The standard technology of steel pipe production is the high frequency (HF) inductive welding. A mechanically formed profile is introduced into an inductor. Inside the pipe, in the position of the inductor there is an impeder, whose function is to form a suitable distribution of the electromagnetic and temperature field. In previous paper of the authors, the new magneto-dielectric (MD) material for the impeder is proposed and results of extraordinary energy saving are shown.This paper treats the aspect of the pipe quality, which represent the essential parameter in a production technology. The analyses were made for the widely spread ferrite impeder and for the proposed MD impeder. From this point of view, the MD impeder appeared to be advantageous material also. In addition to the standard mechanical tests of pipes quality, extensive chemical and physical analyses of the material in the weld, as well as in the basic section of the pipe, have been performed. The aim of the investigation was to explain the bad results in the standard flattening and hydrostatic testing of pipes produced using the ferrite impeder of TDK-IP1 type.

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High frequency inductive welding has been the subject of many researches, both in theoretical and

SUMMARYThis paper deals with the analysis and calculation of characteristic values of the transistor converter of power with energy dosage that can be used for inductive heating and welding. First, the analysis of the current solutions is taken into account, then the disadvantages of certain calculation methods and algorithms are identified, and finally, new theoretical approaches in the calculation of converter parameters are presented. New formulae make it possible for the calculations to be more precise which can be confirmed by the numerical example to do with the problem solving in practice.

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