Ndt Lec 2 Rtpart1

INDUSTRIAL RADIOGRAPHY TESTING (RT) Lecturer: Dr. Ab. Razak Hamzah, Fabrication & Joining Section, UniKL MFI Bangi.

OUTLINES 1. Properties of X and Gamma Ray 2. Equipment for x-ray radiography 3. Equipment for Gamma Radiography

Electromagnetic Spectrum

103

10

10-1

10-3

Wavelength in cm 10-5 10-7 10-9

10-11

10-13

Visible Characteristic

light

X-ray Shortwave and microwave radiowave

10-7

10-5

10-3

ultraviolet infrared

10-1

10 103 105 Photon energy in eV

Soft

Penetrating

X-ray

X-ray

107

109

Radiography Testing (RT) • RT is an examination that uses a beam of penetrating electromagnetic radiation to create the shadow image of a specimen's internal and external structure. • Any examination that does not show apparent discontinuities is meaningless, misleading, and can create a false sense of security in a less than qualified product.

Properties of x- and gamma ray • Both are electromagnetic radiation with energy proportional to the wavelength • No electrical charge and mass • Travel in straight line • Can penetrate matter • Harmful to human tissues • Can fog radiographic film • Fluoresce in some material • invisible

EQUIPMENT FOR X-RAY RADIOGRAPHY

Generation of X-ray

Components in x-ray tube

• Envelope

– High melting point glass – High strength to withstand vacuum

• Cathode – Focusing cup + filament – Filament made of tungsten

• Anode – High thermal and electrical conductivity – Tungsten (high atomic number)1 or gold or platinum embedded in copper (high thermal and electrical conductivity and economic)

X-Ray Tube Glass envelope

Tube window

diaphragm X-ray beam Copper filter

X-ray tube

X-ray energy • Determine penetrating power • Depend on the energy of electrons striking the target • Control by kV • Increasing kV will increase energy thus penetrating power

X-ray intensity • Number of ray striking through a unit area in a given time • Changed with kV and mA • In practice controlled by mA • Increasing current increase the intensity of x-ray but not the energy

Effect of kV and mA on X-ray Output 100kV

2mA

50kV intensity

intensity

4mA

20kV 10kV

wavelength

wavelength

Varieties of X-ray tube

X-Ray Applications at various kV Voltage

Application

50kV

Wood, plastic, about 5mm thickness of steel Light material and alloys and about 100 mm aluminum Heavy section of light materials and 25 mm of steel Heavy section of steel, copper and 50 mm of steel Very heavy ferrous and nonferrous from 100 mm to 200 mm thick

100kV 150kV 250kV 10002000kV

Gamma Radiography Equipment

Introduction • Gamma is very penetrating thus useful for high density and thick materials, e.g. >19mm of steel (ASME Section V)

Radioisotopes for Radiography source

type

Radium Radon-222 Co-60 Cs-137 Th-170 Ir-192

Natural Natural Art. Art Art Art

Se-75 Yb-169

Art Art

halflife Energy (MeV) 1590yrs 3.28 days 5.3 years 33 years 127 days 74 days 120 days 32 days

0.6, 1.12, 1.76 0.6, 1.12, 1.76 1.17, 1.33 0.667 0.084 0.29, 0.58, 0.60, 0.61 0.12-0.97 0.008-0.31

Gamma Ray Spectrum

Intensity

Energy Discrete gamma ray line spectrum.

Source Encapsulation •Source in the form of pellets •Source to be as small as possible for sharp radiographs •Diameter of pellet: 0.5mm20mm •Length: 0.5-8mm •Could also spherical with diameter 6-20mm

SEALED SOURCE FOR RADIOGRAPHY

source assembly-pig tail

Factors Influencing the Selection of Radiography Source • Half life • Energy of gamma source • Size of the source • Specific activity • availability

TYPICAL GAMMA PROJECTOR Tripod stand

Model 660 exposure device Extender source guide tube

Model 693 control unit

Source stop Master source guide tube Model 661 control cable connector

Collimators • A device use to limit the emission of gamma to area of interest • Normally made of lead • reduce radiation levels • dose to radiographers is reduced • size of controlled area is smaller • dose of intruders into controlled area will be smaller

Examples of collimator

Advantages and Disadvantages of Using Radioisotopes (compare with x-ray) • Advantages

• Disadvantages

– Cheaper – Easier to transport – Smaller size allow to pass smaller diameter opening – Equipment is rugged and easy to operate – High penetrating power (good for thick material)

– Cannot be turned off – Produce less contrast radiograph – Energy cannot be varies – Need frequent replacement

Advantages • can be used for most materials • permanent visual image record. • disclose fabrication errors - provide information for correction. • reveal structural discontinuities and assembly errors.

Limitations • • • • •

High capital cost require electrical supply (for X-ray machine) safety hazard to personnel not sensitive to laminar type disc. require accessibility from both sides (film side and source side).

THANK YOU! Q&A

DR AB.RAZAK

31