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Visual Testing (Nde)

Visual testing (NDE) uses borescopes and other optical devices to detect and examine surface flaws. Borescopes are long tubular devices that illuminate and allow inspection of inaccessible areas through rigid or flexible tubes of varying lengths and diameters. Flexible borescopes come in two main types - flexible fiberscopes using light and image guide bundles, and videoscopes using a CCD image sensor for electronic transmission of images to a video monitor. Borescopes and other visual testing methods are widely used to inspect surfaces for cracks and other defects in various industrial applications.

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Gaurav Chopra
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160 views3 pages

Visual Testing (Nde)

Visual testing (NDE) uses borescopes and other optical devices to detect and examine surface flaws. Borescopes are long tubular devices that illuminate and allow inspection of inaccessible areas through rigid or flexible tubes of varying lengths and diameters. Flexible borescopes come in two main types - flexible fiberscopes using light and image guide bundles, and videoscopes using a CCD image sensor for electronic transmission of images to a video monitor. Borescopes and other visual testing methods are widely used to inspect surfaces for cracks and other defects in various industrial applications.

Uploaded by

Gaurav Chopra
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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VISUAL TESTING (NDE)

 Means of detecting and examining variety of surface flaws.


 Widely used for surface cracks.

Borescopes
 Long tubular optical device.
 Illuminates and allow inspection of inaccessible areas.
 Rigid or flexible tube
 Wide variety of length & diameters available.
 Types of optical connection(between objective & ocular lens)
1- Rigid tube with series of relay lens.
2- Tube normally flexible but rigid with bundle of optical fibers
3- Normally flexible tube wires carrying image signals from CCD (charged coupled device) at
distal tip.

 Objective lens may have fixed or adjustable focusing.


 Distal tip may have prisms and mirrors for direction and field of view.
 Illumination- by fiber optic light guide or lamp, sometimes LED used in videoscopes with working
length 15m.

Rigid Borescopes
 Limited to straight-line path.
 Length range 0.15 to 30m (0.5 to 100ft).
 Diameter range 0.9 to 70mm (0.035 to 2.75”).
 Magnification 3 to 4 X, up to 50 X available.
 Field of view generally 55° (60° in handbook). It may range from 10 to 90°.
 Some borescopes have orbital scan with rotating optical shaft. Amount of rotation vary from 120 to
370°.
Basic Design
 Series of achromatic relay lens in tube.
 Diameter range 4 to 70mm.
 Illumination by distal lamp or light guide bundle.

MiniBorescopes
 Series of achromatic relay lens in tube.
 Diameter range 0.9 to 2.7mm.
 Length range 110 to 170mm.
 High magnification up to 30 X.

Hybrid Borescopes
 Series of rod lens combined with convex lens.
 Have fewer glass-air boundaries reducing scattering.
 Diameter range 5.5 to 12mm.
 Length up to 990mm.

Extendable Borescopes
 Can construct longer borescopic tubes by joining extension tubes.
 Maximum length up to 30m.

Flexible borescopes
 Two types- flexible fiberscopes & videoscopes with a CCD image sensor.

Flexible fiberscopes
 Consist of light guide bundle and image guide bundle.
 Diameter range 1.4 to 13mm
 Length up to 12m
 Special quartz fiberscopes up to 90m.
 Small dia fibers give brighter image and better resolution.
 Field of view-40 to 60°, can range from 0 to 120°.

Videoscopes with CCD probes


 Involve electronic transmission of image to video monitor.
 Distal end has CCD chip, having thousands of light sensitive element array.
 Videoscopes have higher resolution than fiberscopes.
 Have longer working length.
 Reduces fatigue to eye
 No honeycomb or irregular shaped patterns.

Direction of View
 Circumference or panoramic heads- good for tubing or large cylinder structures.
 Forward head-for facing walls or bottom of blind holes and cavities.
 Forward-oblique/retrospective- viewing area just passed by advancing scope
 Suited for inspecting inside neck of cylinders and bottles.

Environment
 Special scopes for temperatures up to 1925°.
 Quartz fiberscopes- for radiation exposed area.

Image sensors
 Image orthicons and image isocons
 Vidicon or plumbicon television tubes
 Secondary electron coupled (SEC) tubes
 Charged coupled device (CCD)
 Optical holography

Vidicon- used at higher light levels


Orthicon, isocons & SEC- used at lower light levels
CCD- used for information processing applications. Better than above.

Magnification System
Toolmakers’ microscope
 Magnification range from 10 to 200X

Optical comparator
 Magnifications range 5 to 500X
 Comparison device
 Silhouette of part is magnified on large screen and compared to a optical comparator chart.

Lasers
 Used for surface inspections
 In-process surface flaws and measurement of surface defects and roughness

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