ndt_sdp_1

Supervisory Development Programme-I(SDP-I)

Topic : Non Destructive Testing (NDT)

Faculty : Naveen Seth

L&T Heavy Engineering DivisonHazira

Outline

What is NDT ?

Where is NDT used ?

When is NDT used ?

Types of Discontinuities.

Common NDT methods.

NDT in L&T

Questions & Answers

What is NDT ?

NDT- Non Destructive TestingThe use of noninvasive techniques to determine the integrity of a material, component or structure or quantitatively measuresome characteristic ofan object.i.e. Inspect or

measure without doing harm.

What is NDT ? Contd.. The field of Nondestructive Testing (NDT) is a very broad, interdisciplinary field that plays a critical role in assuring that structural components and systems perform their function in a reliable and cost effective fashion. NDT technicians and engineers define and implement tests that locate and characterize material conditions and flaws that might otherwise cause planes to crash, reactors to fail, trains to derail, pipelines to burst, and a variety of less visible, but equally troubling events.

What is NDT ? Contd..

Because NDT allows inspection without interfering with a product's final use, it provides an excellent balance between quality control and cost-effectiveness. Technology that is used in NDT is similar to those used in the medical industry; yet, typically nonliving objects are the subjects of the inspections.

Where is NDT used ?

NDT is used where we need to ensure the serviceability of a specimen. That may be the use of a raw material such as a casting, the use of fabrication such as welding, or the use of a finished part or completed system. We apply NDT where we cannot afford the cost of a failure of the specimen because failure would be financially unacceptable or cause harm to us.

When is NDT used ?

NDT is used both before and after production of raw materials such as ingots and castings, before and after fabrication, and before and after assembly of parts into a completed system. Using NDT "before" prevents a substandard material or part from wasting time and increasing scrap production. The "when" is right if profit, quality, and safety are the result of using NDT.

Discontinuities

Definition : The change in the geometry or composition of an object, it may be intentional or unintentional.

Such changes inherently affect the physical properties of the object and may in turn have an effect on the objects ability to fulfill its intended use or service life.

Every discontinuity is not a defect but every defect is a discontinuity.

Discontinuities Contd…

The definition of defects changes with the type of component, its construction, its materials and the specifications or codes in force.

It is possible that discontinuity in one object may be defect in another.Detection of discontinuities is largely dependent on the discontinuity’s physical characteristics.


While performing NDT it is also important to consider how the material is produced, what manufacturing process are used to form the finished product and what discontinuities are typically initiated by the process operations. Discontinuity is categorized by the stage of manufacturing or use in which it initiates.


Discontinuity is categorized in four stages

Inherent discontinuities.

Primary processing discontinuities.

Secondary processing discontinuities.

Service induced discontinuities.


Inherent discontinuities :

When ferromagnetic materials are produced, molten metal solidifies into ingot form producing what is known as inherent discontinuities.

Such discontinuities then can be rolled, forged and section along with the material in its subsequent processing operations.

Inherent Discontinuities

Cold shut

Location : Surface or Subsurface

Cause : The meeting of two streams of liquid metal that do not fuse together.


Porosity


Cause : Entrapped gases during solidification of metals


Inclusions


Cause : Contaminant introduced during the casting process


Hot tears

Location : Surface

Cause : Restraints from the core or mold during the cooling process.

Segregation

Location : Surface or subsurface

Cause : Localized differences in material composition.


Primary Processing discontinuities :

Discontinuities those originate during hot or cold forming are said to be primary processing discontinuities. The processing of a wrought product by rolling, forging, casting or drawing may introduce specific discontinuities into the product and inherent discontinuity that were at one time undetectable or insignificant may propagate and become detrimental

Primary Processing Discontinuities (Weld)

Porosity


Cause : Vaporized constituents in the molten weld metal are entrapped during solidification.


Cluster Porosity


Cause : Vaporized constituents in the molten weld metal are entrapped during solidification.


Slag Inclusion

Location : Subsurface

Cause : Improper cleaning of previous weld pass and mixing of oxides on the base metal surface into the weld pool


Lack of Penetration


Cause : Inadequate penetration of the weld joint root by the weld metal.


