Assessment of Structural Integrity of Submerged Concrete Structures Using Quantitative Non-Destructive Techniques Deployed from Remotely Operated Underwater Vehicles (ROV)

Abstract

Marine assets in ports, harbors, and those which are part of our civil infrastructure including dams and bridges undergo persistent structural deterioration over time. Several national and international disasters, in recent times, have proved that these ageing infrastructures pose high risk from both social and economic perspectives. Therefore, periodic inspection of marine assets is essential to detect early deterioration, to schedule maintenance and restoration plans to prolong their life, prevent catastrophic damages and loss of lives.Non-destructive testing of concrete structures is performed using numerous techniques including ultrasonic tomography, ground penetrating radar, and radiography to identify structural anomalies and predict remaining life. However, conventional inspection procedures are limited to areas of the structures which are easily accessible and safe to work. Concrete structures operating underwater, are subject to rates of corrosion and impact damage which are often higher than the part of the structure above water. However, today, there are few quantitative NDT techniques available to inspect submerged concrete assets — qualitative visual inspection by professional divers is the most widely used technique in the industry. Diver-based visual inspection operations are subject to inherent risks, especially when operating under poor water visibility, underwater currents, and confined spaces. They also often mandate shutdown of operations of the asset. Manned underwater operations are also often inadequate to confidently comment on the assets’ integrity. Furthermore, often, several critical defects in concrete structures do not manifest on the surface to be visible in visual inspection routines until their severity is significant. Therefore, to mitigate these risks, this paper introduces a first-of-its-kind quantitative NDT technique for concrete structures operating underwater using robotic remotely operated vehicles (ROV) indigenously by Planys Technologies, an IIT Madras incubated company.The remotely operated vehicle (ROV) can be controlled from a safe location by a pilot. The ROV can be thought of as a platform which can carry payloads to perform operations as per the requirements of the application. ROV Beluga, described in this paper, carries numerous payloads including marine cameras to provide live visual feed for visual inspection and navigation, lasers for quantification of defect dimensions, sonars to conduct waterbed surveys, and transducers to perform NDT. ROV-based operations offer numerous advantages over diver-based operations including unlimited endurance, enhanced visual inspection in turbid waters, improved systems for data acquisition and repeatability.Widely accepted concrete NDT techniques, Schmidt hammer and ultrasonic pulse velocimetry were chosen to be reengineered for underwater inspection on a robotic drone. Key constraints including operational complexity, power and communication, and data acquisition and processing requirements were considered in this process. Preliminary experimental studies performed in a lab-scaled facility, and in real field conditions, described in this paper, demonstrate the potential of ROV-based quantitative NDT of underwater concrete structures. Key realizations and limitations to practical implementation are also described. The work presented in this paper will be of interest to asset owners and managers, enabling them to make confident post-inspection decisions.