Introduction ofIntroduction of Non-Destructive Test

ENCE710 – Advanced Steel StructuresENCE710 Advanced Steel Structures

C. C. Fu, Ph.D., P.E.Department of Civil & Environmental Engineering

University of MarylandCollege Park, MDCollege Park, MD

Definition of NDT

The use of noninvasive techniques to determine qthe integrity of a material, component or structure

or quantitatively measuresome characteristic ofsome characteristic ofan object.

i.e. Inspect or measure without doing harm.2

What are Some Uses of NDE Methods?

Flaw Detection and Evaluation

Leak DetectionLeak Detection

Location Determination

Dimensional Measurements Fluorescent penetrant indication

Structure and Microstructure Characterization

Estimation of Mechanical and Physical Properties y p

Stress (Strain) and Dynamic Response Measurements

Material Sorting and Chemical Composition Determination

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When are NDE Methods Used?

There are NDE application at almost any stage in the production or life cycle of a component

To assist in product development To screen or sort incoming materialsTo monitor, improve or control manufacturing processesT if i h h tTo verify proper processing such as heat treatingTo verify proper assemblyTo verify proper assemblyTo inspect for in-service damage

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Nondestructive Testing

• AdvantagesCan test in service structures– Can test in-service structures

– Evaluate surface and internal conditions

– Cost efficient• Disadvantages

l b l ( d d l )– Reliability (measurements are made indirectly)– Qualitative

Requires a skilled professional for– Requires a skilled professional for interpretation of results

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Destructive Testing• Advantages

– Reliable (direct measurements)– Quantitative– Directly relates to material properties

Di d t• Disadvantages– Cannot test in-service structures

Requires a model– Requires a model• Costly & Time Consuming

– Multiple tests are sometimesprequired

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Six Most Common NDT Methods

• Visual• Liquid Penetrant

M ti• Magnetic • Ultrasonic• Eddy Currenty• X-ray

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Most basic and common

Visual InspectionMost basic and common inspection method.

Tools include fiberscopes,Tools include fiberscopes, borescopes, magnifying glasses and mirrors.

Portable video inspectionPortable video inspection unit with zoom allows

inspection of large tanks and vessels, railroad tank

Robotic crawlers permit b ti i h d

,cars, sewer lines.

observation in hazardous or tight areas, such as air ducts, reactors, pipelines. 8

Liquid Penetrant Inspection• A liquid with high surface wetting characteristics is

applied to the surface of the part and allowed time to seep into surface breaking defects.

Liquid Penetrant Inspection

seep into surface breaking defects.• The excess liquid is removed from the surface of

the part. • A developer (powder) is applied to pull the• A developer (powder) is applied to pull the

trapped penetrant out the defect and spread it on the surface where it can be seen.

• Visual inspection is the final step in the process• Visual inspection is the final step in the process. The penetrant used is often loaded with a fluorescent dye and the inspection is done under UV light to increase test sensitivity.g y

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Liquid PenetrationProcess:

Clean surfaceApply liquid penetrantRemove excess penetrantRemove excess penetrantApply developerInspectPost-cleaning

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DYE PENETRANTS

These are an aid to visual inspectioninspection

Will only find surface defects

Use correct type

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DYE PENETRANTSDYE PENETRANTS

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DYE PENETRANTSTypes

Red Flouresant

CAUTIONOil basedW t h blWater washable

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Dye Penetrant Test

• Dye penetrant testing locates minute surface cracks and porosity

• Dye types that may be used include:

Color contrast dye - which shows up under ordinary light

Fluorescent dye – which shows up under black light

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Fluorescent dye which shows up under black light

• The dye is normally applied by spraying it directly on the weld

(AISC & NISD 2000)

Magnetic Particle InspectionThe part is magnetized. Finely milled iron particles coated with a dye pigment are then applied to the specimen. These particles are attracted to magnetic flux leakage fields and will cluster to form an g gindication directly over the discontinuity. This indication can be visually detected under proper lighting conditions.

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Magnetic ParticleProcess:Process:

Magnetize surfaceDi ti iti tDiscontinuities create amagnetic flux

Sprinkle magnetic particlesInspectp

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Magnetic Particle Crack Indications

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MAGNETIC PARTICLEMainly for surface defectsSome sub surface defects can be foundfoundOnly ferrous metal

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Magnetic Particle Inspection

• Magnetic particle inspection uses powdered magnetic particles to indicatedefects in magnetic materials

• A magnetic field is induced in the part

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• The magnetic powder is attracted to and outlines cracks within the material

(AISC & NISD 2000)

RadiographyThe adiation sed in adiog aph testing is a

High Electrical Potential

X-ray Generator or Radioactive Source Creates

Radiation

The radiation used in radiography testing is a higher energy (shorter wavelength) version of the electromagnetic waves that we see as visible light. The radiation can come Electronsgfrom an X-ray generator or a radioactive source.

