Download - Liquid Penetrant Testing - azarata.irazarata.ir/wp-content/uploads/2014/07/3-Liquid-Penetrant-Testing.pdf · vTest Method Scope vObject’s ... Liquid Penetrant Method l A liquid

Liquid Liquid PenetrantPenetrant TestingTesting

What is nondestructive testing?

A method of evaluating the physical integrity of an item without destroying it.

The Testing of a specimen that determines its serviceability without damage

that could prevent its intended use.

Where,When is NDT Used ?Where,When is NDT Used ?

1) To ensure product integrity, and in turn, reliability2) To avoid failures, prevent accidents and save human life3) To make a profit for the user4) To ensure customer satisfaction and maintain the manufacturer’s

reputation5) To aid in better product design6) To control manufacturing processes7) To lower manufacturing costs8) To maintain uniformity quality level9) To ensure operational readiness

Why do you use it ?Why do you use it ?

1. Ensuring the Integrity and Reliability of a Product

R=0.999 =0.9057

The possibility of failure of the assembly is then :

1.00 – 0.9057 = 0.0943 = %9.43

1000


2. Preventing Accidents and Saving Lives


3. To make a profit for the user


4. Ensuring Customer Stisfation


5. Aiding in Product Design


6. Controlling ManufacturingProcesses


7. Lowering Maufacturing Costs


8. Maintaining Uniform Quality Level


9. To Ensure Operational Readiness


v Mechanical and Opticalv Penetrating Radiationv Electromagnetic and electronicv Sonic and Ultrasonicv Thermal and Infraredv Chemical and Analytical

Classification of NDT Methods :

v Discontinuitiesv Structure or Malstructurev Dimensions and Metrologyv Physical and Mechanical Propertiesv Composition and Chemical Propertiesv Composition and Chemical Analysisv Stress and Dynamic Responsev Signature Analysis

Informations Provided from each Method :

v Visual Testingv Radiographic Testingv Liquid Penetrant Testingv Magnetic Particle Testingv Ultrasonic Testingv Eddy Current Testingv Acoustic Emission Testingv Neutron Radiographic Testingv Thermal/Infrared Testingv Leak Testingv Vibration Testingv Microwave Testingv Thermal Testingv Holography

v Composition testingv Radiographic Tomographyv Ultrasonic Tomographyv Laminographyv Laser Profilometryv Krypton Gas Penetrant Imagingv Elastographyv Thermographyv Resonant Ultrasonic Spectroscopyv Remote Field Eddy Current Testingv Remote Field Magnetic Particle Testingv Electronic Speckle Pattern Interferometryv …

Some NDT Methods :

v Visual Testing (VT)v Radiographic Testing (RT)v Liquid Penetrant Testing (PT)v Magnetic Particle Testing (MT)v Ultrasonic Testing (UT)v Eddy Current Testing (ET)v Acoustic Emission Testing (AET)v Neutron Radiographic Testing (NRT)v Thermal/Infrared Testing (TIR)v Leak Testing (LT)

Classic Methods :

v Test Method Scopev Object’s Conditions & Propertiesv Sensitivity Requiredv Availabilityv Costv Safety & Environmentv …

Choosing NDT Methods :Choosing NDT Methods :

American Society for Non-Destructive Testing

Society for Non-Destructive TestingTechnical Council

First Document

SNT-TC-1A

Most basic and common inspection method.

Tools include fiberscopes, borescopes, magnifying glasses and mirrors.

Robotic crawlers permit observation in hazardous or tight areas, such as air ducts, reactors, pipelines.

Portable video inspection unit with zoom allows

inspection of large tanks and vessels, railroad tank

cars, sewer lines.

Visual Inspection

Surface Examination

l Discloses flaws open to the surface, or very close to the surface.

l Magnetic Particle (MT) may be used ONLY on ferromagnetic materials.

l Liquid Penetrant (PT) may be used, within limits, on ANY material (metal, plastic, glass, ceramic).

History of Penetrant Method

l In the 1920’s RT was the only truly NDT that could give critical and accurate information about the internal soundness of a part.

l In 1930’s MT was introduced under “Magnaflux” trade name but only for ferromagnetic materials.

l The use of Fluorescent Penetrant Inspection for finding flaws in structural materials was introduce in 1942 by Magnaflux Corporation under trade name of Zyglo.


l Etching – The surface of the part was etched or pickled by corrosive liquids.

l The use of Acid or Alkali on a large scale presented operating problems and discouraged the use of the process on a production basis.

l All cracks must still be sought by a careful visual inspection, with magnifier and fine cracks were still missed.

l The surface of smooth finished parts were highly damaged.

The following methods were in use for testing of non-magnetic materials prior to 1942.

l Useful for inspection of Aluminum forgings in the as-forged condition. Forging Laps are tight and likely to be filled with oxide.

l Etching is also useful in confirming a crack found by other methods.


l Anodizing – This variation of etching is used on Aluminum and Magnesium.

l The surface of these metals is treated with an oxidizing agent, such as a Chromate or Chromic Acid, a corrosion resistant surface film is produced.

l Where a crack or other open defects exists, the oxidizing liquid enters and later makes the crack visible either by the etching action at the crack edges or by the stain produced by the liquid at the defect.

l Actually a combination Etching and Penetrant method.l Effective on certain cracks and surface defects, but is reliable only on

the Larger Cracks.l Proven to be unable to find very fine defects because they are

bridged over by the protective film.


l Oil and Whiting Method – This method is definitely very similar to modern penetrant method.

l Used for detecting gross cracks in Railroad Industry in maintenance of steam locomotives, rods; axles; crank pins; etc..

l Useful only for detecting large cracks.l First cleaned the parts usually by Boiling in a Caustic Soda solution,

dried and then immersed in a tank of the diluted 600 W oil.

l The Penetrant Time was from a Few Hours to 24 Hours or more.l The surfaces then were cleaned and dried and painted with a mixture

of Whiting (chalk).l This coating dried rapidly and left a dead white and quite uniform

surface.


Oil and Whiting Method Continued …….l Then the parts were usually Vibrated by striking with a sledge or by

means of an air hammer.l The vibration cause to squeeze the dirty oil of the penetrant back out

to the surface.l Wherever oil came back to the surface, the white coating would be

Stained a Dirty Brown and a crack would be indicated.l The method found many cracks but was inadequate to locate Fine

Cracks, Specially Fine Shallow Fatigue Cracks.l This method was used mostly on steel parts, and by 1940 had been

largely discredited for this use by the magnetic particle method.l No one was successful in applying this method to non-magnetic

parts.


l In 1935 – Carl E. Betz and F. B. Doane, working for Magnaflux Corporation worked to improve the magnetic particle method, wereconscious of the need for a similar method for non-ferrous metals.

l A method was actually worked out based on electrolysis and colorcontrast but proved to be entirely impractical.

l Robert C. Switzer of Switzer Brothers, Inc. (Glo Color Corp., Cleveland, Ohio) began his experiments independently of Magnaflux.

l His work was directed toward location of defects by penetrants using Colored Dyes in the penetrants to increase the color contrast of indications against a background.

l He realized that superior contrast were secured by means of Fluorescent Dyes and the use of black light to cause them to fluoresce.


