配管の高速自動溶接に関する研究 Ｉ 溶接施工

Abstract

Pipeline installation requires the use of a welding method presenting high pipe-laying efficiency and therefore high welding speed.The present report describes the development of welding procedure by the automatic one side downhill welding method using high-current-density GMAW with regard to the girth welding of pipe. In this method, the groove root is made tight and non-gapped, and welding is performed in the narrow gap with little deposit metal, in order to shorten the pipe alignment and welding time. An appropriate procedure for this method was established by developing the downhill welding which uses copper backing on the pipe inside and small diameter solid wire on the pipe outside. When the standard welding conditions are deviated from, the welding arc will touch the copper backing sometimes causing the copper to deposit on the root bead. This deposition of copper on root beads causes not only cracking of beads, but decreasing pipelaying efficiency due to consumption of copper backing. As a result of various researches, this problem was resolved by preparing another groove on the pipe inside in addition to the groove on the pipe outside. The use of the improved shape of groove expanded the zone of appropriate welding conditions for root pass toward the high-speed welding side. The built-up sequence was divided basically into three kinds of passes, the root pass, intermediate pass and cap pass, and each pass was expressed graphically to facilitate the selection of welding conditions for assuring no welding defects and high welding efficiency.This welding method was applied into a welding system with the development in computor control technique and with the development in internal clamp.