Vi self study exam preparatory note part 1

ASNT Level III Visual Testing, VT2014-August My Self Study Exam Preparatory Notes

Charlie Chong/ Fion Zhang

Fion Zhang2014/August/15

http://meilishouxihu.blog.163.com/


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ASNT Certification Guide NDT Level III / PdM Level III- VT - Visual Testing

Length: 2 hours Questions: 90

1. Fundamentals

• Vision and light• Ambient conditions• Test object characteristics

2. Equipment Accessories

• Magnifiers/microscopes• Mirrors• Dimensional• Borescopes• Video systems• Automated systems• Video technologies


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• Machine vision• Replication• Temperature sensitive markers and surface comparators• Chemical aids• Photography• Eye

3. Techniques/Calibration

• Diagrams and drawings• Raw materials• Primary process materials• Joining processes• Fabricated components• In-service materials• Coatings• Other applications• Requirements


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4. Interpretation/ Evaluation

• Equipment including type and intensity of light• Material including the variations of surface finish• Discontinuity• Determination of dimensions (i.e.: depth, width, length, etc.)• Sampling/scanning• Process for reporting visual discontinuities• Personnel (human factors)• Detection

5. Procedures and Documentation

• Hard copy• Photography• Audio/video• Electronic and magnetic media


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6. Safety

• Electrical shock• Mechanical hazards• Lighting hazards• Chemical contamination• Radioactive materials• Explosive environments

Reference Catalog NumberNDT Handbook: Second Edition: Volume 8,Visual and Optical Testing 133ASNT Level III Study Guide: Visual andOptical Testing 2263ASM Handbook: Vol. 17, NDE and QC 105


SI Multiplier


http://www.poynton.com/notes/units/

Other Reading:

http://quizlet.com/29958394/visual-inspection-test-flash-cards/


Reading 1


Key Points Only


Reading 1


Section 1: Introduction to Visual & Optical TestingChapter 1: Fundamental of Light & Lighting


About Vision


Keywords:

Wavelength that excite retina 380~770 nm (380 x10-9 ~ 770 x10-9 m) Electromagnetic theory also known as Maxwell Theory Plank’s Quantum theory E= hv, h = plank’s constant (1.626 x 10-34 Joule.

Second), v = frequency (Hz)


Keywords:

Light Spectrum


Keywords:

Scoptic & Photopic Visions


Keywords:

Photopic--daylight--response of the human eye


380nm 770nm

Keywords:

Scotopic- night response of the human eye. Note the loss of sensitivity to blue and red wavelengths.


Keywords:

Scotopic & Photopic

Charlie Chong/ Fion Zhanghttp://www.nature.nps.gov/night/science.cfm

Keywords:

Subtractive primaries Additive primaries


Magenta


Cyan


Keywords:

Refraction Index n = Vv / Vm ,

Speed of light in medium, C = λv / n

Vv = Velocity of light in vacuumVm = Velocity of light in material



Light Refraction: Refractive Index of Medium

Refraction Index n = Vv / Vm ,

Speed of light in medium, C = λv / n

Light Refraction: Snell Law

Sin ϴ1 / V1 = Sin ϴ2 / V2 , Sin ϴ1 n1 = Sin ϴ2 n2

As the speed of light is reduced in the slower medium, the wavelength is shortened proportionately. The frequency is unchanged; it is a characteristic of the source of the light and unaffected by medium changes.



Sin ϴ1 n1 = Sin ϴ2 n2



http://www.physicsclassroom.com/shwave/refraction.cfm


Surface Luminance: Inverse Square Law

Surface Luminance:

E = I / d2

E = Source luminance, I= Source illuminances, d= distance


Surface Luminance: Inverse Square & Lambert Law

Surface Luminance:

E = I / d2 x CosαE = Surface luminance, I= Source illuminances, d= distance, α = angle of incidence from normal


Surface Luminance: Inverse Square & Lambert Law

Surface Luminance:E = I / d2 x Cosα


Surface Luminance: Lambert’s Law

In optics, Lambert's cosine law says that the radiant intensity or luminous intensity observed from an ideal diffusely reflecting surface or ideal diffuse radiator is directly proportional to the cosine of the angle θ between the observer's line of sight and the surface normal. The law is also known as the cosine emission law[3] or Lambert's emission law. It is named after Johann Heinrich Lambert, from his Photometria, published in 1760.

