Non-Destructive Testing (NDT) Explained

• Non-destructive testing (NDT) is vital in material science and engineering
• NDT techniques evaluate material properties without causing damage
• NDT is crucial for quality control and material evaluation

Importance of NDT

• Ensures product quality by detecting flaws before they become critical
• Reduces risks and saves costs by preventing failures and rework
• Provides insights into material properties
• Allows engineers to assess component integrity for specific applications
• Allows thorough evaluation and analysis without compromising material integrity
• Enables early detection of potential issues, akin to x-ray vision
• Invaluable in industries where safety is paramount such as aerospace, power generation, and oil and gas

NDT Classification

• Based on area of analysis, NDT has three categories.
• Defectology
• Metrology
• Material characterization

Defectology

• Detection of defects, heterogeneities, discontinuities, fissures, and microcracks
• Leak detection
• Evaluation of deterioration caused by environmental agents
• Determination of stresses
• Subdivided into techniques:
• Detection of surface defects
• Detection of internal defects

Metrology

• Control of part dimensions
• Thickness measurements (of parts, coatings)
• Filling levels

Material Characterization

• Evaluation of chemical properties like corrosion problems
• Evaluation of structural properties like mechanical hardness
• Evaluation of physical properties such as electrical conductivity and magnetic permeability
• Evaluation of technological properties and heat transfer

Defectology Techniques

• Detecting surface defects
  • Visual inspection
  • Laser inspection
  • Penetrating liquids
  • Magnetic particles
• Detecting internal defects
  • Industrial radiology
  • Ultrasound
  • Induced, parasitic or Foucault currents
  • Acoustic emission
  • Thermography

Metrology Instruments

• Calipers
• Micrometers
• Dial gauges
• Ultrasound

Defect Origins

• Defects are introduced while manufacturing materials or components
• Defects will influence the future behavior of the material
• Defects can also originate in service, such as fatigue fracture or corrosion.
• Detecting defects in the manufacturing process and detecting the growth or formation of new defects
• Detecting defects in service is important
• Defects during manufacturing of raw materials or in casting process include:
  • Porosity due to retained gas
  • Slag inclusions
  • Segregations
  • Porosity introduced in the solidification process
  • Cracks
  • Fissures caused by stress.
• Defects introduced during manufacturing of components:
  • Defects produced by the machine
  • Defects introduced by heat treatment
  • Welding defects
• Defects introduced in the assembly of the component:
  • Missing parts
  • Incorrect assembly
  • Additional welding defects
  • Cracks
  • Fissures caused by stress
• Defects generated during service life:
• Fatigue, corrosion, creep, due to working at high temperatures

Common NDT Methods

• Visual Testing
• Hardness Testing
• Micro-hardness Testing
• Magnetic Particle Testing
• Liquid Penetrant Testing
• Ultrasonic Testing
• Radiography Testing
• Eddy Current Testing

Key Principles of NDT

• Reflection of ultrasonic waves off material defects
• Distortion of magnetic fields caused by cracks in metal object
• Use of electric current or magnetic field to detect flaws in electromagnetic testing
• Thermal/infrared testing uses heat waves to reveal surface and subsurface defects

NDT Techniques Principles

• Ultrasonic Testing (UT)
• Relies on the reflection and refraction of sound waves to detect internal flaws
• The time taken for the waves to return is used to determine the depth of the defect
• Eddy Current Testing (ET)
  • Utilizes the principle of electromagnetic induction
  • Generates eddy currents within the material
  • Defects disrupt these currents, which can be detected and analyzed
• Liquid Penetrant Testing (PT)
  • Utilizes the capillary action of the penetrant
  • The penetrant is drawn into surface-breaking defects.
  • A developer is then used, so the flaw will be made easily visible

Visual Inspection (VT)

• Simplest NDT method
• Uses the naked eye or magnifying instruments to detect visible surface defects

Ultrasonic Testing (UT)

• Employs high-frequency sound waves
• Used to detect internal flaws
• Used to measure material thickness
• Widely used to detect cracks, voids, and inclusions.

Radiographic Testing (RT)

• Utilizes x-rays or gamma rays
• Creates images that reveal internal structures and defects
• Effective for detecting cracks, porosity, and inclusions.

