Method for in-situ eddy current inspection of coated components in turbine engines

#The invention relates generally to in-situ inspection of coated components and, more particularly, to in-situ eddy current inspection of coated components in turbine engines, for example airfoils in gas turbine engines and coated turbo components in locomotive diesel engines.

#A gas turbine engine typically includes a compressor that supplies pressurized air to a combustor. The air is mixed with fuel in the combustor and ignited to generate hot combustion gases. The hot gases flow downstream to one or more turbines that extract energy from the hot gases to power the compressor and provide useful work, such as generating power at a power plant or powering an aircraft in flight.

#Each turbine stage typically includes a turbine rotor assembly and a stationary turbine nozzle assembly for channeling combustion gases into the turbine rotor assembly disposed downstream therefrom. The turbine rotor assembly 50 commonly includes a number of circumferentially spaced apart rotor blades 20 extending radially outwardly from a rotor disk 30 that rotates about the rotor 10, as illustrated schematically in FIG. 1. Rotor blades generally include airfoils (also indicated by reference numeral 20) and are commonly called “buckets” for land based turbine engines. As used here, the term “blade” encompasses “buckets” as well as blades. The rotor assembly is housed within a case 40.

#These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

#FIG. 1 schematically depicts basic elements of a turbine rotor assembly, in cross-sectional view;

#FIG. 2 schematically depicts basic elements of a stationary turbine nozzle assembly, in cross-sectional view;

#A method for in-situ eddy current inspection of at least one coated component 20, is explained with reference to FIGS. 4 and 5. As used here, the phrase “in-situ” means that the inspection is performed while the coated component 20 is installed in its operational environment typically while the operational environment is not running. For example, “in-situ” eddy current inspection of an airfoil (also indicated by reference numeral 20) is performed while airfoil 20 is mounted in a turbine engine (not shown) and typically while the turbine engine is not running. Similarly, “in-situ” eddy current inspection of a coated turbo component (not shown) is performed while the coated turbo component is mounted in a locomotive diesel engine (not shown). The in-situ inspection method includes applying a drive pulse at a measurement position 28 on an outer surface 11 of coated component 20. Coated component 20 includes a base metal 24 and a coating 22, as exemplarily shown for an airfoil 20 in FIG. 3. Exemplary airfoils 20 include stationary airfoils (indicated by reference numeral 21 in FIG. 2) mounted in nozzle assemblies 60 and rotating airfoils (also indicated as 20) mounted in rotor assemblies 50, as discussed above and as shown for example in FIGS. 1 and 2.

#Exemplary drive pulses include electromagnetic pulses. An exemplary application of a drive pulse includes energizing a drive coil 12 with a pulse of electrical current, drive coil 12 being positioned at measurement position 28, as schematically indicated in FIG. 4. For example, a pulse generator 70 supplies a fixed duration pulse to drive coil 12, as shown for example in FIG. 4. The fixed duration pulse comprises a continuum of frequencies, and because penetration depth depends on the excitation frequency, use of a fixed duration pulse provides information from a range of depths. Exemplary drive pulses have a pulse width of about 10 μs to about 100 [s, and more particularly, about 20 μs. Still more particularly, the drive pulse is a square wave pulse (or more generally a rectangular wave pulse), for example having a pulse width of about 20 μs. Other exemplary drive pulses include delta function pulses and sawtooth pulses, and the inventive method is not limited to any particular pulse waveform. Optimal drive pulse amplitudes vary based on the materials forming drive coil 12, magnetic field sensor 14, and coated component 20.

#Exemplary drive coils 12 include eddy current coils. Eddy current coils are conductive coils with a variety of coil diameters and turn numbers. An exemplary eddy current coil is formed from copper and has a coil diameter of about 5 mm to about 25 mm. Other exemplary eddy current coils include single eddy current array probes (SECAPs) (not shown). SECAPs are single, conducting coils formed on a flexible substrate by known photolithographic methods. A variety of conductive materials, such as copper, silver, and gold are used to form SECAPS.