A surface which obeys Lambert's law is said to be Lambertian, and exhibits Lambertian reflectance. Such a surface has the same radiance when viewed from any angle. This means, for example, that to the human eye it has the same apparent brightness (or luminance). It has the same radiance because, although the emitted power from a given area element is reduced by the cosine of the emission angle, the apparent size (solid angle) of the observed area, as seen by a viewer, is decreased by a corresponding amount. Therefore, its radiance (power per unit solid angle per unit projected source area) is the same.


Surface Luminance: Lambert’s Cosine Law

http://en.wikipedia.org/wiki/Lambert%27s_cosine_law


Surface Luminance: Lambert’s Cosine Law

Surface Luminance:E = I / d2 x Cos ϴ,

Sin ϴ1 / V1 = Sin ϴ2 / V2 , Sin ϴ1 n1 = Sin ϴ2 n2 ,


Keywords:

Absorptive Characteristic Selective absorptive material – distinctive color Non-selective absorptive material- black or gray appearance

Transmitive Characteristics Transparent materials- Transmitted light without apparent scatter. Translucent materials- Transmitted large part of light with scattered some

portion due to diffusion (diffusion?) Opaque materials- Transmit no light, all of the spectrum is absorbed or

reflected or combination of both.


Surface irregularities reflected the light toward from camera

Flood the surface with as much light as possible and minimize shadow.


Surface irregularities reflected the light away from camera


As with dark field front, this set-up requires the camera to shown dark field.

Edges detection on opaque objects


The lambert (symbol L, la or Lb) is a non-SI unit of luminance named for Johann Heinrich Lambert (1728–1777), a Swiss mathematician, physicist and astronomer. A related unit of luminance, the foot-lambert, is used in the lighting, cinema and flight simulation industries. The SI unit is the candela per square metre (cd/m²).

http://en.wikipedia.org/wiki/Lambert_(unit)


Chapter 2: Physiology of Vision

Charlie Chong/ Fion Zhanghttp://starizona.com/acb/basics/observing_theory.aspx


The Eyes


Keywords:

Iris- Contracted, dilatedPupils-Chromatic aberrationSpherical aberration

Note: An aberration is something that deviates from the normal way.


Rods and Cones

The retina contains two types of photoreceptors, rods and cones. The rods are more numerous, some 120 million, and are more sensitive than the cones. However, they are not sensitive to color. The 6 to 7 million cones provide the eye's color sensitivity and they are much more concentrated in the central yellow spot known as the macula. In the center of that region is the " fovea centralis ", a 0.3 mm diameter rod-free area with very thin, densely packed cones.

The experimental evidence suggests that among the cones there are three different types of color reception. Response curves for the three types of cones have been determined. Since the perception of color depends on the firing of these three types of nerve cells, it follows that visible color can be mapped in terms of three numbers called tristimulus values. Color perception has been successfully modeled in terms of tristimulus values and mapped on the CIE chromaticity diagram.


Rod and Cone Density on Retina

Cones are concentrated in the fovea centralis. Rods are absent there but dense elsewhere.

Visual examination of small detail involves focusing light from that detail onto the fovea centralis. On the other hand, the rods are absent from the fovea. At a few degrees away from it their density rises to a high value and spreads over a large area of the retina. These rods are responsible for night vision, our most sensitive motion detection, and our peripheral vision.

Measured density curves for the rods and cones on the retina show an enormous density of cones in the fovea centralis. To them is attributed both color vision and the highest visual acuity.


Rod and Cone Density on Retina


Cone Details

Current understanding is that the 6 to 7 million cones can be divided into "red" cones (64%), "green" cones (32%), and "blue" cones (2%) based onmeasured response curves. They provide the eye's color sensitivity. The green and red cones are concentrated in the fovea centralis . The "blue" cones have the highest sensitivity and are mostly found outside the fovea, leading to some distinctions in the eye's blue perception.

