• simple and easiest method to apply
• first and most widely used
• involves inspecting and evaluating components for:
  ✅ surafce condition
  ✅ presence of defects
  ✅surafce roughness
  ✅dimensional changes
• surface required and its capability relies on good illumination (lighting) and the eyesight of the inspector
  

• APPLICATION
  ✅ weld inspection
  ✅ metrology
  ✅ monitoring in service

• enhanced by using various aids:
  ✅magnifying glasses
  ✅ borescopes
  ✅ TV camera systems

STEP TO APPLY:
1) make sure the components is clean and dry (vapour cleaning, solvent cleaning, ultrasonic cleaning)

2) liquid with high surface wetting characteristics is applied to the surface of a components under test (brushing, spraying, dipping/immersing, flow-on)

3) the penetrant penetrates into surface-brekaing discontinuities via capillay action (named as dwell time)

4) then, the excess penetrant is removes from the surface

5) next, deloper is applied to pull the trapped penetrant back to the surface

6) with good inspection, visual indication of any discontinuities present can be seen.

✅ LPI can inspect material that has smooth and non-porous surface
❌ LPI cannot inspect material that has rough surfaces (sand casting), porous ceramics, wood, and palstics parts that absors penetrant mnaterial

TYPES DISCONTINUITIES CAN BE DETECTED
✏ rolled products: cracks, lamination
✏ castings: cold shuts, blow holes
✏ forging: cracks, laps
✏ weld: cracks, overlap

CLASSIFIED BASED ON THE METHOD USED FOR REMOVAL OF EXCESS PENETRANT:
✅ water washable (Method A)
✅ post emulsifier, lipophilic (Method B)
✅ solvent removable (Method C)
✅ post emulsifier, hydrophilic (Method D)
❗maksudnya kena depends dekat cara kita kena nk remove excess penetrants. contoh kalau nak water wasable, kena guna dye. kalau post emulsifier, kena guna fluorescent.

DEVELOPER:
✅ dry powder - mix of light fluffy powder
✅ wet, water soluble - is a crystalline powder that forms a clear solution when mixed with water (not recommend for use with water-washable penetrant)
✅ wet, water suspendable - is a power that is suspended in a water that cobers the surface with a relatively uniform layer of developers when the water is evaporated (hard to maintain as the powder settles out over time)
✅ wet, non-aqueous - supplied in a spray can (most sensitive developer for inspecting small areas)

PROPERTIES OF PENETRANT
1) Penetration - ability to enter fine surface defects

2) Fluidity - ability to drain away

3) Stability - stable to over a wide range of temperature and humidity

4) Washability - possible to remove excess penetrants from components surfaces easily ❗ (without affecting the penetrant within the defect)

5) Drying characteristics - resist drying out during hot air drying (after the wash has been completed)

6) Wetting ability - good wetting ability and able to maintain a surface film on the component ❗ (hence continue to feed into a defect over a considerable period of time)

❤ higher the sensitivity level, the samller the defect that the penetrant system is capable of detecting

❤ increase the sensitivity level, so does the number of nonrelevenat indications

✏ SURFACE ENERGY

• has ability to freely wet the surface of the object being inspected
• liquid-solid surface interface :
  ✅ molecules of the liquid have a stronger attraction to the molecules of the solid surface than to each other (wetting of the surface ocurs - adhesive force stronger than cohesive force)
  ❌ liquid molecules are more strongly attracted to each other than the molecules of the solid surface (wet does not occur - cohesive force stronger than adhesive force)

• contact angle : angle that formed by the solid/liquid interface and the liquid/vapor interface measured from the side of the liquid. hence contact angle for most liquid penetrant is very close to 0 degrees

  
  
  

  p

✏ DENSITY/ SPECIFIC GRAVITY - increasing the specific gravity by decreasing the percent of solvent (by volume) in the solution will increase the penetration speed

✏ REMOVABILITY - removing the penetrant from the surface of teh sampel without remove it from the flaw

• adhesive force of the penetrant must be weak enough so that they can be broken by the removal method used
• formualtion of the liquid penetrant:
  ✏ proper formulation to balance the force
  ✏ it should not easily commingle and become diluted by the cleaning soution
  ⚠ dilution of the penetrant liquid will affect the concentration of the dye and reduce the dimensional threshold fluorescence

✏ COLOUR AND FLUORESCENCE BRIGHTNESS
1) dye penetrant - dye must provide good contrast againts the developer/ part being inspected
2) fluorescent - effect of colour and fluorescence is not so straightforward

• material fluorescence contain one or more dyes that absorb electromagnetic radiation over a particular wavelength
• the absorption of photons leads to changes in the electronic configuration of the molecules
• radition absorbtion and emission will take place the number of times until teh desied colour and brightness is acieved.
• 2 different fluorescent colours can be mixed to interact by a mechanism called cascading
• emission of teh visible light by this pricess involves one dye absorbing ultraviolet radiation to emit a band of radiation that makes a second dye glow

✏ DIMENSIONAL THRESHOLD OF FLUORESCENCE

• to determine the sensitivity of a fluorescent penetrant

• the ability of a penetrant to yield an indication depends primarily on its ability to fluoresce as a very thin film

  
  
  

  

• intensity of the transmitted energy is directly propotional to the intensity of the incident light and varies exponentially with the thickness of the penetrant layer and its dye concentration

✏ ULTRAVIOLET AND THERMAL STABILITY

• fluorescent material can lose their brightness after a period of exposure to high intensity UV light
• Excessive heat:
  i) increases viscosity and adversely affects the rate of penetration
  ii) alters wash characteristics
  iii) "boils off" chemicals that prevent separation
  iv) kills the fluorescence of tracer dyes
• thermal damage occur at above 71deg

VERIFICATION OF PENETRANT SYSTEM PERFROMANCE (TOOLS)

• TAM Panels
• Crack Sensitivity Panels
• Run Check Panels

PENETRANT INSPECTION ARE MORE EFFECTIVE AT FINDING

• small round defects than small linear defect
• deep flaws than shallaw flaws
• flaws on smooth surfaces than rough surfaces

ADVANTAGES :
✅ can be used on a wide range of material types
✅initial equipment investment is low
✅aerosol spray cans can make equipment very portable
✅ materials can be inspected rapidly and at low cost

DISADVANTAGES :
❌ only detects surface breaking defect
❌ requires relatively non-porous materials
❌ checimal handling precautions necessary
❌ post cleaning is necessary to remove chemicals