What is NDT?

The field of Nondestructive Testing (NDT) is a very broad, interdisciplinary field
that plays a critical role in assuring that structural components and systems perform
their function in areliable and cost effective fashion. NDT technicians and

Pipeline NDT Inspection

engineers define and implement tests that locate and characterize material
conditions and flaws that might otherwise cause planes to crash, reactors
to fail, trains to derail, pipelines to burst, and a variety of less visible, but
equally troubling events. These tests are performed in a manner that does
not affect the future usefulness of the object or material. In other words,
NDT allows parts and material to be inspected and measured without
damaging them. Because it allows inspection without interfering with a
product's final use, NDT provides an excellent balance between quality control and
cost­effectiveness. Generally speaking, NDT applies to industrial inspections. The
technologies that are used in NDT are similar to those used in the medical industry,
but nonliving objects are the subjects of the inspections.

 

What is NDE?

flange NDE inspection

Nondestructive evaluation (NDE) is a term that is often used interchangeably
with NDT. However, technically, NDE is used to describe measurements that
are more quantitative in nature. For example, an NDE method would not
only locate a defect, but it would also be used to measure something about
that defect such as its size, shape, and orientation. NDE may be used to
determine material properties, such as fracture toughness, formability,
and other physical characteristics.

 

Visual and Optical Testing (VT)

Visual and Optical Testing

The most basic NDT method is visual examination. Visual examiners follow
procedures that range from simply looking at a part to see if surface
imperfections are visible, to using computer controlled camera systems
to automatically recognize and measure features of a component.

 

 

 

Radiography (RT)

Pipe fitting RT

RT involves using penetrating gamma­ or X­radiation on materials and products
to look for defects or examine internal or hidden features. An X­ray generator
or radioactive isotope is used as the source of radiation. Radiation is
directed through a part and onto film or other detector. The resulting
shadowgraph shows the internal features and soundness of the part. Material
thickness and density changes are indicated as lighter or darker areas on
the film or detector.

 

Magnetic Particle Testing (MT)

Magnetic Particle Test

This NDT method is accomplished by inducing a magnetic field in a
ferromagnetic material and then dusting the surface with iron particles
(either dry or suspended in liquid). Surface and near­surface flaws disrupt
the flow of the magnetic field within the part and force some of the field
to leak out at the surface. Iron particles are attracted and concentrated
at sites of the magnetic flux leakages. This produces a visible indication
of defect on the surface of the material.

 

Ultrasonic Testing (UT)

Pipe fitting UT Inspection

In ultrasonic testing, high­frequency sound waves are transmitted into a
material to detect imperfections or to locate changes in material properties.
The most commonly used ultrasonic testing technique is pulse echo, whereby
sound is introduced into a test object and reflections (echoes) from internal
imperfections or the part's geometrical surfaces are returned to a receiver.
Below is an example of shear wave weld inspection. Notice the indication
extending to the upper limits of the screen. This indication is produced by
sound reflected from a defect within the weld.

 

Penetrant Testing (PT)

Pipe fitting PT inspection

With this testing method, the test object is coated with a solution that
contains a visible or fluorescent dye. Excess solution is then removed from
the surface of the object but is left in surface breaking defects. A
developer is then applied to draw the penetrant out of the defects. With
fluorescent dyes, ultraviolet light is used to make the bleedout fluoresce
brightly, thus allowing imperfections to be readily seen. With visible dyes,
a vivid color contrast between the penetrant and developer makes the bleedout
easy to see. The red indications in the image represent a defect in this component.

 

Electromagnetic Testing (ET)

Electrical insulation test

There are a number of electromagnetic testing methods but the focus here will
be on eddy current testing. In eddy current testing, electrical currents
(eddy currents) are generated in a conductive material by a changing magnetic
field. The strength of these eddy currents can be measured. Material defects
cause interruptions in the flow of the eddy currents which alert the inspector
to the presence of a defect or other change in the material. Eddy currents are
also affected by the electrical conductivity and magnetic permeability of a
material, which makes it possible to sort some materials based on these properties.
The technician in the image is inspecting an aircraft wing for defects.