l In October 14, 1941 R.C. Switzer work led him to receive a patent on various Penetrant Methods of Finding Flaws in Solid Materials.

l The original patent covered both Fluorescent Penetrants and Color Contrast Penetrants.

l In February of 1942 Robert C. Switzer offered an exclusive license to Magnaflux Corporation.

l Later Greer Ellis, Taber de Forest, F. S. Catlin, J. L. Switzer, and R. A. Ward did most of the research.

l Water Washable fluorescent penetrant materials and techniques were discovered from this research.

l R. A. Ward received a patent for the water washable technique and material issued July 30, 1946.


l The Post Emulsification method was developed in the Magnaflux Laboratories to meet the critical needs of Jet Engine Industry.

l Turbine Buckets and Blades and more critical parts were tested using this method.

l In September 17, 1957 a patent was issued to Magnaflux Corporation under trade name Pentrex covering the post emulsification method.

l Donald W. Parker and Taber de Forest led the research on the method, achieving greatly increased sensitivity for all types ofdefects.

l This method also increased ability to locate fairly open and shallow defect types.

Liquid Penetrant Method

l A liquid with a tracer to make it more visible (colored dye or a fluorescent compound) is applied to the surface.

l Capillary action draws the liquid down into surface-breaking discontinuities such as pits and cracks.

l After cleaning the surface of excess penetrant material, a blotting material is applied to the surface to draw out, again by capillary action, the liquid that has been pulled down into the discontinuities.


l In the liquid penetrant method, the liquid is applied to the surface of the specimen, and sufficient time is allowed for penetration of surface discontinuities. If the discontinuity is small or narrow, as in a crack or pinhole, capillarity assist the penetration.


l After sufficient time has passed for the penetrant to enter the discontinuity, the surface of the part is cleaned. Capillary action is again employed to act as a blotter to draw penetrant from the discontinuity.


Ø

Ø

Poor Wetting

Good Wettingl Cleanliness of the surfacel Configuration of the cavityl Size of the cavityl Surface tension of the liquidl Ability of the liquid to wet the surface


l Anything that could block the penetrant from entering the discontinuity must be removed.

l A list of contaminates that must be removed would include dirt, grease, rust scale acids and even water. The cleaning solvent used must be volatile (readily vaporized) so that it easily evaporates out of the discontinuity and does not dilute the penetrant.

l Surface preparation by shot or sandblasting is not recommended.

l Discontinuities that were open to the surface may be closed by the shot or sandblasting operation.

Liquid Penetrant Testing

l Penetrant types– Visible Dye (Red Dye)– Fluorescent (Fluorescent Dye)– Dual Sensitivity (Combined)


l Type I – Fluorescent Penetrant Examination:– Method A – Water washable– Method B – Post emulsified, lipophilic– Method C – Solvent removable– Method D – Post emulsifiable, hydrophilic

l Type II – Visible Penetrant Examination– Method A – Water washable– Method C – Solvent removable


l Penetrant Removal types– Water Washable– Post Emulsified– Solvent Removed


Water WashablePre-Clean Pre-Clean Pre-Clean

Solvent RemovedPost Emulsified

Apply Emulsifier

Apply Penetrant Apply Penetrant Apply Penetrant

Water Wash Solvent Wipe

Wet DeveloperDryDryDry Developer

Dry Developer NonaqueousWet Developer

InspectPost Clean


Dual SensitivityPre-Clean

Solvent Wipe

Apply Penetrant

Water Wash

Dry

Dry PowderDeveloper

NonaqueousWet Developer

InspectPost Clean


l Selection of best process depends upon:– Sensitivity required– Number of articles being tested– Surface of part being tested– Configuration of test article– Availability of water, electricity, compressed air, good testing area, etc.

l Penetrant testing is successfully used on metals such as aluminum, magnesium, copper, brass, stainless steel, titanium and most other common alloys.

l It can also be used to test other materials including ceramics, plastics, molded rubber, powered metal and glass.

Liquid Penetrant Advantages

l The method has high sensitive to small surface discontinuities. l The method has few material limitations, i.e. metallic and nonmetallic,

magnetic and nonmagnetic, and conductive and nonconductive materials may be inspected.

l Large areas and large volumes of parts/materials can be inspected rapidly and at low cost.

l Parts with complex geometric shapes are routinely inspected. l Indications are produced directly on the surface of the part and

constitute a visual representation of the flaw. l Aerosol spray cans make penetrant materials very portable. l Penetrant materials and associated equipment are relatively

inexpensive.

Liquid Penetrant Disadvantages

l Only surface breaking defects can be detected. l Only materials with a relative nonporous surface can be inspected. l Pre-cleaning is critical as contaminants can mask defects. l Metal smearing from machining, grinding, and grit or vapor blasting

must be removed prior to LPI. l The inspector must have direct access to the surface being inspected. l Surface finish and roughness can affect inspection sensitivity. l Multiple process operations must be performed and controlled. l Post cleaning of acceptable parts or materials is required. l Chemical handling and proper disposal is required.

Jet Engine Inspection• Aircraft engines are overhauled after

being in service for a period of time.

• They are completely disassembled, cleaned, inspected and then reassembled.

• Fluorescent penetrant inspection is used to check many of the parts for cracking.

Sioux City, Iowa, July 19, 1989

A defect that went undetected in an engine disk was responsible for the crash of United Flight 232.

Crash of United Flight 232

Lesson 1 Quiz

1. Nonmetallic inclusions and porosity in the steel ingot are commonly found using liquid penetrant inspection techniques.

2. Type II penetrants, according to our test, are those containing a fluorescent dye.

3. Because of the capillary action of penetrants, this process of inspection works well on parts with very porous surfaces.

4. When doing a liquid penetrant test, the configuration of the specimen has little effect on the effectiveness of the test.

False

False

False

False

Lesson 1 Quiz

5. Liquid penetrant inspection can be used only on the metals such as aluminum and steel.

6. The penetrant inspection method is used only on the finished product.

7. Oil and whiting are the names of the two men who invented the penetrant test method.

8. The first important step in penetrant testing is surface preparation.

9. One of the most common contaminations in the penetrant method iswater.

False

False

False

True

True

Lesson 1 Quiz

10. The most common method of surface preparation for penetrant method is water.

11. Chemical etching is sometimes used to remove smeared metal from a surface to open discontinuities.

12. Some subsurface defects can be located with the highly sensitive type II penetrants.

13. Blow holes and gas porosity may be detected with the penetrant method.

False

True

False

True

Lesson 1 Quiz

14. Solvent cleaning is a common method of surface cleaning parts before penetrant testing.

15. The one major limitation to penetrant testing is that the part must be metallic.

16. Grease and rust would usually be considered a contaminant on thesurface of a test piece.

17. To locate a defect with penetrant testing, the defect must be open to the surface.

18. It is considered advantageous for a liquid penetrant material to have low tension and high capillarity.

True

True

True

False

True

Surface Cleaning

l Vapor Degreasing:– Oil Removal– Grease Removal– Organic Contamination– Harmful to certain alloys

l Solvent Cleaning– Easier but less effective

l Steam Cleaning– Large unwieldy parts

l Rust & Surface Scale– Acid or Alkaline rust removers

Surface Cleaning

l Environmental concerns raised in the last decade have changed both the chemistry and hardware technology for degreasing.

l Solvents have been modified or replaced to eliminateozone depletion potential and other hazards.

l Equipment designs and operating processes have been re-engineered to reduce solvent losses to near zero.

l Liquid vapor degreasing with solvent has been an accepted method of precision cleaning for over 50 years.

l It incorporates washing, rinsing, drying, and solvent reclamation in compact, cost-effective unit.

