IntroductionTo

NDT

BY: Omid HEIDARY

NDT Methods

Penetrant Testing

Magnetic Particle Testing

Eddy Current Testing

Ultrasonic Testing

Radiographic Testing

Acoustic Emission

Infrared Testing

Visual Testing

Other methods

NDT

Which method is the best ?

Depends on many factors and conditions

NDT

Industries involved with NDT:

•Oil and Gas

•Construction

•Metal Fabrication

•Chemical

•Aerospace

•Power Generation

•Transportation

•Medical

•Electronic

•Metal Manufacturing

•Composite Manufacturing

•Inspection and Testing

•Research and Development

•Training and Certification

Penetrant Testing

Surface Testing method

For detecting surface breaking defects (opened to surface)

Applicable to all materials -except for excessively porous (absorbing) materials

Also known as Dye Penetrant Inspection (DPI)

Penetrant Flaw Detection (PFD)

Liquid Penetrant Inspection (LPI)

Basic Steps

•Penetrant application

•Removal of excess

penetrant

•Pre-cleaning

•Application of

Developer

•Inspection

•Post-cleaning

Penetrant Testing

• Penetrating fluid (penetrant) applied to

component

Aerosol Spraying

Immersion Brushing

Electrostatic

Advantages of PT

Applicable to non-ferromagnetics

Able to test large parts with a portable kit

Batch testing

Applicable to small parts with complex geometry

Simple,cheap easy to interpret

Sensitivity

Disadvantages of PT

Will only detect defects open to the surface

Careful surface preparation required

Not applicable to porous materials

Temperature dependant

Cannot retest indefinitely

Compatibility of chemicals

Magnetic Particle Testing

Test method for the detection of

surface and sub-surface defects

in ferromagnetic materials

Magnetic Particle Testing

Equipment

Depth below surface

SN SN

Ultrasonic Testing

Ultrasonic Testing

High frequency sound sound waves are introduced into a material

Reflected sound gives information on the material under test and signals displayed on a CRT

Principle

What is Sound ?

A mechanical vibration

The vibrations create Pressure Waves

Sound travels faster in more ‘elastic’ materials

Number of pressure waves per second is the ‘Frequency’

Speed of travel is the ‘Sound velocity’

Sound at an Interface

Sound will be either transmitted across or reflected back

Reflected

Transmitted

Interface

How much is reflected and

transmitted depends upon the

relative acoustic impedance of

the 2 materials

VZ acoustic impedance

Steel

AirSteel

Air

Steel

Steel Aluminum

Steel

Large Acoustic Impedance

Ratio

Large Acoustic Impedance

Ratio

No Acoustic Impedance

Difference

Small Acoustic Impedance

Difference

Snell’s Law

Perspex

Steel

C

CS

If the angle of Incident is

increased the angle of

refraction also increases

Up to a point where the

Compression Wave is at

90° from the Normal

90° This happens at the

FIRST CRITICAL ANGLE

Probes

Compression / Longitudinal

Vibration and propagation in the same direction / parallel

Travel in solids, liquids and gases

Propagation

Particle vibration

Shear / Transverse Vibration at right angles / perpendicular to

direction of propagation

Travel in solids only

Velocity 1/2 compression (same material)

Propagation

Particle vibration

Ultrasonic Displays A scan

The CRT (Cathode Ray Tube) display

The Horizontal axis :Represents time base / beam path length / distance / depth

The Vertical axis :Represent the amount of sound energy returned to the crystal

Ultrasonic Inspection

defect

0 10 20 30 40 50

defect

echoBack wall

echo

CRT DisplayCompression Probe

Material Thk

initial pulse

The depth of the defect can be read with reference

to the marker on the screen

0 10 20 30 40 50 60

60 mm

Thickness / depth measurement

A

A

B

B

C

C

The THINNER the material

the less distance the sound

travel

The closer the reflector

to the surface, the signal

will be more to the left of

the screen

The thickness is read from the screen

684630

Scanning Procedure

Parent Material

0 degree both sides

To maximum range for angle probes

Full skip distance for 60 or 70 probes

Scanning Procedure

Weld Root

Half skip from both sides

For PCN exams :

70 degree probe at half skip from both sides

Scanning ProcedureWeld Fusion Faces

Half to full skip from both sides

A probe which strikes fusion faces at 90 degrees

Probe angle = 90 - (1/2 Root angle)

Defect OrientationONLY DEFECTS HAVING A SUITABLY ORIENTATED

REFLECTING SURFACE CAN BE DETECTED BY PULSE ECHO METHODS!!

