Feasibility study of a touch-enabled active sensing approach to inspecting subsea bolted connections using piezoceramic transducers

Abstract Pipelines that stretch on for miles and miles are linked together through a multitude of bolted connections. However, each bolted connection represents a point of vulnerability that can suffer from leakage. In subsea environments, leakage can spread farther and cause even more disastrous to both economy and environment. A number of structural health monitoring methods have been proposed and explored. However, most monitoring methods require permanent installation of sensors on the structures to be monitored, which can be difficult for subsea locations. In this paper, a piezoceramic transducer enabled touch-based active sensing approach is proposed to inspect subsea bolted connections without the requirement of permanent installation of sensors on the structures. The proposed approach also aims for an easy integration with a subsea robotic system, such as a remotely operated vehicle (ROV) for bolted connection inspection. To study the feasibility of the proposed approach, a spring-loaded C-clamp shaped device that mimics two robotic fingers equipped with a pair of piezoceramic transducers is designed and fabricated. Two piezoceramic transducers are mounted on the inner surfaces of the two robotic fingers. In addition, a pair of permanent magnets are employed to ensure a temporary while constant coupling between the transducers and the both surfaces of the bolt connection, upon touching. In this way, one piezoceramic transducer generates stress waves that propagate across the connection interface, and the other PZT transducer detects the propagating stress wave. By analyzing the received stress wave signals via spectrograms and wavelet packet transformation, the status of the connection can be derived. Experimental investigations are performed on a bolted connection with different applied torques in air and in salt water (3.5% salinity), and results demonstrate effectiveness of the proposed touch-enabled active sensing for inspection of submerged bolted connection.