Development of high power laser pipe welding process

The world's first 25 kW laser welding machines at its 24 inch pipe mill has been installed. The technology for the high-power laser pipe welding process that assures welds with the same properties as those of the base metal while maintaining high productivity has been started to develop. Key technologies for this process such as high power laser welding, high-accuracy seam tracking and nondestructive inspection have been successfully established. The results obtained are as follows. (1) The productivity of this process is much higher than conventional fusion weldings, e.g., SAW for less than steel plate 16 mm thick. (2) High energy density of laser beam helps to produce finely distributed oxides. (3) Fine oxide particles with a size of 0.1-0.2 μm were found in weld metal. And they also prevent the heat-affected zones from deteriorating low temperature toughness and so on, a problem that occurs in conventional fusion weldings. (4) The performance of the welds was as sound as the base metal by using the heat treatment process after high-power laser welding. (5) The characteristics of low temperature toughness and SSCC etc. of the laser welds are almost at the same level as the base metal.