Non-Destructive Examination

The four basic methods:

 Magnetic particle inspection (MT)
 Dye penetrant inspection (PT)
 Radiographic inspection (RT)
 Ultrasonic inspection (UT)

1. Dye Penetrant Inspection

 Detecting surface breaking defects only
 Penetrant applied to the component and drawn into the defects by capillary action
 Applicable to all non- porous and non absorbing materials.
 Penetrants are available in many different types
 Water washable contrast
 Solvent removable contrast
 Water washable fluorescent
 Solvent removable fluorescent
 Post emulsifiable fluorescent

1.1 Dye Penetrant Inspection

1.1.1 Step 1. Pre-Cleaning
Cleaning preparation is very important on this method. Usually solvent removal is used.

1.1.2 Step 2. Apply penetrant

After the application of the penetrant, normally it will be left on the components surface for
approximately 15 minutes (dwell time). The penetrant enters any defects that may be present by
capillary action
1.1.3 Step 3. Clean off penetrant
After sufficient penetration time (dwell time),excess removal penetrant stage take place. A damped
lint free tissue with solvent is used to clean the excess penetrant.

1.1.4 Step 4. Apply developer

After the excess penetrant is been removed, a thin layer of developer is applied. A penetrant drawn
out by reversed capillary action.

1.1.5 Step 5. Inspection / development time

Inspection should take place immediately after the developer has been applied. Any defects present
will show as a bleed out during development time.
1.1.6 Step 5. Post-Cleaning
After the inspection has been performed post cleaning is required to prevent corrosion.

Fluorescent Penetrant Colour contrast Penetrant

Bleed out viewed

under a UV-A light
source

Bleed out viewed

under white light

1.2 Advantages
 Simple to use
 Inexpensive
 Quick results
 Can be used on any material except porous material
 More sensitive than visual inspection
 Low operator skill required

1.3 Disadvantages
 Surface breaking defect only
 little indication of depths
 Penetrant and developer may contaminate component
 Surface preparation is critical
 Post cleaning required
 Not applicable on porous material
2. Magnetic Particle Inspection
 Detecting Surface and slight sub-surface
 Relies on magnetization of component being tested
 For ferro-magnetic materials only
 A magnetic field is introduced into a specimen being tested (can’t be used for SS material)
 Methods of applying a magnetic field, yoke, permanent magnet, prods and flexible cables.
 Fine particles of iron powder are applied to the test area
 Any defect which interrupts the magnetic field, will create a leakage field, which attracts the
particles
 Any defect will show up as either a dark indication or in the case of fluorescent particles under
UV-A light a green/yellow indication

Electro-magnet
(yoke) DC or AC

Crack
indication
Prods
DC or AC

Crack
indication

A crack
indication
 Alternatively to contrast inks, fluorescent
inks may be used for greater sensitivity.
These inks require a UV-A light source and a
darkened viewing area to inspect the
component

2.1 Typical sequence of operations:

 Clean area to be tested
 Apply contrast paint
 Apply magnetisism to the component
 Apply ferro-magnetic ink to the component during magnetising
 Interpret the test area
 Post clean and de-magnetise if required

2.2 Advantages
 Simple to use
 Inexpensive
 Rapid results
 Little surface preparation required
 More sensitive than visual inspection

2.3 Disadvantages
 Surface or slight sub-surface detection only
 Magnetic materials only
 No indication of defects depths
 Detection is required in two directions
3. Radiographic Inspection
3.1 The principles of radiography
 X or Gamma radiation is imposed upon a test object
 Radiation is transmitted to varying degrees dependant upon the density of the material through
which it is travelling
 Thinner areas and materials of a less density show as darker areas on the radiograph
 Thicker areas and materials of a greater density show as lighter areas on a radiograph
 Applicable to metals, non-metals and composites

X - Rays Gamma Rays

Electrically generated Generated by the decay of unstable atoms

Source
Radiation Image quality indicator
beam
1

Radiographic film Test specimen

Source

Radiation beam Image

1
1
0
f

Test specimen

Radiographic film with latent image after exposure

3.2 Radiographic Sensitivity

7FE12

Step / Hole type IQI Wire type IQI

3.3 Image Quality Indicators

Step / Hole type IQI Wire type IQI

3.4 Radiographic Techniques

 Single Wall Single Image (SWSI)
→ Film inside, source outside
 Single Wall Single Image (SWSI) panoramic
→ Film outside, source inside (internal exposure)
 Double Wall Single Image (DWSI)
→ Film outside, source outside (external exposure)
 Double Wall Double Image (DWDI)
→ Film outside, source outside (elliptical exposure)
3.4.1 Single wall single image (SWSI)

IQI’s should be placed source side

3.4.2 Single wall single image (SWSI) panoramic

 IQI’s are placed on the film side

 Source inside film outside (single exposure)

3.4.3 Double wall single image (DWSI)

 IQI’s are placed on the film side

 Source outside film outside (multiple exposure)
 This technique is intended for pipe diameters over 100 mm

Identification
 Unique identification
 IQI placing
 Pitch marks indicating readable film length
3.4.3 Double wall double image (DWDI) elliptical exposure

 IQI’s are placed on the source or film side

 Source outside film outside (multiple exposure)
 A minimum of two exposures
 This technique is intended for pipe diameters less than 100mm

Identification
 Unique identification
 IQI placing
 Pitch marks indicating readable film length Shot A Radiograph

3.5 Advantages
 Permanent record
 Little surface preparation
 Defect identification
 No material type limitation

3.6 Disadvantages
 Expensive equipment
 Bulky equipment ( x-ray )
 Harmful radiation
 Detection on defect depending on orientation
 Slow results
 Required license to operate
4. Ultrasonic Inspection
 Sub-surface detection
 This detection method uses high frequency sound waves, typically above 2MHz to pass
through a material
 A probe is used which contains a piezo electric crystal to transmit and receive ultrasonic pulses
and display the signals on a cathode ray tube or digital display
 The actual display relates to the time taken for the ultrasonic pulses to travel the distance to the
interface and back
 An interface could be the back of a plate material or a defect
 For ultrasound to enter a material a couplant must be introduced between the probe and
specimen

V2 (A4) Block Thickness 12 or 20mm

V1 (A2) Block Thickness 25mm

4.1 Advantages
 Rapid results
 Sub-surface detection
 Safe
 Can detect planar defect
 Capable of measuring the depth of defects
 May be battery powered
 Portable

4.2 Disadvantages
 Trained and skilled operator required
 Requires high operator skill
 Good surface finish required
 Difficulty on detecting volumetric defect
 Couplant may contaminate
 No permanent record