Magnetic Particle Testing (MT)

• Applies a magnetic field to the material.
• Uses iron particles to detect surface and near-surface defects.
• Commonly used for inspecting ferrous metals for cracks and other discontinuities

Liquid Penetrant Testing (PT)

• Applies a liquid penetrant to the surface of the material.
• Allows detection of surface cracks and other defects by making them visible.

Eddy Current Testing (ET)

• Uses electromagnetic fields
• Detects changes in electrical conductivity and permeability.
• Used for detecting surface and near-surface defects in conductive materials.

Visual Inspection (VT) Techniques:

• Unaided visual inspection: Examining the material with the naked eye
• Aided visual inspection: Using tools like magnifying glasses, binoculars, or microscopes
• Remote visual inspection: Using devices like borescopes or fiberscopes to inspect areas difficult to access

Applications of Visual Testing

• Used in industries such as aerospace, automotive, and construction to detect surface defects like cracks, corrosion, or wear
• Used as a precursor to more advanced non-destructive testing methods

Additional Visual Inspection Techniques:

• Use of a stereoscopic microscope to detect small cracks
• Use of a lamp, magnifying glass, low magnification microscope, mirrors, or video cameras

Defects Detectable Via Visual Test

• Corrosion points
• Surface contamination
• Cracks, pores, segregations or decarburizations
• Defective surface finishes

Factors of Visual Inspection

• A chemical attack can be conducted on the surface if needed
• Considered most economical NDT
• Some NDT's require use of more sophisticated and expensive instruments.

Laser Inspection (LT)

• Welding is a forming technique where two or more metal parts are joined to form a single piece.
  • Weld is metallurgical
  • Welds have diffusion
    • Welding can introduce defects
      • It is important to check the quality of welds for arc, gas, and laser welding.

Laser Inspection Techniques

• Detect and quantify surface defects
• Dimensional control of parts
• Measure surface roughness

Laser Inspection Technique Basis

• Interaction of laser light with a surface If light hits defect, the light collected is modified, generating a scattered light
• This gives a value for number of surface defects
• A profilometer determines the surface roughness of a part. Laser Inspection can check:
  • Cast and forged products
  • Materials obtained by powder metallurgy techniques
  • Non-metallic materials
  • Welds

Liquid Penetrant Testing (PT) Uses

• Detect surface defects
• Works on many types of metal, polymeric materials, glass, and glazed ceramics

Liquid Penetrant Testing Technique Steps

• Penetrating liquid completely covers the surface of the sample and penetrates discontinuities
• The phenomena of capillarity, contact angle with the penetrating liquid, surface tension, and penetration time must be taken into account.
  • A liquid is applied that penetrates the defect
  • After using a developer, the surface defect is naked eye
  • The liquid must have a persistent and bright color or contain some fluorescent compound.
  • The most commonly used penetrating liquid is red and visible in natural or ultraviolet light

Liquid Penetrant Testing (PT) Steps

• Follows five essential steps:
  • Surface preparation.
  • Application of penetrating liquid.
  • Removing excess of penetrating liquid.
  • Development.
  • Observation and inspection 1 - Surface preparation.
  • Thoroughly clean and dry the surface Remove any traces of oil, water, grease, or other contaminants
• Steel brushes, abrasive products, or ultrasonic baths can be used to clean the surface

2 - Application of penetrating liquid.

• Apply as directed by the standard/manufacturer. -Cover surface with a thin layer for 20 seconds up to 30 minutes Sometimes parts are immersed in a penetrant

3 - Removing excess of penetrating liquid.

• Some liquids can be easily cleaned with water, others use solvents.
• Control the process to not remove liquid that has penetrated any defects. If water cannot be used, a suitable solvent is used.

4 - Development.

