The system consists of a steerable magnetic climbing vehicle with its own encoders to measure the distance traversed and turning angles. The vehicle has dimensions of only 25 cm length, 16 cm width, 5 cm height and a weight of only 2.3 kg without the NDT sensors. The payload consists of a 2.5 MHz ultrasonic dry contact wheel probe. Additionally the crawler can carry the following, with a maximum payload of 1.5 kg, up to a height of 20 m:

1. a wet contact ultrasonic probe or an EMAT can be used to measure the thickness of vertical walls of storage tanks. This system can be used on tank roofs to which access, to measure the wall thickness, is often prohibited for safety reasons

2. an eddy current probe to measure paint thickness

3. a small TV camera can also be carried as payload for remote visual inspection in a nuclear plant.

Ultrasonic data from the output of a conventional pulser/receiver are collected directly by a 250 MHz A/D card plugged into the expansion bus of a PC. All features including the sampling rate, trigger selection, threshold levels etc. are programmed. A digital reading of the remaining wall thickness is shown on the PC screen along with a line scan of the cross-sectional thickness of the tank wall or tank roof under inspection. The encoders reveal the distance of the thickness scan from a predetermined starting point. The total system is self contained and operates from batteries or a 110 V supply.

large c-scan images (up to 1.5 m x 1.5 m) can also be produced with a resolution of 2 mm using the magnetic climbing crawler in conjunction with the "SEE-SCAN" system developed by Sonomatic Ltd. Some typical results are presented.

The crawler consists of a DC motor, a differential gear box (for high maneuverability) and a speed of 1 m per minute is presently achieved. The operator can safely and remotely control the speed and direction of the crawler, which is connected to a PC by a 25 m umbilical. The umbilical contains all the cables for a NDT probe, drive motor and encoders, and also a couplant supply hose if wet contact ultrasonic probes are used.
With some modification the crawler system can be used to carry out weld inspection around large diameter steel tubes.