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Automated underwater ship weld inspection system

A weld in a ship hull is a possible structural weak point mainly due to potential flaws that may be present.  At the moment, only visual inspections are carried out for in service ships.  There is currently no system or procedure to inspect flaws below the surface and this could potentially result in flaws being missed until it is too late.

Contracted by the Marine Materials Joining Innovation Centre (MAJIC) in Malaysia, TWI developed the first automated underwater phased array inspection system to fill this gap.  The system has been successfully tested in a simulated environment within TWI laboratories and has now been shipped to our client site for commissioning.

The core and most innovative part of the product is its ability to provide full volumetric inspection for underwater welds in the hull of a ship.  An advanced multi-probe phased array technique is used to achieve this.  At the same time, the product has global and local guidance systems to assist the operator navigate the vehicle underwater.  The body of the vehicle is made of marinised aluminium material to minimise corrosion.

Objectives

  • Navigate on the side of a ship hull via remote control
  • Capable of inspecting ship hulls with a thickness range of 8-20mm
  • Operable up to 20m under water
  •  Find and follow the weld using guidance systems
  • Provide full weld volume inspection using an advanced, encoded, phased array technique
  • Track the path of the vehicle while it’s travelling underwater
  • Offer off-line data analysis capability

System design and functionality

To achieve these objectives, the vehicle carries multiple systems for underwater operation.  These include a 3-probe 128-element phased array instrument, with 2 probes used for inspecting the weld and 1 probe as a weld follower; laser and camera guidance systems; sonar and depth sensor based tracking systems; and inclinometer for posture monitoring. Although it carries an advanced inspection system, the software was designed so that inspectors without extensive ultrasonic knowledge can operate the vehicle and collect data.

Conclusion

The fully integrated system was successfully tested on 6mm and 8mm thick welded steel plates with artificial flaws in UniKL-MIMET. It was able to track the weld with the guide system and acquired the data for analysis.  The location system was also used to track the vehicle’s path and display its posture.

The live inspection at UniKL-MIMET
The live inspection at UniKL-MIMET
The inspection system operating underwater on a vertical plate
The inspection system operating underwater on a vertical plate
Avatar Lu Zhao Principal Project Leader - Non-destructive Testing

Lu is a Chartered Engineer and Member of The Welding Institute, with a BA and MEng in Chemical Engineering from the University of Cambridge prior to embarking on her professional career. She joined TWI in November 2009 as a Project Leader. Her main interests are in developing advanced inspection techniques for industrial applications and prototypes for automation and advanced inspection solutions. Lu has worked on a range of development projects including laser ultrasonic testing (UT) inspection techniques, high precision immersion measurements, prototypes for an underwater ship inspection vehicle, a UT simulator and an automated railway track inspection device.

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