• Developer is white, such as chalk powder, is used to reveal any defects
• A layer is applied to the entire surface using a nebulizer
  • Liquid will penetrates the pores of developer powder, making visible any defects. As the penetrating liquid is colored, a contrast is visible between the defect area and surface

5 - Observation and inspection. Use strong or ultraviolet light to inspect piece and identify marks 1 - Crack filled with dirt, 2- Ideally Cleaned, 3 - Application of Penetrant, 4 - Intermediate cleaning, 5 - Application of developer, 6 - Crack indication

Desired Characteristics of Penetrating Fluids

• Penetration into defects.
• Good ability to wet the surface and remain in defects.
• Easy to remove from the surface, without being removed from the defect.
• Stable to temperature and humidity, not losing their properties when stored.
• Drying easily after washing.
• Possessing powerful colored pigments.
• Safe for the person who handles them

Penetrating liquids must

• Read any precautions for use as many can be harmful
• Waste from liquids must be treated appropriately.

Types of Penetrating Liquids

• Most liquids include halogenated hydrocarbons which are added to colored pigments.
• Halogenated hydrocarbons are very toxic and should not be handled in closed spaces.
• Two types of liquids:
  • Type I: Fluorescent penetrants
  • Type II: Colored penetrants
• Depends on how the liquid is removed from the surface.
• Liquids that can be removed with water (water-washable or self-emulsifying penetrants).
• Liquids removed with an emulsion that can be
  • Oil-based (lipophilic post-emulsifiable penetrants)
  • Water-based (hydrophilic post-emulsifiable penetrants). Removed by washing solvent (solvent-washable penetrants).It is necessary to periodically check that the penetrating liquid is in good condition.

Liquid Penetrant Testing Advantages

• Economical and fast
• Easy application
• For a wide range of materials
• Portable technique
• Can be used on different sized components
• No electricity required
• A large number of parts can be inspected
• The entire surface can be observed

Liquid Penetrant Testing Disadvantages

• Can cause health and environmental problems
• Final inspection is visual
• Cannot be applied to porous materials
• Only for detection of surface defects
• Layer of paint/surface protection must be removed
• It is dirty
• Surfaces must be within 4-175 °C temperature range

Liquid Penetrant Testing Applications

• Check solidification processes, ingots, bars ...In raw material processing industries
• Inspect materials in: processing industries. welded, cut, cast or forged.Inspect machines
• Inspect light alloys that are used: Aerospace industry. Since failures cause catastrophes need inspections.
• Inspect pipes and containers: petrochemical plants, electricity generating plants
• Detect fatigue cracks: nuclear plants, automotive industry, railways, shipping industry

Liquid Penetrant Testing Characteristics

• A dye is applied to the material's surface and allowed to seep into defects
• Dye helps inspectors inspect and assess varieties of surface defects. cracks, seams, porosity, and leaks.

Magnetic Particle Testing (MT) Uses

• It is a sensitive inspection technique for detecting surface and sub-surface defects
• Works on ferromagnetic components such as steel, iron, cobalt and nickel
• Does not work on: paramagnetic materials such as (aluminum, titanium or platinum) or diamagnetic materials (such as copper, silver, tin or zinc).
• Can detect discontinuities lying below the surface but is mainly a surface inspection method: surface discontinuities

Magnetic Particle Testing (MT) Process

• Conducted by polarizing the part being evaluated and covering its surface with magnetic particles
• Particles may or may not be in a liquid suspension -The magnetic particles then aggregate over the discontinuities. -Indications are visible with ultraviolet light or naked eye. Discontinuities that are perpendicular to the magnetic field lines
• Are easy to see, while parallel are hard to see
  • To account for it, MPI is conducted at two test orientations that are 90 degrees
• Multi-dimensional fields (3D magnetization) can find hidden orientations hidden otherwise

Magnetic Particle Testing (MT) Basis of the technique

• Magnetic field induced to ferromagnetic material, and dipoles are oriented in the magnet
• Discontinuities perpendicular deform the local magnetic flux Magnetic particles are suspension on the surface, they are attracted to the flux deformed area i.e, defects Surface discontinuity generates a magnet with corresponding N & S magnets at edges - attracting magnetic particles If defects are parallel to the applied field lines can cannot detected Method must allow the direction and placement of the applied field to be varied.

Magnetic Particle Testing (MT) First stage of method

• Is the magnetization of the piece Can be done in the following ways: a- Use of portable magnetic circuits; magnetic alternation with direct current b- Place inside coil through intensity electric current c- Passing electric current directly

• Once magnetized, the particles are applied. Can be powder or suspension form.

