Question

Q1) Identify five Nondestructive Testing methods and the principles that govern those

inspection techniques?

Answer 1

five Nondestructive testing (NDT) methods and their governing principles are:

Visual Inspection : The basic principle used in visual NDT is to illuminate the test specimen with light
usually in the visible region. The specimen is then examined with the eye or by
light sensitive devices such as photocells or phototubes. The equipment required
for visual inspection is extremely simple but adequate illumination is absolutely
essential. The surface of the specimen should be adequately visible before being
inspected.

Radiography testing:In radiographic testing, the part to be inspected is placed between the
radiation source and a piece of radiation sensitive film. The radiation
source can either be an X-ray machine or a radioactive source (Ir-192,
Co-60, or in rare cases Cs-137). The part will stop some of the radiation
where thicker and more dense areas will stop more of the radiation. The
radiation that passes through the part will expose the film and forms a
shadowgraph of the part. The film darkness (density) will vary with the
amount of radiation reaching the film through the test object where
darker areas indicate more exposure (higher radiation intensity) and
lighter areas indicate less exposure (lower radiation intensity).
This variation in the image darkness reveal the presence of any flaws or
discontinuities inside the material.

Ultrasonic testing:Ultrasonic testing is one of the major NDT methods used internal
discontinuities. Ultrasonic waves are waves of high frequency and inaudible to
human ears.

Ultrasonic experiences change in its propagation due to material properties and
presence of discontinuities. The resulting changes are detected by testing
system and displayed as an indication. Indications are analysed for acceptance
as per standard.these changes indicate the defect present in specimen.

Dye penetrant testing:A liquid penetrant or dye is applied on the test surface and it is allowed to seep
through the openings at the surface such as a crack or surface pore. After
sufficient time is given for the dye to seep through even minute opening, the
dye and the surface is removed. The dye that has seeped through the opening
comes out and is seen. To assist in the drawing out of the dye from the opening,
developer is applied which acts as a blotting agent for drawing the dye out and
acting as a contrast for seeing the coloured dye.

Magnetic Particle testing:The job is suitably magnetized and magnetic flux of enough density is made
available. Discontinuities in the path of the magnetic flux create a disturbance in
the uniform magnetic field causing flux leakage. The flux leakage sets up magnetic
poles and these poles attract iron powder when dusted over the testing zone and
form of a pattern of the discontinuity. The flaw is indicated as a pattern on the
surface giving the location and to some extent the nature of discontinuity. (Fig.1)
shows the flux leakage due to the presence of a flaw perpendicular to the
direction of the magnetic field.