Longitudinally welded tubes with particular alloy ratios and/or for particular purposes undergo an additional heat treatment. The coarse-grained microstructure in the weld seam can be normalised by partial heat treatment. For this, the tube is fed continuously beneath the inductors and heated to the required temperature.
Weld seam annealing machines equipped according to requirements with different numbers of linear inductors and power ratings, depending on the wall thickness, material and production rate, are used for this.
According to the modular design of ELO-SEAM, the machine can be designed and dimensioned exactly to the requirements of the heating/annealing process for longitudinally welded ferritic steel pipes. The ELO-SEAM consists of one or more induction stations and heat up the seam area of the longitudinally welded pipe. Inductors use induction method to transfer the required energy, which is regulated by modern frequency converters, into the pipe. The required material area is heated above the upper transformation temperature AC3 (approx. 880°C) for normalization. This improves the quality of the tubes.
Ferrite sheets (concentrator sheets) are incorporated in the water-cooled inductors. As a result, the power input is concentrated in the seam area and the efficacy or efficiency of the inductors rises. The power input is regulated to avoid surface overheating.
A pilot line is applied to mark the exact position of the weld seam. Tube drift is detected by a camera and the EloSeam control system automatically adjusts the inductor position, which ensures a constantly precise annealing process.