Surface Cleaning

l The most attractive aspect of liquid vapor degreasing as a cleaning technology is the simplicity of the process itself:

l Parts are placed in a basket or carrier l Then moved into the vapor zone (A) for pre-cleaning with hot vapors l Then transferred to precision cleaning sump(B) for ultrasonic cleaningl Parts cooled in the cleaning

sump are returned to the hot vapor zone (A) for final rinsing

l A final stop in the freeboard area (C) allows any residual solvent vapors to return to the vapor zone

Surface Cleaning

l Paint Removal– Dissolving Hot Tank Paint Strippers– Bond Release– Solvent Paint Strippers

l Etching– For Parts being grounded or machined– Uses an Acid or an Alkaline solution

l Surface Cleaning To Be Avoided:–Shot, Sand, Grit, or Pressure Blast–Liquid Honing, Emery Cloth, Wire Brush–Peening or Cold Working


l Pre-cleaning Stationl Penetrant Station (Tank)l Drain Stationl Emulsification Stationl Rinse Stationl Developing Stationl Drying Stationl Inspection Station with

proper lightingl Post-cleaning Station

Stationary Penetrant Test Equipment


l Visible Dye Penetrant Kit:– Pressurized Spray Cans Of Cleaning or Removal Fluid– Pressurized Spray Cans Of Visible Dye Penetrant– Pressurized Spray Cans Of Nonaqueous Developer– Wiping Cloths and Brushes

Portable Penetrant Test Equipment

Liquid Penetrant MethodPortable Penetrant Test Equipment

l Fluorescent Dye Penetrant Kit:–A Portable Black Light and Transformer–Pressurized Spray Cans Of Cleaning or Removal Fluid–Pressurized Spray Cans Of Fluorescent Dye Penetrant–Pressurized Spray Cans Of Nonaqueous Developer–Wiping Cloths and Brushes

Penetrant Testing Materials

Visible

Emulsifier Solvent

Dual SensitivityFluorescent

WaterWater Solvent

Wet

Water

WaterSoluble

WaterSuspended

Particle

Dry Nonaqueous Wet

Developer

Remover


l Water Washable Penetrants– Contain an emulsifying agent which makes them easily

removable by a water rinse or wash– Available with either visible or fluorescent dye

l Post Emulsifiable Penetrants– Highly penetrating oily visible or fluorescent– Not soluble in water– Must be treated with an emulsifier before water rinse or wash

l Solvent Removable Penetrants– Oily penetrants that DO NOT contain emulsifying agent– Removable only by solvents specifically designed

Penetrant Testing Materialsl Penetrants are then classified based on the strength or detect-ability

of the indication that is produced for a number of very small and tight fatigue cracks. The five sensitivity levels are shown below:

l Level ½ - Ultra Low Sensitivity l Level 1 - Low Sensitivity l Level 2 - Medium Sensitivity l Level 3 - High Sensitivity l Level 4 - Ultra-High Sensitivityl The major US government and industry specifications currently rely

on the US Air Force Materials Laboratory at Wright-Patterson Air Force Base to classify penetrants into one of the five sensitivity levels.

l This procedure uses titanium and Inconel specimens with small surface cracks produced in low cycle fatigue bending to classifypenetrant systems.


l Emulsifiers– Materials when applied to a penetrant coated specimen make

the resultant mixture easily removable by water rinse or wash– Emulsifiers have low penetrant characteristics and DO NOT

remove indications from the specimen surfacel Removers (Solvent)

– Designed to aid specific penetrants– Available in bulk or pressurized spray cans

l Dry Developers– Fluffy, absorbent white powder that is used in both fluorescent

and visible penetrant tests– It draws penetrant indications to surface & making them visible


l Wet Developers– Function similarly to dry developer– Mixture of a developing powder and water

l Nonaqueous Wet Developers– Mixed with a rapid drying liquid solvent– Like wet developers but available pressurized spray cans

l Liquid Oxygen (LOX) Compatible Materials– Must be used when parts have contact with either liquid or

gaseous oxygen– Designed specifically to be inert when LOX is present

l Low Sulfur & Low Chlorine Penetrants–Designed to avoid harm caused on some Nickel & Titanium Alloys

Safety Precautions

l General– Penetrant inspection materials can be flammable and can cause

skin irritations– The ultraviolet light rays can cause sunburn, may be injurious to

eyes– Proper filter will filter out the harmful rays

l Fire– Safe practice requires that penetrant materials used in open

tanks have a Flashpoint of greater that 120° Fl Skin Irritation

– Can be avoided by use of gloves, aprons, and hand creamsl Air Pollution

– Exhaust fans should installed in confined areas

Lesson 2 Quiz

1. Wire brushing is a common and acceptable method of surface cleaning a test part that is to be penetrant inspection.

2. A good exhaust system is recommended when working with cleaning solvents.

3. Vapor degreasing is often used to remove oxidation, rust, and scale before a part is penetrant inspected.

4. Parts that have been painted usually cannot be inspected with penetrants because suitable paint removing techniques have been developed.

False

False

True

False

Lesson 2 Quiz

5. Detergent cleaning is acceptable for post-cleaning but should never be used for pre-cleaning because it may affect the emulsifier during the penetrant test.

6. Etching is often effective in pre-cleaning a part that has been machined to a specific tolerance by surface grinding.

7. Only visible dye penetrants are available in portable kits because fluorescent dyes will not function in pressurized spray cans.

8. Dry developers are usually only used with visible dye penetrant.

False

True

False

False

Lesson 2 Quiz

9. Emulsifiers and solvents are both commonly used in penetrant testing as post-cleaners.

10. Wet developers should never be used when they will come into contact with gaseous or liquid oxygen because of the results caused by oxygen and water mixing.

11. Emulsifiers must have high penetrating characteristics to emulsify penetrants that lie in fillets and corners.

12. The black light used in fluorescent penetrant inspection is not hazardous to the human eyes if the correct filter is in place and not broken or cracked.

False

False

False

True

Lesson 2 Quiz

13. Penetrant materials are often placed in groupings that assure a valid test with materials that are compatible with each other.

14. Nonaqueous developer refers to a powder that is applied dry.

15. Post-emulsifiable penetrants are usually soluble in water after the application of an emulsifier.

16. Water washable penetrants are commonly used with either a visible or fluorescent dye.

17. Flashpoint refers to the lowest temperature at which vapors will ignite when exposed to flame.

True

True

True

False

True

Liquid Penetrant MethodSurface Preparation & Penetrant Application

The effectiveness of penetrant testing is based upon on the ability of the penetrant to enter surface discontinuities.

