Early use of titanium pipes no domestic manufacturers of standard titanium tube, titanium and more people have to weld type (commonly known as "miter" type) elbow in Figure 4, it's complicated process. The tubes usually multistage bevel cut, welded or sheet metal unfold under a multi-section leaf material, and then rolled welding, weld volume. Due to the geometry of the weld is not continuous, would produce a higher concentration of stress, therefore, that the tube temperature and the working pressure must be made stricter requirements. 2 weld will greatly reduce the corrosion resistance, easy to leak, and poor appearance, the inner surface is folded surface increases the resistance of the tunnel and back seam severely erosion-corrosion and reduces life expectancy.