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

本文的研究将有助于拓宽管壁厚度< 5mm纵缝高频焊接的工艺认识和应用领域。为此，该项目的目的是开发一个考虑到焊接间隙中的物理和化学过程的整体过程模型。到目前为止，根据API 5L（材料X52， X65），研究只存在板厚bb50 mm的管道生产。此外，还对Cr-Mo钢进行了研究。研究只能表明，焊接间隙的形成和熔化行为取决于能量输入，并影响接头区氧化物的形成。此外，在给定的焊接间隙形式下的氧化物形成是由基材的化学成分决定的。在给定的工艺参数下，焊接间隙的形成以及由此产生的工艺失效灵敏度也取决于待焊材料的微观结构。其原因是微观结构对材料物理性能（电导率、渗透率、导热性、热容等）的影响。焊接非合金钢和低合金钢时，它们的化学成分影响焊缝间隙的形成和熔融材料本身的粘度和表面张力的熔化行为。到目前为止，还没有对这两个因素对焊缝缺陷形成的影响进行系统的研究。此外，目前文献中缺陷形成机制的表述不一致。在项目中，将通过半连续过程模型的实验分析对缺陷形成机制进行系统的研究。该模型反映了实验室尺度下的钢管纵缝焊接，保证了观察过程的全面性。通过设置适当的参数并使用惰性气体保护工艺，可以单独考虑上述因素（及其对工艺的影响）。在半连续过程模型的科学研究成果的基础上，建立了纵向焊缝管道焊接的有限元仿真模型。该模型应能根据微观结构规格（电导率、渗透率、导热系数等）和化学成分规格（熔浴表面张力、熔浴粘度）生成非合金钢和低合金钢的参数场。一方面，这使得首次确定合金元素变化对给定钢种的影响成为可能。另一方面，不需要大量的焊接试验就可以确定尚未加工的牌号的可焊性，以扩大非合金钢和低合金钢的工作范围。

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.