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Questions and Answers
Liquid penetrant testing is based on the principle of:
Liquid penetrant testing is based on the principle of:
The liquid penetrant method is used to detect discontinuities open to the surface in solids and essentially porous materials.
The liquid penetrant method is used to detect discontinuities open to the surface in solids and essentially porous materials.
True
Which is not a developer form
Which is not a developer form
Water soluble developers are supplied as a dry powder concentrate which is then dispersed in water in recommended proportions usually
Water soluble developers are supplied as a dry powder concentrate which is then dispersed in water in recommended proportions usually
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Method D hydrophilic emulsifiers are water based and are usually supplied as concentrates that are diluted in water to concentration of ______ for dip applications.
Method D hydrophilic emulsifiers are water based and are usually supplied as concentrates that are diluted in water to concentration of ______ for dip applications.
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The height to which the liquid rises in the capillary is inversely proportional to
The height to which the liquid rises in the capillary is inversely proportional to
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A penetrant that is self-emulsifying is called:
A penetrant that is self-emulsifying is called:
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What type of emulsifier is indented to use without dilution
What type of emulsifier is indented to use without dilution
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How is the correct emulsifier contact time determined?
How is the correct emulsifier contact time determined?
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If contact angle = 90° then there is
If contact angle = 90° then there is
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The tendency of dissimilar particles or surfaces to cling to one another is called
The tendency of dissimilar particles or surfaces to cling to one another is called
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The most important penetrant test processing time to control is
The most important penetrant test processing time to control is
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The penetrant process best suited to use on pars with rough surface is
The penetrant process best suited to use on pars with rough surface is
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Which of the following discontinuity types could typically be found with a liquid penetrant test
Which of the following discontinuity types could typically be found with a liquid penetrant test
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Which of the following pre cleaning processes is not recommended?
Which of the following pre cleaning processes is not recommended?
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A hydrometer is used to measure
A hydrometer is used to measure
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Which of the following developers is applied by spray only?
Which of the following developers is applied by spray only?
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Which of the following is an indication of porosity in visible liquid penetrate method?
Which of the following is an indication of porosity in visible liquid penetrate method?
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______ causes surface tension between molecule of a liquid
______ causes surface tension between molecule of a liquid
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Liquid penetrate seep into various type of minute surface opening by
Liquid penetrate seep into various type of minute surface opening by
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The height to which the liquid rises in the capillary is directly proportional to
The height to which the liquid rises in the capillary is directly proportional to
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For fluorescent penetrant the developer background should appear ______ when illuminated with UV light
For fluorescent penetrant the developer background should appear ______ when illuminated with UV light
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A minimum dwell time of ______ minutes may be allowed after penetrant application.
A minimum dwell time of ______ minutes may be allowed after penetrant application.
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Which of the following is most desirable method of precleaning a test piece to penetrant testing
Which of the following is most desirable method of precleaning a test piece to penetrant testing
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What is preferred cleaning precleaning process for removal of oil and grease?
What is preferred cleaning precleaning process for removal of oil and grease?
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How is the size of the liquid penetrant indication usually related to discontinuity?
How is the size of the liquid penetrant indication usually related to discontinuity?
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The time during which the penetrant remain on the surface of the test piece is
The time during which the penetrant remain on the surface of the test piece is
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Which of the following developer is applied by immersion only?
Which of the following developer is applied by immersion only?
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Magnetic line of force enter and leave a magnet at
Magnetic line of force enter and leave a magnet at
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Magnetic line of force
Magnetic line of force
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The opposition that a ferromagnetic material shows to the establishment of a magnetic field is called
The opposition that a ferromagnetic material shows to the establishment of a magnetic field is called
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The best method of inducing a circular field in a tube is by a
The best method of inducing a circular field in a tube is by a
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Magnetic particles testing is most likely to find subsurface discontinuities in:
Magnetic particles testing is most likely to find subsurface discontinuities in:
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A magnetic field which is contained completely within the test piece is called a:
A magnetic field which is contained completely within the test piece is called a:
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Magnetic particle inspection is not a reliable method of detecting
Magnetic particle inspection is not a reliable method of detecting
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In magnetic particle inspection, a flaw is indicated by
In magnetic particle inspection, a flaw is indicated by
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______ is the ease with which a material can be magnetized
______ is the ease with which a material can be magnetized
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Permeability can be numerically expressed as
Permeability can be numerically expressed as
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Which of the following are ferromagnetic materials
Which of the following are ferromagnetic materials
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Field produced by ______ generally penetrate the cross section of the part
Field produced by ______ generally penetrate the cross section of the part
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Which of the following material have magnetic permeability less than 1
Which of the following material have magnetic permeability less than 1
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The magnetic field outside a conductor decreases
The magnetic field outside a conductor decreases
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The most common method of demagnetizing a small test piece is
The most common method of demagnetizing a small test piece is
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The type of discontinuity which magnetic particle testing most effectively locate is
The type of discontinuity which magnetic particle testing most effectively locate is
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Magnetic particle is a non-destructive examination method used for
Magnetic particle is a non-destructive examination method used for
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A detect open to the surface produces an indication which is
A detect open to the surface produces an indication which is
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The types of discontinuities potentially most harmful to the part is
The types of discontinuities potentially most harmful to the part is
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Magnetic lines of force that run circumferentially around the perimeter of a part is called
Magnetic lines of force that run circumferentially around the perimeter of a part is called
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Which of the following are diamagnetic materials?
