Flanged Immersion Heaters

This is a manufacturing-process reference. Manufacturing methods, inspection scope and acceptance criteria must follow approved drawings, procedures and the technical agreement.

Design and Incoming Material Inspection

1. Application design: determine sheath material (304/316L/Incoloy800 or other suitable materials), watt density, unheated length, flange specification and thermocouple thermowell position based on the medium (water/thermal oil/acids or alkalis), power, voltage, vessel flange standard and hazardous-area requirements. Verify material compatibility.
2. Incoming inspection:
   • Check material certificates, appearance and dimensions of metal tubes, nickel-chromium resistance wire, high-purity magnesium oxide powder, terminal rods and flange materials. Confirm tube construction against the drawing.
   • Dry insulating powder and segregate nonconforming materials.

Manufacture of Individual Tubular Elements

1. Cutting: cut sheath tubes, resistance wire and terminal rods to drawing lengths; deburr, clean and degrease.
2. Wire assembly: wind the resistance wire, connect terminal rods at both ends and insert it into the sheath, keeping it centred and clear of the tube wall.
3. MgO filling: vibration-fill with high-purity insulating and heat-conducting MgO powder; control fill density. Moisture can impair insulation.
4. Tube reduction: compact the MgO using equipment suited to the product, controlling dimensions and insulating and heat-transfer performance.
5. Bending: perform any required annealing under the approved procedure, form U-shaped elements using the layout fixture and control bend radius to prevent cracking.
6. End cleaning and drying: clean tube ends and bake under the specified procedure to remove residual moisture.
7. End sealing: select suitable epoxy, high-temperature silicone, ceramic or other sealing construction for terminal temperature and environment to prevent moisture ingress and insulation deterioration.

Flange Assembly and Welding

1. Flange machining: machine the flange, bolt holes, element holes and thermowell holes to the selected standard and drawing; inspect sealing faces.
2. Element positioning: arrange and secure U-shaped elements to the drawing and fit the thermocouple thermowell.
3. Suitable welding process, such as TIG: connect elements to the flange using the designed joint and approved procedure. Control porosity, cracks and other defects to meet pressure-retention and sealing requirements; perform liquid penetrant testing (PT) or other checks under the inspection plan.

Two connection arrangements may be reviewed: directly welded elements; or elements installed with threaded fittings, nuts and matching seals to facilitate replacement. Removable designs also require verified sealing and pressure-retention design.

4. Post-weld and surface treatment: determine stress-relief requirements from materials and welding procedures. Clean welds; stainless-steel parts may be pickled and passivated as specified, protecting sealing faces and electrical terminations.

Terminal Enclosure and Temperature-Sensor Assembly

1. Fit insulating supports, terminals and the protective-earth connection.
2. Install the specified thermocouple, such as type K/J, in its thermowell.
3. Fit the enclosure and seals suited to the environment. IP54 or other ingress-protection ratings and explosion-protected configurations must be confirmed against the actual design and certification requirements.

Final Inspection and Acceptance

Distinguish individual-unit checks from sampling tests under the approved inspection plan; sampling tests must not be described as “100% inspection”.

1. Insulation resistance: measure cold insulation resistance with an insulation tester; use the applicable test voltage and acceptance limit.
2. Dielectric withstand: perform the specified power-frequency test to check insulation withstand capability.
3. Resistance: measure total element resistance and verify power against rated voltage.
4. Leak/hydrostatic testing: test flange-to-element connections as specified; medium, pressure and procedure depend on pressure design and inspection documents.
5. Temperature-rise or electrical performance testing: follow the inspection plan. Do not directly energise a liquid-immersion heater dry without an approved procedure. Provide appropriate heat-transfer conditions and protective measures.
6. Visual and dimensional inspection: check flange holes, element length and enclosure integrity.
7. For explosion-protected products, perform the required additional checks of marking, terminal enclosure, electrical connections and supporting documents.

Surface Treatment, Identification and Packaging

1. Remove rust and paint carbon-steel flanges as specified, protecting sealing faces; clean stainless-steel parts.
2. Mark the nameplate with model, voltage, power, material and serial number as required.
3. Protect elements, tube ends and sealing faces; package with conformity documents, drawings and test reports under the agreed supply scope.

On-Site Installation at the Vessel

1. Provide the opening, nozzle and mating flange according to the vessel design; work on pressure equipment must meet applicable requirements.
2. Clean sealing faces and fit a compatible gasket.
3. Lift the heater into place and tighten bolts diagonally in the specified sequence and to the specified torque.
4. Connect thermocouple cables, main power and protective earth.
5. Connect temperature control, level protection and overtemperature interlocks; verify protective functions.
6. Follow the approved pressure-testing procedure and check insulation. Before energising, confirm that the medium covers the effective heated length, protection is functional and no leakage is present; commission and accept before service.

Process Control Points and Common Quality Risks

• Damp MgO or failed end seals → leakage current and reduced insulation resistance.
• Weld porosity or other defects → process-medium leakage.
• Excessive watt density → local overheating, coking and element damage.
• Unsuitable unheated length or low liquid level → dry heating and element damage.

Petroleum and Oil & Gas

Heating and temperature maintenance in crude oil, heavy oil and bitumen tanks to reduce viscosity for pumping; warming thermal-oil tanks, lubricating-oil tanks and ethylene-glycol antifreeze tanks; heating materials in hazardous-chemical mixing tanks and reaction vessels. Oilfield or hazardous-area duties require assessment of explosion-protected equipment and protection against the area classification.

Water Treatment and Utilities

Heating industrial hot-water tanks and electric boilers; maintaining purified and deionised water tanks; warming wastewater-treatment chemical tanks and neutralisation baths; freeze protection for outdoor tanks and process lines to reduce disruption from freezing.

Food and Biopharmaceuticals

Maintaining sugar solutions and animal or vegetable oils in mixing and fermentation tanks; heating cleaning solutions in clean-in-place (CIP) systems; temperature control in pharmaceutical-liquid tanks and biological water-bath sterilisation vessels. Review 316L and hygienic polishing together with seals, hygienic design and cleaning requirements.

Surface Treatment

Temperature maintenance in electroplating, phosphating, degreasing and pickling baths. Assess titanium, PTFE coatings or other compatible sheaths against bath composition, concentration, temperature and corrosivity.

Power and New Energy

Preheating generator lubricating-oil tanks and boiler auxiliary feedwater; heating molten-salt tanks for solar thermal storage; maintaining media in thermal-storage tanks to meet startup, shutdown and operating-temperature requirements.

Rubber, Plastics and Advanced Materials

Heating oil reservoirs in mould-temperature controllers; maintaining paraffin and resin melting tanks; warming polymer raw materials during pretreatment to support material flow and transfer.

Marine and Offshore Engineering

Warming ship fuel-oil, lubricating-oil and freshwater tanks; freeze protection for offshore-platform tanks. Review titanium or other suitable sheaths for seawater duties against the actual medium and marine-environment protection requirements.

Coating and General Manufacturing

Temperature maintenance in industrial cleaning baths, degreasing baths and paint-storage tanks. Heating process gases in enclosed vessels requires gas-specific heat-transfer design and protection for the intended temperature-maintenance duty.

Selection guidance: match sheath material, watt density and protective components to the medium, temperature, corrosive environment and hazardous-area classification. Provide operating parameters for technical assessment of a suitable solution.