• A ultraviolet light lamp may be needed to observe the defects

• End result is demagnetizing the piece and eliminating the magnetic particles.

The magnetic particles in Magnetic Particle Testing

• Are iron oxide particles in small (1 to 60 mm) or big sizes (60 to 150 mm)
• Having varied particle sizes and shapes helps get into different crack sizes
• Particles used dry are colored
• particles used are 10x bigger than with suspension
• Are red (usual),gray to gray castings or black ( high sensitivity but low contrast) Magnetic particle testing must use fluorescent compounds and ultraviolet lamp if suspension

Magnetic Particle Testing (MT) Applications

• There are two forms: continuous and residual

• Irons and steels are easily magnetized

• Continuous method is used

• Materials difficult to magnetize; residual method is used if slowly demagnetized

• The continuous method consists of applying the particles

• Wet or dry while magnetized is applied discontinuously

• In residual method, at piece is first magnetized and then the particles are applied. Residual is less sensitive.

Magnetic Particle Testing Factors affecting sensitivity of testing

• Defect orientation with respect to induced magnetic field ( defects that are placed perpendicular will not be detected)
• Magnetic particle shapes and sizes. Nature of solvent used in the magnetic field. Strength of the magnetic field (generally increases the sensitivity as the strength increases.Intensity must be determined by trial and error Cracks with depths up to 10-3 mm can be determined; sub-surface 3- 7mm Has high sensitivity alterable by defects perpendicular to magnetic field, solvent nature, strength

Advantages of MT

• Accurate and reliable technique and is easy to perform
• There is no limit on component shapes and sizes
• Operators need little training, plus functions well on painted materials
• Test on a small equipment investment
• Inspection can use lines for production

Disadvantages of MT

• Can only be applied to Ferro magnetic materials or use surfaces and sub-surface defects
• Sensitivity requires part cleanliness or require that pieces be demagnetized
• Must manually handle part. Some parts require separate inspections. Can burn edges
• Some areas must use high intensity electricity on very large Parts
• The main applications are checking of the quality control (raw reception, control and final inspection )
• The industries related to the transport infrastructure, roads, aircraft, and ships use for in service controls.
• Establish inspections for parts such as: aircraft, turbine shafts. Magnetic particles inspected for thrust bearings
• Establish inspections for parts susceptible to fatigue failure such as: frames, turbine shafts

Ultrasonic Test (UT) Imagine bouncing sound

• Ultrasound bounce is like sonar for underwater detection
• Sound in materials can detect flaws and thickness It uses high-frequency sound waves to:
• detect flaws
• measure material thickness
• assess material properties. In this field is a technique is phased array ultrasonic testing.
• When waves make a crack, they reflect to receiver, signal, or analyze defect

Ultrasonic Test method

• Effective for cracks abrasions, pitting, corrosion, thinning defects Acoustic emission test
• A conversation where all answers are there

Ultrasonic Test Basis Technique

• Ultrasounds are acoustic waves whose frequency is above audible frequency of the human ear (approximately 20,000 Hz)
• It can propagate at a very high speed of propagation in metallic and solid materials in general
• The speed changes when passing from gaseous to liquid or solid. Capable of passing through thicknesses of several meters
• Ultrasounds is capable of detecting interior defects inside materials. Can undergo changes

Ultrasonic Test speed

• Must use: v = x *f to find the speed of propagation in different media Ultrasound where A is the wavelength and f is the frequency of the wave

Ultrasonic Test Generation Method

• Ultrasound (UT) Generation and Detection. Ultrasound speed varies on the medium. Can obtain information about damages
• Different process for ultrasound generation
• Use of piezoelectric 1 - (1880 Pierre /Jacques Curie) discovered deforming face will mean voltage. Piezoelectric ( voltage produced from deformation

Ultrasonic Testing Processes

• Piezo electric can produce ultrasound
• Generating ultrasound subjected to electric process and generates an electric device
• Can have the opposite as crystals be used to detect ultrasound and electrical crystal used to detect waves.
• Generating electric pulse if applied with high potential

Locating Defects in Ultrasound testing

There are three methods for locating.