Which of the following are diamagnetic materials?
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Study Notes
Nondestructive Testing (NDT) - Dye Penetrant Inspection
- Liquid penetrant method detects discontinuities open to the surface of solids and essentially porous materials.
- The method applies a penetrating liquid to the cleaned surface of the component.
- Liquid enters discontinuities via capillary action.
- Excess penetrant is removed by solvent or water.
- A developer layer is applied to draw out any remaining penetrant in the discontinuities.
- Indications appear on the developer layer indicating the presence of discontinuities.
- Penetrants consist of a tracer dye and a carrier fluid (vehicle).
Penetrant Characteristics
- Easily spread over the surface for complete coverage.
- Drawn into surface imperfections by capillary action.
- Easily removed from the surface of the part.
- Remaining penetrant can be drawn back to the surface through drying and developing steps.
- High visibility (visible or fluorescent) for easy indication recognition.
- Non-harmful to the material or inspector.
Penetrant Types
- Type 1 - Fluorescent Penetrants: Contain dyes that fluoresce under UV light. More sensitive than visible penetrants due to the pronounced glow of the fluorescing indication.
- Type 2 - Visible Penetrants: Contain a red dye offering high contrast against the white developer background. No need for dark area or UV light.
Penetrant Removal Methods
- Method A - Water Washable: Excess penetrant can be removed by rinsing with water alone. Penetrants contain an emulsifying agent.
- Method B - Post-Emulsifiable, Lipophilic: Penetrant is oil-soluble and interacts with oil-based emulsifier for removal.
- Method C - Solvent Removable: Solvent is used to remove the penetrant from the part.
- Method D - Post-Emulsifiable, Hydrophilic: Water-soluble detergent emulsifier lifts excess penetrant from the part.
Developers
- Developers increase the brightness intensity of fluorescent and visible penetrant indications.
- Developers blot the penetrant and enlarge the flaw appearance.
- Developers provide contrast between penetrant and the surface, enhancing flaw visibility.
- Speed up the inspection process.
Required Developer Properties
- Adsorptive: Maximizes blotting.
- Fine grain size and specific particle shape: Effective dispersal and exposure of indications.
- Contrast background: Distinguish indications when using color-contrast penetrants.
- Easy to apply uniformly as a thin coating.
- Easily wetted by the penetrant: Effective extraction of penetrant from the flaws.
Dry Powder Developer
- Least sensitive, but inexpensive and easy to apply.
- Applied by: dipping, puffing, or placing in a dust cabinet.
- Powder sticks only to wet areas around indications.
- Seldom used for visible inspections.
Water Soluble Developer
- Chemicals dissolved in water form a developer layer when the water evaporates.
- Applied by spraying.
- Dipping, pouring, or brushing is less desirable but sometimes used.
- The part should be wet or dry.
Water Suspendable Developer
- Insoluble particles suspended in water.
- Requires frequent stirring or agitation to prevent settling.
- Applied like water soluble developers; dried using warm air.
Nonaqueous Developer
- Developer suspended in a volatile solvent.
- Applied using a spray gun.
- The solvent tends to pull the penetrant out of the indications.
- Forced drying is usually not required. (due to volatile solvent)
Special Application Developers
- Primarily used for permanent inspection records.
- Used with plastics or lacquer.
Surface Preparation
- Critical step in liquid penetrant testing.
- Defects must be open to the surface for penetrant entry.
- Contaminants like scales, flakes, grease, paint, and dirt must be removed to prevent false or masking defects.
- Cleaning and drying the surface are essential.
Penetrant Application
- Penetrant fluid is applied to the cleaned surface.
- Fluid spreads freely and evenly, moving into the cracks.
- Dwell time varies depending on crack size and environmental conditions.
- Methods: Dipping, spraying, or brushing.
- Minimum dwell time is 20-30 minutes.
Excess Penetrant Removal
- Delicate step: Removing excess penetrant avoids masking defects.
- Methods include cleaning with solvent, rinsing with water, or emulsifier prior to rinsing.
- Insufficient cleaning leaves a background of penetrant, obscuring defect indications.
