NDT of HVOF Coatings

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NDT of HVOF Coatings

• John Sauer
• Sauer Engineering
• HCAT Toronto
• September 25th, 2002

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NDT

• Outline
• Where have we been??
• Where are we going??

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NDT

• Where have we been? Chrome
  plating
• Common usage of magnetic particle and fluorescent
  penetrant
• Recent inclusion of Barkhausen inspection on
  critical components
• Some applications require stripping of chrome
  regardless of condition-no NDT issues

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NDT

• What are we looking for??
• Chrome is already cracked so we are not looking
  for plating defects
• Looking for substrate defects or grinding burn
  via Barkhausen
  

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NDT

• What do we see??
• Recent studies by AFRL and Boeing St.Louis say
  that any defects under .250 ( that size may be
  larger) cannot be found with common methods
• Barkhausen can detect burn but cracks??

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NDT

• Hill AFB
• Estimate that 50 of the parts that come in
  for repair with chrome are not stripped and put
  back into service
• Question
• Are .250 defects OK from a damage tolerance
  standpoint??
• What size defect do we really need to find??

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NDT

• Where are we going?? HVOF
  Coatings
• A positive aspect of HVOF is the possibility that
  the coating may not require stripping thru
  multiple repair cycles
• However, this highlights the issue
• What is happening in and under the coating??

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NDT

• What are we looking for??
• Cracks/defects in coating
• Delaminations
• Substrate cracks/defects
• Size of substrate defects
• Must be in the .250 critical size range since we
  must be better or EQUAL to chrome ?

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NDT

• What do we see??
• Limited work shows varied forms of ultrasonic are
  the best methods for seeing smaller defects down
  to .050

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NDT

• How do we get there??
• Define the requirements
• Understand the applications
• Assess production feasibility

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NDT

• What are we looking for??
• Size
• Location
• How does that vary from application to
  application?
• What is the production feasibility for use of the
  technique on a reliable basis in the field?

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NDT

• Research has shown some ideas on the horizon
  might be
• JENTEK's MWMTM-Array sensor to involving
  eddy-current technology
• EWI suggests either eddy current or USI C scan
• GEAE suggests Pulsed Eddy Current (PEC)
• Naval Center has performed work on corrosion
  under paints using
• Real time Ultrasound Imaging
• Thermal Imaging
• Near Field Microwave Imaging

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NDT

• JENTEK's MWMTM-Array sensor technology can be
  used to develop surface-mountable eddy-current
  sensors that can be modified for
  difficult-to-access locations on complex
  configurations
• Work has been performed on coatings for Gas
  Turbine Industry and WCCo

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NDT

• Ultrasonic inspection by EWI (similar to AFRL)

Ultrasonic C-Scan Image of a Coated Sample
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NDT

• GEAE suggests Pulsed Eddy Current (PEC)
• Most existing Eddy current inspections use single
  frequency excitation
• Uses a current pulse in a drive coil to transmit
  transient electromagnetic flux into the structure
  
• Advantages of this are the presence of wide range
  of frequency components in the exciting field
• Work would be performed by GE's Global Research
  Center (GRC)

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NDT

• Naval Center has performed work with on corrosion
  under paints using
• Real time Ultrasound Imaging
• Basis is patented two dimensional piezo
  microelectric array to generate real time C-scan
• Thermal Imaging
• Active Thermography-External source for heat -use
  IR camera
• Sonic Thermography-high amplitude sonic waves
  cause frictional heat-use IR camera
• Near Field Microwave Imaging
• Rely on rlection properties of metallic surfaces
  using open ended microwave probes

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NDT

• Cannot resolve this issue today
• Significant issue for both HCAT/PEWG
• Subcommittee being formed with Chuck Alford(PEWG)
  and John Sauer (HCAT) as co-chairs to pool
  resources and address issue

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NDT

• Any one interested please see Chuck or myself
  during this meeting
• Possible side discussion tonite if people are
  interested