-+

Radiation Penetrate the Sample

Exposure Recording Device

p

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Fil R di hFilm RadiographyThe part is placed between the radiationThe part is placed between the radiation source and a piece of film. The part will stop some of the radiation. Thicker and

d ill t f thmore dense area will stop more of the radiation.

The film darkness

X-ray film

(density) will vary with the amount of radiation reaching the film through X ray film

= less exposure

g gthe test object.

Top view of developed film

= more exposureess e posu e

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Radiographic Images

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RADIOGRAPHICX-RAYGAMMA RAYElectro magnetic

radiation of short duration

Both of these methods are a danger to health

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Radiographic Inspection

• Radiographic inspection, or X-ray, can also be used to detect flaws inside welds

• Invisible rays penetrate the metal and reveal flaws on an x-ray film orfluorescent screen (above)

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fluorescent screen (above)

• This is the most costly of the inspection methods

(AISC & NISD 2000)

X- RAY

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X- RAY

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X-RAY VIEWERPictures taken are

viewed as negatives

will only give flat i i himage not in three dimensional

d k d tdarkened area must be used for viewingviewing

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Eddy Current Testing

Coil's

Eddy Current Testing

Coil magnetic field

Eddy current's

Eddy

ymagnetic field

Conductive

ycurrents

Conductivematerial

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Eddy Current TestingEddy current testing is particularly well suited for detecting surface cracks but can also be used to make electrical conductivity and coating thickness measurements.  Here a small surface probe is scanned over the part surface in an attempt to detect a crack.

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High frequency sound waves are introduced into a material

Ultrasonic Inspection (Pulse-Echo) High frequency sound waves are introduced into a material and they are reflected back from surfaces or flaws.Reflected sound energy is displayed versus time, and inspector can visualize a cross section of the specimen

finspector can visualize a cross section of the specimen showing the depth of features that reflect sound.

initial pulsepulse

crackecho

back surfaceecho

plate

crack

0 2 4 6 8 10

echo

Oscilloscope, or flaw detector screen 31

Ultrasonic ImagingHigh resolution images can be produced by plotting signal strength or time-of-flight using a computer-controlled scanning system.

Gray scale image produced using the sound reflected from the front surface of the coin

Gray scale image produced using the sound reflected from the back surface of the coin (inspected from “heads” side) 32

ULTRASONIC TESTINGThis uses high pitched

soundThe sound will not

pass through an air b b kgap so bounces back

and is picked up on a receiverreceiver

The reader is a oscilloscopeoscilloscope

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ULTRA SONIC Device

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Ultrasonic Inspection

• Ultrasonic inspection can be used to detect flaws inside welds

• High frequency sound waves are directed into the metal with a probe held at a• High frequency sound waves are directed into the metal with a probe held at aspecific angle

• The flaws reflect some energy back to the probe

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• Flaws show up as indications on a screen (above) and are subject tointerpretation by an inspector

(AISC & NISD 2000)

Ultrasonic

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Usage: Inspection of Raw ProductsForgings,Castings,Extrusions,etc.

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Usage: Inspection FollowingUsage: Inspection Following Secondary Processing

MachiningWeldingGrindingHeat treatingPlatingPlatingetc.

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Usage: Inspection ForUsage: Inspection For In-Service Damage

CrackingCorrosionErosion/Wear/Heat Damageetc.

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Usage: Power Plant InspectionUsage: Power Plant InspectionPeriodically, power plants are h td f i tishutdown for inspection.

Inspectors feed eddy current probes into heat exchanger tubes to check for corrosion damageto check for corrosion damage.

Probe

Signals produced by various

Pipe with damage

amounts of corrosion thinning.

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Usage: Storage Tank InspectionUsage: Storage Tank Inspection

Robotic crawlers use ultrasound to inspect the walls of large b d t kabove ground tanks

for signs of thinning due to corrosion.

Cameras on long articulatingarticulating arms are used to inspect underground

kstorage tanks for damage.

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Usage: Pressure Vessel InspectionUsage: Pressure Vessel InspectionThe failure of a pressure vessel can result in the rapid release of a plarge amount of energy. To protect against this dangerous event, the tanks are inspected using radiography and ultrasonic testing.

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Usage: Pipeline InspectionNDT is used to inspect pipelines to prevent leaks that could damage the en i onment Vis al inspection

Usage: Pipeline Inspection

environment. Visual inspection, radiography and electromagnetic testing are some of the NDT methods used.

Remote visual inspection using a robotic crawlera robotic crawler.

Magnetic flux leakage inspection. This device, known as a pig, is

Radiography of weld joints.

s de ce, o as a p g, splaced in the pipeline and collects data on the condition of the pipe as it is pushed along by whatever is being transported. 44