The document describes two non-destructive testing techniques: liquid penetrant testing and acoustic emission testing. Liquid penetrant testing uses a low-viscosity liquid applied to the test material's surface to seep into surface-breaking defects, then a developer pulls the liquid out to reveal indications of flaws. Acoustic emission testing passively detects ultrasonic bursts from cracks under load using sensors, allowing detection and location of damage as it occurs. Both methods are used to inspect for issues like cracks in a variety of industrial applications with certain advantages and limitations.

1. LIQUID PENETRANT TEST &
ACOUSTIC EMISSION TEST

2. • It also known as liquid penetrant inspection (LPI) or dye penetrant testing is
based on the properties of surface wetting and capillary action, which causes a
liquid to rise when confined to a small opening.
• After applying the penetrant and wiping away the excess, the penetrant that
rises to the surface can indicate surface breaking.
• Dye penetrant inspection (DPI) also called liquid penetrant inspection (LPI)
or penetrant testing(PT).
• It is used to detect any surface connected discontinuities such as cracks from
fatigue, quenching, and grinding as well as fractures, porosity, incomplete
fusion, and flaws in joints.
LIQUID PENETRANT TEST

3. PRINCIPLE :
• Liquid penetrant testing involves the application of a fluid with low viscosity on
the material to be tested.
• This fluid seeps into any defects such as cracks or porosity before a developer is
applied which allow the penetrant liquid to seep upwards and create a visible
indication of the flaw.
• Liquid penetrant tests can be conducted using solvent removable penetrants, water
washable penetrants or post emulsifiable penetrants.
LIQUID PENETRANT TEST –PRINCIPLE

4. Basic Processing Steps of a Liquid Penetrant Inspection

5. Surface Preparation – Removal of Oil, grease, water….
Penetrant Application – Applying penetrant by spraying, brushing or
immersing.
Penetrant Dwell – Penetrant is left on the surface for a sufficient time.
Time vary depends on penetrant material, the material, and form of
material being inspected, type of defect. (usually range from 5 to 60
minutes)
Excess penetrant removal – It may involve, cleaning with a solvent,
direct rinsing with water, or first treating the part with an emulsifier and
then rinsing with water.
Developer Application – A thin layer of developer is applied – to visible
of flaws. It may be applied by dusting (dry powdered), dipping or spraying
(wet developer)
Indication Development – After a period of time (Min. of 10 minutes)
permit the extraction of the trapped penetrant out of any surface flaws.
LIQUID PENETRANTTEST

6.  Inspection – with appropriate lighting to detect indication from any flaws
which may be present.
Clean surface – Thoroughly clean the part surface to remove the
developer from the parts that were found to be acceptable.

7. PENETRANTS
It is used for detection of surface imperfections in non-porous materials and
basically consists of applying a flow of liquid to the surface of the material to
be tested.
Types of Penetrants
• Fluorescent Penetrants : They contain a dye or several dyes that
fluorescent when exposed to ultraviolet radiation.
• Visible Penetrants: They contain a red dye that provides high
contrast against the white developer background.
Methods used for excess removal of penetrants
Water washable
Solvent removable
Post emulsifiable
• Lipophilic
• Hydrophilic

8. DEVELOPERS
The role of the developer is to pull the trapped penetrant material out of defects
and spread it out on the surface of the part so it can be seen by an inspector.
Standard forms of developers are,
 Dry powder
 Water soluble
 Water suspendable
 Non aqueous
 Type 1: Fluorescent (Solvent based)
 Type 2: Visible Dye (Solvent based)

9. ADVANTAGES
High sensitivity (small discontinuities can be detected).
Few material limitations (metallic and nonmetallic, magnetic and non-
magnetic ,conductive and nonconductive materials may be inspected).
Rapid inspection of large areas and volumes.
Suitable for parts with complex shapes.
Indications are produced directly on the surface of the part and constitute a
visual representation of the flaw.
Portable (materials are available in aerosol spray cans)
Low cost (materials and associated equipment are relatively inexpensive)

10. DISADVANTAGES
• Only surface breaking defects can be detected.
• Only materials with a relatively nonporous surface can be inspected.
• Pre-cleaning is critical since contaminants can mask defects.
• Metal smearing from machining, grinding, and grit or vapor blasting must be
removed.
• The inspector must have direct access to the surface being inspected.
• Surface finish and roughness can affect inspection sensitivity.
• Multiple process operations must be performed and controlled.
• Post cleaning of acceptable parts or materials is required.
• Chemical handling and proper disposal is required.

11. APPLICATION
Aerospace
Automobile
Railways
Tools and dies
Inspection on reactor and tank

12. From YouTube Some Useful Videos
1. https://www.youtube.com/watch?v=53Yl2U78s_Y
2. https://www.youtube.com/watch?v=xEK-c1pkTUI

13. ACOUSTIC EMISSION
• This is a passive NDT technique, which relies on detecting the short bursts of
ultrasound emitted by active cracks under a load. Sensors dispersed over the
surface the structure detect the AE.
• It is even possible to detect from plasticization in highly stressed areas
before a crack forms.
• Frequently a method for use during proof tests of a pressure vessel, AE testing
is also a continuous structural health monitoring (SHM) method, for Example
On bridges. Leaks and active corrosion are detectable AE sources too.

14. ACOUSTIC EMISSION (AE) -PRINCIPLE
 Acoustic emission may be defined as a transient elastic wave generated by
the rapid release of energy within a material.
 When a structure is subjected to an external stimulus ( change in pressure ,
load or temperature) , localized sources trigger the release of energy , in the
form of stress wave, which propagate to the surface and are recorded by
sensors. This occurs when a small surface displacement of a material is
produced.

15. Basic Components in AE testing
(a) Source
(b) Sensor
(c) Cable
(d) Data acquisition device

16. WORKING OF ACOUSTIC EMISSION (AE)
• AE testing works by mounting small sensors onto a component under test.
• The component is stressed; the built up state of stress spontaneously discharges at
a leak, thereby generating sound impulses. As the damage grows in the
component, there is a greater release of energy.
• The energy thus discharged is received by sensors applied on the surface of the
tested object. The rates in which the acoustic emission is detected, the activity,
and the intensity of the acoustic emission, the loudness, are monitored and used
for assessing structural integrity and for health monitoring of components.
• The signal are received at different times by different sensors. By measuring these
differences in time, the sound source can be located.

18. ADVANTAGES
• Ability to detect a range of damage mechanisms including, but not limited
to, fibre breakages, friction, impacts, cracking, delamination and corrosion in
their early stages, before they become significant issues.
•Can be conducted during operation, during qualification (proof) testing or
development testing.
• Can locate damage sources and can be differentiate these based on acoustic
signatures.
• Global monitoring of a structure.
• Assesses the structure or machine under real operational conditions.
• A non-invasive method
• Operational in hazardous environments, including high temperatures, high
pressures and corrosive and nuclear environments.

19. LIMITATIONS
• Limited to assessing structural integrity or machine health by
locating issues, further inspection is usually required to fully
diagnose issues.
• Cannot detect defects that may be present, but that do not
move or grow.
• Can be slower than other non-destructive testing techniques

20. Application of AE
 Monitoring of Bridges .
 Aerospace Structures.
 Inspection of Pressure Vessels.
 Weld Monitoring.
 Bucket Truck (cherry pickers) integrity evaluation.
 Gas Trailer Tubes

21. From YouTube Some Useful Videos
• https://www.youtube.com/watch?v=Upg0sQp_hIE
• https://www.youtube.com/watch?v=7N_ozHv1qDk
• https://www.youtube.com/watch?v=Lomf1NYd4O8