Non-Destructive Testing – NDT Ultimate Guide

Plant Inspection October 11, 2021

What is Non-Destructive Testing?

Non-destructive testing or NDT refers to a range of inspection methods and tools or analysis techniques used in the science and technology industry to evaluate the properties of a material, system or component without altering it permanently or causing any damage.

When it comes to testing the integrity and proper functioning of mining equipment, NDT is considered incredibly useful. The reason for this is that NDT methods can be used to inspect the properties of a material without altering the item permanently or causing undue damage to it.

NDT saves companies time and money, making it a convenient time and money-saving product evaluation, troubleshooting, and research technique. It can also yield data useful for conducting a root cause analysis.

There are various NDT methods, although the ones most frequently used are eddy-current, liquid penetrant, magnetic-particle, radiographic, ultrasonic, and visual testing. These methods depend on the application of electromagnetic radiation, sound or other kinds of signal conversion for material inspection.

Aside from being widely used in the mining industry, different NDT methods are utilised in several other sectors, including aeronautical engineering, civil engineering, electrical engineering, mechanical engineering, medicine, petroleum engineering, and systems engineering.

Since NDT can be used in a wide variety of industries and applications, it is one of the most widely used analysis methods in modern scientific research and quality assurance.

Purpose of NDT

Non-destructive testing involves the inspection of a component or material in a cost-effective, reliable, and safe manner. It is a popular material testing method as it can often be done without the need to shut plant operations down, so a company does not lose income, and since it does not alter the structure of the material or damage it, NDT is considered safe.

The purpose of non-destructive testing is to detect, identify or measure the presence of certain elements like corrosion, surface cracks, sub surface cracks, or anomalies in the component being evaluated.

In the mining industry, there are several possible issues that can significantly impact the profitability and sustainability of mining projects. All projects rely on various equipment whose reliability and proper working condition are crucial for operations to proceed smoothly.

Therefore, regular testing is a primary concern among project managers and entire companies. Moreover, mining companies are also subject to Australian and internationally agreed sets of regulations and standards that they must always be in compliance with.

Components that can fail in a mining operation include electrical wiring, wire ropes, hydraulic cylinders, drills, bearings, circulating pumps, pressure vessels, cranes and motors. These need to be tested for flaws, especially since mining equipment tends to be complex, with many different moving parts. Even a seemingly insignificant flaw in any component, no matter how minute, can cause serious system-wide issues down the line.

It must also be noted that sometimes, the same assets may exhibit different failure behaviour depending on the environmental conditions. An example of this would be a completely, normally functioning asset in a highly silicified gold mine whose performance deteriorates substantially when used in a bituminous coal mine.

By using NDT to assess the materials used in different mining equipment components, project managers and companies can choose suitable products designed for optimum functionality, reliability, and suitability.

When to Use Non-Destructive Testing?

Non-Destructive testing is a growing analysis technique within the asset inspection industry employing specific methods to evaluate the condition of plant without causing damage to the equipment.

In recent years the plant inspection industry has recognised the value of NDT techniques in saving time and money in product evaluation, troubleshooting and research. In 2009 – 2013 the global NDT market size grew at a compound annual growth rate (CAGR) of 88% with a year-on-year growth rate of approximately 9%.

Successful and consistent application of NDT depends heavily on personnel training, experience and integrity. AME’s Perth Manager Grace Jenkins says successful NDT can only be carried out by qualified, experienced and knowledgeable personnel.

“Without experience in using NDT techniques, it can be easy to misread false indicators or non-relevant indications of what may look like a simple reading and approve a piece of plant as fine when in fact it has discontinuities.” Says Grace.

The first level of NDT is a comprehensive visual inspection, which although important, more in depth NDT techniques such as Ultrasonic Testing (UT), Eddy Current Testing (ET) and Magnetic Particle Testing (MT) can tell an experienced inspector if and what needs to be repaired.

