Inline Inspection Pig

Overview

An inline inspection pig, often called a smart pig, is an instrumented tool that travels inside a live pipeline and records the condition of the pipe wall as it goes. It is launched into the flow at one end, pushed along by the product itself, and caught at the other end, where its recorded data is downloaded and analyzed. The result is a map of every place the wall has corroded, cracked or dented, located precisely enough that a crew can dig down to the exact spot. This is the main way operators inspect a buried pipeline without exposing it.

The tool carries its own power, sensors, and memory, because once it enters the pipe there is no connection to the outside until it is recovered. Everything about its design follows from running unattended for hundreds of kilometers: it seals against the wall to catch the flow, presses sensors onto the steel, logs continuously, and keeps track of exactly where it is the whole time.

Tool body and drive

The Tool Body is the chassis. Two or more Body Tube sections house the electronics and battery, joined by an Articulation Joint universal coupling so the tool can flex around pipe bends rather than jam in them. Sealed End Cap closures keep line pressure out of the electronics, and a Tow Link gives a recovery tool something to grab if this one stalls.

The Drive System is what makes the tool move. Polyurethane Drive Cup seals span the pipe bore so the product cannot slip past, and the pressure difference across them pushes the tool along, the same principle a piston uses. Guide Disc elements center the tool and carry its weight, clamped by Cup Flange rings. A Bypass Port bleeds a controlled amount of flow through the tool to keep its speed in the window the sensors need, because too fast and the readings blur.

Sensors and measurement

The Sensor Ring is the measuring head. The primary method is magnetic flux leakage: a Magnetizer built from a Magnet Yoke and rare-earth Permanent Magnet elements saturates the pipe wall with magnetic flux, coupled into the steel through Brush Block wire brushes. Where metal is missing, at a corrosion pit or a gouge, the flux leaks out of the wall, and an array of MFL Sensor Hall sensors on sprung Sensor Arm holders reads that leakage. The size and shape of the leakage signal tells the analyst how deep and how wide the metal loss is.

Many tools add a set of Ultrasonic Sensor ultrasonic transducers that measure wall thickness directly by timing an echo through the steel. MFL is fast and robust in gas lines; ultrasonic gives a direct thickness number in liquid lines. The sensor arms are held against the moving wall by springs so they keep contact as the pipe diameter varies and the tool rocks.

Electronics and power

Every sensor channel feeds the Electronics Module. Banks of ADC Board converters digitize the channels at high speed, processors organize the stream, and Memory Module solid-state storage writes the entire run to memory, often hundreds of gigabytes for a long line. There is no telemetry out of the pipe, so the data has to survive onboard until recovery.

All of this runs off the Power Module. A Battery Pack of high-density lithium cells supplies the tool for the full run, a converter conditions the voltage rails, and a Battery Monitor protects the cells and tracks how much capacity is left. Battery capacity is one of the limits on how far a single run can reach.

Positioning and use

A defect reading is useless without knowing where it is, so two systems pin down location. The Odometer System uses sprung Odometer Wheel units on Wheel Arm holders with Wheel Encoder counters that measure distance traveled, giving the linear position of every reading. The Mapping Module adds an Inertial Unit inertial unit built from Gyro and Accelerometer sensors that records the three-dimensional route, so the survey also produces a precise map of where the buried pipe actually lies.

Tools are built in sizes to match the pipe, from small gathering lines to large transmission lines up to four feet across. A run is planned around line flow rate, distance and the battery, and operators schedule inspections on a cycle set by the pipe's age and corrosion history. After recovery, the recorded data is processed into a defect list ranked by severity, which feeds the dig program and the operator's integrity-management plan.