Design and Development of Key Subsystems for a Sheet Pile Inspection Device
T.P.A. van Leeuwen (TU Delft - Industrial Design Engineering)
G. Nijenhuis – Mentor (TU Delft - Industrial Design Engineering)
J.H. Boyle – Mentor (TU Delft - Industrial Design Engineering)
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Abstract
Sheet pile walls are a key part of Dutch maritime infrastructure. As these structures age, inspections are becoming increasingly important, particularly in areas where corrosion is difficult to detect. Current inspection methods, such as divers, cofferdams, and elevated platforms, are effective, but they are often slow, costly, and disruptive to daily port operations. This project, carried out in collaboration with AquaSmartXL, explores how a different type of inspection platform could make the inspection process more efficient.
The research phase mapped out what makes sheet pile inspection difficult. Corrosion concentrates in the splash zone and near the mudline, underwater visibility is unpredictable, and while sheet pile profiles vary widely, their outer face remains consistently flat and free of obstacles such as anchor heads. These findings pointed toward a clear direction: a platform that attaches to the outer surface, moves vertically along the wall, and carries swappable modules for cleaning, measuring, or visual inspection.
Several attachment methods were tested early on. Clamping failed because the angled sheet pile profile caused gripping forces to slide off rather than lock on, and suction could not form a reliable seal on corroded, uneven steel. Magnetic wheels performed best, but attaching and detaching them safely required addressing how strongly and unpredictably the magnetic pull increases at close range. This led to a ramp-shaped separator mechanism that gradually increases the distance between the magnets and the steel, releasing the wheels smoothly instead of forcing them off.
A working prototype combining magnetic wheels, thrusters, and the separator was built and tested in a water-filled sea container used as a stand-in for a sheet pile wall. The thrusters moved and aligned the prototype reliably, the magnetic wheels held firmly even when wet, and the separator released the wheels consistently, with an average gap of 4.91 mm before detachment. Belt tension proved more important than expected, as insufficient tension caused the drive belt to skip under the magnetic load.
The tests show that combining magnetic wheels, thrusters, and a separator mechanism allows a platform to move, attach, climb, and detach from a steel surface underwater. Building on this, a final concept was developed: the SP Crawler, a modular platform that can be fitted with different inspection tools depending on the task. Testing on real sheet piles, with marine growth and corrosion present, is needed to confirm how the system performs outside a controlled test setup.