The cones are less sensitive to light than the rods, as shown a typical day-night comparison. The daylight vision (cone vision) adapts much more rapidly to changing light levels, adjusting to a change like coming indoors out of sunlight in a few seconds. Like all neurons, the cones fire to produce an electrical impulse on the nerve fiber and then must reset to fire again. The light adaption is thought to occur by adjusting this reset time.

The cones are responsible for all high resolution vision. The eye moves continually to keep the light from the object of interest falling on the fovea centralis where the bulk of the cones reside.


Rod Details

The rods are the most numerous of the photoreceptors, some 120 million, and are the more sensitive than the cones. However, they are not sensitive to color. They are responsible for our dark-adapted, or scotopic, vision. The rods are incredibly efficient photoreceptors. More than one thousand times as sensitive as the cones, they can reportedly be triggered by individual photons under optimal conditions. The optimum dark-adapted vision is obtained only after a considerable period of darkness, say 30 minutes or longer, because the rod adaption process is much slower than that of the cones.

The rod sensitivity is shifted toward shorter wavelengths compared to daylight vision, accounting for the growing apparent brightness of green leaves in twilight.


While the visual acuity or visual resolution is much better with the cones, the rods are better motion sensors. Since the rods predominate in the peripheral vision, that peripheral vision is more light sensitive, enabling you to see dimmer objects in your peripheral vision. If you see a dim star in your peripheral vision, it may disappear when you look at it directly since you are then moving the image onto the cone-rich fovea region which is less light sensitive. You can detect motion better with your peripheral vision, since it is primarily rod vision.

The rods employ a sensitive photopigmentcalled rhodopsin.


Keywords:

Cones are responsible for color perceptions and details

Rods are responsible for night vision, our most sensitive motion detection, and our peripheral vision.

Rods is one thousandth times more efficient photoreceptors than cones Rods are efficient motion sensors Rod adaptation is much slower than cones Night vision is best at peripheral vision (not viewing the object right at the

center of field of vision)


Visual Acuity

Resolution Acuity (识别视力)Recognition Acuity (识别视力)Temporal Resolution (瞬时清晰复,瞬时清晰度)

Note: Temporal resolution refers to the accuracy of a particular measurement with respect to time. It is often in contest with spatial resolution which is a measure of accuracy with respect to the details of the space being measured.


Visual Angle


Snellen’s Acuity Fraction


Visual Acuity: What is 20/20 Vision

20/20 vision is a term used to express normal visual acuity (the clarity or sharpness of vision) measured at a distance of 20 feet. If you have 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance. If you have 20/100 vision, it means that you must be as close as 20 feet to see what a person with normal vision can see at 100 feet.

20/20 does not necessarily mean perfect vision. 20/20 vision only indicates the sharpness or clarity of vision at a distance. There are other important vision skills, including peripheral awareness or side vision, eye coordination, depth perception, focusing ability and color vision that contribute to your overall visual ability


Approximate table of equivalent visual acuity notations for near vision

http://courses.ttu.edu/edsp5383-ngriffin/letter.htm


Color Vision:Photopic Vision depends on:

■ Quantity of light■ Quality of light■ Adeptness of eye

Inspection Color Temperature: 6700ºC with full spectrum is optimum

Color Deficiencies affect approximately ■ 10% of Male population. ■ Women only constituted 0.5% of those affected.


Ishihara Plates


Color Deficiencies


Optical Illusion-Due to Contrast


Optical Illusion- The Logvinenko illusion. Although gray diamonds are identical, there appear to be light-gray ones and dark-gray ones (LOGVINENKO, 1999).


Optical Illusion- Due to Contrast


Optical Illusion- A & Bhttp://en.wikipedia.org/wiki/Optical_illusion


Optical Illusion- The square A is exactly the same shade of grey as square B.


