Development And Application Of A High Speed Automatic Field Welding Method For Pipeline

Abstract

Abstract A automatic field welding method of high speed and good reliability was developed with one-side downhill gas metal arc welding (GMAW) method. The results are followings:Diagrams for selection of the appropriate welding conditions in which high efficiency without any defects can be gained in narrow groove welding.A novel groove shape was developed for preventing deposition of copper onto the root bead when the bead was welded from outer side with copper backing from inside.The effect of new-type groove was confirmed by means of a direct observation of root bead with a special device from the reverse side.The new-type groove makes an appropriate welding condition range enlarge and quality and efficiency increases. Copper does not deposit onto root bead even at an experimental welding speed of 210 cm/min. Introduction Pipeline installation requires the use of a welding method presenting high pipe-laying efficiency and therefore high welding speed. Also, petroleum and natural gas pipelines require high-quality welds. The present report describes the development of a computer-controlled 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. Experimental Procedure The welding test was conducted by tack-welding the end of a steel pipe ring (5), for which the prescribed pipe and bevel preparation had been made in advance, to an end face of a fixed steel pipe (2)on a stationary frame (1), fitting another steel pipe ring to the other end face of the pipe in the same way, aligning the grooves of the rings, expanding the pipe by internal clamp (4) and performing downhill. GMAW of the pipe by welding machine (3) as shown in Fig. 1. The internal clamp was provided with a backing copper ring fixed into its clamp shoe for alignment so that backing was effected simultaneously with clamping. Chemical elements and mechanical properties of the tested wire were as shown in Table 1. Wire diameters of 0.9 mm and 1.2 mm were studied, and wire 0.9 mm in diameter was decided to be used in the testing because of its less amount of sputtering and greater stability of arc. For the shielding gas, both CO2 and Ar were used. The test results revealed that the narrow-gap one-side downhill welding of pipe performed at high speed by GMAW method involved the problems shown in Table 2. Basic Shape of Groove Groove shape largely influences the pipe alignment operation and the selection of appropriate welding conditions. To shorten the aligning time, the groove should preferably be non-gapped, in addition to having root face.