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NEWS

Non-destructive testing

available

dvanced field services, transformer chemistry testing,
reliability solutions – these are some of the extra services
Aoffered by condition monitoring specialists, WearCheck, in
addition to traditional used oil analysis following recent expansion.
The company’s advanced field services (AFS) division Jaco Venter, a senior machinery inspector at WearCheck, conducts
incorporates specialist monitoring techniques such as rope ultrasonic testing on a winder’s brake components during a non-
testing, technical compliance, and non­destructive testing (NDT). destructive testing (NDT) routine.
Adri Ludick, NDT manager for WearCheck, outlines the
benefits and details of various non­destructive testing techniques.
“The NDT approach features a variety of testing techniques Liquid penetrant testing
through which the properties and condition of a component or This is typically performed on non­magnetic materials (e.g., copper, aluminium),
system are evaluated without causing any permanent damage to and is essentially a non­magnetic version of magnetic particle testing.
it. NDT is typically used in critical component assessments,
machine condition assessments and inspection of ancillary It involves a five­step process:
equipment such as main vent fans, compressors, mills, pumps, • The surface is cleaned of all foreign material.
and conveyors. • Next, it is saturated with a non­harmful penetrating ink. The surface does
“WearCheck’s NDT team delivers quality assurance and not have to be horizontal.
quality control of new as well as refurbished components. • The penetrant is wiped off the surface of the material. Fourth, a developing
“Our main array of NDT tests includes eddy­current­, chemical is applied over the ink.
magnetic­particle­, liquid penetrant­, radiographic­, ultrasonic­ • The developer draws the penetrant from any cracks to form a visible
testing and visual inspection,’ he says. indication.
The main advantage of NDT methods is that they do not • The component surface is visually examined during and after the
permanently alter the test object undergoing inspection, making development process and results are recorded.
NDT a valuable tool that can save both money and time in a
condition monitoring programme. This method is used to test such items as vehicle components and ventilation
fan blades.
Ludick explains some of the test methods in more detail:
Radiographic testing
Eddy-current testing This is like the X­rays used on humans but different types of X­ray sources are
This detects surface defects, such as early­stage cracks, on used which penetrate the material and display onto an X­ray plate behind the
metallic machine components, and is used across a wide range of component. It is a widely used technique which detects sub­surface defects
industries, from aerospace to beer brewing. which cannot be detected visually.
During the testing process, a high frequency electric current For thinner materials, such as a metal plate, a weak X­ray source is used,
(an eddy current) is induced into the material, then the response while thicker components (e.g., ventilation fan) require a stronger X­ray. The X­
of that eddy current field is measured. The information is ray sources are contained in a “bomb”, which is aimed at the target.
processed to yield a profile of the component. Radiographic testing is often used on welds to test the integrity of the bond
Defect­free material has a specific “fingerprint”, therefore, between the weld metal and the parent metal. Using an electronic form plate
when the test results are compared to this, the presence of defects instead of a photographic form is a new trend in this technique,
can be assessed.
When it comes to cracks, the earlier they can be detected, Ultrasonic testing
the less potential damage they can cause to the component. Like a “fish finder” on a fishing boat reveals the depth and size of the fish,
Eddy­current testing can detect crack formation at extremely ultrasonic testing uses similar methodology, allowing technicians to see sub­
early stages. surface defects in both metal and non­metal components. During the process, an
An advanced option is phased array eddy current testing, ultrasonic flaw detector instrument fires ultrasonic pulses into the material, and
which creates a 3D picture of the component, giving a more visual simultaneously detects the reflection. By measuring the time difference between
insight into anomalies. the pulse and the reflection and knowing the speed of sound in the test material,
you can pinpoint the location of the defect. It is widely used across all industries
Magnetic-particle testing to detect anomalies.
This is a similar application to eddy­current testing, in that both An advanced option is phased array ultrasonic testing, where, instead of one
techniques detect surface cracks on magnetic materials. This is pulse, 64 pulses are fired into the component. By fine­tuning the pulse­strength,
used across a wide range of industries. we can “steer” the beam in different directions. The advanced option enables us
The process in this test is to magnetise the component and to get a 3D picture of the component, instead of merely a pulse on a screen.
then saturate it with a very fine magnetised ink or a fine powder.
Any anomaly in the surface being tested causes a Visual inspection
concentration of the magnetic field around it, therefore drawing WearCheck’s highly experienced, well­trained technicians conduct a multitude of
the magnetic ink to the crack and making the defect visually visual inspections on a range of components daily. Their eyes are conditioned to
detectable. Eddy­current testing requires the interpretation of a recognise early­stage defects which are visible, and to identify potential
signal on an oscilloscope screen. “hotspots” which require further testing. n
An advantage of magnetic particle testing is that it can be
used to test very large surface areas, very quickly. Contact WearCheck, Tel 031 700-5460, marketing@wearcheck.co.za

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