Optical Illusion- In this illusion, the coloured regions appear rather different, roughly orange and brown. In fact they are the same colour, and in identical immediate surrounds, but the brain changes its assumption about color due to the global interpretation of the surrounding image. Also, the white tiles that are shadowed are the same color as the grey tiles outside the shadow.


Optical Illusion- Simultaneous Contrast Illusion. The background is a color gradient and progresses from dark grey to light grey. The horizontal bar appears to progress from light grey to dark grey, but is in fact just one colour.


Optical Illusion – Due to BrightnessBright objects look larger than the dark objects of the same size.


Chapter 3: Fundamental of Imaging


Keywords:

Plano Concavo / Convexo Convex Concave


Keywords:

Thin lens: The thickness of the lens is small compare to its focal length.The thin lens equation:

1/f = 1/d = 1/u


Lenses and the focal lengths


Chapter 4: Test Object Characteristics


Keywords:

Surface Features: Affected by (1) Form, (2) Waviness & (3) Roughness


Surface Roughness with & without profile variation

Profile = Form ? Waviness?

Form- Variation i form or profile are typically controlled by the dimensional or geometric tolerance specifications.


Surface Roughness

Surface roughness, often shortened to roughness, is a component of surface texture. It is quantified by the vertical deviations of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small, the surface is smooth. Roughness is typically considered to be the high-frequency, short-wavelength component of a measured surface (see surface metrology). However, in practice it is often necessary to know both the amplitude and frequency to ensure that a surface is fit for a purpose.

Roughness plays an important role in determining how a real object will interact with its environment. Rough surfaces usually wear more quickly and have higher friction coefficients than smooth surfaces (see tribology). Roughness is often a good predictor of the performance of a mechanical component, since irregularities in the surface may form nucleation sites for cracks or corrosion. On the other hand, roughness may promote adhesion.


Although roughness is often undesirable, it is difficult and expensive to control in manufacturing. Decreasing the roughness of a surface will usually increase exponentially its manufacturing costs. This often results in a trade-off between the manufacturing cost of a component and its performance in application.

Roughness can be measured by manual comparison against a "surface roughness comparator", a sample of known surface roughnesses, but more generally a Surface profile measurement is made with a profilometer that can be contact (typically a diamond styles) or optical (e.g. a white light interferometer).

However, controlled roughness can often be desirable. For example, a gloss surface can be too shiny to the eye and too slippy to the finger (a touchpad is a good example) so a controlled roughness is required. This is a case where both amplitude and frequency are important.


A roughness value can either be calculated on a profile (line) or on a surface (area). The profile roughness parameter (Ra, Rq,...) are more common. The area roughness parameters (Sa, Sq,...) give more significant values.


Profile roughness parameters

Each of the roughness parameters is calculated using a formula for describing the surface. Although these parameters are generally considered to be "well known" a standard reference describing each in detail is Surfaces and their Measurement.

There are many different roughness parameters in use, but Ra is by far the most common though this is often for historical reasons not for particular merit as the early roughness meters could only measure Ra. Other common parameters include Rz, Rq,and Rsk. Some parameters are used only in certain industries or within certain countries. For example, the Rk family of parameters is used mainly for cylinder bore linings, and the Motif parameters are used primarily within France.


Since these parameters reduce all of the information in a profile to a single number, great care must be taken in applying and interpreting them. Small changes in how the raw profile data is filtered, how the mean line is calculated, and the physics of the measurement can greatly affect the calculated parameter. With modern digital equipment it makes sense to look at the scan and make sure there aren't some obvious glitches that are skewing the values - and if there are, to re-measure


Keyword:

Ra:Roughness average is the universally recognised and most used international parameter of roughness. It is the arithmetic mean of the absolute departures of the roughness profile from the mean line. Ra is reported in microns.http://www.finetubes.co.uk/products/technical-reference-library/tube-surface-finishes/

Ra- Arithmetic average of absolute valuesAverage distance of the profile to the mean line - Area under the curve between the surface profile and the surface mean after applying a mathematical filter to eliminate the effect of waviness.

Ra- Arithmetic average of absolute valuesArea under the curve between the surface profile and the surface mean after applying a mathematical filter to eliminate the effect of waviness.


