Non-Contact Acoustic Emission Monitoring of Corrosion-Fatigue Damage in Submerged Steel Structures

Abstract

Corrosion-fatigue is considered one of the main degradation mechanisms affecting the structural integrity of offshore support structures and mooring systems. These structures are typically covered with marine growth of various types. This paper highlights a feasibility assessment of detection and localization of corrosion-fatigue damage in submerged steel structures using non-contact Acoustic Emission (AE) technique. An accelerated corrosion-fatigue experiment was conducted on a dog-bone steel specimen. A dedicated experimental set-up was designed to simultaneously apply accelerated corrosion and cyclic loading on the dog-bone steel specimen submerged in artificial seawater. Ultrasound signals were continuously measured using an array of underwater AE transducers (in the frequency range between 50-450 kHz) placed at a fixed distance from the tested coupon. A source localization algorithm for corrosionfatigue- induced ultrasound signals was successfully implemented. The results of the accelerated corrosion-fatigue experiment suggest that corrosion-fatigue-induced ultrasound signals can be detected with a satisfactory signal-to-noise ratio using noncontact AE transducers. Four stages of corrosion-fatigue damage growth were identified which may be used as the basis for possible damage characterization.