Development of technologies and equipment for orbital welding and repair of pipelines in space

1Lobanov, LM, 1Asnis, EA, 1Ternovoj, EG, 1Shulym, VF, 1Bulactev, AR, 1Kryukov, VA, 1Likarenko, TA
1E.O. Paton Electric Welding Institute of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
Space Sci.&Technol. 2018, 24 ;(4):41-50
Publication Language: Ukrainian
Abstract: 
The orbital space stations consist of a large number of pipelines made of various types of corrosion-resistant materials (stainless steel, titanium alloys, etc.). They are located both inside and outside the space station. These pipes can wear out for various reasons (corrosion, mechanical damage, etc.) during the long-term exploitation of the station, and so there is a need for their repair in space conditions. Studies conducted at the Paton Electric Welding Institute of the NAS of Ukraine showed that a reliable and prospective pipeline repair process in space conditions is the welding. We present the results of a development of specialized equipment and welding technologies for the repair of pipelines inside and outside the manned spacecrafts. The issues related to the design of the laboratory equipment for the welding of tubular connections as well as the development of welding technologies and equipment for the repair of fixed pipelines in the space environment are considered.
          We have developed the technology of orbital welding of pipes of stainless steels and titanium alloys by means of the argon arc and the electron beam welding methods. The technological requirements for modes of welding (welding current, arc voltage and the accelerating voltage of the electron beam, the speed of welding) are defined. Preliminary modes of the orbital weld penetration of solid tube samples and butt joints welding modes with single and multi-pass seams were studied. On the first pass the welds were performed with the formation of the penetration bead. The repeated passes along the first and subsequent seams were performed as a surfacing with the final formation of the top bead and gradual formation of the crater. Mechanical properties of the obtained welded joints at the room and low temperatures and their chemical composition as well as their macro and microstructure and hardness are studied. The resistance of welded joints to intergranular corrosion was tested. Tests for temporal resistance to rupture of tubular butt-joints of stainless and titanium alloys were made at the test temperatures of + 20 °C and –196 °C. They showed that the welding with orbital argon-arc and electron-beam methods makes it possible to obtain the joints that are close in strength to the base metal.
        The studies on a chemical heterogeneity have shown that welded joints performed by argon-arc and electron-beam methods are equivalent in chemical composition to the base metal. Studies of macro and microstructures, geometry and hardness of joints made of stainless and titanium alloys and performed by orbital methods have demonstrated a satisfactory and stable quality of these joints. The results of tests carried out at the International Space Station showed the resistance of tubular joints from the 12Х18Н10Т steel and PT-3В titanium alloy to intercrystalline corrosion. Both joints are performed by orbital methods with the argon-arc and electron-beam welding.
         For the first time, the prototypes of equipment and basic technologies of orbital argon-arc and electron-beam welding inside and outside the operating space station are developed and manufactured. During the tests of the equipment, the prototypes of butt-type tubular joints for mechanical and physicochemical studies were obtained by the orbital method. The results of the studies have shown that the orbital methods of argon-arc and electron-beam welding make it possible to obtain qualitative joints that are close in strength and chemical composition to the main metal.
Keywords: argon arc welding, autopressurization, chemical properties, electron beam welding, electron beam welding modes, external defects, heater, intergranular corrosion, internal defects, macro- and microstructure, mechanical properties, microhardness, mikrokamera, pipelines, space stations, stainless steel, titanium alloys, toggling joints, tubular joints