All paint, carbon, oil, varnish, oxide, plating, water, dirt, and similar coating Must Be Removed before application of the penetrant.

Liquid penetrant placed on the surface of a specimen does not merely seep into discontinuties. It is pulled into them by Capillary action. This is the reason one can cover the under surface of an item with a penetrant and still have a valid test.


Typical cleaning methods:

1. Detergent Cleaning

2. Vapor Degreasing

3. Steam Cleaning

4. Ultrasonic Cleaning

5. Rust and Surface Scale Removal

6. Paint Removal

7. Etching


Modern penetrants must have:

1. Ability to Hold a Dye material in suspension

2. Ability to Spread the Dye evenly over the surface

3. Ability to Carry the Dye into any discontinuity open to the surface

4. Ability to Bring Up the Dye as it is “Coaxed” back to the surface

5. Ability, when desired, to be Easily Removed


There are two types of Dye used in modern penetrant:

1. Visible – A brightly colored dye that is highly visible under normal lighting conditions.

2. Fluorescent – An almost colorless dye which emits visible light rays when reviewed under black light.

A dye with Dual Sensitivity contains both a Visible Dye for examination in white light and a Fluorescent Dye for a more sensitive evaluation of small discontinuities.

Penetrant Application

Penetrants can be applied by one of the following methods:

1. Spraying – Usually using a low pressure circulation pump or from pressurized spray cans.

2. Brushing – Applied with rags, cotton waste, or brushes.

3. Immersion – The entire part is dipped into a tank of penetrant.

4. Pouring – Penetrant is simply poured over the surface.

Penetration Dwell Time

Penetration (Dwell) Time• The period of time during which the penetrant is permitted to

remain on the specimen is a vital part of the test.Tight crack-like discontinuties may require in access of 30 minutes for penetration that will give an adequate indication. However, gross discontinuities may be suitably penetrated in 3 to 5 minutes.The temperature of the specimen and temperature of the penetrantcan affect the required Dwell Time.

Warming the specimen to 70° F or higher accelerates penetration and shortens Dwell Time. However, care should be taken Not to Overheat the specimen since too much heath may cause evaporation of the penetrant from discontinuity.

Penetration Dwell Time

Penetration (Dwell) TimeDwell Times are based on the assumption that the penetrant will remain Wet on the part surface. Additional penetrant may be applied during Dwell Time.

The penetrant manufacturer will provide suggested Dwell Times for the various penetrants that it produces.

Penetration Dwell Timel The below information is intended for general reference and no

guarantee is made about its correctness or current-ness.


Penetrant Testing ProcessesPenetrants, either Fluorescent or Visible, can be further categorized as follows:

1. Water washable

2. Post Emulsification

3. Solvent Removable


Water Washable PenetrantsHave a built in emulsifier and the penetrant is easily removed by a water rinse. Care must be taken to insure that the spray volumeand force does not wash penetrant out of the discontinuity.

Water temperatures above 110° F are not recommended because this may speed up the evaporization of the penetrant.

Water washable penetrants are usually preferred for use on articles with a Rough Surface or if they contain Threads or Keyways.

The built in Emulsifier provides the best penetrant removal blind holes and other hard to reach locations but is Poor in detecting wide or shallow discontinuities.


Water Washable Penetrant testing Process


Solvent Removal PenetrantsHave advantage of Portability and can be used out doors without using heavy, complex equipment.Excellent for many Maintenance Inspections and for checking portions of a larger structure.

Penetrant is often applied from a Pressurized Spray can which makes the system very portable.

After Dwell Time, the Excess Penetrant is first removed by wiping with absorbent towel and then cleaned with towels dampened with solvent.

Solvent is Never Applied Directly to the specimen as it might wash out or dilute the penetrant in the discontinuity.


Post Emulsification PenetrantsA two step removal process. The emulsifier is usually applied by dipping or immersion. The amount of Dwell Time in the emulsifier is in the range of One to Fourminutes.


LEAK-THROUGH TECHNIQUE-The use of liquid penetrant is suited for finding leaks in such articles as tanks, piping, tubing, and hollow castings. Illustrated in the sketch below;


Fixing and Recording Indications

1. Photographs – Typical black and white and color films are used.

2. Special Wax and Plastic Film Developers – These developers absorb and fix the penetrant indications for permanent record keeping.

1. Strippable Lacquers are sprayed in several coats over the indication and when dry can be Lifted to provide a permanent record.

2. Special Fixers are sprayed over the indication and when dry are lifted with transparent tape.

Water Washable Method

Advantages:1. Easily washed with water.

2. Good for quantities of small specimens.

3. Good on rough surfaces.

4. Good on rough surfaces.

5. Good on wide range of discontinuities.

6. Fast, single step process.

7. Relatively inexpensive.

8. Available in oxygen compatible form.

Disadvantages:1. Not reliable for detecting scratches

and similar shallow surface discontinuities.

2. Not reliable on reruns of specimens.

3. Not reliable on anodized surfaces.

4. Acids and chromates affect sensitivity

5. Easily over-washed.

6. Penetrant subject to water contamination.

Solvent Removable Method

Advantages:1. Portability.

2. No water required.

3. Good on anodized specimen.

4. Good for spot checking.

5. Specimen can be rerun.

Disadvantages:1. Flammable Materials.

2. Removal of excess surface penetrant is time consuming.

3. Materials can not be used in open tanks.

4. Difficult to use on rough surfaces such as cast magnesium.

Post Emulsification Method

Advantages:1. High sensitivity for very fine

discontinuities.

2. Good on wide shallow discontinuities.

3. Easily washed with water after emulsification.

4. Short penetration time.

5. Can not be easily over washed.

Disadvantages:1. Two step process.

2. Equipment required for emulsification application.

3. Difficult to remove penetrant from Threads, Keyways, Blind Holes, and Rough surfaces.

Lesson 3 Quiz

1. A dual sensitivity penetrant contains a special dye that is visible in white light and will fluoresce without the use of a black light.

2. A part of being penetrant inspected must stay immersed in the penetrant tank for the entire specified dwell time.

3. The liquid penetrant leak-through test refers to the ability of a penetrant to spread through the dry developer evenly.

4. Visible dye penetrants are usually considered to be less sensitive than fluorescent penetrants.

False

False

False

True

Lesson 3 Quiz

5. Water-washable penetrants have a built-in emulsifier that permits good results in penetrant removal from parts suspected of having wide or shallow discontinuities.

6. Solvent-removable penetrants are available in both visible and fluorescent dye.

7. Excess post-emulsifiable penetrant is commonly removed by spraying the surface of the part with cleaner (solvent) and then wiping with a lint-free towel.

False

True

False

Lesson 3 Quiz

8. Water-washable penetrant systems are usually very portable because the materials are commonly used in pressurized spray cans.

9. Warming the specimen to temperatures up to about 70º F tends to accelerate penetration and shortens dwell time.

10. For the dwell time to be accurate, the surface of the specimen must stay wet with penetrant for the entire time specified.

