Monitoring of corrosion damage using high-frequency guided ultrasonic waves

Abstract

Due to adverse environmental conditions corrosion can develop during the life cycle of industrial structures, e.g., offshore oil platforms, ships, and desalination plants. Both pitting corrosion and generalized corrosion leading to wall thickness loss can cause the degradation of the integrity and load bearing capacity of the structure. Structural health monitoring of corrosion damage in difficult to access areas can in principle be achieved using high frequency guided waves propagating along the structure from accessible areas. Using standard ultrasonic transducers with single sided access to the structure, high frequency guided wave modes were generated that penetrate through the complete thickness of the structure. Wall thickness reduction was induced using accelerated corrosion in a salt water bath. The corrosion damage was monitored based on the effect on the wave propagation and interference of the different modes. The change in the wave interference was quantified based on an analysis in the frequency domain (Fourier transform) and was found to match well with theoretical predictions for the wall thickness loss. High frequency guided waves have the potential for corrosion damage monitoring at critical and difficult to access locations from a stand-off distance.

Corrosion monitoring using high-frequency guided waves

“…One specimen was then milled down in approximately 0.2 mm steps to a final thickness of 9.43 mm to achieve uniform thickness reduction. Two of the specimens were subjected to accelerated corrosion using reverse impressed current cathodic protection (16,17) . The setup consisted of a DC voltage source, the steel plate partially submerged as the anode in salt water solution, suspended above the copper cathode (Fig.…”

“…The stand-off distance from the transducer to the defect was varied between 50 mm and 250 mm in steps of 50 mm. Experimental setup for laser measurement of high frequency guided ultrasonic wave propagation on steel specimen (16) .…”

“…The concept was initially demonstrated using milled specimens to gain an understanding of the sensitivity of the methodology for uniform thickness reduction. Thickness reduction due to accelerated corrosion of steel specimens was monitored to verify the applicability for actual corrosion monitoring (16) . The detection of hidden, simulated (milled) pitting corrosion using pulse-echo measurements with single sided access was investigated.…”

“…Figure 1. Accelerated corrosion setup impressing DC current on steel plate specimen in salt water, with steel specimen, copper cathode connected to DC source, water tank with filters and heater (16) .…”