Introduction to Ndt Basic

8/9/2019 Introduction to Ndt Basic

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Introduction to Nondestructive

Testing


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What is Nondestructive Testing

Non-destructive testing is a method of

testing equipment and materials which

does not destroy them or effect their

future performance or properties

i .e . Inspect or measure wi tho ut doing harm


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What are Some Uses of NDT Methods?

• Flaw Detection and Evaluation

•

Leak Detection• Location Determination

• Dimensional Measurements

• Structure and Microstructure Characterization

• Estimation of Mechanical and Physical Properties

• Stress (Strain) and Dynamic Response Measurements

• Material Sorting and Chemical Composition Determination


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► Visual Inspection (VI)

► Penetrant Testing (PT)

► Magnetic Particle Testing (MT or MPI)► Ultrasonic Testing (UT)

► Radiographic Testing (RT)

► Eddy Current

Basic Methods of NDT


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Visual Inspection (VI)

► It is the most cost effective method of inspection

► Most basic and common inspection method

► Visual Inspection requires little equipment, to name a few;

Good eyesight & sufficient light

Welding Gauge

Pocket Rule, small steel rule

Inspection mirror

Square for checking straightness, alignment & perpendicularit

Standards, codes & specification


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Visual Inspection tools

Inspection Mirror

Checking Fillet Weld Size

Checking Weld Reinforcement

Checking Bevel Angle

Checking Fillet Weld Throat


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The following measurements are possible either in inches or millimeters

Weld Gauge or Bridge Cam Gauge

Angle of Preparation

Scale reads 0

to 60

in

5

increments.

Angle is read against the

chamfered edge of the dial.

Fillet Weld Throat

Small sliding pointer reads to 20mm

and 3/4".

Gage also fits flush in 90

corners.

Excess Weld Metal

Scale reads in Inches and Millimeters.

Gage is placed on lower peice and dial

rotated until it contacts higher piece

• Fillet weld throat size

• Fillet weld length

• Misalignment (high-low)

• Angle of preparation, 0º to 60º

• Excess weld metal (capping size)

• Depth of undercut

• Depth of pitting


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Penetrant Testing (PT)

• The liquid is pulled into surface-

breaking defects by capillary action

• Penetrant solution is applied to the

surface of a precleaned componentSolid

Penetrant

• After a period of time called the “dwell

time” has elapsed, excess penetrant iscarefully cleaned from the surfaceSolid

Penetrant

Basic Principles


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• A developer is applied to pull the trapped

penetrant back to the surface where it

spread out and forms an indication

• The indication is much

easier to see than the

actual defect

Solid

Developer


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Main Uses of PT

• Used to locate cracks, porosity and other defects that is open to

the surface of a material.

i.e. Fatigue cracks Porosity Pin holes in weld

Quench cracks Laps Lack of fusion breakingGrinding cracks Seams the surface

• Can be use to inspect almost any material provided that its

surface is not extremely rough or porous.

i.e. Metals, Glass, Ceramics, Rubber, Plastics


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Advantages and Disadvantages

Advantages

• Low operator skill

• Large surface can be inspected rapidly and at low cost

• Portable, simple, cheap and easy to interpret

•Applicable to non ferrous material

Disadvantages

• Detects only surface breaking defects

• Surface preparation is critical as contaminant may mask defect

• Not applicable to porous material• Potential hazardous chemicals


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Magnetic Particle Testing (MPI or MT)

Magnetic particle inspection is a

method of locating surface and

subsurface defects in ferromagnetic

materials

Basic Principles

A magnetic field is introduced in a

ferromagnetic material. The magnetic lines offorce travel through the material, and exit and

reenter the material at the poles


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• Defects such as cracks or voids cannot support as much flux,and force some of the flux outside of the part creating “fluxleakage”

• Magnetic particles distributed overthe component will be attracted to

areas of flux leakage and produces avisible indication

FLUX LEAKAGE

S N


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Electromagnetic Yoke

Crack Indications


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Main Uses of MT

• Used to inspect ferromagnetic materials( those that can be

magnetized) for surface defects and those that are slightly

subsurface (near surface defects)

• This method may be used to inspect plate edges prior towelding, in process inspection of each weld pass, and to

inspect repair

• It is good method for detecting surface crack of all sizes in

both weld and base metal, subsurface cracks, incomplete

fusion, undercut as well as defects on the repaired edges ofthe base metal


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Advantages and Disadvantages

Advantages• Pre-cleaning not as critical as PT

• Can detect surface and subsurface defects

• Relatively low equipment cost and simple equipment

• Possible to inspect through thin coating

Disadvantages

• Only ferromagnetic materials can be inspected

• Requires relatively smooth surface

• Proper alignment of magnetic field and defect is critical

• Demagnetization is usually required


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Ultrasonic Testing (UT)

Basic Principles

plate

crack

0 2 4 6 8 10

initial

pulse

crack

echo

back surface

echo

Oscilloscope, or

flaw detector

screen

•

A typical UT inspection consist of pulser/receiver, transducerand display devices


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• Driven by the pulser, the transducer (probe) generates a highfrequency ultrasonic (sound wave) energy and is introduced

and propagates through the material

Basic Principles

• When there is a discontinuity (such as crack) in the wave path,

part of the energy will be reflected back from the flaw surface

• The reflected wave signal is transformed into electrical signal

by the transducer and is displayed on the screen

• From the signal, information about the flaw location, size,

orientation and other features can sometimes be gained


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Main Uses of MT

• Used to locate surface and subsurface defects in many

material including metals, plastics and wood

• It is also used to measure the thickness of material

• Ultrasonic inspection has long been the preferred method for

nondestructive testing in welding application

• Ultrasonic scanning systems are used automated data

acquisitioning and imaging


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Advantages and DisadvantagesAdvantages

• Can be used in ferrous and non ferrous material

• Portable with instant result

• Able to detect subsurface defects, measure depth & through wallextent

• Can easily detect lack of sidewall fusion in welds

Disadvantages

• High operator skill level

• Requires calibration and difficult to interpret

•

Not easily applied to complex geometry• Linear defects oriented parallel to the sound beam may go

undetected


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Radiographic Testing (RT)

• Radiography is based on the ability of X-

rays and gamma rays to pass through

metal and other material.

• The object is placed is placed between

radiation source and a piece of film.

Basic Principles

Radiation Source

Object

FILM


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• The thickness and the density

of the part affects the amount

of radiation reaching the film

• Thicker and more dense area

will stop more radiation toreach the film

• The film darkness (density)

will vary with the amount of

radiation reaching the film

Basic Principles

X-ray film

Top view of developed film

= less exposure

= more exposure


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Welding Consumable

Images of Porosity on weld


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Images of Slag on weld


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Main Uses of RT

• Used to inspect almost any material for surface and

subsurface defects

• Radiography can also be used to locate and measure internal

features of material

• It can also be used to confirm the location of a hidden parts in

an assembly and to measure thickness of materials


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Advantages and DisadvantagesAdvantages

• Most material can be tested• Detects internal flaw & give permanent record

• Ability to inspect complex shapes

• Gives direct images of flaw

Disadvantages

• Extensive operator & film interpretation training & skill required

• Access to both sides of the structure is usually required

• Orientation of the radiation beam to planar flaws is critical

•

Relatively high capital cost• Radiation Hazard to personnel

Documents

Introduction to Ndt Basic