Developer Application
- Developer is applied after excess penetrant removal and draws the penetrant from the cracks to the surface.
- Contrast between developer and penetrant is important for defect visibility.
- Longer dwell is necessary for tight cracks.
- Developers come in various forms: dry powders, dipping solutions, or spraying.
Inspection and Evaluation
- Indications are scanned under visible (or UV) light for recognition with human eye or automated optical scanners.
- Each indication is evaluated.
- False, non-relevant, unacceptable, and acceptable indications are possible.
- Acceptance/rejection of the component based on relevant standards.
Procedure Flow Chart (Visual Aid)
(A flowchart showing the sequence of steps).
Interpretation of Results
- Table showing typical indications for different defect types (e.g., cracks, porosity) under visible and fluorescent penetrant methods.
- Images of typical defect indications (e.g., coarse cracks, porosity, shrinkage).
Penetrant Removal Methods
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Method A: Water Washable: Penetrants removed using water rinse.
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Method B: Post-Emulsifiable, Lipophilic: Penetrants are removed using an emulsifier, then rinsing with water
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Method C: Solvent Removable: Penetrants are removed by hand-wiping with a solvent-moistened cloth.
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Method D: Post-Emulsifiable, Hydrophilic: Penetrants requiring a hydrophilic agent /water-soluble detergent, followed by water rinse are removed.
Advantages of Dye Penetrant Inspection
- High sensitivity for detecting small discontinuities.
- Applicable to many materials (metallic, nonmetallic, etc.).
- Inspection of large areas and complex-shaped parts.
- Portable and relatively inexpensive.
Disadvantages of Dye Penetrant Inspection
- Limited to surface-breaking defects.
- Pre-cleaning is critical for effective inspection (prevent contaminants masking defects).
- May require additional processes (like post-cleaning/demagnetization).
Safety Precautions (NDT)
- Ventilation, appropriate protective gear like gloves and eye protection, and following manufacturer's instructions ensure safety during inspection procedures.
Magnetic Particle Inspection
- Used for testing easily magnetized materials.
- Detects open-surface and just below-the-surface flaws.
- Ferromagnetic materials are typically tested (e.g., iron, nickel, cobalt, and some steels).
- Equipment is relatively cheap and robust, handled by semi-skilled personnel..
- Theory of Magnetism: -Magnets are permanent or temporary—they retain magnetism as long as magnetization force is applied.
Theory of Magnetism
- Ferromagnetism is the ability of materials, like iron, nickel, and cobalt alloys, to attract other ferromagnetic materials.
- Diamagnetic materials are repelled weakly by magnets.
- Paramagnetic materials are weakly attracted by magnets.
Magnetizing Force (H) and Flux Density (B)
- Magnetizing force (H): Sets up magnetic flux in a material.
- Flux density (B): Flux (magnetic lines of force) per unit area in a material (measured in gauss).
- Reluctance: Resistance offered by a material to magnetic flux establishment; comparable to electric resistance.
- Permeability: Ease with which a material can be magnetized. (Often expressed numerically as B/H) High permeability means low reluctance.
Magnetization Methods (Using Electric Current)
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Magnets can be used for creating magnetic field on the part to be inspected
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Induction Method (used for ring-shaped parts): AC or DC passed through a coil, inducing a current and field in the component; no chance of damaging component surfaces from arcing.
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Circular Field Method (used for multiple types of parts): Current is passed through the part itself, and the current magnitude is systematically reduced to zero.
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Longitudinal Field Method (used for multiple types of parts): Current passed through a coil, magnetizing the part lengthwise or longitudinally.
Demagnetization
- Components often retain some residual magnetism after inspection, and demagnetization is necessary for further processing or preventing interference with subsequent operations (e.g., welding, machining).
- Methods for removing residual magnetism include:
-Coil withdrawal
- Step-down reduction of current
- Reversing DC current
General Procedure for Magnetic Particle Testing
- Surface preparation (degreasing, removing contaminants) is crucial.
- Parts with magnetic paints require removal of those too to ensure good contact with the magnetic field.
- Magnetic particles, in appropriate concentration, are dispersed in a carrier solution.
- The magnetized part is inspected.
- Appropriate illumination/lighting is used to view the indications produced by the dispersed particles on the part, locating discontinuities.
Viewing/Detecting
- Black/red paste is observed with an appropriate light source.
- Fluorescent particles under UV light.
Marking Defects
- Marking defects is essential for documentation and future reference. -Using a permanent marker or transparent film to mark indicated areas/flaws is useful.
Removal of Ink/Residue
- Use of a stripper like paraffin oil wash for removing the magnetic ink.
Residual Magnetism Issues
- Parts retain some magnetism after testing, which can interfere with subsequent operations; and requires demagnetization.
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