Induction heating of pipes and long workpieces

Three technological schemes

Local ring heating is used before welding, flexible, rolling or landing the connection. The detail remains stationary or rotates, and the inductor covers a short zone. With successive heating, the inductor moves along the part with programmable speed, stops, and power changes. In a passing line, the pipe or bar moves through a stationary inductor; performance is determined by the feed rate and the energy that needs to be transferred to each meter of the product.

For uniformity in circumference, the round part is often rotated, especially if the gap between it and the inductor is different. For the long length provide supports or rollers, sagging protection and position control. UralInduktor develops the concept of the complex and forms a technical solution, including the movement of a part or inductor. The Chinese plant performs detailed design and manufactures equipment according to this concept.

What to report for selection

For the pipe, it is especially important to separate the outer diameter from the wall thickness: two pipes of the same diameter can differ in metal mass several times per meter. If the weld is heated or only the end of the product, this is noted in the drawing.

material, external and internal diameters or sectional profile;

total length, straightness, mass and location of supports;

zone length, initial and final temperature;

local, scanning or continuous pass mode;

required speed in m/min, cycle time or number of parts per hour;

allowable temperature difference in thickness and circumference;

restrictions on inductor access, rotation, power supply and cooling.

Selection of series and layout

For a small local area, ABC or ABB may be suitable. AVZ is considered for more powerful heating of medium sections. AVN, including 1–20 kHz performance, is evaluated for deep heating of thick-walled products, long inductor and high performance. The LH with the inductor is convenient where the operator has to bring the heater to a fixed large part; the standard length of a flexible water-cooled cable is usually up to 5 m. The choice of series is not made by diameter in isolation from the wall, temperature and speed.

The frequency inside the operating range of the installation depends on the oscillating circuit, the inductor and the part. Therefore, the final compatibility is confirmed with the inductor that is ordered for the project. A simple inductor is usually included in the price, and a complex circuit, a set of replaceable inductors or a quick-change connection are calculated separately.

Approximate calculation of the passing heating

The example is intended for the primary assessment. Let's take the steel tube Ø 60 × 5 mm. The calculated mass of one metre is about 6,8 kg. The heating from 20 to 800 °C and the mean thermal capacity of the steel 0,60 kJ/(kg°C) requires 6,8 × 0,60 × 780 * ≈ 3180 kJ or 0,88 kWh heat per metre. With a imputed total CPD of 55%, the electrical energy would be approximately 1,60 kWh per metre.

If the pipe passes at the speed of 0,20 m/min, 12 m is heated in an hour, and the average estimated power consumed from the network is about 19 kW. Taking into account the terminal losses, pauses, surface condition and unstable clearance, preliminary check the available electrical power of the order 25–35 kW. This is not the nominal value of the converter: the test should confirm the temperature at the outlet and the difference in wall thickness.

Completeness and acceptance

The installation is completed with Russian-language management and documentation. At the plant it is checked after assembly together with the ordered inductor. By agreement, the customer receives the necessary photo and video materials. In Miass, before shipment, a second check is carried out with a full connection without load.

At the facility, specialists perform commissioning with customer details: check the direction and speed of movement, rotation, pauses, power and temperature conditions, train personnel and sign acts. The liquid cooling system is selected according to the thermal calculation and the expected duration of operation. The warranty is 18 months, and the exact point of its countdown - the date of shipment or the act of commissioning - is fixed by the contract.

What to send for selection

Send drawing or pipe sketch, heating length, temperature and required speed. We will offer the scheme of movement, range of converter, inductor, supports and cooling. Price on request.