VI- Self Study Exam Preparatory Note-Part 1

ASNT Level III Visual Testing, VT 2014-August My Self Study Exam Preparatory Notes

Charlie Chong/ Fion Zhang



Fion Zhang 2014/August/15

http://meilishouxihu.blog.163.c Charlie Chong/ Fion Zhang

ASNT Certification Guide NDT Level III / PdM Level III- VT - Visu al Testi ng Length: 2 hours Questions: 90 1. Fund amenta ls •• Vision and light Ambient conditions • Test object characteristics 2. Equi pment A ccesso ries • Magnifiers/microscopes • Mirrors • Dimensional • Borescopes • Video systems • Automated systems • Video technologies


• 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


4. Interpr etati on / Evalu atio n • 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. Proc edur es and Docu mentation • Hard copy • Photography • Audio/video • Electronic and magnetic media


6. Safety • Electrical shock • Mechanical hazards • Lighting hazards • Chemical contamination • Radioactive materials • Explosive environments Reference Catalog Number NDT Handbook: Second Edition: Volume 8, Visual and Optical Testing 133 ASNT Level III Study Guide: Visual and Optical Testing 2263 ASM Handbook: Vol. 17, NDE and QC 105


SI Multiplier

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


Oth er Readin g: http://quizlet.com/29958394/visual-inspection-test-flash-cards/


Readi ng 1


Key Poi nt s Onl y


Readi ng 1


Sect ion 1: Int rod uct io n t o Visu al & Opt ical T est ing Chapter 1 : Fund amenta l of Lig ht & Lig hti ng


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: 

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 blue and red wavelengths.


Keywords: 

Scotopic & Photopic

http://www.nature.nps.gov/night/scien


Keywords:  

Subtractive primaries Additive primaries


Magenta


Cyan


Keywords: Refraction Index n = Vv / Vm Speed of light in medium, C = v V Vm

,

v

/n

= = Velocity Velocity of of light light in in vacuum material


Lig ht Re fr act io n: Re fr act iv e Index of Me diu m Refraction Index n = Vv / Vm , Speed of light in medium, C =

v

/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.


Lig ht Re fr act io n: Re fr act iv e Index of Me diu m

Sin


ϴ1

n1 = Sin

ϴ2

n2

Lig ht Re fr act io n: Re fr act iv e Index of Me diu m

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


Sur face Lum in ance: Inverse S qu are Law

Surf ace Lum in anc e:

E = I / d2 E = Source luminance, I= Source illuminances, d= distance


Surface Luminance : Inverse S quare & Lambert Law

Surf ace Lum in anc e:

E = I / d2 x Cos E = Surface luminance, I= Source illuminances, d= distance, = angle of incidence from norma


Surface Luminance : Inverse S quare & Lambert Law

Surf ace Lum in ance: E = I / d2 x Cos


Surf ace Lumi nance: La mbert’ 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 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.


Surf ace Lumi nance: La mbert’ s Cosin e Law

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


Surf ace Lumi nance: La mbert’ s Cosin e Law

Surface Luminance: E = I / d2 x Cos ϴ,

Sin Sin


ϴ1

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



Keywords: Absorptive Characteristic  Selective absorptive material – distinctive color  Non-selective absorptive material- black or gray appearance Transmi ti ve Chara ct eris ti cs  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.



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


Surface irregularities reflected the light toward from camera

Surface irregularities reflected the light away from camera


Edges detection on opaque objects


As with dark field front, this setup requires the camera to shown dark field.

The l amb ert (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 pe square metre (cd/m²).

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


Chapter 2 : Phys io log y of Vis io n



http://starizona.com/acb/basics/observing_theor


The Eyes


Keywords: Iris- Contracted, dilated PupilsChromatic aberration Spherical aberration Note: An aberration is something that deviates from the normal way.


Rod s 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 cone 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 D ensi ty on Reti na Cones are concentrated in the fovea centralis. Rods are absent there but dense elsewhere. Measured density curves for the rods and cones on the retina show an density cones theenormous fovea centralis. Toofthem is in attributed both color vision and the highest visual acuity.

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.


Rod and Cone D ensi ty on Reti na


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 on measured 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 daynight 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 Detail s

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 rod 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 dayligh 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 youitsee dim star in your peripheral vision, mayadisappear 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 photopigment called rhodopsin.


Keywords: 

Cones are responsible for color perceptions and details

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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

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Rods are efficient sensors Rod adaptation is motion much slower than cones Night vision is best at peripheral vision (not viewing the object right at the center of field of vision)


Visu al Acu ity 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 measuremen 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


Vis ual Angl e


Snellen’s Acui ty Fracti on


Vis ual Ac ui ty : What is 20/20 Vis ion 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 Charlie Chong/ Fion Zhang

Approximate table of equivalent visual acuity notations for near visi

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


Color Visi on: Photopic Vision depends on: ■ ■ ■

Quantity of light Quality of light Adeptness of eye

Insp ect io n Colo r Tempera tu re: 6700ºC with full spectrum is optimum Col or Defi ci enci es affect approximately ■ 10% of Male population. ■ Women only constituted 0.5% of those affected.


