In-line Inspection (ILI) is a non-destructive practice to provide information about the pipeline condition while it is in service. It is alternatively referred as “intelligent pigging” or “smart pigging”. By employing sophisticated sensors and instrumentation, it can supply various functionalities, such as metal loss, geometry measurement, crack detection, profile mapping or monitoring, bending measurement, etc. For instance, Magnetic Flux Leakage (MFL), Ultrasonic Testing (UT), Electro-magnetic Acoustic Transducer (EMAT), Eddy Current Testing (ET) are the popular anomaly detection tools. Each tool has its own capability and limitation, which is usually explained in its specification. Sometimes different modules are combined in a single run to give a more comprehensive picture of the pipeline. Nowadays, ILI plays an essential role in the maintenance of pipeline operation. In addition, due to this stringent need, the technologies of this area are developing very quickly.