11. The typical dwell time for most penetrant inspections is about 20-30 minutes.

False

True

True

False

Lesson 3 Quiz

12. List two (2) of the commonly used methods of applying penetrant to a specimen that is to be inspected.

13. List four (4) of the commonly used methods of pre-cleaning the specimen before penetrant inspection.

14. If you were asked to examine 200 steel bolts, each ¾ x 3 inches with rolled threads, which penetrant method would you choose?

b. Water Washable

4. Vapor Degreasing

1. Spraying 2. Brushing

1. Detergent Cleaning 2. Paint removing

3. Steam Cleaning


Post-emulsification penetrantThis type of penetrant emulsification is accomplished by dipping the part in a chemical emulsifier prior to washing. The emulsifier will break down the penetrant and make it water soluble.

The emulsifier can be applied by Dipping or Spraying, but Not by Brushing. the bristles of the brush may enter the discontinuity.


Post Emulsification Penetrant ProcessA two step removal process. The emulsifier is usually applied by dipping or immersion. The amount of Dwell Time in the emulsifier is in the range of One to Fourminutes.

Post-Emulsification Penetrant

If Too Short an Emulsification Time is used, not all penetrant will be removed, which will cloud over discontinuities.

If Too Long a Time is used, penetrant within the discontinuities will also become water soluble and be washed away with excess penetrant.

The post emulsified penetrant makes the water wash less critical.

Water Washable Post EmulsificationPENETRANT

Developer Application

Some indications maybe visible prior to the application of a developer, but this step will ensure that all discontinuities are visible to the naked eye.

Developing is accomplished when a highly absorbent powder is applied to the item being tested after excess penetrant is removed.

The penetrant is actually drawn out of the discontinuity by the strong capillary action of the developer.

As shown here, the image of the discontinuity in the developer will Actually be Larger than the Actual Sizeof the discontinuity.


Wet DevelopersA. The Nonaqueous developer is held in suspension in a Solvent

Base and is usually supplied in pressurized cans.

B. Another type of wet developer holds the white powder in

suspension in a Water Base.

This type of wet developer is generally used with water washable or post emulsified penetrants and is applied by dipping or spraying. after application, a short time is allowed for the water to evaporate leaving a thin layer of white powder if an oven is used. the temperature should not exceed about 225° F as this could evaporate penetrant in the discontinuity.


l water soluble developers consist of a group of chemicals that are dissolved in water and form a developer layer when the water is evaporated away.

l The best method for applying water soluble developers is by spraying.l The part can be wet or dry. Dipping, pouring, or brushing the solution on to

the surface is sometimes used but these methods are less desirable.l Aqueous developers contain wetting agents that can lead to additional

removal of entrapped penetrant.l Drying is achieved by placing the wet but well

drained part in a recalculating warm air dryer with the temperature held between 70 and 75°F.

l If the parts are not dried quickly, the indications will be blurred and indistinct.

l Properly developed parts will have an even, pale white coating over the entire surface.


l Water suspendible developers consist of insoluble developer particles suspended in water.

l Water suspendible developers require frequent stirring or agitation to keep the particles from settling out of suspension.

l Water suspendible developers are applied to parts in the same manner as water soluble developers.

l The surface of a part coated with a water suspendible developer will have a slightly translucent white coating.

l Parts coated with a water suspendible developer must be forced dried just as parts coated with a water soluble developerare forced dried.


l Nonaqueous developers suspend the developer in a volatile solvent and are typically applied with a spray gun.

l Nonaqueous developers are commonly distributed in aerosol spray cans for portability.

l The solvent tends to pull penetrant from the indications.l Since the solvent is highly volatile, forced drying is not required.

l A nonaqueous developer should be applied to a thoroughly dried part to form a slightly translucent white coating.


Dry Developers - A dry developer is a Fluffy White Powder that is not carried in a liquid.

Dry developers are applied directly to the article as a powder, usually done with slight air pressure or articles may be dipped into a container of dry developer. Dry developer is usually used on Fluorescent Penetrants.

It is necessary to have a Dry Surfaceprior to application of a Dry Powder.

A wet surface will result in uneven layers of powder.


l Dry powder developer is generally considered to be the least sensitive but it is inexpensive to use and easy to apply.

l Parts can also be placed in a dust cabinet where the developer is blown around and allowed to settle on the part.

l Electrostatic powder spray guns are also available to apply the developer. The goal is to allow the developer to come in contact with the whole inspection area.

l Unless the part is electro-statically charged, the powder will only adhere to areas where trapped penetrant has wet the surface of the part.


l The penetrant will try to wet the surface of the penetrant particle and fill the voids between the particles, which brings more penetrant to the surface of the part where it can be seen.

l Since these developers only stick where penetrant is present, this developer does not provide a uniform white background like other developers.

l Having a uniform light background is very important for a visible inspection to be effective and since dry developers do not provide one, they are seldom used for visible inspections.

l With dry developers, indications tend to stay bright and sharp since the penetrant has a limited amount of room to spread.


Advantages of Developers

Wet Developers:Better on Smooth Surfaces where the dry developer will not adhere.

When a Wide, Shallow Discontinuity is sought, a wet developer will leave a more even coat of developer.

Dry Developers:On Rough Surfaces, and on Sharp Fillets, holes, and threaded articles, the wet developer tends to leave too much developer.

Lesson 4 Quiz

1. When using a post-emulsified penetrant, if too long a time is used for emulsification, penetrant within the discontinuities will be washed away with the excess penetrant.

2. During the rinse cycle, an emulsifier is added to a solvent-removable penetrant to make it water soluble.

3. Water-washable penetrants have a built-in emulsifier.

4. Post-emulsification penetrants are commonly available in both visibleand fluorescent dyes.

5. Post-emulsification penetrants usually require a two-step penetrant removal process.

True

True

False

True

True

Lesson 4 Quiz

6. The penetrant removal process with water-washable penetrants is very critical because of the danger of over-wash.

7. Solvent-removable penetrants are commonly used because they will withstand a very forceful water wash without the danger of over-wash.

8. An advantage of the solvent-removable penetrant is that the excess penetrant is easily removed by dipping the part in a tank of solvent solution.

9. Wet developers are usually chosen over a dry developer for use on a smooth surface.

True

False

False

True

Lesson 4 Quiz

10. A major advantage of the dry developer over wet is that is will not leave the same amount of excess build-up in threads and fillets.

11. The emulsification time required to detect wide or shallow discontinuities is usually longer than for finding narrow and deep discontinuities.

12. To avoid over-wash when using water-washable penetrants the water spray nozzle is usually held at a 90º angle to the surface.

13. When using a water-washable penetrant, the part must be completely dried in an oven (not in excess of 225º F) before the wet developer can be applied.

True

False

False

False

Lesson 4 Quiz

14. A major advantage of a Nonaqueous developer is that it can be applied to a part that is heated above 225º F without evaporation on the developer vehicle.

15. Solvent-removable fluorescent penetrants require the use of a rather time-consuming method of excess penetrant removal.

16. Post-emulsified visible dye penetrants commonly use both wet and dry developers.

True

False

False

Visual Acuityl Eye has a visual acuity threshold below which an object will go undetected.l This threshold varies from person to person, but as an example, the case of

a person with normal 20/20 vision can be considered.l As light enters the eye through the pupil, it passes through the lens and is

projected on the retina at the back of the eye.l Muscles called extraocular muscles, move the eyeball in the orbits and allow

the image to be focused on the central retinal or fovea.

