Fault detection for pipelines

The invention concerns structural integrity assessment apparatus for determining stress concentration zones in a structure, such as a pipeline. The apparatus allows particularly to detect defects in buried pipelines using magnetometric surveying where anomalies in the magnetic field around the pipelines are detected. The apparatus has a plurality of triaxial magnetic field sensors, each sensor being arranged to measure magnetic field components in a plurality of directions. A support is provided to maintain said sensors in a predetermined relative spacing and orientation. The support is moveable relative to a structure under assessment in use and may be portable. Three or more magnetic field sensors are provided which may be arranged in a linear, two-dimensional or three-dimensional array. The apparatus may include position determining means, such as a global positioning system (GPS), so that stress concentration zones can be located on the structure.