Lack of Fusion

Location : Subsurface

Cause : Failure of filler metal to coalese with the base metal.


Suck Back


Cause : where the weld metal has contracted as it cools and has been drawn up into the root of the weld.


Internal Undercut

Location : Surface

Cause : Over sized weld pool (related to excessive amperage, travel speed and electrode size.)


External Undercut

Location : Surface

Cause : Over sized weld pool (related to excessive amperage, travel speed and electrode size.)


Offset or mismatch

Location : Surface

Cause : where two pieces being welded together are not properly aligned.


Cold / Hot Crack

Location : Surface or Subsurface.

Cause : A combination of atomic hydrogen, hardenable material and high residual stress.


Inadequate weld reinforcement

Location : Surface.


Excess weld reinforcement

Location : Surface.


Tungsten Inclusion

Location : Subsurface.

Cause : Molten weld pool or filler metal comes in contact with the tip of tungsten electrode.


Burn Through

Location : Surface.

Cause : Too much heat causes excessive weld metal to penetrate the weld zone.

Secondary processing Discontinuities Grinding Cracks

Location : Surface

Cause : Localized overheating of the material due to improper grinding procedures.

Heat Treating Cracks

Location : Surface

Cause : Uneven heating and cooling that produces stresses exceeding the tensile strength of the material.

Secondary processing Discontinuities

Quench Cracks

Location : Surface

Cause : Sudden cooling from elevated temperature

Pickling Cracks

Location : Surface

Cause : Residual stress being relieved

Service Induced Discontinuities

Fatigue

Location : Surface

Cause : Cyclically applied stress below the ultimate tensile strength.

Creep

Location : Surface

Cause : Material subjected to elevated temperatures and stress below the yield strength.

Service Induced Discontinuities

Stress Corrosion Cracking

Location : Surface

Cause : Combined effect of static tensile load and corrosive environment.

Hydrogen Cracking

Location : Surface

Cause : Combined effect of applied tensile or residual stress and hydrogen enriched environment.

Common NDT Methods

The most common NDT methods used are as

follows :

Ultrasonic Testing.

Magnetic Particle Testing.

Penetrant Testing.

Radiography Testing. Eddy Current Testing.

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 showing the depth of features that reflect sound.

f

plate

crack

0 2 4 6 8 10

initial pulse

crack echo

back surface echo

Oscilloscope, or flaw detector screen

Ultrasonic Testing

f

Ultrasonic Testing

A typical UT inspection system consists of several functional units, such as the pulsar/receiver, transducer, and display devices. A pulsar/receiver is an electronic device that can produce high voltage electrical pulse. Driven by the pulsar, the transducer generates high frequency ultrasonic energy. The sound energy is introduced and propagates through the materials in the form of waves. When there is a discontinuity (such as a crack) in the wave path, part of the energy will be reflected back from the flaw surface.

f

Ultrasonic Testing

The reflected wave signal is transformed into electrical signal by the transducer and is displayed on a screen. The reflected signal strength is displayed versus the time from signal generation to when a echo was received. Signal travel time can be directly related to the distance that the signal traveled. From the signal, information about the reflector location, size, orientation and other features can sometimes be gained.

Ultrasonic Testing

Types Of Sound Waves & Propagation

In solids, molecules can support vibrations in other directions so the number of different types (modes) of sound waves are possible. On the basis of particle displacement in the medium ultrasonic waves are classified as longitudinal waves , transverse waves , surface waves and lamb waves . Velocity remains the same in the given medium but differs when the method of vibration changes.


There are four types of sound waves :

Longitudinal - Parallel to wave direction

Transverse - Perpendicular to wave direction

Surface (Rayleigh) - Elliptical orbit symmetrical mode

Plate Wave (Lamb) - Component perpendicular to surface (extensional wave)


Longitudinal or Compressional Wave

These waves mostly used in the inspection of materials.The velocity of longitudinal waves is about 6000 m/sec in steel,1500 m/sec in water and 330 m/sec in air.

Longitudinal waves have particle vibration in a back and forth motion in the direction of wave propagation. These waves are readily propagated in the liquids,gases and elastic solids.


