Flow line

A Flow line, used on a drilling rig, is a large diameter pipe (typically a section of casing) that is connected to the bell nipple (under the drill floor) and extends to the possum belly (on the mud tanks) and acts as a return line, (for the drilling fluid as it comes out of the hole), to the mud tanks.

The flow line will typically have equipment attached to it, such as a flow show which shows whether drilling fluid is flowing down the flow line or not and any changes in that flow. High-pressure jets are typically attached along its length to dislodge any obstructions (such as drill cuttings collecting in one spot) that may occur.

See Drilling rig (petroleum) for a diagram.