WELDING OPERATIONS I - OD1651 - LESSON 1/TASK 2
(b) Nondestructive Tests.
a This nondestructive test is used to check the quality of
welds on closed containers such as pressure vessels and liquid
tanks.
b One method of performing this test is to fill the vessel
with water and apply a pressure greater than the working pressure
of the vessel.
The outside surface of the vessel is then
observed for leaks through the welds.
To check welds in
nonpressurized tanks, they may be filled with water and observed
for seepage or leaks through the welds.
2 Magnetic Particle Test. This method of testing is used on
welds and parts made of magnetic alloy steels. It is applicable
only to ferromagnetic materials in which the deposited weld is
also ferromagnetic.
A strong magnetic field is set up in the
ferromagnetic specimen by an electric current. Any discontinuity
in the metal will set up a leakage field with local magnetic
poles of its own.
These poles then attract the magnetic
particles sprinkled on the surface of the specimen indicating a
discontinuity in the overall pattern of the magnetized specimen.
This discontinuity indicates that a defect, such as a crack,
exists on or close to the surface of the specimen.
3 Fluorescent
Penetrant
Test.
Fluorescent
penetrant
inspection is a nondestructive test whereby cracks, pores, leaks,
and other discontinuities can be located in solid materials. It
is
particularly
useful
for
locating
surface
defects
in
nonmagnetic materials such as aluminum, magnesium and austenitic
steel welds and for locating leaks in all types of welds. This
test makes use of a water-washable and highly fluorescent
material. This material is applied to the clean, dry surface of
the specimen by brushing, spraying, or dipping.
The excess
material is removed by rinsing, wiping with clean water-soaked
cloths, or by sandblasting. A wet or dry type developer is then
applied.
Afterwards, a black light is used to reveal
discontinuities in the weld specimen.
The discontinuities will
show up as brilliant fluorescent spots on the surface of the
specimen.
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