Some types of damage of high interest in gas turbines and other rotating equipment are:

• Stress corrosion cracking of turbine discs, blades and retaining rings
• Creep damage in blades
• Cracking in rotor bores.

Many of the non-destructive testing techniques applied to turbine components are conventional (such as dye penetrant testing and magnetic particle testing, for cracks), but the applications for these ordinary techniques that have evolved are very specific to the materials and characteristic damage of turbines.  Quest Reliability’s materials engineering staff in conjunction with our NDT specialists and in-house testing laboratory have developed protocols for conventional NDT of turbine components and a very specialized materials database to support the testing.

More highly specialized NDT techniques used by Quest Reliability in addition the conventional methods are:

• High resolution electron microscopy, to detect and characterize voids associated with creep damage, and detect material degradation of other types.
• Specialized ultrasonic tests requiring extensive logistical efforts, generally performed by others under contract to Quest.  Quest’s materials engineering and NDT staff are skilled and very experienced in the interpretation and supply of ultrasonic data in the following cases:
  • Borosonic inspection of turbine rotor bores, to identify mainly manufacturing based defects and subsequent crack defects that can initiate in the bore of older vintage rotors containing bores.  
  • Disc bore inspection of turbine disc keyways and bores shrunk on rotor shafts.
  • Fir tree groove and blade inspections (offering non-intrusive inspection when circumstance permits).
  • Solid rotor shaft inspections.
  • Generator end ring inspections of austenitic material for stress corrosion cracking and arcing type defects.
• Eddy current testing (electromagnetic induction), to detect stress corrosion cracking in blades, discs, retaining rings and to supplement rotor bore scans.  Quest NDT staff perform these tests.
• Magneto-optical imaging (MOI™), another eddy current-based technique, this is a relatively new proprietary technology that images magnetic field differences in the metal surface, used for detection of cracks and other anomalies – very fast.  Quest developed this system.
• Induction Thermography System (ITS™), a new proprietary technology that uses an induced RF current to temporarily elevate the temperature in the surface of a component, coupled with computer thermography to visualize anomalies in the near surface of the inspected object.  This technique is particularly well suited for detection of disbonding of coatings in turbine blades, anomalies in composite materials, and surface cracks.

For further information about Gas Turbines and Rotating Equipment, please contact us.