Radiographic testing of welds- principle and procedure.

Whats is the procedure of radio graphic testing?

RT procedure

Radio graphic testing process:-


Index:-

  1. Introduction
  2. Basic principal of radio graphic testing
  3. Three basic essentials in producing a radio graph 
  4. Equipment’s required for the radiographic testing 
  5. Types of radigraphic testing
  6. Application
  7. Advantages 
  8. Limitations


Introduction:-


Radiography is a process of testing materials that uses penetration radiation such as x-rays or gamma rays. This allows examination of the interior of objects or assemblies that are opaque to the light. Radiography is called a nondestructive method of testing since objects that are tested are not damaged by the test and may still be used when the testing is completed.
In passing through the material, some of the radiation is absorbed or changed. The amount of absorption is dependent upon the thickness of the material, the density of the material, and the atomic number of absorber. Industrial radiography has grown out of engineering, and is a major element of nondestructive testing. It is a method of inspecting materials for hidden flaws by using the ability of short X-rays and gamma rays to penetrate various materials. Two ways to inspect materials for flaws is to utilize X-ray computed tomography or Industrial computed tomography scanning.

Basic principal of radiographic testing:-

In radiographic technique components are exposed to radiations of short wavelengths i.e. x rays or gamma rays. Generally X-rays are having wavelength less than 0.001*10-8 cm to 40*10-8 cm and Gamma rays from 0.005*10-8 to 3*10-8 cm which is produced from suitable sources such as X-rays tube or Cobalt-60.0
           X-rays that operate at 4000 kv can inspect casting having thickness up to 62 mm. Mostly, Gamma rays are produced by radium and radioactive isotope such as cobalt-60, Iridium-192, Caesium-167 and can inspect casting of bigger thickness than inspected by x-rays.

The three basic essentials in producing a radiograph are:-

1)  A source of radiation, usually x-rays or gamma rays
2)  The object to be tested
3)  A cassette containing the film.



Equipment’s required for the radiographic testing are as below:

1)  X rays or gamma rays source of radiation
2)  Specimen
3)  Cassette or film holder
4)  Film
5)  Screens
6)  Darkroom

 Types of Radigraphic testing

 

X-rays Radiographic procedure:-

Step 1:-
X-rays are procedure in an X-rays tube in which tungsten filament acts as cathode and water cooled copper block containing tungsten target acts as anode.
Step 2:-
The setup consists of a high voltage transformer, one end of which is connected to the filament and other to the ground.
Step 3:-
The filament (cathode) provides high velocity electrons which travels towards the target (anode), strike and are sudden stopped.
Step 4:-
Hence, kinetic energy of electrons is converted into radiation energy i.e. X-rays

 Fig. Arrangement of X rays radiographing for a welded joint

Gamma-rays Radiography procedure:-
Step 1:-
Gamma-rays are produced by radioactive decay of Radium and its salts and extensively used for testing of casting and welding joints.
Step 2:-
Radium and its salts or isotope such as Cobalt-60 decompose at a constant rate, producing gamma rays of shorter wavelength and are more penetration than X-rays.
Step 3:-
Cobalt-60 is an isotope produced by neutron irradiation and used in place of radium and it is cheaper than others.
Step 4:-
A very simple apparatus is required for Gamma rays radiography, in which cylindrical cobalt-60 sources with dimensions of 3 mm in diameter and 3 to6 mm in length are used.
Step 5:-
These sources are sealed in an appropriate container or capsule.
Step 6:-
From the source, gamma rays emitted in all the directions, so a number of separate casting having cassette containing film are disposed in a circle around the source that is placed in a central position as shown in figure below.
Step 7:-
Generally, the cassette containing film are fastened to the back of each component (here castings).

Fig. Gamma-rays radiography

Application:-

1)  Inspection of casting, forging and welds parts.
2)  Used to detect the cracks, broken wires, unsoldered connections, forging materials, etc. in semiconductor devices.
3)  Use to detect the change in material composition, measurement of thickness, etc.
4)  Use to detect cracks in electronic components, in missiles and power plant equipment.


Advantages:-
  1. Permanent records are provided on film by this method.
  2.  Thin and thick section can be tested.
  3. It is very sensitive method.
  4. Suitable for all types of materials.
  5. It is reliable method.
  6. Hidden flaws are detected.
  7. It is fast and accurate method of testing flaws.

    Limitations:-

  1. Set up cost is very high.
  2. Skill operators are required.
  3. Rays used for testing is harmful to human health.
  4. Small defect is cannot be detected.
  5. External power source is required for testing which produce rays.
  6. It can not detect the flaws if it is not parallel to the direction of the ray beam. 

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