Titanium absorbs hydrogen above 250 °C, oxygen above 400 °C, and nitrogen above 600 °C. The infiltration of these elements will greatly reduce the mechanical properties of titanium. Therefore, the protection of hot welds by argon gas is a key factor for the quality of welded joints. The welding protection of titanium pipes is carried out by passing argon inside the pipe and using a special protective cover outside the pipe. The protective cover generally has a whole cover structure, a half cover structure and an elbow cover structure.
The argon filling protection in the tube adopts the method of segmented argon filling: in the place of 200~300mm on both sides of the welding joint, make a sealing device and seal the argon filling. The sealing device adopts rubber and stainless steel splint sealing. The air outlet adopts a diameter of φ4mm, and the air inlet adopts a diameter of φ8mm, which can ensure that the air in the tube is driven clean, achieve the purpose of argon protection, prevent the entry of external air, and facilitate the formation of welds. The air inlet should be tightly sealed to prevent the argon protection from being damaged due to air being brought in from the gap when entering argon.
It is more difficult to fill the weld with argon for all-position welding, because the distance between both ends of the weld is long, and there are elbows and so on. Argon filling adopts the method of segmented argon filling. Before the welding seam is assembled, the sealing gasket (composed of stainless steel splint and rubber, the argon filling tube is a soft rubber tube, and a stainless steel wire with a certain strength in parallel) is placed on the The inner distance of the pipeline is 200 to 300mm from the weld. After the welding of the welding seam group is completed, the sealing gasket can be taken out.
Most of the above protective cover designs for pipeline welding are made of complete sets of pipe specifications. Obviously, it can be applied when there are not many pipe specifications, but when there are many specifications, the cost is high, and it is very inconvenient to disassemble and assemble frequently during construction. The following introduces an easy-to-operate partial protective drag cover, which effectively solves the problem of on-site welding protection of titanium tubes.
The size of the drag cover is determined according to the size of the temperature field in the high temperature zone (above 400°C) during titanium welding (usually 80x1500px). The drag cover is made of copper skin, and the top is an oval argon filter ball wrapped with copper mesh to wrap titanium chips (stainless steel or copper mesh group can also be wrapped with copper mesh). The purpose is to ensure that argon gas fills the air cavity of the drag hood and forms a stable laminar flow. The upper part of the ellipsoid is connected to the copper tube, and high-purity argon gas is used for internal welding.
