This is an improved process of induction welding of steel pipe and an improved product of such process. After steel skelp is formed into a tubular blank with an open longitudinally extending seam, the seam edges are continually heated, converged and pressure-welded. Heat is applied to the converging edges in a novel manner to eliminate entrapment of harmful scale during welding, to prevent thermal stressing or cracking of the seam after welding, to arrest the growth of martensite and to produce a pipe product characterized by a substantially pure metal interface extending the width of the pipe wall.
A roll set adjacent the welding point forms the outside weld bead that is produced in welded tube manufacture into a thin fin that may be easily removed by a conventional scarfing tool.
An impeder for use in an apparatus for resistance tube welding by which a strip-shaped skelp continuously formed into a tubular or spirally tubular shape having spaced opposed edge portions defining a gap therebetween has the edge portions heated and pressed together for being welded. The impeder has a generally tubular casing and a core within the casing consisting of a plurality of laminated bodies each consisting of a plurality of substantially flat planar foils of metallic magnetic material, the core, when viewed in cross-section traverse to the central longitudinal axis of the casing, having the transverse cross-sections of the laminated bodies on parts of at least one circle concentric with the longitudinal axis of the casing and having the planes of the foils extending substantially radially outwardly from the longitudinal axis.
This invention relates to the means of continuously seam-welding the areas to be joined together of steel strips formed like tubes in the production of hot-dip metal-coated steel tubes from steel strips in a continuous supply. This seam welding device is capable of manufacturing electric seam-welded tubes with high efficiency and operational safety.
An impeder for use in a mill for roll-forming tubing. The mill includes a feed station for supplying an elongated steel strip in flat form and a station where the strip is transversely bent from its planar condition causing the lateral edges of the strip to be brought together in abutting relationship. An induction coil is positioned about the bent portion of the strip for inducing current flow through the location where the lateral edges first abut to heat the lateral edges to plasticity. The mill also includes a weld rolls station where the plastisized lateral edges are firmly pushed together to complete welding of the tube. The impeder is disposed inside the induction coil adjacent the location where the lateral strip edges are first brought into abutting relationship. The impeder includes an outer shell made of a strong, heat-resistant material, a core disposed inside a shell and formed by an aggregation of ferromagnetic material, and components for causing passage of a coolant through the core material.
An apparatus and method for making a seam-welded steel pipe free of untempered martensite without seam anneal. The method includes selecting a steel containing a carbon concentration below a predetermined level, for example, 0.14% or 0.12% by weight. The method also includes flooding both outside and inside of the strip with a coolant while the weld seam is being formed, and continuing to immerse the welded strip for a sufficient time after the weld seam is formed to prevent the formation of untempered martensite. The apparatus includes a heater capable of heating the strip to a temperature sufficient to form a welded seam, a cooling module configured to supply a coolant to the welded seam both inside and outside of the strip as the weld seam is being formed, and another cooling module configured to immerse the welded strip in a coolant after the weld seam is formed for a sufficient length of time to prevent the formation of untempered martensite.
