Local vacuum electron beam welding has been developed to apply it to pipe welding from the inside of a pipe. The gun of this machine with the maximum output of 15 kW (30 kV×500 mA) is able to weld pipes which are 267 mm in outer diameter and 6 m in length.
In order to establish pipe welding by using local vacuum electron beam welding, we investigated the method of local vacuum seal, the control of the penetration bead formation, and the problem about the electron gun discharge. The results obtained are as follows:
(1) Local vacuum seal mechanism by combining the air expansion tube and 0 rings can keep the vacuum pressure lower than 3×10^-3 Torr.
(2) The uniform and stable penetration beads are formed by controlling piercing beam current in welding carbon steel pipes of 9.3-30.9 mm in thickness in flat and vertical positions.
(3) It is effective for preventing weld defects caused by the electron gun discharge to provide a highspeed turn off-turn on circuit on high voltage secondary side of the power supply.