Orientation favourable, sound reflected back to

point of origin

Orientation unfavourable, sound not reflected back

to point of origin

Ultrasonic Displays

B scan

The End View Display

B

Ultrasonic Displays

C scan

The Plan View Display

C

Ultrasonic Displays

D scan

The Side View Display

D

Advantages of UT

Sensitive to cracks at various orientations

Portability

Safety

Able to penetrate thick sections

Measures depth and through wall extent

Disadvantages

No permanent record (unless automated)

Not easily applied to complex geometries and rough surfaces.

Unsuited to course grained materials

Requires highly skilled and experienced technicians

Radiographic Testing

Radiographic Testing

Electromagnetic radiation is imposed upon a test object

Radiation is transmitted to varying degrees dependant upon the density of the material through which it is travelling

Variations in transmission detected by photographic film or fluorescent screens

Applicable to metals,non-metals and composites

Shorter Wavelength = Increased Energy

Shortening Wavelength

10-10 10-8 10-6 10-4 10-2 1cm 102 104 106 108

Wavelength

Electric

Waves

TV

Microwaves

Infra

red

Ultra

violet

Industrial

radiography

Electromagnetic Spectrum

Re

lati

ve

Inte

ns

ity M

ev.

Gamma line spectrum (discrete energies), the wave

length is not of a fixed nature. A number of frequencies

will be emitted for most sources.

Long Short

Co 60

1.17 to1.3 Mev

Ir 192

0.3 to 0.47 MevYb 169

0.06 to 0.2 Mev

Wavelength l

Wavelengths

7FE12

Step / Hole type IQI Wire type IQI

Radiographic Sensitivity

Radiation beam

Radiographic Inspection

Test specimen

Image quality indicator

Source

Radiographic film

Film

Source

Low dense

discontinuity

High dense

discontinuity

Lighter

region on

radiograph

Darker

region on

radiograph

The basis of radiography

Source

Film

Thin part

Thick

part

Darker

region on

radiograph

Lighter

Region on

radiograph

The basis of radiography

Radioactive isotope

It is small,typically 1mm x 1.5 mm cylinders,that give off gamma rays

It occurs in nature and also in artificial isotopes

Artificial isotopes are created by bombarding an element with an excess of neutron in the nuclear reactor.

Example of nature isotopes are radium and uranium

Example of artificial isotopes are iridium 192 and cobalt 60

MEASUREMENT OF RADIOACTIVITY

THE BASIC UNIT IS CURIE

IN SI UNIT, IT IS MEASURED IN BECQUEREL

1 CURIE = 3.7 X 1010 BECQUERELS

HALF LIFE OF AN ISOTOPE IS THE

TIME IT TAKES FOR 1/2 OF THE ATOMS TO DECAY

RADIOGRAPHIC FILM

IT HAS TWO TYPES

SLOW FILM

-FINE GRAIN AND NEED MORE EXPOSURE

FAST FILM

- LARGE GRAINS AND NEED LESS EXPOSURE

KNOWLEDGE OF FILM CAN HELPS THE RADIOGRAPHER TO WORK OUT EXPOSURES WHEN CHANGING FILM BRANDS. E.G IN TABLE 5.3

FILM ALSO SHOULD BE STORED IN EDGES, IN COOL DRY CONDITIONS AND AWAY FROM CHEMICALS OR RADIATION

Radiographic

Techniques

IQI’s should be placed source side

Film

Film

Single Wall Single Image

SWSI

IQI’s are placed on the film side

Source inside film outside (single exposure)

Film

SWSI panoramic

Single Wall Single Image Panoramic

Film

IQI’s are placed on the film side

Source outside film outside (multiple exposure)

This technique is intended for pipe diameters over 100mm

Double Wall single Image

DWSI

Film

IQI’s are placed on the source or film side

Source outside film outside (multiple exposure)

A minimum of two exposures

This technique is intended for pipe diameters less than100mm

Double Wall Double Image

DWDI

Base

Subbing

Subbing

Emulsion AgBr

Emulsion AgBr

Supercoat

Supercoat

Radiographic Film

Dev

eloper

Sto

p

bat

h Running water

MANUAL SYSTERM

PROCESSING FILM

Advantages of Radiography

Permanent record

Detection of Internal flaws

Can be used on most materials

Direct image of flaws

Real - time imaging

Disadvantages of Radiography Health hazard

Sensitive to defect orientation

Limited ability to detect fine cracks

Access to both sides required

Limited by material thickness

Skilled interpretation required

Relatively slow

High capital outlay and running costs