NDT is carried out at all stages of the asset life cycle from the construction of plant and equipment through to regular testing during planned shut downs or at set intervals throughout its asset life to ensure compliance to the applicable standards and that there has been no deterioration of the plant or equipment between inspections.

NDT can even be used to determine the effective lifetime of plant and equipment by comparing how much deterioration has occurred between each testing interval.

Employing these processes as a preventive maintenance measure will enhance:

• Plant and equipment safety
• Site and personnel safety
• Compliance with Australian Regulations and Standards
• Prevention of loss of productivity in unplanned downtime
• Cost effective savings in simple repairs instead of complicated repairs or equipment replacement.

Destructive vs Non-Destructive Testing

The difference between destructive and non-destructive testing primarily rests on the fact that the former method is qualitative and NDT is not.

Destructive testing, being a qualitative analysis method, evaluates a material based on certain factors like elongation property, hardness value, impact toughness, tensile strength, and so on.

However, to be able to establish the aforementioned qualitative or mechanical properties, NDT methods cannot be applied. You will have to apply load on the material which, in turn, can damage or ruin the material, rendering it unusable.

Advantages of Non-Destructive Testing

When it comes to the advantages of non-destructive over destructive testing, the one benefit that stands out the most is the fact that NDT does not damage the material or component being inspected. Hence, if the material is intact or is fixed, it can still be reused.

This advantage helps companies minimise replacement costs, as subjecting the material or item to NDT ensures no physical damage during testing occurs.

NDT Types & Methods Explained

There are several types of non-destructive testing methods each with its own uses and limitations. Below are some types of NDT testing, including their pros and cons:

Eddy Current Testing (ECT)

Eddy current testing or ECT uses electromagnetic induction using AC current to detect surface and sub-surface flaws in conductive material. Eddy current array probes are customisable depending on the application and required coverage.

Some of the advantages offered by ECT include:

• Surface defect sensitivity
• Ability to detect defects in multi-layer structures
• Can locate defects in non-conductive surface coatings that are more than 5mm thick
• Precision in conductivity measurements
• Can be done using automated or semi-automated equipment
• Very little preparation time
• Portability

Meanwhile, some limitations of eddy current testing include:

• Highly susceptible to changes in magnetic permeability
• Useful only on conductive materials
• Inability to detect defects parallel to the surface
• Unsuitable for complex geometries or large sections
• Need for signal interpretation

➜ Learn more about Eddy Current Testing or check out our Eddy Current Testing Services

Ultrasonic Testing (UT)

The non-destructive testing ultrasonic method utilises high-frequency sound to detect internal material defects. Ultrasonic tests are widely used and considered indispensable in the mining industry.

UT offers the following benefits, particularly for the mining industry:

• Useful for analysing complex geometries
• Immediate results; relatively fast testing method
• High probability of critical defect detection
• Very reliable
• Can penetrate internal structures

Some limitations of UT include the following:

• Skilled technicians required for manual operation
• Impractical for use with rough, irregularly shaped, very small or thin materials
• Surface preparation or cleaning is necessary
• Couplants necessary for effective ultrasonic wave energy transfer
• Items under inspection should be water-resistant

➜ Learn more about Ultrasonic Testing

Magnetic Particle Testing (MPI)

Magnetic particle testing detects surface and near-surface defects in ferromagnetic materials like steel by using magnetic fields. Magnetic particle tests require the use of a fine pigmented ferromagnetic powder that becomes drawn into the magnetic leakage field caused by a flaw.

Advantages of magnetic particle testing techniques:

• Relative low cost
• Portability
• Ease of inspection
• Can be used to evaluate irregular shapes easily

Disadvantages of magnetic particle testing:

• Provides only surface and very near-surface indications
• Use is limited to ferromagnetic materials
• May require de-magnetization in certain situations

➜ Learn more about Magnetic Particle Testing

Liquid Penetrant Testing (LPT)

NDT liquid penetrant testing or dye penetrant inspection (DPI) is used to locate surface material defects through the application of a die penetrant and developer powder.

