Page 246 - CITS - Welder - Trade Theory

WELDER - CITS

used to test the human body. In fact methods from the medical field have often been adapted for industrial use,
as was the case with Phased array ultrasonic and Computed radiography.
While destructive testing usually provides a more reliable assessment of the state of the test object, destruction
of the test object usually makes this type of test more costly to the test object’s owner than nondestructive testing.
Destructive testing is also inappropriate in many circumstances, such as forensic investigation. That there is a
tradeoff between the cost of the test and its reliability favors a strategy in which most test objects are inspected
nondestructively; destructive testing is performed on a sampling of test objects that is drawn randomly for the
purpose of characterizing the testing reliability of the nondestructive test.
Non Destructive Testing (NDT) plays a significant part in maintaining the quality of the products at various stages
of manufacture. Raw material stage i.e. before the start of manufacture, intermediate stages, and final stage after
manufacture all utilizes Nondestructive testing techniques.
Since the 1920s, nondestructive testing has developed from a laboratory curiosity to an indispensable tool of
production. No longer is visual examination the principal means of determining quality. Nondestructive tests in
great variety are in worldwide use to detect variations in structure, minute changes in surface finish, the presence
of cracks or other physical discontinuities, to measure the thickness of materials and coatings and to determine
other characteristics of industrial products.
Modern nondestructive tests are used by manufacturers (1) to ensure product integrity, and in turn, reliability;
(2) to avoid failures, prevent accidents and save human life; (3) to make a profit for the user; (4) to ensure
customer satisfaction and maintain the manufacturer’s reputation; (5) to aid in better product design; (6) to control
manufacturing processes; (7) to lower manufacturing costs; (8) to maintain uniform quality level; and (9) to ensure
operational readiness
Methods And Techniques
NDT is divided into various methods of nondestructive testing, each based on a particular scientific principle.
These methods may be further subdivided into various techniques. The various methods and techniques, due
to their particular natures, may lend themselves especially well to certain applications and be of little or no
value at all in other applications. Therefore choosing the right method and technique is an important part of the
performance of NDT. Below are many NDT methods and they are merely mention to grasp the fact that NDT is
more vast and the method to be applied is specific for each and every application.
1 Visual Inspection
2 Dye penetrant test /Liquid penetrant testing D(PT or LPI)
3 Magnetic-particle inspection (MT or MPI)

4 Ultrasonic testing (UT)
5 Radiographic testing (RT)
6 Eddy-Current Testing (ECT)
Visual inspection - Visual inspection is observing the weld externally using simple hand tools and gauges to
know whether there is any external weld defects. This is one of the important inspection methods without much
expense. This method of inspection needs a magnifying glass, a steel rule, try square and weld gauges. Visual
inspection is made in three stages namely:
a Before welding
b During welding

c after welding
Visual inspection before welding
a The operator must be familiar with the type of work, electrode and welding machine.
b The following factors are to be ensured.

c The material to be welded is of weld able quality.
d The edges have been properly prepared for welding as per thickness of the plate.
e Proper cleaning of the base metal. Setting of proper root gap.

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