Transverse or Shear Wave

These wave have particle vibration perpendicular to the direction of wave motion.These waves will not travel through liquid, gases because force of attraction between molecules are too small . the velocity of these waves is about 50% the longitudinal waves for the same medium.


Surface or Reyleigh Wave

These waves travel along the flat or curved surface of relatively thick solid parts.The velocity of these waves are 90% of the transverse waves in the same material. Surface waves are useful for detecting surface cracks.Vibration of particle follow an elliptical path.


Plate or Lamb Wave

These waves also another type of ultrasonic waves used to detect surface defect and penetrates only upto half of wave length.These waves propagate in plate only.

Transducer or Probe in UT

The conversion of electrical pulses to mechanical vibrations and the conversion of returned mechanical vibrations back into electrical energy is the basis for ultrasonic testing. The active element is the heart of the transducer as it converts the electrical energy to acoustic energy, and vice versa.


Transducers or probes are very important tool in the system. They act through couplant.The sensitivity of a transducer is defined as its ability to detect smallest discontinuities and it is measured by the response of reflection from artificial discontinuity in reference block.Transducers are classified into groups according to the application.


Four basic types of transducers:

•

•

Immersion

Probe

Normal Probe

T/R Probe

Angle Probe

Couplant

A couplant is a material (usually liquid) that facilitates the transmission of ultrasonic energy from the transducer into the test specimen. Couplant is generally necessary because the acoustic impedance mismatch between air and solids, such as the test specimen, is large and, therefore, nearly all of the energy is reflected and very little is transmitted into the test material.

Couplant

The couplant displaces the air and makes it possible to get more sound energy into the test specimen so that a usable ultrasonic signal can be obtained. In contact ultrasonic testing a thin film of oil, glycerin or water is generally used and in immersion testing water is between the transducer and the test surface.

Probe Placement for several weld configuration

Main uses of UT

Used to locate surface and subsurface defects in many materials including metals, plastics, and wood. Ultrasonic inspection is also used to measure the thickness of materials and otherwise characterize properties of material based on sound velocity and attenuation measurements.

Advantages of UT It is sensitive to both surface and subsurface discontinuities.

The depth of penetration for flaw detection or measurement is superior to other NDT methods.

Only single-sided access is needed when the pulse-echo technique is used.

It is high accuracy in determining reflector position and estimating size and shape.

Minimal part preparation required.

Electronic equipment provides instantaneous results.

Detailed images can be produced with automated systems.

It has other uses such as thickness measurements, in addition to flaw detection.

Disadvantages of UT Surface must be accessible to transmit ultrasound.

Skill and training is more extensive than with some other methods.

It normally requires a coupling medium to promote transfer of sound energy into test specimen.

Materials that are rough, irregular in shape, very small, exceptionally thin or not homogeneous are difficult to inspect.

Cast iron and other coarse grained materials are difficult to inspect due to low sound transmission and high signal noise.

Linear defects oriented parallel to the sound beam may go undetected.

Reference standards are required for both equipment calibration, and characterization of flaws.

Magnetic Particle Testing

This NDT method is accomplished by inducing a magnetic field in a ferromagnetic material and then dusting the surface with iron particles (either dry or suspended in liquid). Surface and near-surface flaws produce magnetic poles or distort the magnetic field in such a way that the iron particles are attracted and concentrated. This produces a visible indication of defect on the surface of the material.

Magnetization

There are basically two types of magnetic field:

1. Longitudinal Magnetic field.

2. Circular Magnetic Field.

Magnetization

1. Longitudinal Magnetization : When the length of a component is several time larger than its diameter, a longitudinal magnetic field can be established in the component. The component is often placed longitudinally in the concentrated magnetic field that fills the center of a coil or solenoid. This magnetization technique is often referred to as a "coil shot."

Yoke for Longitudinal Magnetization

Magnetization

2. Circular Magnetization : when current is passed through a solid conductor, a magnetic field forms in and around the conductor. The following statements can be made about the distribution and intensity of the magnetic field.

The field strength varies from zero at the center of the component to a maximum at the surface.

