PURPOSE: To improve the productivity of a welded steel pipe of large diameter having good quality and to improve the productivity to reduce cost thereof by a simple method, by roughening the end faces of a blank steel plate, and joining both end faces by O-pressing by means of an Al foil having the limited thickness then subjecting the steel plate to piping welding.
CONSTITUTION: A blank steel plate 1 is beveled, whereafter end faces 51, 52 are blasted by shot blasting or the like to rough the surfaces. Al foil 7 of 0.01W0.1mm thickness is pressed and adhered to one end face 51 by means of a roll 8. Both end faces 51, 52 of such plate 1 are joined to each other by O-pressing after C- pressing and U-pressing to press stick the foil 7 to the joint surfaces. In this state, the end faces are subjected directly to pipe making and welding without going through the stage for tack welding. If the thickness of said foil 7 is ≤0.01mm, the strength of the mechanical sticking between the end faces 51 and 52 is insufficient and if the thickness is >0.1mm, a large amt. of Al remains in the weld metal in the stage of pipe welding and there is possibility of a welding defect; therefore, the thickness is limited in the above-mentioned range.
YAMAUCHI NOBUYUKI
KASHIMOTO FUMIO
