Welding joints can be connected to pipes, tanks or oil tanks by welding, which is convenient for installing various spare parts, such as: oil tank caps, high-pressure valves, high-pressure gauges, oil pipes... and other products. The flat surface is machined and can be used as a sealing surface with suitable sealing elements. When welding, the wall thickness of the appropriate size can prevent deformation or burn-through. Welding joints with flanges can be used when precise positioning is required through positioning holes or a lower overall height is required.