Corrosion 4: Non-Destructive Testing (NDT) Overview C4

• Non-Destructive Inspection (NDI) / Non-Destructive Testing (NDT) is the inspection of aircraft parts/units without altering or destroying the integrity/ physical/material properties.
• NDT determines the continued serviceability for other inspection periods.
• NDT Methods range from visual inspection to ultrasound.

Canadian General Standards Board (CGSB)

• CGSB is the governing body establishing Recommended Practices for NDT methods.
• CGSB establishes the requirements for personnel certification.

Natural Resources Canada (NRCan)

• NRCan manages the National NDT Certification Body (NDT CB).
• NRCan conducts the certification requirements per CGSB.
• NRCan is responsible for grading written/practical exams across Canada.
• NRCan must ensure candidate meet CGSB standard requirements.
• NRCan provides certificates to successful candidates.
• Application renews certification.
• Appropriate training and work experience is needed to become certified in NDT.

NDT Training Requirements

• Candidates must provide evidence acceptable to the NDTCB of course completion regarding specific NDT methods before challenging examinations.
• Training organizations must issue documentary proof of satisfactory training completion detailed in the Rules of Implementation.
• NDT training courses must follow the NDTCB curriculum.
• NDTCB decides on the acceptability of courses and instructors.
• Training Hours Required:
  • Eddy Current Testing (ET): Level 1 (40 hours), Level 2 (80 hours), Level 3 (48 hours)
  • Magnetic Testing (MT): Level 1 (16 hours), Level 2 (24 hours), Level 3 (40 hours)
  • Penetrant Testing (PT): Level 1 (16 hours), Level 2 (24 hours), Level 3 (40 hours)
  • Radiographic Testing (RT): Level 1 (40 hours), Level 2 (80 hours), Level 3 (40 hours)
  • Ultrasonic Testing (UT): Level 1 (40 hours), Level 2 (80 hours), Level 3 (40 hours)
  • Visual Testing (VT): Level 1 (16 hours), Level 2 (24 hours), Level 3 (40 hours)

Industrial Experience

• Months of Experience Required:
  • ET, RT, UT: Level 1 (3 months), Level 2 (9 months), Level 3 (18 months)
  • MT, PT, VT: Level 1 (1 month), Level 2 (3 months), Level 3 (12 months)
• Legend:
  • ET = Eddy Current
  • RT = Industrial Radiography
  • PT = Liquid Penetrant
  • MT = Magnetic Particle
  • UT = Ultrasonics
  • VT = Visual Testing

CARs Requirements Std 571 Appendix K (Training to perform Specific Non-destructive Testing (NDT) Tasks)

• Appendix outlines alternative training requirements for qualifying technicians to perform Non-Destructive Testing (NDT) tasks, serving as an alternative to national standards certification.
• Appendix provisions apply only to NDT using liquid penetrant, magnetic particle, ultrasonic, and eddy current methods.
• X-ray inspections cannot be performed.
• NDT conducted under the provisions of this appendix is limited to inspecting specified components for predictable discontinuities with clear, objective acceptance criteria.
• Privileges differ from NDT AMOs and CGSB holders, and they may be granted privileges within methods rated, with no limits on the inspection of components.

Destructive Testing

• Hardness is the ability of a material to resist abrasion, penetration, cutting action, or permanent distortion.
• Hardness is increased both by cold working on metals and by heat treatments of steel/aluminum alloys.
• Structural parts are formed soft and then heat-treated to harden, retaining the finished shape because Hardness and strength are closely related.
• Material hardness is tested at the manufacturing level and after hardening.

Surface Hardness Testing

• Hardness testing equipment measure by resistance to penetration.
• Some hardness testers are Brinell and Rockwell.
• A portable-type hardness tester is also popular.

Brinell Tester

• The Brinell hardness tester uses a hardened spherical ball, 10 millimeters (0.3937 inch) in diameter against the metal surface.
• A pressure of 3000 kilograms for ferrous metals and 500 kilograms for nonferrous metals.
• Pressure is maintained: 10 seconds for ferrous metals and 30 seconds for nonferrous metals using hydraulic pressure.
• The pressure gauge indicates pressure amount, and the release mechanism allows relieving pressure after the test.
• A calibrated microscope is provided to measure the indentation diameter.
• The machine has anvils for supporting specimens and an elevating screw to contact specimens.
• For a metal's Brinell hardness number, measure the impression diameter using a calibrated microscope.
• Convert measurement into Brinell hardness number with a conversion table.

Rockwell Tester

• The Rockwell hardness tester measures resistance to penetration and indicates hardness using a dial.
• It measures penetration depth, and hardness numbers are based on penetration depth at major/minor loads.
• Greater the difference, the lower the hardness number and softer material.
• Two penetrator types are used: Diamond cone (hard material) and hardened steel ball (softer material).

Fabric Testing

• Most modern aircraft is metal, but many aircraft fabrics have requirements.
• The AME must know approved fabric testing processes.

Fabric Puncture Test

• Mechanical devices test fabric via pressing or piercing, are not FAA approved, and are bases in an on the fly test of fabric condition.
• Punch test accuracy depends on device calibration, coating thickness/brittleness, and fabric types.
• Mechanical devices are not applicable to glass fiber because it easily shears and indicates a low reading despite breaking strength.
• If punch tests break with low strength or the coating conditions are poor, more accurate field tests can be made.
• Cut a 1-1/4" by 4" sample, remove all coatings, and ravel edges to a 1" width.
• Clamp each end, supporting a load of sand suspended above the floor.

Fabric Types

• TSO-C15d airplane cloth is for all aircraft and aircraft with wing loading of 9 psf or greater, or the placard never exceeds 160 mph.
• TSO-C14b airplane cloth is for aircraft with wing loading less than 9 psf or never exceeds 160 mph.
• AMS 3802 airplane cloth is for gliders with wing loading of 8 psf or less, provided the placard never-exceed speed is 135 mph or less.
• Aircraft linen is British 7F1 and meets the minimum strength requirements of TSO-C15

Puncture Type Fabric Testers

• Puncture tests offer a good indication of fabric strength, but not the most accurate measurement.
• Seyboth:
  • Pushed against fabric until the tester punctures it.
  • Harder pushed indicates, the higher the plunger protrudes.
  • Red indicates weak fabric, yellow as deteriorating fabric, and green as strong fabric.
  • Fabric does not have to be removed from aircraft.
  • Easy to use.
  • Has no real relation to Table 2-1 of the Ac43-13-1B.
  • Has to make a small repair from the puncture.
  • Finished surfaces affect the test.
• Maule Tester:
  • Housing is pressed down against the fabric until a desired scale reading is acquired, and fabrics fails test if punctured.
  • Fabric does not have to be removed from aircraft, and it is easy to use.
  • Corresponds with Table 2-1 of the AC43-13-1B.
  • Fabric may have to be repaired.
  • Finished surfaces affect the test.
• Pull or Grab Test:
  • Validates fabric airworthiness, where a 1 1/4" by 4" fabric strip is taken from aircraft which is installed into the tested after stripping it.
  • Tester applies tensile force until ripping happens.
  • Reading indicates a pound scale correlated Table 2-1 of AC43-13-1B.
  • Can be positively validated airworthiness of the fabric.
  • Easy to use and correlates directly with table 2-1 of the AC43-13-1B.
  • Repair to aircraft is required