Inspector Systems is a specialist in manufacturing of tethered self-propelled pipe robots for internal inspection, non-destructive testing and machining of complex un-/piggable, buried & trenchless pipelines. The industrial sectors, which originates from 30 years of experience in the nuclear industry, are Gas & Oil (On-/Offshore), Chemical, Petrochemical, District Heating Lines, Water etc. Due to its flexible modular design the pipe robots are able to get inserted through poor access points (e.g. valves) and to pass in bi-directional travelling vertical sections and numerous bends with small arc radius. The paper describes the system concept and performance of the pipe robot technology. A modular construction allows the adaption of different operational elements for the respective application. Focus is the procedure and application of ultrasonic modules for wall thickness determinations and detections of anomalies, especially in district heating networks.