In the application of Magnetic Flux Leakage (MFL) pipeline inspection technology, corrosion anomalies are detected and identified via their leakage field due to changes in wall thickness. This leakage field is a three dimensional magnetic vector consisting of three distinct components: axial, radial, and circumferential. A new pipeline inspection technology is the first to use the circumferential component in data analysis. The three leakage fields are described in detail with an emphasis on the circumferential field. Examples of practical application are given to illustrate the effectiveness of this field in identifying and sizing defects.