Non-Destructive Testing (NDT)

• Non-Destructive Testing (NDT) or Non-Destructive Examination (NDE) is similar to a doctor diagnosing a patient
• This involves using investigation methods to assess the health of parts without damaging them
• NDT specialists interpret test results against pre-set criteria in consultation with the part's designer
• NDT means assessing a product’s condition without altering its characteristics

CND (Contrôles Non Destructifs)

• Aims to ensure the absence of defects that could affect a part's performance
• Successful NDT execution combines investigation techniques, their limitations, and matching detection power with specified criteria
• Current emphasis is on training operators in NDT
• COFREND improves research, standardizes actions, and certifies operators

NDT Goals

• Highlight defects and confirm their presence
• Characterize defects by determining the mechanics of failure
• Measure parts to determine thickness
• Non-destructively evaluate parts by searching for defects without causing damage

Applications

• Used in the aeronautics and automobile sectors
• Seen in the energy sector such as nuclear, petrochemistry, and gas
• Utilized in railway transport
• Used in metal transformation and metallurgy
• Seen in naval, military, and civil contexts
• Used to ensure the safety of mechanics and metallic constructions

Timing is Key

• Before manufacturing or transformation, NDT is used for:
  • Receiving inspection (product check)
  • Check if parts meet specifications/standards
  • Check if parts are suitable for transformation

Post-Manufacturing Checks

• Used for conformity checks with specifications and standards
• Indirect process checks verify process regulation, such as welding operation qualifications

On-Going Maintenance

• Involves on-site preventive maintenance and periodic checks of installations for corrosion and damage
• Corrective maintenance is used during disassembly or other service such as aeronautics, mechanics, and railway

Importance considerations

• NDT is costly and does not add value to the part

• Reserved for:

  • Safety parts
  • Expensive parts which have costly discards
  • Critical parts that, if faulty,halt production
  • Costly processes/value of the part

• Primarily used to guarantee that manufactured parts are free of material defects or manufacturing flaws

• NDT is applied on a case-by-case basis following the sector.

• After assessment, hypothesis could be:

  • Part is not fit for purpose
  • Has poor working conditions
  • There are rupture initiations due to machining
  • Is the elaboration faulty

• It's important to replace a flawed element with a pristine one to ensure reliability

Maintenance Checks

• Checks the degradation of boiler pipes
• Inspects the structure of an aircraft
• Checks the status of high-stress safety components
• Examines a part before reassembly to forestall future breakdowns
• Verifies welds on a piece

Objective

• Detect material and manufacturing defects and fatigue that are not visually detectable, preventing equipment failures
• Follow defect evolution to implement changes and prevent part failure

Common Defect Origins

• Manufacturing and processing flaws
• Casting defects like porosity, cavities, and cracks
• Forging defects include laps and cracks
• Rolled parts may contain inclusions
• Drawn parts may have surface cracks
• Fabrication or assembly issues
  • Welded parts may have inclusions and porosity
  • Thermal Treatments cause cracks
  • Machining issues, environmental wear, and tool marks can create defects
• Operational Deficiencies
  • Fatigue
  • Overstressing

Processing Imperfections

• Shrinkage cavities are caused by metal contraction during solidification
• Porosity results from trapped gas during solidification
• Cracks are tears in the skin from high stress during cooling

Method for detecting defects during Manufacturing and Assembly

• Quenching Cracks happen from extreme thermal cycle stress
• Welding Defects can be inclusions and lack of fusion

Operational defects

• Primarily depend on part utilization conditions
• Defect causes intrinsic pre-existing quality

Types Of Ruptures

• Static Rupture: Part failure due to stress
• Fatigue Rupture: Rupture due to crack evolution due to repetitive stress

Common NDT Methods

• Optical Methods
• Dye Penetrant Inspection
• Magnetic Particle Inspection
• Radiography
• Eddy Current Testing
• Ultrasonic Testing

Visual Inspection

• Simple and common method using equipment like magnifying glasses, mirrors, endoscopes, and video cameras
• Robots can be used for inspections

Liquid Penetrant Testing

• Used for approximately 50 years
• It identifies defects on a part's surface
• It requires applying a liquid penetrant, eliminating excess, applying a developer, then visually inspecting its surface under UV light

Magnetoscopy

• This involves magnetizing a part then exposing it to fluorescent powder
• Particles gather and show defects under appropriate lighting
• Only appropriate for ferromagnetic materials and surface defects, to 10 mm depth

Process

• The principle is that iron filings on a ferromagnetic surface align in the direction of the magnetic field
• When a defect is present within proximity of the surface, the magnetic field's orientation gets changed and increases surface intensity

Radiography

• Places the part between a radiation source and film
• Material density affects radiation absorption which in turn affects the film's shade
• Radiography is primarily effective for identifying interior defects with most material being radiographable
• X-rays pass through materials and create electrical charges

Ray creation

• X-rays are made by shooting accelerated electrons at a tungsten target
• Gamma rays come from spontaneous decay from radioactive isotopes

Industrial Techniques

• Using film to create radiographic images is common
• Quality images can be achieved through meticulous attention to detail and precise control over the process
• The best quality image is achieved by this process

Eddy Current Testing

• This testing creates a current within conductive substances through a magnetic field
• These currents are called "Foucault Currents"
• Eddy Current Testing is only correct for parts made with electrically conductive materials
• Tracks the variation of an alloy's composition and detects surface or subsurface flaws
• Using a coil with electric current, an induced electric field is created
• Induced current trajectories are altered by local variations
• Moving the coil enables anomaly detection by detecting impedance variations
• Technique is best for thin parts

Ultrasonic Testing

• Transmits high-frequency sound waves into a material with a reflection of signals collected by an ultrasonic transducer
• It is based upon the speed of sound in the test material to derive data and definitively find defect depth

Ultrasonic Testing Process

• Applies a couplant between the transducer and part for the ultrasound to travel
• Uses angled transducers for some applications
• Automated checks involve water submersion of parts and transducers
• Ultrasonic pulses are bursts of sound, whose frequency is adjusted based on the material's characteristics, usually within 1 and 10 MHz
• To guarantee all echoes are collected, multiple transducers may be used for reception