Extension of process understanding and application fields for the longitudinal seam high frequency welding of pipes by the use of model process and finite element simulation reproducing techniques

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The proposed research will serve to extend the process understanding and application fields for the longitudinal seam high frequency welding of pipes with wall thicknesses < 5 mm. For this, the aim of the project is the development of a holistic process model taking into account the physical and chemical processes in the welding gap.Studies exist so far only with sheet thicknesses > 5 mm for the pipe production according to API 5L (materials X52, X65). In addition, work carried out on Cr-Mo steels. The investigations can only state that welding gap formation and melting behaviour depends on energy input and influences the oxide formation in the joint zone. Furthermore, the oxide formation at a given welding gap form is determined by the chemical composition of the base material. The welding gap formation at given process parameters and thereby process failure sensitivity depends also on the microstructure of the materials to be welded. The reason for this is the influence of the physical material properties (electrical conductivity, permeability, thermal conductivity, heat capacity, etc.) by the microstructure. When welding non- and low-alloyed steels their chemical composition affects the weld gap formation and the melting behaviour itself over viscosity and surface tension of the molten material. Until now, no systematic investigation of both factors with regard to the formation of weld defects, took place. Furthermore, the defect formation mechanisms in the present literature are represented inconsistently.Within the project a systematic investigation of the defect formation mechanisms by means of experimental analysis of a semi-continuous process model will be done. The model reflects longitudinal seam welding of tubes at laboratory scale and ensures a comprehensive process of observation. By setting appropriate parameters and shielding the process using inert gas, the factors mentioned above (and their process influences) can be considered separately.Based on the scientific findings gained on the semi-continuous process model, a finite element simulation model that imitates the longitudinal seam pipe welding will be developed. The model should be able by the specification of microstructure (electrical conductivity, permeability, thermal conductivity, etc.) and chemical composition (melting bath surface tension, melting bath viscosity) to generate parameter fields for non- and low alloyed steels. On the one hand, this makes it possible to determine for the first time the effects of alloying element variation for a given steel grade. On the other hand, the weldability of not yet processed grades can be determined without extensive welding trials to extend the workable range of non- and low alloyed steels.