A pig launcher is the trap that inserts a pig into a live pipeline and sends it on its way without interrupting the product flow. This guide explains the parts of a launcher, how the launch sequence works, and why launcher operation is one of the higher-risk routine jobs on a pipeline.
Pig Launcher in one line: A pig launcher (launching trap) is a fabricated barrel and pipework assembly that loads a pig and drives it into a flowing pipeline. It has an oversized barrel with a quick-opening closure to insert the pig, isolation valves that separate the trap from the mainline, a kicker line that directs flow behind the pig, and vent and drain connections to depressurize safely. The operator seats the pig, pressurizes and equalizes the trap, then opens the valves so line flow pushes the pig into the mainline.
The launcher barrel is a larger-diameter section, tapering down to the pipeline bore through a reducer, so the pig can be loaded and then guided into the smaller line. A quick-opening closure (a hinged or threaded door) seals the barrel end for loading. A trap or major isolation valve separates the barrel from the mainline, and a bypass or mainline valve on the pipeline lets flow be routed either straight down the line or through the trap.
A kicker line taps off upstream and feeds product into the back of the barrel behind the loaded pig, providing the push that ejects it. Vent, drain, and pressure-indication connections let the operator depressurize and confirm the trap is empty before opening the closure. A pig signaler downstream confirms the pig has left the trap and entered the mainline.
A typical launch runs in a strict order: verify the trap is depressurized and drained, open the closure, load the pig against the reducer, close and lock the closure, then slowly pressurize and equalize the trap with the mainline. With pressures equal, the operator opens the trap valve, opens the kicker to route flow behind the pig, and throttles the mainline bypass so flow diverts through the trap and launches the pig. The signaler confirms departure, after which the trap is isolated again.
Launching is hazardous because a barrel can hold trapped pressure and product. Opening a closure that has not been fully vented and drained has caused serious incidents, so interlocked pressure-relieving closures, positive drain verification, and permit procedures are standard. In oil and gas, launchers appear at the upstream end of any piggable gathering line, transmission line, or subsea trunk line.
A launcher inserts a pig into the line and sends it downstream; a receiver catches and removes the pig at the other end. Mechanically they are similar barrel-and-closure traps, but a launcher has a kicker line to push the pig out and a receiver has a bypass to draw the pig in.
The barrel can retain line pressure, liquids, and hydrocarbon or toxic gas even after isolation. Opening a closure before the trap is fully vented and drained can release stored pressure violently, so pressure-relieving interlocked closures and strict permit procedures are required.
Once the trap is equalized with the mainline and valves are opened, the kicker line routes product flow into the barrel behind the pig. That flow, combined with throttling the mainline bypass, creates a pressure differential that pushes the pig out of the trap and into the pipeline.
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