Which step follows throttling down during the procedure for shutting down a line?

Throttling down is an important step in managing fluid dynamics during the shutdown of a line, as it helps to reduce flow and pressure within the system gradually. Following this step, gating down is crucial to secure the system. Gating down refers to the process of closing valves to isolate the line from the rest of the system and ensure that no further flow occurs. This action is vital for both safety and maintenance purposes, as it prevents unintended fluid movement that could lead to leaks or spills.

Filling a tank, shutting down the pump, and communicating are all necessary actions in the overall maintenance and operational procedures, but they occur either before or after the gating down step. Filling a tank, for example, would not happen immediately after throttling down since the fluid needs to be contained and isolated first. This sequencing helps ensure a safe and controlled shutdown process.