Research On Characteristic Of Hyperbaric Welding Arc And Behavior Of Droplet Transfer

In the new century, the Chinese offshore oil develops rapidly, while the underwater part of offshore oil platforms, underwater pipelines and other underwater structures require extensive using of underwater welding. Welding method has potential advantages for deepwater pipeline installation, hot tap and repair. Welding characteristics determine that the welding method is the best choice for the structure repair and the underwater operation. The underwater hyperbaric environment has important impact on the welding arc and metal transfer behavior. To achieve a reliable implementation of the welding process in hyperbaric environment, it is important to study the welding arc and droplet behavior in hyperbaric environment in depth.The hyperbaric welding research testing chamber was used in this paper. The synchronous multi-information acquisition system was built independently. The hyperbaric pulsed MIG welding arc and metal transfer behavior were studied in depth. A theoretical and experimental analysis was carried out for the effect of longitudinal magnetic field on TIG and MIG welding process. The feasibility of improving the hyperbaric welding process by the longitudinal magnetic field was demonstrated. Specific research works are as follows:1. High-speed camera protection was designed. The image acquisition was successful implemented using the high-speed camera in hyperbaric environment. The system achieved a stable transmission of high-speed image data through the chamber. Using the synchronous multi-information acquisition system in hyperbaric environment, a truly synchronous analysis was achieved of welding process high-speed image, arc voltage and welding current in hyperbaric environment. A program for synchronized display, collection, and analysis of hyperbaric welding process information was programmed. Trough a certain algorithm, the automatically synchronized display of collected signal and high-speed image was achieved. As a result the process of experimental data analysis was greatly simplified, and the efficiency of the experiment was improved.2. Using the finite element analysis software, the physical characteristics of hyperbaric welding arc was analyzed. The effect of environment pressure on arc temperature, electron density, plasma flow and other physical parameters was studied. And the welding arc was regarded as plasma for the first time to analyze the distribution of argon ion density in arc-column area.3. The hyperbaric MIG welding process was studied. Using the hyperbaric high-speed camera system, the hyperbaric pulsed MIG welding droplet behavior was studied. Accordingly the feasibility and the improvements of hyperbaric MIG welding process were intuitively comprehended. The results showed that the maintenance phase arc in hyperbaric pulsed MIG welding process is adverse to the stability of the welding process. It increases the difficulty of arc pulse reburning, which makes the failure rate of pulsed arc higher, and even results in the extinction phenomenon in the maintenance phase.4. The effect of reverse flow of plasma on the welding process was studied in hyperbaric MIG welding process. The research found that the strength of the reverse flow of plasma decreased with the increase of welding current intensity. In the pressure of 0.3MPa, when the welding current was greater than 300A, the reverse flow of plasma was buried, so the stability of droplet transition could be achieved. The study also found that the anode and cathode jets were not coaxial. This phenomenon of different axes was beneficial to stabilize the welding process. Because this phenomenon could effectively prevent that the droplet was cumbered with the reverse flow. The research of reverse flow in hyperbaric environment lay a good theoretical foundation for carrying out hyperbaric MIG welding interiorly.5. Using the high-speed camera system, the DC TIG welding arc with the external longitudinal magnetic field was studied. The effect of the longitudinal magnetic field on arc behavior was revealed in depth. The study found that, in the normal pressure, the magnetic DC TIG welding arc was a closed hollow cone. While in the hyperbaric environment, owing to the cooling effect of the atmosphere, the vertical magnetic arc was difficult to form a closed hollow cone, which was a spiral curve in the form. The fluctuation of voltage waveform was mainly caused by the rotation of the welding arc, which was characterized by periodic fluctuation instead of the irregular fluctuation of TIG welding arc signal in high-pressure environment. This made the behavior of TIG welding arc more controllable and more stable. The stability of arc motion behavior on the one hand reduced the performance requirements of welding power sources. On the other hand, it improved the bead formation. Therefore, applying longitudinal magnetic field in hyperbaric TIG welding process is an effective method for reducing the welding cost and improving the welding quality.6. Using the high-speed camera system, the pulsed MIG welding process with the external longitudinal magnetic field was studied. The results showed that the longitudinal magnetic field could restrain the cathode plasma jet of the pulsed MIG welding in high-pressure environment.In this paper, the hyperbaric welding process was studied in depth by means of finite element analysis and experimental study. The theoretical foundation was laid for the application of hyperbaric MIG welding to domestic offshore oil and other areas.