(1)When the medium in the pipeline needs to flow in the opposite direction and the layout space is insufficient, the client can use a 180-degree elbow to solve it; (2)If a 90-degree elbow is used, a certain short pipe is generally required in the middle. The cost for welding will be increased and the stress resistance is greater. (3)The 180-degree elbow is used a lot in the evaporator of the ammonia refrigeration system.