A single sensor performs NDT pipe inspections circunferentially reflections up to 3m-10’ in front of the sensor. The technique is mainly used for detection of corrosion under supports (as a complement to the axial inspection technique), inspection of lamp posts, inspection of air-to-soil or air to cement interfaces or any area where the pipe or structure is not accessible.
Check this paper to know more about inspection of inaccesible areas:
Inspection of lamp posts and other non-accessible areas with EMAT Medium Range Guided Waves.