• Transparency or shadow method
  • Measuring the intensity of ultrasound as it passes by defect area, receptor is sent to picking waves
  • The receiver picks where the intensity decreases through defect
• Resonance method. This decreases the intensity of wave reflected on the opposite side of the material.

Impulse-Echo method in Ultrasound testing

• This method that transmits and receive and uses for a scope that records all from surface

• The ultrasonic passes the peak screen from material that generates echo Waves collected by transmitter are collected by receiver

• The distance from peaks creates a width

• There can be one peak if defect and therefore difference

Ultrasound Testing Advantages

• Thick Materials can be inspected well and has a high sensitivity
• Can be automatic or manual
• Portability offers automated equipment that can be used.
• The technique causes problems with thin or irregular surfaces
• The Cost is moderate to high
• Needs calibration and is dependent on operator training.
• Inspection requires you prepare surfaces. Sometimes needs products for transmission

Ultrasound Testing Applications

• Ultrasound can be used for plastics, glass, metal and concrete
• Detects defects parallel is superficial or needs a proper probe: can detect all Cracks, cavities, inclusions and all kinds is of defects

It is useful for:

• Inspect welding parts as surfaces are smooth needs calibration blocks
• Some cars need inspections

Ultrasonic Determination Thickness process steps

• Ultrasonic technology determines sizes in materials and components and ensures they meet needed specs and or coatings
• Thickness of material, we measure ultrasonic pulse that has passed and needs to undergo the sample for passing

Equipment setup for ULTRASONIC TESTING

• To determine use "2e=VT" were E is the thickness that is speed and time is length. Calibrated can be ordered as an application to coat If calibrated is not material as inspected then experimentally must determine speed

EDDY CURRENT TESTING (ET)

• Foucault Currents. Eddy current = a test that is a can be performed on conductive materials.
• A test coil that energized current is placed to surface.
• In a coil, if there are flaws it shows changed.
• Changes Impedance.
• Change of Impedance.
• Can detect degradation of materials. In addition to electrical conductivity and tick is needed

Eddy Current Testing (ET) Basis of the technique

• Is based on Eddy currents. o If you take a magnet to copper: noting will happen. But move it against copper; there will be heat
• *The (1851) discover happened due electron passage and currents in conductor.**. Applied field means conductivity.

Eddy Current Technique Equipment

• Eddy current source is a coil connected to current, producing a magnetic circuit that produces and modifies magnetic field by the coil The Impedance will depend on the magnetic permeability, electrical conductivity.
• There are coils the measure based on if near/not near surface

Equipment for Eddy Current Calibration:

• It Eddy/ Foco need calibration based defers materials.
• Must select material with that is similar to the material. Used Must have varied sizes by a criteria or the blocks or by a criteria.

Advantages of EE

• Safe and faster. Small lightweight, cost is medium. wide temperatures

Desadvantages

• Only conducts material or parts · Surface or close.
• Sensitive which can get complex. (Magnetic geometry) need analysis.
• There is a method for alloy surface cracks heat-treatments pipes boilers heat exchanges
• Eddy current testing serves: aerospace or fatigue

Industrial Radiographic Testing

• Test uses XRays to capture images
• Just a doctor checks broken, technique detects cracks porosity holes.
• Revealing whats hidden provides value to a material

Test Process For Radiology

• Film absorbs rays location development. Material the XRays need to go depends on indications. The film has records

Radiographic Testing Advantages

• Must follow many codes and specifications

Radiology Test basis

• This method is useful when XRays penetrate image by materials
• Intensity to obtain: I=lo*e-md-1 ·
• Most rays will give color: porosity in parts can show different qualities

Gamma Rays process

• Penetrate steel plate and must account half points that has computer screen too.
• Can obtain radio by x-ray test by machine

NDT Advantages for Radiology

• Able to inspect complex parts while being fast has density to get thickness measurements

NDT Disadvantages for for Radiology

• The technique can be expensive and cause hazards that need personnel trainings The shape of the pieces must also be taken into tests along with measurements in solids.