Nakai Electric Bolt Heaters for Turbine and Compressor Maintenance

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Introduction

Large bolts and tie rods used in turbines, compressors, hydraulic presses, and similar heavy equipment may require controlled thermal expansion during assembly, tightening, loosening, or scheduled maintenance.

The Nakai Bolt Heater uses an electric resistance heating element inserted directly into the bolt’s axial bore. Localized heat produces controlled bolt elongation, supporting the tightening or removal procedure without relying exclusively on high mechanical force.

After the electrical supply is disconnected and the bolt cools, the resulting thermal contraction contributes to the required tightening effect.

Electric resistance bolt heaters (straight and flexible types) designed for precise thermal expansion during maintenance of turbines, compressors, and heavy equipment.

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Electric Resistance Bolt Heating

The Nakai Bolt Heater operates through direct heat transfer from the electrical heating element to the internal surface of the bolt bore.

The assembly incorporates:

• Insulated handle

• Metallic housing

• Electrical terminal section

• Non-heating zone

• Active heating element

• Industrial power cable

The heater must be matched to the actual bolt geometry, insertion bore, required heating zone, site voltage, and maintenance procedure.

The equipment does not independently determine final bolt preload. Tightening values and operating procedures remain subject to the responsible engineering and maintenance team.

Straight and Flexible Configurations

Configuration	Technical Characteristics	Appropriate Access Condition
Straight Type	Rigid linear heating element for direct insertion	Bolt bore is accessible along a clear axial path
Flexible Type	Adaptable heating section for restricted or irregular access	Direct alignment is limited by surrounding equipment or installation geometry

The type should be selected according to the available insertion path. A flexible configuration should not automatically be selected when the bolt bore can be accessed directly with a straight heater.

Technical Parameters Required for Selection: Nakai Bolt Heater

Parameter	Required Definition
Heater Type	Straight or Flexible
Capacity	Required electrical heating capacity in kW
Voltage	Site electrical supply voltage
Diameter — D	Outside diameter of the heating element
Overall Length — L	Complete insertion length
Heating Zone — H	Active section transferring heat to the bolt
Non-Heating Zone — NH	Section that remains outside the required heating area
Cable	Required length and electrical configuration
Plug	Connection compatible with the destination site
Quantity	Number of heaters required

The relationship between the bolt-bore diameter and heater diameter is critical. Excessive clearance can reduce heat-transfer effectiveness, while insufficient clearance may prevent correct insertion or removal.

Reference Diameter Options

The current product information lists the following standard diameter options. Availability and final configuration remain subject to technical confirmation.

Heater Type	Listed Standard Diameters
Flexible Type	15, 17.5, 19, 20, 23.5 and 26 mm
Straight Type	9.5, 15.3, 18, 19, 20, 24 and 26 mm

Capacity, voltage, overall length, heating-zone length, and non-heating-zone length may vary according to the required bolt and operating conditions.

The listed standard configuration includes a two-meter 2PNCT 3C 2 mm² cable. Plug type and compatibility with the destination electrical system must be confirmed before production.

Exploded assembly view of the Nakai Bolt Heater highlighting key components including the handle, housing, non-heating zone, heating element, and flexible power cable, designed for industrial applications such as turbine and compressor maintenance.

Industrial Applications

Nakai Bolt Heaters may be evaluated for large fastening systems used in:

• Steam and gas turbines

• Industrial compressors

• Hydraulic presses

• Large tie-rod assemblies

• Heavy rotating equipment

• Plant overhaul and scheduled maintenance

Product suitability depends on the bolt material, axial-bore dimensions, required elongation, surrounding equipment, electrical supply, and approved maintenance procedure.

Bolt Heater Specification Logic

The heater should be defined from the bolt inward:

Bolt Bore → Heater Diameter → Insertion Length → Heating Zone → Non-Heating Zone → Capacity → Voltage → Type

Selecting only the voltage, diameter, or total length is insufficient. The active heating zone must correspond to the section of the bolt where thermal expansion is required.

Likewise, the non-heating zone must be defined so that the heater housing, terminal section, and handle remain outside the active heating area.

Information Required for a Replacement Heater

A replacement requirement should include:

• Existing heater nameplate

• Manufacturer or product identification

• Heater type

• Rated voltage and capacity

• Heater diameter

• Overall length

• Heating-zone length

• Non-heating-zone length

• Cable and plug configuration

• Bolt-bore diameter and depth

• Equipment where the heater is used

• Required quantity

A visually similar heater should not be considered interchangeable without confirmation of its electrical rating, dimensions, heating-zone arrangement, and installation geometry.

Operational and Electrical Verification

Before use, the responsible engineering team should verify:

• Heater voltage matches the site power supply

• Heater diameter is compatible with the bolt bore

• Required insertion depth is available

• Heating and non-heating zones are correctly positioned

• Cable and plug are suitable for the installation

• Heater condition has been inspected

• The applicable maintenance procedure has been approved

Operation should follow the manufacturer’s instructions and the end user’s electrical and maintenance safety procedures.

International Sourcing from Japan

Nichiboku supports international industrial users, maintenance departments, power-generation companies, engineering contractors, and procurement teams requiring Nakai Bolt Heaters for defined equipment and maintenance applications.

Support may include:

• Straight or Flexible type identification

• Technical specification coordination

• Dimensional requirement review

• Manufacturer quotation management

• Inspection documentation

• Export documentation and international supply
  

View the Nakai Bolt Heater product page:

https://www.nichiboku.com/nakai-bolt-heater

Nakai Bolt Heater Product Inquiry & Order App: https://www.nichiboku-mkt.com/nakai-bolt-heater-rfq-generator/

Japanese Industrial Products

Review Nichiboku’s virtual catalogue of Japanese industrial equipment and components for plant maintenance, replacement requirements, and defined industrial projects worldwide.

https://www.nichiboku.com/japanese-industrial-products

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