The field strength at the surface of the conductor decreases as the radius of the conductor increases when the current strength is held constant. (However, a larger conductor is capable of carrying more current.)

Magnetization

The field strength outside the conductor is directly proportional to the current strength. Inside the conductor the field strength is dependent on the current strength, magnetic permeability of the material.

The field strength outside the conductor decreases with distance from the conductor.

Magnetic Fields

Circular Magnetic Field for Longitudinal Defects.

Longitudinal Magnetic field for Circular Defects.

Prods for Circular Magnetization

Examples of Magnetic Particle Indication

Indications of Cracks

Before and after inspection pictures of cracks

emanating from a hole


Indication of a crack in a saw bladeExamples of Magnetic Particle Indication

Indication of cracks running between

attachment holes in a hinge


Indication of cracks originating at a fastener hole


Magnetic particle wet fluorescent indication

of a cracks in a drive shaft


Magnetic particle wet fluorescent indication of a crack in a bearing


Main uses of MT

Used to inspect ferromagnetic materials (those that can be magnetized) for defects that result in a transition in the magnetic permeability of a material. Magnetic particle inspection can detect surface and near surface defects.

Advantages of MTLarge surface areas of complex parts can be inspected rapidly.Can detect surface and subsurface flaws.

Surface preparation is less critical than it is in penetrant inspection.

Magnetic particle indications are produced

directly on the surface of the part and form an

image of the discontinuity.

Equipment costs are relatively low.

Disadvantages of MT Only ferromagnetic materials can be inspected.

Proper alignment of magnetic field and defect is critical.

Large currents are needed for very large parts.

Requires relatively smooth surface.

Paint or other nonmagnetic coverings adversely affect sensitivity.

Demagnetization and post cleaning is usually necessary.

Penetrant Testing

Penetrant solution is applied to the surface of a precleaned component. The liquid is pulled into surface-breaking defects by capillary action. Excess penetrant material is carefully cleaned from the surface. A developer is applied to pull the trapped penetrant back to the surface where it is spread out and forms an indication. The indication is much easier to see than the actual defect.

http://www.ndt-ed.org/GeneralResources/MethodSummary/PT1.jpg

Steps of Penetrant Testing

1. Surface Preparation: One of the most critical steps of a liquid penetrant inspection is the surface preparation. The surface must be free of oil, grease, water, or other contaminants that may prevent penetrant from entering flaws. The sample may also require etching if mechanical operations such as machining, sanding, or grit blasting have been performed. These and other mechanical operations can smear the surface of the sample, thus closing the defects.


2. Penetrant Application: Once the surface has been thoroughly cleaned and dried, the penetrant material is applied by spraying, brushing, or immersing the parts in a penetrant bath.

Steps of Penetrant Testing3. Penetrant Dwell: The penetrant is left on the surface for a

sufficient time to allow as much penetrant as possible to be drawn from or to seep into a defect. Penetrant dwell time is the total time that the penetrant is in contact with the part surface. Dwell times are usually recommended by the penetrant producers or required by the specification being followed. The times vary depending on the application, penetrant materials used, the material, the form of the material being inspected, and the type of defect being inspected. Minimum dwell times typically range from 5 to 60 minutes. Generally, there is no harm in using a longer penetrant dwell time as long as the penetrant is not allowed to dry. The ideal dwell time is often determined by experimentation and is often very specific to a particular application.


4. Excess Penetrant Removal: This is a most delicate part of the inspection procedure because the excess penetrant must be removed from the surface of the sample while removing as little penetrant as possible from defects. Depending on the penetrant system used, this step may involve cleaning with a solvent, direct rinsing with water, or first treated with an emulsifier and then rinsing with water .


5. Developer Application: A thin layer of developer is then applied to the sample to draw penetrant trapped in flaws back to the surface where it will be visible. Developers come in a variety of forms that may be applied by dusting (dry powdered), dipping, or spraying (wet developers).


6. Indication Development: The developer is allowed to stand on the part surface for a period of time sufficient to permit the extraction of the trapped penetrant out of any surface flaws. This development time is usually a minimum of 10 minutes and significantly longer times may be necessary for tight cracks.


