Objective 07: Liquid Penetrant Testing Flashcards
Liquid Penetrant Testing
NDE technique that enhances the visibility of material surface cracks that are open to the surface of the specimen under inspection
What kind of flaws does Liquid Penetrant Testing expose?
Those open to the inspected part’s surface
What is the process of Liquid Penetrant Testing?
- A liquid with a low surface tension that is spread on the surface of the material
- The liquid penetrant is allowed to soak into any cracks that are open at the surface
- After a period of time, the excess liquid penetrant fluid is removed and a developer is applied to the test surface to draw the liquid penetrant remaining in the cracks back to the surface and make it visible
- The surface flaws become increasingly more visible to the human eye because the liquid penetrant contains a dye indication that broadens the trace of the surface crack
- The dye indicator is coloured wither red or blue on a white background or appears greenish yellow on a dark violet background when the surface is illuminated by a UV lamp
What 2 factors does the detection of flaws by the Liquid Penetrant Test depend on?
The general condition and finish of the surface of the material
What 6 things limit the effectiveness of the Liquid Penetrant Test?
- Materials which are porous
- Subsurface defects
- Very wide and shallow defects
- Contaminated surfaces that have not been thoroughly cleaned
- Insufficient penetrant dwell time
- Surface temperature too high or too low
What does the procedure for Liquid Penetrant entail?
- The inspection conditions (ambient light and UV illumination conditions)
- The penetrant, penetrant remover, emulsifier and developer to be used
- The pre-cleaning and post-cleaning required
- The penetrant dwell time, removal of excess and the drying of the surface before the application of the developer
- The developer dwell time before interpretation
Why is Pre-Cleaning an important part of the Liquid Penetrant Test?
The care taken in this determines the level of inspection success
What kinds of surface residues does Pre-Cleaning for Liquid Penetrant Test attempt to remove from the surface of the specimen?
- Dirt
- Scales
- Oil
- Finger prints
- Layers of paint
- Galvanic Corrosion
What is the purpose of Pre-Cleaning for Liquid Penetrant Testing?
To clean the surface so that the penetrant medium can penetrate into surface defects
Why must care be taken while grinding the specimen surfaces while Pre-Cleaning for Liquid Penetrant Testing?
Grinding can roll material over an exposed surface crack and prevent the crack from opening up to the surface
How is Liquid Penetrant Testing process initiated after preparation?
The entire surface of the specimen is covered with the dye penetrant liquid medium
What are different ways the dye penetrant is applied to the specimen surface in Liquid Penetrant Testing?
- Dipping
- Coating
- Spraying
- Immersing
- Electrostatic
What does the appropriate method of applying dye penetrant depend on for Liquid Penetrant Testing?
The dimensions and location of the part being inspected
What is the temperature range in which the test liquid medium is applied to the specimen in Liquid Penetrant Testing?
Between 15ºC and 50ºC
What does the penetrant dwell time depend on for Liquid Penetrant Testing?
- Specific Test Medium
- Specimen Material
- Ambient Temperature
- Material Temperature
What is the dwell time range that is possible in Liquid Penetrant Testing?
Between 5 and 30 minutes
Interim Cleaning for Liquid Penetrant Testing
The residual dye penetrant medium is removed from the specimen surface
What about the dye penetrant facilitates Interim Cleaning for Liquid Penetrant Testing?
It can be disolved or re-emulsified so that it can be washed with water
How is Interim Cleaning for Liquid Penetrant Testing carried out?
A low pressure water spray is used to clean the surface and the surface is checked for residual penetrant under UV light
Why must care be taken when Interim Cleaning with a water spray for Liquid Penetrant Testing?
To ensure that the penetrant soaked into the surface cracks is not agitated out of cracks which can reduce the test sensitivity or completely remove the penetrant from the crack
How can the surface of a specimen be dried after Interim Cleaning for Liquid Penetrant Testing?
- Low Pressure Air Drying
2. Oven drying at a maximum temperature of 50ºC
Developing Procedure for Liquid Penetrant Testing
Residual Penetrant Medium is drawn to the surface through the application of wet or dry developers, enhancing the detected crack indication
How is Developer applied in Liquid Penetrant Testing
Spraying (aerosol cans, low pressure spraying systems, spraying pistols or compressed air) or electrostatic pistols
Is it acceptable to brush on or paint the Developer?
No
How does Developer work in Liquid Penetrant Testing?
Through the lateral expansion of the penetrant medium within the crack, the crack width is enlarged, and the visibility of even the smallest defects and hair line cracks is ensured
How long is the Developer Dwell Time for Liquid Penetrant Testing?
5 to 30 minutes
What type of material requires more than 60 minutes of Developer Dwell Time for Liquid Penetrant Testing?
Austenitic Steels
How is the final Inspection for Liquid Penetrant Testing performed?
The operator controls the inspection parameters, making sure that ambient light intensity and UV intensity are constant during the visual inspection. Measurements of the indications are documented with reference to position, size, number, and location.
How is it ensured that the specimen is not overwashed during Liquid Penetrant Testing?
The Interim Cleaning allows a low-level coloured background to remain after the developing procedure against which the negative indications remain in clear contrast
What are typical indications revealed by Liquid Penetrant Testing?
- Continuous Line
- Intermittent Line
- Rounded Areas
- Small Dot
- Diffuse
- Brilliance
When is a final post-cleaning process necessary for Liquid Penetrant Testing?
If the inspected surface must be free of developer for subsequent visual checks, further processing, coloring, or anodizing.
How can the Developer Coating be removed from the specimen for Liquid Penetrant Testing?
- Water
- Air-Liquid Mixture
- Liquid Solvent Immersion Tank
