Non Destructive Testing (NDT) covers a vast array of testing techniques used on materials without damaging them. These techniques are used on everything from large Plant and Machinery, Storage Tanks & Vessels to Aircraft and almost everything in between. The main advantage of Non Destructive Testing (NDT) is that it leaves the parent material, and hence structure, intact while still finding cracks, inclusions and other irregularities that indicate a possible problem. Non Destructive Testing (NDT) is not just for thickness testing on mine sites. Non Destructive Testing (NDT) is used to control Manufacturing Quality at production facilities, Plant and Machinery In-Service Inspections, Fabrication & Repair of structures and during Construction.

NDT Summary

AdvantagesNDT Method
[Main Uses]
Easy, minimal training required.Visual Testing (VT)
[In-Service inspections]
Limited to identifying obvious surface flaws.
Minimal Preparation.
Superior depth penetration.
Ultrasonic Testing (UT)
[Shell Thickness, Welds, Ball Studs]
Skilled technician required.
Surface finish can interfere.
Indications very visible. Rapid test method. Magnetic Particle Inspection (MT or MPI)
[Welds, Pressure Vessels]
Only for ferromagnetic materials.
Proper alignment of field and defect required.
Large and complex parts done rapidly.
Indications visible on surface.
Liquid Penetrant Testing (PT)
[Welds, QA/QC]
Only surface defects.
Handling of chemicals.
Can be used on virtually any material.
Can inspect multi layer and complex structures.
Radiographic Testing (RT)
[Pressure Vessel Welds]
Possible radiation hazard.
Access to both sides of material required.
Can be installed in hazardous areas and left.
Accessed remotely.
Acoustic Emission Testing (AE)
[Large Structures/Vessels]
Only detects active defects.
Skilled analyst required.
Minimum preparation required.
Detects surface and sub-surface defects.
Eddy Current (RT)
[Boiler Tubes]
Equipment relatively expensive.
Only conductive materials can be tested.
Accurate detection and sizing of defects.
All scan data recorded.
High Probability of Detection
Time of Flight Diffraction (ToFD)
ToFD rig can be difficult to handle in confined spaces.
Has blind spots which may require additional UT.

Non Destructive Testing (NDT)- Visual Testing (VT)

Visual inspection is the simplest and easiest of the Non Destructive Testing (NDT) methods. Since most Non Destructive Testing (NDT) methods require being at the test site, VT is used in almost all Non Destructive Testing (NDT) inspections. VT is an inspection to find surface discontinuities (cracks), corrosion, misalignment of parts, physical damage and other fabrication errors such as defective welds. VT may be enhanced via instruments such as magnifying glasses, scopes, boroscopes and mirrors.

Non Destructive Testing (NDT) – Ultrasonic Testing (UT)

Ultrasonic Testing UT defection of defect

Ultrasonic Testing (UT) defection of defect

While sharing the same theory as other ultrasonic devices such as Sonar and Medical Ultrasounds, Ultrasonic Testing (UT) is used in the Non Destructive Testing (NDT) industry to detect cracks and other abnormalities in a material. Most commonly this is used to check welds for cracks, inclusions, areas of non fusion and other indications. UT is used in conjunction with ‘In Service’ inspections regularly when an Inspector either requires the thickness of an item or thinks there may be a flaw due to surface observations. Critical welds on machines are also sometimes required to be tested depending on the Plant and Machinery’s Original Equipment Manufacturer (OEM) requirements. UT works by sending an Ultrasonic frequency wave through the material and then listening for the echoes from that wave. If there is a crack or flaw in the material, the echo will be interrupted. This shows on the UT set as an indication. Using both NDT training and experience, Technicians are able to identify the type of indications from the speed and amplitude of the wave received back. UT is an accurate form of NDT for thickness testing. Once the UT unit is calibrated to the material being tested, the time that the wave takes to return to the receiver indicates the depth of the material.

Non Destructive Testing (NDT) – Magnetic Particle Inspection (MT or MPI)

Ball Stud Magnetic Particle Testing Inspection MP MPI

Ball Stud Magnetic Particle Testing after UT identified a crack in-situ

Magnetic Particle Inspection (MPI) is used on ferrous materials only. The nature of the test requires a magnetic field to be created using the Electromagnetic Yoke. Only Ferromagnetic materials can do this. The other limitation of MPI is that it can only detect surface and near surface defects and cracks. For commercial MPI a solution is sprayed onto the surface which contains fine ferromagnetic particles. When the yoke is applied to the material it creates a magnetic field. Where there is a discontinuity in the material a flux leakage is created. This deforms the magnetic field created by the yoke. The magnetic particles sprayed on the surface are attracted to this flux leakage and create a visual indication.

Non Destructive Testing (NDT) – Liquid Penetrant Testing (PT)

Liquid Penetrant Testing PT Method

Liquid Penetrant Testing (PT) Method

Unlike MPI, PT can be performed on non ferrous materials. However it does not perform well on porous materials. This is because PT works by letting a liquid (the penetrant) seep into cracks or fissures in the surface. After a certain ‘dwell time’, excess penetrant is wiped from the surface. A developer is then applied. The developer is often a contrasting colour to the penetrant. During another ‘dwell time’ the penetrant is drawn into the developer, giving an indication at the point where a crack or fissure is. As the process implies, PT is only viable for surface penetrating defects. PT does however highlight porosity well, which is a common defect in welds.

Non Destructive Testing (NDT) – Acoustic Emission Testing (AE)

Acoustic Emission is a very under utilised Non Destructive Testing (NDT) method. It has been used effectively for decades in the aeronautical industry and off shore oil rigs in the North Sea. In Australia it has been used very little compared to the other NDT methods described above. AE works by attaching a series of small sensors to a structure, surface or vessel.

Acoustic Emissions AE

Acoustic Emissions (AE) defect location

These sensors act like microphones, listening for bursts of energy or noise. This noise can come from multiple sources such as active cracking, corrosion or system/ background noise. The one major advantage of AE is it can be installed and left in place for long periods of time, building a picture of the normal use of an item and hence finding any anomalies which may be identified as defects. When a crack in material is propagating, or growing, it releases energy which expands from the propagation point like a shock wave. The AE sensors pick up this energy and using the time difference, the source of energy can be triangulated. One example is a large LNG storage tank. By installing a series of sensors to the vessel’s walls and recording data from several loading and unloading cycles, the background and system noise can be separated from any other noise picked up by the sensors. What is left over may be identified as corrosion or even a potentially catastrophic crack forming.

Rapallo Non Destructive Testing (NDT)

Rapallo has experienced Non Destructive Testing (NDT) technicians and the equipment to carry out almost every NDT task imaginable. With over 25 years experience in Non Destructive Testing, Engineering and Inspections, Rapallo has the staff, equipment and capability to take on your projects.

Perth, Kalgoorlie and Western Australia Wide

Rapallo carry out Non Destructive Testing NDT through out Western Australia from the Goldfields to the Pilbara and the Perth surrounds via our Perth and  Kalgoorlie offices.

Rapallo Perth NDT

10 Elmsfield Road Midvale Western Australia

To discuss a job or estimate please call Stephen Niederberger on 08 6279 0900 Or email at

Rapallo Kalgoorlie Goldfields NDT

10 Broadwood St Kalgoorlie Western Australia

In the Goldfields call Henry Were Rapallo’s Level III NDT technician on 08 9021 8399 or email to discuss your NDT requirements.

For more info on Rapallo’s  Non Destructive Testing NDT capabilities click here.

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