Non Destructive Testing

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Non Destructive Testing

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Introduction to NDT

Transcript of Non Destructive Testing

Non Destructive Testing

Non Destructive Testing

What is Nondestructive TestingNon-destructive testing (NDT) is the testing of material to detect internal and surface defects or discontinuities using methods that do not damage or destroy the material under test.

i.e. Inspect or measure without doing harmWhere is NDT used?where we need to ensure the serviceability of a specimenwhere we cannot afford the cost of a failure of the specimen because failure would be financially unacceptable or cause harm to usexist to prevent injury or death to the human user of the tested item

Why we need NDT?Generally, NDT is employed in various industries for the following reasons;To prevent accidents and save human livesTo improve product reliabilityTo give profit to the user by;Ensuring customer satisfactionHelping in better product designControlling manufacturing processesLowering manufacturing processesMaintaining a uniform quality level

When is NDT used?NDT is used both before, during and after constructionUsing NDT "before or during construction" prevents a substandard material or part from wasting time and increasing scrap productionUsing NDT after to monitor performance after being service.

Basic Methods of NDT Visual Testing (VT)

Penetrant Testing (PT or DPI)

Magnetic Particle Testing (MT or MPI)

Ultrasonic Testing (UT)

Radiographic Testing (RT)

Eddy Current Testing (ET)

Eddy CurrentTestingVisualTesting

Other NDT methods;Leak testingStrain gaugingAcoustic emissionIR ThermographyLaser shearography

Visual Testing (VT) 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 & perpendicularity Standards, codes & specification

Visual Inspection tools

Inspection MirrorChecking Fillet Weld SizeChecking Weld ReinforcementChecking Bevel AngleChecking Fillet Weld Throat

Most basic and common inspection method.

Tools include Lights, Mirrors, fiberscopes, borescopes, magnifying glasses and CCTV.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 toolsPenetrant Testing (PT)The liquid is pulled into surface-breaking defects by capillary actionPenetrant solution is applied to the surface of a pre-cleaned componentSolidPenetrantAfter a period of time called the dwell time has elapsed, excess penetrant is carefully cleaned from the surfaceSolidPenetrantBasic Principles

A developer is applied to pull the trapped penetrant back to the surface where it spread out and forms an indicationThe indication is much easier to see than the actual defect

SolidDeveloperMain Uses of PTUsed to locate cracks, porosity and other defects that is open to the surface of a material.i.e. Fatigue cracks PorosityPin holes in weldQuench cracks LapsLack of fusion breakingGrinding cracks Seamsthe 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

Advantages and Disadvantages AdvantagesLow operator skillLarge surface can be inspected rapidly and at low costPortable, simple, cheap and easy to interpretApplicable to non ferrous material

DisadvantagesDetects only surface breaking defectsSurface preparation is critical as contaminant may mask defectNot applicable to porous materialPotential hazardous chemicals

Magnetic Particle Testing (MPI or MT)

Magnetic particle inspection is a method of locating surface and subsurface defects in ferromagnetic materialsBasic Principles A magnetic field is introduced in a ferromagnetic material. The magnetic lines of force travel through the material, and exit and reenter the material at the poles

Defects such as cracks or voids cannot support as much flux, and force some of the flux outside of the part creating flux leakage

Magnetic particles distributed over the component will be attracted to areas of flux leakage and produces a visible indication

FLUX LEAKAGES N

Electromagnetic YokeCrack IndicationsMain Uses of MTUsed 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 to welding, in process inspection of each weld pass, and to inspect repairIt 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 of the base metal

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 requiredUltrasonic Testing (UT)Basic Principles

platecrack0246810initial pulsecrack echoback surface echoOscilloscope, or flaw detector screenA typical UT inspection consist of pulser/receiver, transducer and display devices

Driven by the pulser, the transducer (probe) generates a high frequency ultrasonic (sound wave) energy and is introduced and propagates through the material Basic PrinciplesWhen there is a discontinuity (such as crack) in the wave path, part of the energy will be reflected back from the flaw surfaceThe reflected wave signal is transformed into electrical signal by the transducer and is displayed on the screenFrom the signal, information about the flaw location, size, orientation and other features can sometimes be gained

Main Uses of UTUsed to locate Internal 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 imagingAdvantages and Disadvantages AdvantagesCan be used in ferrous and non ferrous materialPortable with instant resultAble to detect subsurface defects, measure depth & through wall extentCan easily detect lack of sidewall fusion in welds

DisadvantagesHigh operator skill levelRequires calibration and difficult to interpretNot easily applied to complex geometryLinear defects oriented parallel to the sound beam may go undetectedRadiographic 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 SourceObjectFILMThe thickness and the density of the part affects the amount of radiation reaching the filmThicker and more dense area will stop more radiation to reach the filmThe film darkness (density) will vary with the amount of radiation reaching the film

Basic PrinciplesX-ray filmTop view of developed film = less exposure= more exposure

Images of Porosity on weld

Images of Slag on weldMain Uses of RTUsed 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

Advantages and Disadvantages AdvantagesMost material can be testedDetects internal flaw & give permanent recordAbility to inspect complex shapesGives direct images of flaw

DisadvantagesExtensive operator & film interpretation training & skill requiredAccess to both sides of the structure is usually requiredOrientation of the radiation beam to planar flaws is criticalRelatively high capital costRadiation Hazard to personnelEddy Current Testing (ET)Conductive material CoilCoilsmagnetic fieldEddy CurrentsEddy Currentsmagnetic fieldMATERIALFLAWPROBEPROBEPROBEPROBECRACK DETECTIONApplicationsInspect conducting materialsDetect surface and sub-surface discontinuitiesMeasure hardness and thickness of layer and thin sheet Sub surface flaw detectionMulti-layered aircraft structures.- Fuselage- Wings- Around FastenersPhase indicates flaw depthMagnitude indicates flaw severity at depth

Limitations Defect detection is limited to only few mm below surfaceDoes not indicate the shape of discontinuitiesConductivity measurementRaw materials sortingManufacturing process verificationHeat damageReference measurement