How It Works
Induction Heating Systems use non-contact heating. They induce heat electromagnetically rather than using a heating element in contact with a part to conduct heat, as does resistance heating. Induction heating acts like a microwave oven, the appliance remains cool while the food cooks from within.

In an industrial application of induction heating, heat is induced in the part by placing it in a high-frequency magnetic field. The magnetic field creates eddy current inside the part, exciting the parts molecules and generates heat. Because heating occurs below the metals surface, no heat is wasted. The Induction process heats within the part, and the resistance process heats on the surface of the part. The Induction process uses 60 Hz which penetrates deeper into the part which allows heating thicker parts. The induction coil does not heat up because the conductor is large for current being carried.

Benefits of Induction Heating
Some of the benefits of induction heating are good heating uniformity and quality, reduced cycle time, and longer lasting consumables. It’s also safe, reliable, power efficient and versatile. The inverter power supply is 92 % efficient; the power input only requires a 40-amp line for 25 KW of power. Cycle time is reduced on thicker applications such as high-pressure stream lines as much as 2 hours. The technology has proven itself on oil and gas pipelines, heavy construction equipment, refineries and pressure vessel shops. The simplicity of wrapping the induction heaters around complex shapes such as weldolets elbows; valves and other parts further reduce the time to perform the heat treatment.

Welding of P-5B Pipe
Welding of P-5B Grade P-91 requires very precise preheat during welding. If temperature cools below 350 degrees or exceeds 600 degrees or if either of these occur, the weld must be wrapped in a blanket. When the materials has cooled to 200 degrees, one must restart the preheat then proceed with the welding when minimum preheat temperature is reached. With the application of Induction Heating, this process is more feasibly controlled than with Resistance Heating.

Reliability
One of the most important factors affecting productivity in stress relieving is an uninterrupted cycle. In most cases cycle interruption means the heat will have to be rerun, which is significant when a thermal cycle can take a day to complete. The induction heating system components make cycle interruption unlikely. The heater cable for induction is simple, making it less likely to fail. Also, no contractors are used to control the heat input to the part, as is the case in Resistance Heating. Ceramic heaters are fragile and easily damaged, thus requiring frequent replacement due to heater burn out. The electromagnetic field surrounding the part does not affect the weld ability, as does Resistance Heating.

Safety
Safety is a prime concern in preheating and stress relieving. The induction heating method is more user friendly. It does not require hot heating elements and connecters. Very little airborne particulate is associated with the insulation blankets that are exposed to high temperature from the parts. The system is equipped with ground fault protection to prevent accidental shock hazards. Operators and near-by welders are less likely to be burned because coils and connectors are not hot.

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