7. Inspection: Inspection is then performed under appropriate lighting to detect indications from any flaws which may be present.

8. Clean Surface: The final step in the process is to thoroughly clean the part surface to remove the developer from the parts that were found to be acceptable.

Main uses of Penetrant Testing

Used to locate cracks, porosity, and other defects that break the surface of a material and have enough volume to trap and hold the penetrant material. Liquid penetrant testing is used to inspect large areas very efficiently and will work on most nonporous materials.

Advantages of Penetrant Testing

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

Parts with complex geometry are routinely inspected.

Indications are produced directly on surface of the part providing a visual image of the discontinuity.

Equipment investment is minimal.

Disadvantages of Penetrant Testing Detects only surface breaking defects.

Surface preparation is critical as contaminants can mask defects.

Requires a relatively smooth and nonporous surface.

Post cleaning is necessary to remove chemicals.

Requires multiple operations under controlled conditions.

Chemical handling precautions are necessary (toxicity, fire, waste).

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 from an X-ray generator or a radioactive source.

Radiography Testing

High Electrical Potential

Electrons

-+

X-ray Generator or Radioactive Source Creates Radiation

Exposure Recording Device

Radiation Penetrate

the Sample

Radiography Testing

Radiography Testing

RT involves the use of penetrating gamma- or X-radiation to examine material's and product's defects and internal features. An X-ray machine or radioactive isotope is used as a source of radiation. Radiation is directed through a part and onto film or other media. The resulting shadowgraph shows the internal features and soundness of the part. Material thickness and density changes are indicated as lighter or darker areas on the film.

Top view of developed film

X-ray film

X-rays are used to produce images of objects using film or other detector that is sensitive to radiation. The test object is placed between the radiation source and detector. The thickness and the density of the material that X-rays must penetrate affects the amount of radiation reaching the detector.

Radiography Testing

Radiography Testing

This variation in radiation produces an image on the detector that often shows internal features of the test object.The part is placed between the radiation source and a piece of film. The part will stop some of the radiation. Thicker and more dense area will stop more of the radiation.

Main Uses of RT

Used to inspect almost any material for surface and subsurface defects. X-rays can also be used to locates and measures internal features, confirm the location of hidden parts in an assembly.

Advantages of RT

Can be used to inspect virtually all materials.

Detects surface and subsurface defects.

Ability to inspect complex shapes and multi-layered structures without disassembly.

Minimum part preparation is required.

Disadvantages of RT Extensive operator training and skill required.

Access to both sides of the structure is usually required.

Orientation of the radiation beam to non-volumetric defects is critical.

Field inspection of thick section can be time consuming.

Relatively expensive equipment investment is required. Possible radiation hazard for personnel.

Eddy Current Testing

Alternating electrical current is passed through a coil producing a magnetic field. When the coil is placed near a conductive material, the changing magnetic field induces current flow in the material. These currents travel in closed loops and are called eddy currents. Eddy currents produce their own magnetic field that can be measured and used to find flaws and characterize conductivity, permeability, and dimensional features.

Conductive material

CoilCoil's magnetic field

Eddy currents

Eddy current's magnetic field

Eddy Current Testing

Main Uses of Eddy Current Testing

Used to detect surface and near-surface flaws in conductive materials, such as the metals. Eddy current inspection is also used to sort materials based on electrical conductivity and magnetic permeability, and measures the thickness of thin sheets of metal and nonconductive coatings such as paint.

Advantages of Eddy Current Testing

Detects surface and near surface defects.

Test probe does not need to contact the part.

Method can be used for more than flaw detection.

Minimum part preparation is required.

Disadvantages of Eddy Current Testing Only conductive materials can be inspected.

Ferromagnetic materials require special treatment to address magnetic permeability.

Depth of penetration is limited.

Flaws that lie parallel to the inspection probe coil winding direction can go undetected.

Skill and training required is more extensive than other techniques.

Surface finish and roughness may interfere.

Reference standards are needed for setup.

Non-Destructive Testing Method & Application

Material

Flaw type

SurfaceCracks &Flaws

Sub-SurfaceCracks

&Flaws

Internal Flaws

&Discontinuities

Lack of bond

Of lock of

Fusion

Non-Metallic

Inclusions-

Slag, porosity

MaterialQuality

Laminations,Thickness

Measurement

FerrousComponents &Finished

M.T. U.T.E.T.

