A probe device for detecting corrosion in one or more blades of a gas turbine system, the device comprising: (a) a detection head having a shape arranged to conform to a surface geometry of a fillet section of a gas turbine blade, the detection head being operable to move along the axial length of the fillet section for detecting corrosion pitting; (b) at least one primary coil device located within the detection head and operable to induce a first magnetic field within an area of the fillet in contact with the detection head; (c) a receiver device (C2,C3,106a,106b,108) operable to detect a signal corresponding to a second magnetic field received from the area of the fillet exposed to the first magnetic field, wherein the second magnetic field is generated by induced currents in the area by the first magnetic field; (d) a storage medium containing reference data with a plurality of premeasured signal amplitudes corresponding to corrosion pitting with known geometry; and (e) a signal processing device configured to process the detected signal by correlating the amplitude of the detected signal with one of the plurality of the premeasured amplitude values and wherein the signal processing device is further configured to determine the geometry and/or the dimensions of corrosion pitting in the inspected area based on the known corrosion pitting geometry associated with the correlated premeasured amplitude data; and wherein the receiver device comprises: (a) a first and a second coil device (C2, C3) disposed inside the primary coil operable to generate a first and a second received signal from the second magnetic field, respectively; (b) a first and a second band-pass filter device (106a, 106b) respectively coupled to the first and the second coil device (C2, C3), wherein the first and the second band-pass filter device (106a, 106b) are operable to filter the first and the second received signal, respectively; and (c) a differential amplifier device coupled to the first and the second band-pass filter device (106a, 106b), wherein the differential amplifier is operable to differentially amplify the filtered first and the filtered second received signal and generate the detected signal; (a) a detection head having a shape arranged to conform to a surface geometry of a fillet section of a gas turbine blade, the detection head being operable to move along the axial length of the fillet section for detecting corrosion pitting; (b) at least one primary coil device located within the detection head and operable to induce a first magnetic field within an area of the fillet in contact with the detection head; (c) a receiver device (C2,C3,106a,106b,108) operable to detect a signal corresponding to a second magnetic field received from the area of the fillet exposed to the first magnetic field, wherein the second magnetic field is generated by induced currents in the area by the first magnetic field; (d) a storage medium containing reference data with a plurality of premeasured signal amplitudes corresponding to corrosion pitting with known geometry; and (e) a signal processing device configured to process the detected signal by correlating the amplitude of the detected signal with one of the plurality of the premeasured amplitude values and wherein the signal processing device is further configured to determine the geometry and/or the dimensions of corrosion pitting in the inspected area based on the known corrosion pitting geometry associated with the correlated premeasured amplitude data; (a) a first and a second coil device (C2, C3) disposed inside the primary coil operable to generate a first and a second received signal from the second magnetic field, respectively; (b) a first and a second band-pass filter device (106a, 106b) respectively coupled to the first and the second coil device (C2, C3), wherein the first and the second band-pass filter device (106a, 106b) are operable to filter the first and the second received signal, respectively; and (c) a differential amplifier device coupled to the first and the second band-pass filter device (106a, 106b), wherein the differential amplifier is operable to differentially amplify the filtered first and the filtered second received signal and generate the detected signal;