain all installation and post-insulation test values.

10. Documentation, Operation, Maintenance and Repairs

WARNING:

Heating cables reach high temperatures and can cause burns. Avoid contact when powered. Thermally insulate traced pipes/equipment before energizing. Use only trained personnel.

Caution:

Consult documentation prior to maintenance/repair/modification. Test earth-fault device after maintenance.

In case of earth fault or overcurrent interruption, the device shall not be reset until the cause is investigated.

9.1 Documentation:

Retain trace heating system documentation for each circuit. It should include:

• Circuit identification
• Heating cable type
• Operating voltage
• Length/dimensions of heating cable
• Stabilized design: Maintain temperature, max. workpiece temperature, temperature class/sheath temperature, max. ambient temperature, trace ratio, pipe size, insulation type/thickness, cladding specification.
• Controlled design: Maintain temperature, temperature class/sheath temperature, system design parameters, max. ambient temperature, trace ratio, controller/limiter set point, sensor location, sensor mounting details, failure annunciation/monitoring.

This data is usually part of as-built documentation or calculation reports.

9.2 Heating Cable Operation:

• Temperature exposure must be within specified limits to prevent damage.
• Pipe insulation must be complete and dry.

9.3 Inspection and Maintenance:

• Visual inspection: Check for mechanical damage.
• Insulation testing: Test regularly. Check if hazardous area conditions permit testing; a hot work permit may be required.
• Dielectric test: Performed between L (live) and PE (earth).
• Functionality test: Test circuit breakers and RCDs annually or per manufacturer instructions.
• Verify junction boxes are appropriate for area classification and sealed. Ensure gland connectors are tight.
• Check cold leads and glands for damage. Use thread lubricant for stainless steel glands.
• Functionality test of temperature control systems: Test at regular intervals.
• Complete Installation Record Sheet during maintenance.
• Freeze protection systems: measure before winter.
• Temperature maintenance systems: test twice a year.
• Replace IP sealing washers when removing glands.

11. Troubleshooting

WARNING:

Damaged cables can cause arcing or fire. Do not energize damaged cables. Repairs must be done by qualified personnel. Contact Chemelex for assistance.

Evaluate damage severity to determine if repair or replacement is needed.

Symptom and Probable Causes:

A. Insulation resistance less than expected:

1. Rainy or high humidity
2. Nicks or cuts in heating cable sheath with moisture
3. Kinked or crushed heating cable
4. Arcing from cable damage
5. Physical damage causing a direct short
6. Moisture in terminations or connections
7. Damaged termination
8. Moisture in junction boxes

B. Circuit breaker trips:

1. Circuit breaker undersized
2. Defective circuit breaker
3. Short circuit in electrical connections
4. Excessive moisture in connection boxes
5. Nicks or cuts in heating cable sheath with moisture
6. Kinked or crushed heating cable
7. Defective RCD
8. Excessive earth leakage current, RCD trips

C. Power output correct, but pipe temperature below design:

1. Wet or missing insulation
2. Insufficient heating cable on valves, flanges, supports, pumps
3. Temperature controller set incorrectly
4. Improper thermal design
5. Temperature sensor in wrong location
6. Low fluid temperature entering pipe

D. Power output is zero or incorrect:

1. No input voltage
2. Temperature controller wired incorrectly (N.O. position)
3. Limiter has tripped
4. Broken or damaged heating element, hot-cold joint, end cap, or tail
5. Wrong cable used
6. Improper voltage used

Locate Faults:

1. Visually inspect power connections, splices.
2. Look for damage at end seals, valves, pumps, flanges, supports, and areas of recent maintenance.
3. Look for crushed or damaged insulation and cladding.
4. If fault persists, consult Chemelex.

Corrective Actions:

For Insulation Resistance Less Than Expected:

1. Dry tails and face of seal.
2. Inspect cable for damage, especially at elbows, flanges, valves. Repair or replace if damaged.
3. Inspect power connection box for moisture.
4. Dry connections and retest.
5. Check areas of maintenance work for damage. Replace damaged sections if necessary.
6. Dry cold lead/connections and replace termination if needed.
7. Replace termination.
8. Check and replace seals on junction boxes.

For Circuit Breaker Trips:

1. Recalculate load current, resize breaker.
2. Repair or replace breaker.
3. Eliminate short circuit, dry connections.
4. Eliminate short circuit, dry connections.
5. Repair or replace damaged section.
6. Repair or replace damaged section.
7. Replace RCD.
8. Check insulation resistance. Evaluate electrical design for RCD compatibility.

For Pipe Temperature Below Design:

1. Remove wet insulation, replace with dry, and secure.
2. Confirm compliance with system design; additional cable may be needed for changed fittings/supports.
3. Reset temperature controller.
4. Contact Chemelex for design confirmation and modification.
5. Confirm sensor location.
6. Verify fluid temperature.

For Zero or Incorrect Power Output:

1. Repair electrical supply lines and equipment.
2. Confirm wiring using normally closed (N.C.) terminals.
3. Check reason for limiter trip, resolve, and reset limiter.
4. Repair or replace heating cable.
5. Verify installation and replace cable if necessary.
6. Verify voltage and connect to proper voltage.

12. Installation Record Sheet

A record sheet is provided for documenting installation details, including company, project, site, area, installer, circuit number, P&ID number, drawing number, panel/breaker number, heating cable type, and cable length.

Required Value vs. Actual Value:

Sections for visual inspection, insulation resistance tests, and prior to energizing the cable, comparing required values with actual recorded values for spacing, bending radius, sensor installation, insulation resistance, loop resistance, and cable covering.