Gas Material, Processing and Power Technologies

Outline

Spherical storage tanks (spherical gas holders and LPG storage tanks) are inspected periodically for their safety. One of the inspection　methods is called in-service inspection used to inspect the welded seams externally based on ultrasonic waves without opening tanks. Osaka Gas has developed an inspection robot which can detect the welded seams and automatically follow up them for in-service inspection.

Gas holder: The equipment which stores natural gas temporarily for smoothing the change of gas demand

Principle of Automatic Inspection

The robot has ultrasonic flaw detection probe which inspects the welded seams, and a detection sensor which detects the position of welded seam. Ultrasonic flaw detection probe is used a nondestructive inspection system called TOFD, Time of Flight Diffraction mode, method which utilizes the principle that an ultrasonic wave diffracts when it encounters a flaw. A 2-dimensional laser displacement sensor was adopted as the weld seam detection sensor for the robot. This sensor measures the shape of the welded seam and it emits the laser beam. The position of the welded seam center is decided by this shape and the robot attitude is controlled without deviation.

Specifications

Size	(L) 50 cm * (W) 40 cm * (H) 20 cm
Weight	20kg
Magnetic Force	220kg (4 wheels in total)
Speed	0-3m/min
Power Source	DC24V supplied from outside source
Sensors	- 2-Dimensional Laser Displacement Sensor, - Laser Point Displacement Sensors, - 3-Axis Tiltmeter, - Odometers, - Hall Sensors, - Color CCD Camera, - Ultrasonic Flaw Detection Probe (TOFD method)

Benefits

Practical introduction of this robot will cut inspection cost for each tank. It will shorten inspection time by about one week from the conventional 23 days, and will reduce the conventional number of inspectors required from 4 to 2.