Investigations on corrosion monitor reliability, calibration, and coverage

Thickness loss due to internal corrosion and erosion is a critical issue in ferromagnetic steel structures that can cause catastrophic failures. Ultrasonic thickness gauges are widely used for the detection of wall thickness. Recently permanently installed ultrasonic sensors have become popular for the inspection of areas suspected to undergo wall thickness loss. However, these are limited by the high cost and requirement of coupling agents. To address these problems, a novel cost-effective, and smart corrosion monitor based on the magnetic eddy current technique is developed in this research. The performance and reliability of the monitor to track internal wall thickness loss is tested successfully through accelerated and real-life aging corrosion tests.
Due to the handling and safety issues associated with the powerful magnets in magnetic techniques, a particle swarm-based optimisation method is proposed and validated through two test cases. The results indicate that the area of the magnetic excitation circuit could be reduced by 38% without compromising the sensitivity.
The reliability of the corrosion monitor is improved by utilising the active redundancy approach to identify and isolate faults in sensors. A real-life aging test is conducted for eight months in an ambient environment through an accelerated corrosion setup. The results obtained from the two corrosion monitors confirm that the proposed corrosion monitor is reliable for tracking the thickness loss. The corrosion monitor is found to be stable against environmental variations.
A new in-situ calibration method based on zero-crossing frequency feature is introduced to evaluate the in-situ relative permeability. The thickness of the test specimen could be estimated with an accuracy of ± 0.6 mm.
The series of studies conducted in the project reveal that the magnetic corrosion monitor has the capability to detect and quantify uniform wall thickness loss reliably.