Visual Acuityl The retina is a mosaic of two basic types of photoreceptors, rods, and cones.l Rods are sensitive to blue-green light with peak sensitivity at a wavelength of

498 nm, and are used for vision under dark or dim conditions.l There are three types of cones that give us our basic color vision, L-cones

(red) with a peak sensitivity of 564 nm, M-cones (green) with a peak sensitivity of 533 nm, and S-cones (blue) with a peak sensitivity of 437 nm.

Visual Acuity

l Cones are highly concentrated in a region near the center of the retina called the fovea region.

l The maximum concentration of cones is roughly 180,000 per square mm in the fovea region and this density decreases rapidly outside of the fovea to a value of less than 5,000 per square mm.

l The blind spot caused by the optic nerve is void of any photoreceptors.

Visual Acuityl The standard definition of normal visual acuity (20/20 vision) is the

ability to resolve a spatial pattern separated by a visual angle of one minute of arc. Since one degree contains sixty minutes, a visual angle of one minute of arc is 1/60 of a degree.

l The spatial resolution limit is derived from the fact that one degree of a scene is projected across 288 micrometers of the retina by theeye's lens.

l In this 288 micrometers dimension, there are 120 color sensing cone cells packed.

l Thus, if more than 120 alternating white and black lines are crowded side-by-side in a single degree of viewing space, they will appear as a single gray mass to the human eye.

Visual Acuity

l For normal visual acuity the angle Theta is 1/60 of a degree. By bisecting this angle we have a right triangle with angle Ø/2 that is 1/120 of a degree.

l Using this right triangle it is easy to calculate the distance X/2 for a given distance d., X/2 = d (tan Ø /2)

l When visually inspecting an object for a defect such as a crack the distance (d) might be around 12 inches. This would be a comfortable viewing distance. At 12”, the normal visual acuity of the human eye is 0.00349 inch.

l This means is that if you had alternating black and white lines that were all 0.00349 inch wide, it would appear to most people as a mass of solid gray.

Visual Contrast

The contrast sensitivity of the eye is important. Contrast sensitivity is a measure of how faded or washed out an image can be before it becomes indistinguishable from a uniform field.It has been experimentally determined that the minimum discernible difference in gray scale level that the eye can detect is about 2% of full brightness.Contrast sensitivity is a function of the size or spatial frequency of the features in the image. However, this is not a direct relationship as larger objects are not always easier to see than smaller objects as contrast is reduced as demonstrated by this image

Visual Contrast

The luminance of pixels is varied sinusoidally in the horizontal direction.The spatial frequency increases exponentially from left to right.The contrast also varies logarithmically from 100% at the bottom to about 0.5% at the top.

The luminance of peaks and troughs remains constant along a given horizontal path through the image. If the detection of contrast was dictated solely by image contrast, the alternating bright and dark bars should appear to have equal height everywhere in the image.However, the bars seem to be taller in the middle of the image.

Visual Acuity

l The color of the penetrant material is of obvious importance in visible dye penetrant inspection, as the dye must provide good contrast against the developer or part being inspected.

l The higher the contrast, the easier objects are to see.l The dye used in visible dye penetrant is usually vibrant red but other

colors can be purchased for special applications.

Visual Acuity

l PT materials fluoresce because they contain one or more dyes that absorb electromagnetic radiation over a particular wavelength and the absorption of photons leads to changes in the electronic configuration of the molecules.

l Since the molecules are not stable at this higher energy state, they almost immediately re-emit the energy. There is some energy loss in the process causing the photons to be re-emitted at a slightly longer wavelength, which is in the visible range.

l The radiation absorption and emission could take place a number of times until the desired color and brightness is achieved.

Visual Acuity

l Two different fluorescent colors can be mixed to interact by a mechanism called cascading.

l The emission of visible light by this process involves one dye absorbing ultraviolet radiation to emit a band of radiation that makes a second dye glow.

l Since the human eye is the most commonly used sensing device, most penetrants are designed to fluoresce as close as possible to the eyes' peak response.


l Fluorescent Dye penetrant inspection requires a room or booth with dim light and a Black Light with proper intensity.

InspectionProper lighting is the first consideration

l Visible Dye penetrant inspection requires adequate Normal Lighting with proper intensity.


l False Indicationsl The most common source of false indications is Poor

Washing.l The operator can easily tell when a good rinse is obtained

by using a black light during and after the fluorescent penetrant removal process.

TYPICAL INDICATIONSAll Indications found with will be Surface Discontinuities, but the indications may or may not affect the usefulness of the article.


l Penetrant on operator's hands.l Contamination of developer.l Penetrant transferred to clean

specimen from other indications.l Penetrant on inspection table.

False IndicationsAvoid The Following Contaminations:

Lint & Dirt Indication

Patch from Contact

Handling Mark

Fingerprints


l Are actual surface discontinuties.l In most cases are there by design.l They are caused by some feature of assembly such as

articles that are Press-Fitted, Keyed, Splined, or Riveted.

Nonrelevant Indications

l Nonrelevant indications could also include loose scale or a rough surface on a forging or casting.


True IndicationsThose caused by surface discontinuities that have been interpreted as not being false or nonrelevant.

True indications are subject to evaluation as to the Cause and the Effect they will have on the Service Lifeof the article.


1. Continuous Line - This type of indication is often caused by cracks, cold shuts, forging laps, scratches, or die marks.

2. Intermittent Line - These indications could be caused by any of thediscontinuities mentioned above provided they were very tight orwhere the part had been peened, machined, or ground.

3. Round - Usually caused by porosity open to the surface.4. Small Dots - Tiny round indications caused by the porous nature of

the specimen, coarse grain structure, or micro-shrinkage.5. Diffused or Weak - these indications are difficult to interpret and

often the part must be cleaned and retested. in many cases the diffused or weak indications turn out to be false indications caused by an improper penetrant procedure.

True IndicationsTrue indications could be divided into five basic categories:


Depth Determination of Penetrant Discontinuities

The greater the depth of a discontinuity, the more penetrant it will hold and the larger and brighter the indication.

Post-Cleaning

After the specimen has been inspected it is very important that it be thoroughly cleaned. Post-cleaning usually will involve the same types of cleaning operations as were used in pre-cleaning.

QC of Penetrant Test Materials

Aluminum Test Blocks - They provide a good means of evaluating general purpose penetrants. They should be used for Comparisons Only and not for absolute evaluations.

These blocks are non-uniform, and the depth and width of cracks are uncontrolled. the size of the blocks may vary but are about 3/8 by 2 inches of 2024-T-3 aluminum, about 3 inches long.

The blocks are Heated and Quenched to produce an overall Crack Pattern. They can be reused by reheating, quenching, and careful cleaning.


Sensitivity Tests - while there have been No Simple Quantitative tests developed for measuring penetrant sensitivity, a simple comparative test is usually adequate.

A small sample of the penetrant from the testing area is placed on one side of an aluminum test block. and a small sample of new penetrant on the other side, by visual observation it is determined if the old penetrant is contaminated to the point where it must be discarded.

