Page 263 - CITS - Welder - Trade Theory

WELDER - CITS

Recognition of any spurious effects in the radiograph arising from faulty exposure, handling of processing methods,
and Identification of any internal flaws in the specimen by their characteristic appearance in the radiograph. A
fourth and culminating stage exist that it is concerned with the assessment of the provable effect of any defect
upon the serviceability of the specimen.
The interpreter should have in mind the fundamental principles of the formation of radiographic images. Useful
indications are provided by
a The shape of the image
b The distribution of density of the image
c The direction of the incident rays upon the test object and upon the film.
To fulfill his task, the interpreter should know the fundamental characteristics of glass envelope. X-rays produced
leave the tube through a thinner glass window.
A KV control increases or decreases the applied voltage and the penetration is controlled by KV. Higher the KV.
greater the penetration.
A current control knob and meter top increase or decrease current supplied to filament. Increase current supplied
to filament. Increase of milliamp rage results in the hotter filament, more election emission and hence larger
quantity of X-rays. This decides the duration of exposure. A time controlled switch to control the exposure is
provide in the control panel.

film is used as the recording medium in radiography resembling a photographic film. The differences are due top
the penetrating nature of the energy involved and service conditions.
The base is made of polyesters and provides a transparent medium over which the sensitive emulsion may be
coated. The industrial radiographic film has a thicker and tougher base than the photographic film since they are
subjected to lot of handling during exposure.
Density : The function of emulsion coating is to produce opaque deposits when exposed to light or radiation. The
extent of deposit is expressed as density.

Density D= Log (li/lt)
Li = Intensity of Incident light
Li = Intensity of the emergent light Optimum density for an industrial radiograph is 2 to 4.
Exposure : It is the product of intensity of radiation and duration for which the energy was action on the film. To
express radiographic exposure, one has to give Kilo voltage, Mill amperes and Time in case of X-rays and type of
source, its strength in curies and exposure time in minutes for an isotope source.

Speed : Speed of the film is measured in terms of the log of exposure needed to produce a density of 1.0 in
Medical and 2.0 in Industrial radiographic film above the base density. The grain size of the Silver Halide Crystals
embedded in the emulsion control the speed. The larger the grain, the faster is the film. Sensitivity decreases with
increase in grain size.
Ultrasonic testing (UT) principles - Advantage - Limitations

Measuring Techniques- Standard reference blocks - Contact

Testing procedure - Indications and interpretations

Objectives : At the end of this lesson you shall be able to
• describe the principal of UTI
• explain the UTI equipments and machinery
• Explain the UTI measuring techniques.

Ultrasonic Testing :
Introduction: Mechanical vibrations which have frequency higher than the audible range of human car viz. 20 to 20
KHz are called ultrasonic waves. Unlike electromagnetic radiations, these waves require a medium and velocity
of propagation depends on the elasticity of the medium.

250

CITS : C G & M - Welder - Lesson 83 - 97 CITS : C G & M - Welder - Lesson 83 - 97