Ishi hara Plate s


Ishi hara Plate s


Col or Defi ci enci es


Opt ic al Illus ion -Due to C ont rast


Opti cal Illusi on- The Logvinenko illusion. Although gray diamonds are identical, there appear to be light-gray ones and dark-gray ones (LOGVINENKO, 1999).


Optical I llusion - Due to Contra st


Optica l Illusion- A & B http://en.wikipedia.org/wiki/Optical_illusion


Opti cal Illusi on- The square A is exactly the same shade of grey as square B.


Opti cal Illusi on- 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.


Opti cal Illusi on- 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.


Opti cal Illusi on- 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 I llusion – Due to Bright ness Bright objects look larger than the dark objects of the same size.


Chapte r 3: Fundame ntal of Ima gin g


Keywords:    

Plano Concavo / Convexo Convex Concave


Keywords: Thin lens: The thickness of the lens is small compare to its focal length. The th in l ens equation : 1/f = 1/d = 1/u


Lenses a nd t he focal length s


Chapter 4 : Test Object Cha racteristi cs


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


Surface Rough ness wi th & wit hout prof ile va riation Prof il e = Form ? Waviness? Form- Variation i form or profile are typically controlled by the dimensional or geometric tolerance specifications.


Sur face R ou ghn ess

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 idea 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 highfrequency, 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 contro in manufacturing. Decreasing the roughness of a surface will usually increase exponentially its manufacturing costs. This often results in a trade-off betwee the manufacturing cost of a component and its performance in application. Roughness can be measured by manual comparison against a "surface

roughness a sample of known surface roughnesses, butthat more generally a comparator", Surface profile measurement is made with a profilometer 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.


Prof il e rou gh ness para mete rs

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 in use, but is by far the most common though thisroughness is often forparameters historical reasons not Ra for particular mer 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 internation 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 values Average 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 values Area 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 Visu al Comparison for Color Match ing- The two most common systems are the (1) Natural color system and (2) Munsell color ordering system Col or’ s Vari abl es: 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.


Natu ral Color Syst em









Munse ll Color Sy ste m


Geometry Datum Reference: X, Y, Z


Geometri c Tolerances


Sect io n 2: M ateri al Scienc e Basic s and Vis ual Testi ng Appli catio ns Chapt er 5: Types o f Materi als to be Test ed


Metal Cells → Crystals


Metal


Keywords:      

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


Mechanical Properties


Keywords: Electro chemic al Natu re of Corro sio n: General corrosion, Crevice corrosion and Galvanic corrosion are cause by the same mechanism.


Chapt er 6: Vis ual & Opt im al Test ing A ppl ic ati ons


Keywords: Metal Wor ki ng Pro cesses  Primary forming processes  Secondary forming processes  Finishing processes  Joining processes  Service


Metal Cast in g

 http://thelibraryofmanufacturing.com/metalcasting_basics.html


Metal Casti ng


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Formi ng proc esses

Metal Manuf act uri ng- Metal Rolling http://thelibraryofmanufacturing.com/metal_rolling.html


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Primary forming pro cesses - Metal Roll ing


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Prima ry f orming proce sse s - Metal Rolling


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Second ary form ing pro cesses - Metal Roll ing


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Prima ry forming proce sse s - Metal Rolling


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Second ary form ing proc esses


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Second ary for ming proc esses


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Second ary form ing proc esses


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Finishin g f orming proce sse s


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Fini shin g proc esses


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Finishing processes


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Finishing processes


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Joi ning Proce ss


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Joi ning Proce ss


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Joi ning Proce ss


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Services


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Services


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Services


Sect io n 3: Ins pecti on P lanni ng & E qu ip ment Chapt er 7: Insp ect ion Planning & Vis ual Inspe ct ion Tool s


Profilometer


Profilometer


Sect io n 4: D oc umenta ti on & A naly sis Chapt er 8: Docu menta ti on of Vis ual Test in g


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 nondestructively to safely judge the condition of the component. The results obtained can be used to identify previous heat treatment process and to 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 Me tallog raphic Re pl icatio n






The te chn iq ues:

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 paste 3. Chemical or electrolytic etching of the polished area to reveal the microstructure 4. Replication of the microstructure with a cellulose acetate film 5. Observation of the structure with an optical microscope or a scanning electron microscope


The End Charlie Chong/ Fion Zhang

VI- Self Study Exam Preparatory Note-Part 1

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