Induction Preheating for the Submerged Arc Welded Steel Tube Production

Abstract

Tenaris is a leading supplier of tubes and related services for the world’s energy industry that manufactures a complete range of seamless and welded steel tubular products. The welding facilities are located in North and South America, and perform three types of welding processes, namely Electric Resistance Welding (ERW), Spiral Submerged Arc Welding, and Longitudinal Submerged Arc Welding (LSAW). Regarding the ERW process, in recent years we studied both the welding using Comsol [1,2], and the ulterior seam heat treatment using an in-house developed FEM model [3,4]. During the LSAW process, after the plate is conformed through the UOE forming process, the butt joint of the pipe is welded in three phases, first of which aims at presenting the edges and joining them but without filling in the bevels, the second one is to fill in the seam region at the inside of the pipe and the third one to do this operation on the outside. The welds are made by melting with an electric arc the bare metal electrodes. Pressure is not applied on the pipe during welding. Depending on the final product properties sought, a preheating near the edges with a relatively narrow temperature range is required for these three welding stages. In this article we focus on the inductive preheating for the tack welding stage of a continuous production line; it involves an open tubular geometry whose edges are facing and separated approximately 10 mm. There is no need to reheat the full tube, but only a region of ±75 mm from the edges approximately. Given the geometry and the required localized preheating, usual solution would be bar type inductors as those used typically for seam annealing. Alternatively, cylindrical coils can be used instead of inductive bars. 2D and 3D numerical models of different inductor bars and cylindrical coils are used in order to assess both kinds of preheaters and to understand the advantages and disadvantages of each one.