In certain industrial welding processes, controlling the temperature of the material before welding begins is essential to achieve a reliable joint and reduce the risk of defects. One of the technologies used for this purpose is induction preheating, a system capable of providing rapid, localised and controlled heating.
This technique is particularly relevant in projects involving thick components, piping, shells, pressure vessels or metal structures subject to demanding thermal requirements.
But how exactly does induction preheating work, and when is it advisable to use it?
What is induction preheating?
Induction preheating consists of increasing the temperature of the material in a controlled manner before or during a welding operation by means of an electromagnetic field.
To generate this heat, cables or inductors are positioned around the area to be treated. When high-frequency alternating current flows through them, an electromagnetic field is generated, inducing currents within the metallic material itself and causing it to heat up.
Unlike other systems, thermal energy is generated directly within the component, making it possible to reach the required temperature quickly and with a high level of control.
Induction preheating is one of the solutions that can be used as part of a weld preheating process, together with electrical resistance systems.
Why is preheating necessary before welding?
During welding, highly localised heating is followed by cooling. This thermal cycle creates significant temperature differences between the welded area and the rest of the component.
Depending on the material, thickness, geometry and working conditions, excessively rapid cooling can contribute to problems such as:
- Cracking.
- Localised increases in hardness.
- High thermal stresses.
- Undesired behaviour in the heat-affected zone.
- Increased risk of hydrogen-related cracking in certain steels.
Preheating helps reduce the cooling rate of the joint and maintain a more controlled thermal distribution during welding.
However, there is no universal preheat temperature. The values and process conditions must be determined according to the material, thickness, welding procedure and the specifications applicable to each project.
How is induction preheating carried out?
Although each application requires a specific assessment, an induction preheating process can be divided into several stages.
1. Assessment of the component and procedure
Before carrying out the treatment, it is necessary to determine aspects such as:
- Material.
- Thickness.
- Geometry.
- Diameter, in the case of piping or shells.
- Area to be heated.
- Target temperature.
- Environmental conditions.
- Welding procedure.
These parameters make it possible to configure the heating system correctly.
2. Installation of the inductors
The induction cables are arranged around the component according to a previously defined configuration.
The number of turns, cable position and required length must be calculated correctly to promote proper temperature distribution.
3. Installation of measurement systems
Controlling only the applied power is not sufficient.
The actual temperature of the component must be measured and monitored throughout the process using suitable sensors. This makes it possible to verify that the temperature remains within the specified range and to respond to any deviations.
4. Controlled heating
Once the system has been configured, heating begins until the specified preheat temperature is reached.
Induction transfers energy directly to the metal and therefore generally provides a rapid thermal response.
5. Temperature maintenance during welding
In many applications, simply reaching a specific temperature before starting the weld is not enough.
It is also necessary to maintain defined thermal conditions throughout the welding operation, preventing the component from cooling below the values established in the procedure.
Main advantages of induction preheating
The choice of system depends on the characteristics of each project, but induction preheating offers several important advantages.
Rapid heating
Energy is generated directly within the material, allowing its temperature to be increased quickly.
This can be particularly beneficial in operations where production or assembly times are a significant factor.
Localised heating
Heat input can be concentrated on the area requiring preheating without unnecessarily increasing the temperature of the entire component.
Temperature control
Combining induction equipment with measurement and control systems makes it possible to regulate the process and maintain the specified parameters.
This control is essential in industrial applications where a high degree of thermal process traceability is required.
Uniform heat distribution
With the correct inductor configuration, it is possible to achieve homogeneous thermal distribution around pipes, shells and other geometries.
Reduced exposure to heating elements
As the system does not rely on hot resistance heaters applied directly over the entire treated surface, the number of exposed heating elements in the work area is reduced.
Industrial applications of induction preheating
This technology can be applied in numerous industrial sectors where the quality of welded joints is critical.
Industrial piping
Circumferential pipe welds are among the most common applications because induction cables can be easily arranged around the component.
Pressure vessels
Pressure vessels may use materials and thicknesses that require precise thermal control during certain welding operations.
Heavy fabrication
For thick components, controlling the temperature before and during welding can be particularly important in order to maintain the conditions specified in the procedure.
Oil & Gas industry
Pipelines, tanks, refineries and petrochemical plants contain numerous welded joints that are subsequently subjected to demanding service conditions.
Offshore and offshore wind energy
The manufacture of jackets, tubular structures and offshore components requires the control of numerous parameters during welding.
Shipbuilding
The manufacture and repair of marine structures may also require preheating and other heat treatments in order to control the conditions of welded joints.
Induction preheating with Intec-Heat
At Intec-Heat, we develop weld preheating solutions using induction and electrical resistance systems, selecting the most suitable technology for the characteristics of each job.
We analyse the geometry, material, thicknesses, thermal requirements and execution conditions in order to design a procedure adapted to the project.
Our experience in industrial heat treatment enables us to carry out projects in sectors such as Oil & Gas, Defence, offshore, marine, energy, steelmaking and heavy fabrication.
If you need to assess an induction preheating process for a weld or industrial project, contact our technical team and we will analyse the most suitable thermal solution.