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以前,高强度多层螺焊管是将带钢卷成螺旋状后,从待焊过内外焊接而成。为了便于获得用适于管材内外面使用条件的材料制造的双层管,采用宽度相同而材质不同的带钢错位成型,成型后进行内外埠(参阅实公昭39—23261号公报)。为了便于获得特厚壁螺焊管,采用多层带钢分别错位成型,然后对各层带钢待焊边进行焊接(特公昭39—14392号公报)。然而,若采用上述两项发明,则焊缝
Previously, high-strength multi-layer screw pipe was rolled into a spiral strip, to be welded from inside and outside to be welded. In order to make it easy to obtain a double pipe made of a material suitable for use inside and outside of the pipe, dislocation molding using strips of the same width and different materials is performed, and the inner and outer ports are formed after the molding (see Japanese Utility Model Laid-Open Publication No. SHO-39-23261). In order to make it possible to obtain a thick-walled screw-welded pipe, multilayered steel strips are respectively formed by dislocation molding, and then welded to each layer of the steel strip to be welded (Japanese Patent Publication No.39-14392). However, if both the above two inventions are used, the weld seam