JPS55136572A - Automatic tig welding method of stationary pipe - Google Patents

Abstract

PURPOSE: To make operation efficient and assure the even penetration beads without any backing copper strips in the root-pass welding by performing welding with plural welding heads dividedly along the circumferential weld line.

CONSTITUTION: The 1st head 3 is started from the 12 o'clock position to the counterclockwise direction and the 2nd head 4 is started from a suitable position between 3 o'clock and 6 o'clock to the clockwise direction. The shrinkage of the gap owing to weld heat shrinkage at the point when the 2nd head 4 ends welding up to the 6 o'clock position is slight. The 2nd head 4 is returned to the 12 o'clock position upon ending of the welding up to the 6 o'clock position, after which it performs welding in the clockwise direction. On the other hand, the 1st head 3 performs welding continuously but the thermal shrinkage at the C point is small by being restrained by the weld zone (4-1) having previously been welded by the 2nd head 4, where the penetration is perfect and there is no likelihood for weld defects. Similarly, even in the welding from the 12 o'clock position by the 2nd head 4, the reduction of the gap at the D point is small by the restraint of the weld zone (4-1), thus the root-pass welding of even penetration is achieved.

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