Steel reducers, also known as concentric or eccentric size heads, are mainly used for the connection between two pipes with different diameters, serving as a transition for welding between large - and small - diameter pipes. Below are the main applications of steel reducers:

1. Flow rate changes in pipelines: When there is a change in the fluid flow rate within a pipeline, such as an increase or decrease, and the requirement for flow velocity change is not significant, reducers are necessary.
2. Pump inlet: To prevent cavitation, reducers are often used at the inlet of pumps.
3. Connection with instruments: At the joints with instruments, such as flowmeters and control valves, reducers are required to match the instrument joints.

In conclusion, steel reducers play a crucial role in industrial pipeline systems. They not only enable the connection of pipes with different diameters but also can, to a certain extent, regulate fluid flow rates and prevent equipment damage.