Underwater maintenance with the “Crawfish“ robot

Offshore plants make an important contribution to the implementation of the energy transition. Periodic inspection, repair of the corrosion protection and inspection of the weld seams are essential tasks to ensure the longevity of plants. Much of this underwater work is still carried out by industrial divers. This makes maintenance time-consuming, expensive and risky. For maintenance work such as cleaning, repair and coating, the underwater vehicle "Crawfish" was therefore developed at Fraunhofer SOT.

The "Crawfish" underwater vehicle is an extension of the open-source "BlueROV2" robot. The mechanical design of the wheels and axles makes it possible to precisely control the robot, let it drive on various offshore structures and perform precise maintenance work. Four direct-drive wheels are used for this purpose, allowing the robot to move freely on flat and curved surfaces (curvature from 1 m pipe diameter). In the "Crawfish" developed, the contact pressure is generated via the four vertical thrusters in order to be independent of the surface conditions. The "Crawfish" has already been successfully tested in the Baltic Sea at the research platform in the artificial reef off Nienhagen.

Repair of the corrosion protection

A common problem with offshore structures is minor damage to the anti-corrosion paint. Damage to the paint leads to corrosion and premature failure of the structure. An automated solution can be provided by the "Crawfish", where a brush attached to a linear unit repairs the coating at the relevant points. The special two-component coating material is injected via a tube and applied by the "Crawfish".

Reading out measurement data on monitoring systems

Another application for which the "Crawfish" underwater vehicle can be used is the readout of monitoring systems such as the CoMoBelt^® sensor collar. This can detect cracks in weld seams through its ultrasonic sensor technology. To read the cuff, a reading head is used that supplies energy via induction and reads out the measurement data via WLAN. As shown in the video, this reading head can also be attached to the ROV and placed precisely above the cuff under water.