45° seamless elbow are pipe fittings and pipeline connections. Used in main trunk line and the branch pipe. For changing the direction of the pipe. The ways to connect with the pipe are direct welding (the most common way) flange connection, hot melt connection, electrofusion ...
The butt weld reducing tee is also a kind of Tee, but the branch pipe and the main trunk line have an unequal pipe diameter. Reducing Tee is widely used in the construction and maintenance of projects in the petrochemical, petroleum and natural gas, liquefied petroleum gas, ...