This thesis presents the development of an innovative sensor head for detection and characterization of geometric defects in steel pipes that combines three inspection techniques usually employed separately in Caliper and Magnetic Flux Leakage (MFL) PIGs. The novel Geometric Magnetic Discriminator (GMD) sensor performs high- resolution magnetic pipeline readings using MFL with the addition of internal pipe geometry evaluations and discrimination between internal and external defects. The combination of these technologies in a single sensor facilitates characterization of dents and corrosions, while at the same time optimizing the PIG set-up. According to the repair criteria in the standard API1160, combined defects such as a dent with metal loss, which in the past could only be detected through combined data of two different runs (MFL+ Caliper), must be repaired immediately. The GMD sensor was tested in a linear test rig, known as Flat Pig, and data were taken from different defect sets. Evaluation tests demonstrated that the GMD sensor sizes and discriminates a dent with metal loss. Technical aspects of the development, e.g.: the construction details of the sensor, evaluation tests and laboratory results are presented.