New welding process in the manufacturing of UOE pipes.

A new welding process has been introduced in the manufacture of large-diameter UOE pipes at the Kimitsu Works, Nippon Steel Corp. The new process includes the following methods which have been developed on the basis of fundamental research.(1) Observation of molten pools by X-rays was made during welding to find effective means for the prevention of undercuts. Multiple electrode welding is successfully applied to prevent the undercuts because of its dispersion of the arc in the direction of welding line.(2) Four wire welding has been adopted in place of three wire welding to increase the welding speed without loss of the toughness.(3) Metal inert gas welding can be combined with submerged arc welding to manufacture the line pipes for low temperature service.(4) A flux cored tubular wire with melt-type flux is used for large heat-input welding.