Ra- Average distance of the profile to the mean line


Comparison of approximately same Ra value with different profile with different roughness peak Rp and roughness depth Rv

http://www.olympus-ims.com/en/knowledge/metrology/roughness/2d_parameter/


Keywords

Anisotropic Surface: Periodic irregularity usually in one direction.


Rz & Rmax


Keywords:

Anisotropic Surface- has a periodic irregularity usually in one direction


Color & Gloss


Color & Gloss

Visual Comparison for Color Matching- The two most common systems are the (1) Natural color system and (2) Munsell color ordering system

Color’s Variables:

Colors order systems described colors as (1) hue, (2) value (3) saturation

Hue- Chromaticness, describes color as its primary color constituents or mix of color constituents. expressed as redness, blueness and so forth

Value- Described colors as lightness or darkness; Light color has high value and dark color has low value.

Saturation- Measure of distance from natural corresponding color. It is often referred as color strength or intensity.


Natural Color System


Munsell Color System


Geometry

Datum Reference: X, Y, Z


Geometric Tolerances

Section 2: Material Science Basics and Visual Testing ApplicationsChapter 5: Types of Materials to be Tested



Metal

Cells → Crystals


Metal


Keywords:

Atoms Cells Crystals Allotropic- Metal exhibits more than one cell structures Macroscopic evaluation- 10X magnifications or less Microscopic evaluation- >10X magnifications (50X ~ 200X)


Mechanical Properties


Keywords:

Electrochemical Nature of Corrosion:

General corrosion, Crevice corrosion and Galvanic corrosion are cause by the same mechanism.


Chapter 6:Visual & Optimal Testing Applications


Keywords:

Metal Working Processes Primary forming processes Secondary forming processes Finishing processes Joining processes Service


Metal Castinghttp://thelibraryofmanufacturing.com/metalcasting_basics.html


Metal Casting


Forming processes

Metal Manufacturing- Metal Rollinghttp://thelibraryofmanufacturing.com/metal_rolling.html


Primary forming processes - Metal Rolling


Secondary forming processes - Metal Rolling


Primary forming processes - Metal Rolling


Secondary forming processes


Finishing forming processes


Finishing processes


Joining Process


Services


Section 3: Inspection Planning & EquipmentChapter 7:Inspection Planning & Visual Inspection Tools


Profilometer


Section 4: Documentation & AnalysisChapter 8:Documentation of Visual Testing


Replication

One of the purpose of performing in situ replication is to determine the extent of thermal degradation or thermal aging from the microstructure appearance. Prolonged exposure to high temperature will cause microstructures to decompose and eventually result in creep cracking. By replication technique, microstructure can be obtained at site non-destructively to safely judge the condition of the component. The results obtained can be used to identify previous heat treatment process and to verify the required temperature setting for post weld heat treatment (PWHT) for repair work purposes, and as a reference for future inspection and maintenance work arrangement. The processes of producing replica at site are based on international code and standard as follow:


The processes of producing replica at site are based on international code and standard as follow:

a. ASTM E3: Standard Guide for Preparation of Metallographic Specimens

b. b. ASTM E407: Standard Practice for Microetching Metals and Alloys

c. c. ASTM E1351: Standard Practice for Production and Evaluation of Field Metallographic Replicas

d. ASTM E1558: Standard Guide for Electrolytic Polishing of Metallographic Specimens


In-situ Metallographic Replication


The techniques:

A standardized technique (ASTM E 1351, ISO 3057) which can be implemented on most metallic materials using portable polishing and etching devices and a field optical microscope. The procedure to carry out metallographic replicas includes at least five stages

1. Local grinding to eliminate surface layers (paint, decarburised layers, oxidation…)

2. Mechanical polishing using abrasive papers and diamond paste3. Chemical or electrolytic etching of the polished area to reveal the

microstructure4. Replication of the microstructure with a cellulose acetate film5. Observation of the structure with an optical microscope or a scanning

electron microscope


The End

Vi self study exam preparatory note part 1

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