R.T.U.T. U.T. M.T.

U.T. U.T.

Non-ferrousComponentsFinished

P.T. U.T.E.T.

R.T.U.T.

U.T.E.T. U.T.

Aircraft FerrousComponents

R.T.M.T.E.T.

M.T.U.T.

R.T.U.T. U.T. M.T.

U.T. U.T.

AircraftNon-FerrousComponents

R.T.P.T.E.T.

R.T.U.T.

R.T.U.T. U.T. P.T. U.T.


Material

Flaw type


Sub-Surfac

eCrack

s &Flaws

Internal Flaws

&Discontinuities

Lack of bond

Of lock of

Fusion

Non-MetallicInclusions-

Slag, porosity

Material

Quality

Laminations,

ThicknessMeasureme

nt

FerrousForgings &Stampings

M.T.

M.T.U.T.

R.T.U.T.

R.T.U.T.

U.T.

Ferrous rawMaterials &Rolled products

M.T. M.T.U.T. U.T.

M.T.U.T. U.T.

Ferrous tube &pipe

M.T. E.T.

M.T.U.T. U.T. U.T. M.T.

U.T. U.T.


Material

Flaw type


Sub-Surfa

ceCrack

s &Flaws

Internal Flaws

&Discontinuities

Lack of

bondOr

lack ofFusio

n

Non-Metallic

Inclusions-Slag,

porosity

MaterialQuality

Laminations,

ThicknessMeasureme

nt

Ferrous welds

M.T.U.T. P.T.

U.T. R.T.U.T.

R.T.U.T.

R.T.U.T. U.T.

Steel castings M.T. M.T.

U.T.R.T.U.T.

R.T.U.T. U.T.

Iron castings M.T. U.T.E.T. U.T.

R.T.U.T. U.T. U.T.

Non-FerrousComponents &Materials

P.T.E.T.

R.T.U.T. U.T. P.T.

U.T. U.T.

NDT Facility at L&T Hazira

1. Ultrasonic TestingSr.no. Model Make Key Features

1 USM 25 S Krautkramer Recording and printing facility upto 200 nos of A-Scan displays

2 USD 15X Krautkramer Output for permanent recording

3 SS-130/230 Sonatest Multiple DAC and echo dynamics determinations

4 ISONICUDS 3.3

Sonotron Recording and printing of B & C scan, end view, TOFD and probe characteristic determination .

5 EX 10/100 EEC Printing of freeze wave form

6 USK 6/7 Krautkramer More gain reserve and more resolving power

NDT Facility at L&T Hazira

S.No M/c Description Capacity Quantity Key Features

1. LINAC/Mtsubishi

12.5MeV 1 Radiation thickness up to 500mm with micro seconds

2. X-Ray : Seifert

India Ltd.

450KeV 1 High sensitivity. Using in control rods (cd sandwich), for lower thick and nuclear jobs.3. 200KeV 1

4.Gamma ray/

Tech ops

Co.60 2NO. Radiation thickness up to 8” thickness.

5. Ir.192 2NO. Radiation thickness up to 3” thickness

6. AGFA GEVERT

AutoProcessor 2NO.

Reduce cycle time, optimum quality, easy to service, low chemical consumption

2. Radiography Testing.

NDT Facility at L&T Hazira3. Penetrant Testing.

Manufacturer Pre-Cleaner Penetrant Excess PenetrantRemover

Developer

P-Met,

Vadodra

Acetone-CommercialGrade

PP-15 PC-21 PD-31&31A

PP-110 PC-120 PD-130&PD-130 A

Pradeep,

Thane

Acetone-CommercialGrade

FLAW-GUIDEPenetrant-NP

FLAW-GUIDECleaner-NP

FLAW-GUIDEDeveloper-NP

MagnafluxAcetone-CommercialGrade

SPOTCHECKSKL-I SKC-I SPOTCHECK

SKD-S2

Questions & Answers

Thank You

ndt_sdp_1

Documents