Penetrant #1

Penetrant #2


Meniscus Test - A practical test for evaluating the dye concentration in thin-liquid films.

The test utilizes a flat glass platen and a convex lens. When a drop of solution is placed between the lens and platen, a colorless or non fluorescent spot is formed around the point of contact. The resultant contact angle simply indicates the ability of a liquid to wet a surface.


The Diameter of The Remaining “Spot" of colorless penetrant provides a measure of Film Thickness which can be used to compare the dye concentration of penetrants. Prolonged exposure of a film to ultraviolet light or accidental contamination by acids or alkalis will affect the dye concentration and therefore change the spot diameter.

Contact AnglePlaten

LensSpot

Penetrant


Ceramic Block Test-consists of an unglazed ceramic disc which has thousands of micro-pores and cracks on its surface.

A pencil mark is made on the block and a small amount of a test penetrant is placed on one side and a reference penetrant is applied to the other side. After the correct dwell time.

The two penetrants are compared in a side by side visual examination.

A Reduction in the number or apparent Brightness of Pore Indicationsshould be observed when comparing a fresh and old batch of penetrant.


Water Content Test - The ASTM standard D-95 describes a test where 100 ml of penetrant is placed in a boiling flask with a similar quantity of moisture-free Xylene. The condensate is collected in a graduated tube to show percent of water by volume.

If percent of water exceeds manufacturers' recommendations, the penetrant is discarded.

Viscosity Test - A Viscometer tube is used to measure the viscosity in centistokes to determine if the penetrant is within the range recommended by the manufacturer. A typical standard is ASTM D-445.


Fluorescent Penetrant Fade Test - The Aluminum Test Blocks in a side by side Comparison observation is used.

The fluorescent penetrant is placed on both sides of the block and processed normally. one half of the block is then exposed to a standard black light for one hour, while the other side is covered with paper.

The Fluorescent Brilliance of the two sides is observed and, if one side is noticeably less Brilliant, the penetrant is discarded.


Water Washability Test - This test evaluates the Efficiency of The Emulsifier by comparing two different percentage blends of penetrant and emulsifier.

A special steel block is placed at a 75° angle and the two blends are allowed to flow separately down the block, after a five-minute waiting period, the block is washed and examined for traces of remaining penetrant.


Dry Developers Test - Dry developers are simply visually inspected to see that they are not lumpy or caked instead of fluffy and light.

Wet Developers Test - Are often checked using a Hydrometer to assure that the density of the powder in the vehicle is within the range recommended by the manufacturer.

Lesson 5 Quiz

1. A typical false indication could be caused by an assembly that requires the components to be press-fitted.

2. Non-relevant indications could be caused by the rough surface on a casting.

3. Post-cleaning is necessary only when the part must be retested by theliquid penetrant method.

4. A typical true indication producing round indications is commonly caused by porosity.

False

False

True

True

Lesson 5 Quiz

5. Diffused or weak indications are often caused by subsurface discontinuities, and the part must be retested using a highly sensitive penetrant that will penetrant grain structure.

6. True indications are usually those that require evaluation to determine their effect on the service life of the part.

7. The aluminum test blocks used in penetrant evaluation are heated and quenched in water to produce a pattern of cracks on the surface.

8. The sensitivity tests used in penetrant inspection are relatively simple, non-quantitative, and require side-by-side visual observation.

False

True

True

True

Lesson 5 Quiz

9. The meniscus test utilizes a flat glass platen and convex lens to determine the dye concentration of a visible or fluorescent penetrant.

10. The ceramic block test uses an unfired ceramic disc to determine the apparent brightness of the spot diameter.

11. A special steel block, placed at a 75º angle, is used to check the effectiveness of the emulsifier.

12. Dry developer are often checked with a hydrometer to insure that they are still light and fluffy and not settled into a dense mixture.

13. The fluorescent penetrant fade test usually makes use of the aluminum test blocks to perform the test.

True

False

True

False

True

Lesson 5 Quiz

14. The filtered particle method of penetrant inspection used extra fine fluorescent particles that will not pass through a #120 sieve.Nonaqueous developer refers to a powder that is applied dry.

15. The depth of a discontinuity can be compared by observing the relative size or brightness of the indication.

16. Penetrant that has been transferred to a clean article from the indication on another article can cause a false indication.

17. Non-relevant indications often are actual surface discontinuities.

18. If a discontinuity is evaluated as being a true indication, the article should automatically be rejected.

True

True

False

True

False

Types of Discontinuities

Three General Categories:1. Inherent – Usually related to molten metal.

1. Inherent Wrought Discontinuities – Related to the melting and solidification of the original Ingot before forming to Slabs, Blooms, and Billets.

2. Inherent Cast Discontinuities - Relate to the melting, casting, and solidification of a cast article, usually caused by inherentvariables such as inadequate feeding, gating, excessive pouring temperature, and entrapped gases.


2. Processing Discontinuities - Are usually related to the various manufacturing processes such as Machining, Forming, Extruding, Rolling, Welding, Heat Treating, and Plating.

3. Service discontinuities - Are related to the various service conditions such as Stress Corrosion, Fatigue, and Erosion.

Remember: You can find only Open to The Surface discontinuities.

However, during the manufacturing process. many discontinuities that were subsurface can be made open to the surface by machining, grinding, and the like.

Remember: Discontinuities are not necessarily defects. Any indication found by the inspector is called a discontinuity until it can be identified and evaluated as to the effect it will have on the service of the part.


Main types of discontinuities found in Ingots:

• Porosity – Caused by entrapped gas in the molten metal.

2. Nonmetallic Inclusions –Caused by impurities accidentally included in the molten metal.

3. Pipe – Caused by shrinkage at the center of the Ingot as the molten metal solidifies.

Porosity

Nonmetallic Inclusion

Pipe

Ingot


l Ingot is further processed into slabs, blooms, and billets, it is possible for the discontinuities to change size and shape.

l As a billet is flattened and spread out, Nonmetallic Inclusions may cause a Lamination, pipe and porosity could also cause laminations in the same manner.


l Billet is rolled into bar stock, nonmetallic inclusions are squeezed out into longer and thinner discontinuities called Stringers.

Nonmetallic Inclusions


l As a Billet is rolled into round bar stock, surface irregularities may cause Seams. Seams are caused by folding of metal due to improper rolling or by a crack in the billet.


l Seam could also occur when the billet is formed into a rectangular bar.


Forging Discontinuities occur when metal is hammered or pressed into shape, usually while the metal is very hot. A forged part gains strength due to the grain flow taking the shape of the die.Forging Lap is caused by folding of metal on the surface of the forging, usually when some of the forging metal is squeezed out between the two dies.


Forging Burst is a rupture caused by forging at improper temperatures. Bursts may be either internal or open to the surface.

Internal Burst

SubsurfaceExternal Burst or Crack

Open to The Surface


Casting Discontinuities occur when molten metal is poured into a mold and allowed to solidify.Cold Shut is caused when molten metal is poured over solidified metal.

Cold Shut – Open to The Surface

Smooth, Curves Appearance


Hot Tears (Shrinkage Cracks) occur when there is unequal shrinkage between light and heavy sections.

Light (Small) Sections solidify and shrink faster than the heavy sections


Shrinkage Cavities are usually caused by lack of enough molten metal to fill the space created by shrinkage, similar to pipe in the ingot.


Micro-Shrinkage is usually many small subsurface holes that appear at the Gate of the Casting.Micro-Shrinkage can also occur when the molten metal must flow from a thin section into a thicker section of a casting.

Types of Discontinuities Blow Holes are small holes at the Surface of the Casting caused by gas which comes from the mold itself. Many molds are made ofsand, and when molten metal comes into contact with the mold, the water in the sand is released as steam.

Porosity is caused by Entrapped Gas. Porosity is usually subsurface but can occur on the surface depending on the design of the mold.

Types of Discontinuities Grinding Crack are a processing-type discontinuity caused by stresses which are built up from excess heat created between grinding wheel and metal.Grinding Cracks will usually occur at right angles to the rotation of the grinding wheel.

Types of Discontinuities Heat Treat Cracks are often caused by the stresses built up during heating and cooling and Unequal Cooling between light and heavy sections.Heat Treat Cracks have no specific direction and usually start at sharp corners which act as stress concentration points.Fatigue Cracks are service type discontinuities that are usually open to the surface where they start from concentration points.

Fatigue Cracks are possible only after the part is placed into service, but may be the result of porosity, inclusions or other discontinuities in a highly stressed metal part

Lesson 6 Quiz

1. The general category of processing discontinuities relates to discontinuities caused during manufacturing processes such as welding, extruding, and heat treating.

2. During the steel-making process the top of the ingot is usually removed to help eliminate such discontinuities as pipe, porosity and nonmetallic inclusions.

3. When a billet is rolled into bar stock, a nonmetallic inclusion could be formed into a longer and thinner discontinuity called a stringer.

4. Porosity in a billet could cause a lamination if the metal were formed into a flat plate.

True

True

True

True

Lesson 6 Quiz

5. Seams are usually subsurface discontinuities caused by improper rolling of a billet into round stock.

6. During the rolling of a billet into round bar stock, the grain in the metal forms perpendicular to the direction of rolling.

7. In the forging operation, under-heated metal will not allow the metal to flow properly and may cause “forging seams”.

8. Forging bursts are considered subsurface discontinuities and can never be inspected with liquid penetrant techniques.

9. Cold shuts are common discontinuities found in the forging process and are caused by inadequate heating of the forged part.

False

False

False

False

False

Lesson 6 Quiz

10. Blow holes are subsurface discontinuities commonly found in cast parts.

11. Because cold metal occupies more space than hot metal, there is the danger of “hot tears” during the casting process.

12. Porosity if often caused by entrapped gas that is expanded during the heating and pressing in the forging process.

13. Micro-shrinkage is often found at the gate of a casting and is usuallysubsurface.

14. Grinding cracks are usually at right angles to the direction of grinding and caused by the heat build-up between the grinding wheel and metal.

False

False

False

True

True

Lesson 6 Quiz

15. Heat treat cracks are often associated with stress concentration points on the part being heat treated.

16. Porosity may lead to a fatigue crack in a highly stressed part.

17. Crater cracks and tungsten inclusions are both associated with discontinuities formed during the welding process.

18. Lack of penetration and lack of fusion both refer to the same type of welding discontinuity.

True

False

True

True


Testing Method Selection is based upon variables as follows:

1. Type and origin of discontinuity.

2. Material manufacturing process.

3. Accessibility of article.

4. Level of acceptability desired.

5. Equipment available.

6. Cost associated.


Training and Certification

It is important that the technician and supervisor be qualified in the liquid penetrant method before the technique is used and test results evaluated.

The American Society for Nondestructive Testing (ASNT) recommends the use of its document recommended practice no. SNT- TC-1A.

This document provides the employer with the necessary guidelines to properly qualify and certify the NDT technician in all methods.

To comply with this document the employer must establish a “Written Practice" which describes in detail how the technician will be trained, examined, and certified.


Certification of NDT personnel is the responsibility of the Employer and is usually at three levels.

Level I is qualified to perform specific calibrations, specific tests, and specific evaluations according to written instructions.

Level II is qualified to set up and calibrate equipment and to interpretand evaluate results with respect to codes, standards, and specifications. Must be able to prepare written instructions and report test results.

Level III must be capable and responsible for establishing techniques, interpreting codes, and designating the test method and technique to be used. Must have a practical background in the technology and be familiar with other commonly used methods of NDT.


The SNT-TC-1A document recommends that the NDT technician be examined in the following areas:

A. General Examination.

B. Specific Examination.

C. Practical Examination

Training & Experience Requirement


Number of Number ofLevel I Level II

Test Method Questions Questions

Acoustic Emission Testing 40 40

Electromagnetic Testing 40 40

Laser Testing 30 30

Leak Testing 20 20

Liquid Penetrant Testing 40 40

Magnetic Particle Testing 40 40

Neutron Radiographic Testing 40 40

Radiographic Testing 40 40-

Thermal Infrared Testing 40 40

Ultrasonic Testing 40 40

Vibration Analysis 40 40

Visual Testing 40 40

General Examinations


Specific ExaminationsTest Method Level I Questions Level II Questions

Acoustic Emission Testing 20 20

Electromagnetic Testing 20 20

Laser Testing:

1. Profilometry 20 20

2. Holography/Shearography 20 20

Leak Testing:

1. Bubble Test 15 15

2. Absolute Pressure Leak Test(Pressure Change)

15 15

3. Halogen Diode Leak Test 15 15

4. Mass Spectrometer Leak Test 20 40

Liquid Penetrant Testing 20 20

Magnetic Particle Testing 20 20

Neutron Radiographic Testing 15 15

Radiographic Testing 20 20

Radiographic Testing 20 20

Thermal/Infrared Testing 20 20

Ultrasonic Testing 20 20

Vibration Analysis 20 60

Visual Testing 20 20

Lesson 7 Quiz

1. The selection of on test method over another is usually the decision of the Level I technician performing the test.

2. ASNT provides a service for examining Level I, II, and III personnel in the General and Specific areas.

3. The responsibility of issuing a certificate to the NDT technician is always given to the employer if the SNT-TC-1A document is to be complied with.

4. If the SNT-TC-1A document is to be used as a recommended guideline, the Written Practice must be submitted to ASNT for approval.

False

True

False

False

Lesson 7 Quiz

5. If the SNT-TC-1A guidelines are to be followed, the Level III technician should have a knowledge of other commonly used methods of NDT even though certification is needed only in the liquid penetrant area.

6. A Level I technician performing a liquid penetrant test is permitted to accept or reject the part provided that written instructions or procedures are given to him by a Level II or Level III certified individual.

7. To comply with the guidelines of SNT-TC-1A, all three levels of technicians must take a General, Practical, and Specific test ifexaminations are used to determine certification.

True

True

True

Lesson 7 Quiz

8. The June 1975 edition of SNT-TC-1A permits the employer to waive an examination for Level III personnel provided that documentation is on file showing the technician’s qualifications.

9. It is essential that every employer using the SNT-TC-1A document establish a Written Practice.

10. If an employer does not have a Level III technician in his company, he can retain the services of an outside agency to perform these functions.

True

True

True