Advantages of the liquid penetrant testing method:

• Can be used on complex geometric shapes
• Sensitivity to minute surface flaws
• Wide applicability; can be applied to non-metallic, metallic, non-magnetic, magnetic, non-conductive, and conductive materials
• Testing materials very cost-effective
• Real-world results

Disadvantages of liquid penetrant testing:

• Time-consuming pre-cleaning is essential
• Sensitivity to surface interruptions only
• Connection to the surface being tested is necessary
• Only applicable to non-porous surface materials
• Depth sizing unavailable
• Multi-process, time-consuming method
• Recordable data unavailable
• Functions more as a screening tool

➜ Learn more about Penetrant Testing

Visual Testing (VT)

Visual inspection or testing depends on visual data to determine the status of a material. VT is one of the oldest methods of inspection and may be used for internal and external surface inspections.

Advantages of visual testing:

• Highly cost-effective
• Saves time
• Versatile; can be done using a remote visual inspection
• Minimal preparation

Limitations of visual testing:

• Highly trained inspectors are necessary
• Misinterpretation of flaws possible
• Limited to surface indications

➜ Learn more about Visual Inspection

Non-Destructive Testing Technology

Unlike other testing or inspection methods, non-destructive testing technology allows you to evaluate materials, structures, and components quickly and accurately without the need to apply load that can damage them and possibly even render them useless.

NDT involves the use of various tools, instruments, and technology to carry it out efficiently. Examples of these include the following:

• Thickness gauges
• Flaw detectors
• Material condition testers
• Eddy current instruments
• Devices that measure conductivity, resistivity, and corrosion
• Dye penetrants

The type of instruments, tools or materials used depends on the NDT method being carried out.

Whether you are conducting NDT for the testing and inspection of construction/minding equipment or plant components, NDT technology provides the following benefits:

• Enhances onsite safety and improves accident prevention measures
• Reduces the need for costly downtime
• Determines the structural integrity of your assets without causing damage or any negative repercussions
• Helps manage expenses by being a cost-effective and task-suitable solution
• Ensures quality control, consistent product reliability, and compliance with industry guidelines and client requirements
• Mitigates environmental risk posed by structural flaws and deficiencies
• Enables regulatory compliance by providing precise, objective results that show how your company adheres to industry standards

Australian Standards for Non-Destructive Testing

There are various Australian codes, rules, and regulations regarding NDT testing, such as the following:

• Australian Standard AS 3978-2003 – Non-Destructive Testing – Visual Inspection of Metal Products and Components – Western Australia
• Australian Standard AS 1710-2007 – Non-Destructive Testing – Ultrasonic testing of carbon and low alloy steel plate and universal sections – Test methods and quality classification
• Australian Standard AS 1710-2007 REC:2017 – Non-Destructive Testing – Ultrasonic testing of carbon and low alloy steel plate and universal sections – Test methods and quality classification
• Australian Standard AS 2083-2005 – Calibration blocks and their methods of use in ultrasonic testing
• Australian Standard AS 2083-2005 Rec:2017 – Calibration blocks and their methods of use in ultrasonic testing
• Australian Standard AS1171-1998 – Non-destructive testing – Magnetic particle testing of ferromagnetic products, components and structures
• Australian Standard AS4544-2005 – Non-destructive testing – Eddy current testing for the detection of surface flaws – Ferromagnetic and non-ferromagnetic metallic products

A complete list of the guidelines for non-destructive testing of metals and materials of Standards Australia is available in their Standards Catalogue.

AME NDT Technicians & Services

AME is a leading provider of NDT technicians and services.

Through the years, we continue to lend our technical expertise in the following industries:

• Ore Processing and Handling
• Refining
• Power Generation
• Fabrication
• Construction

Our NDT services are suitable for any and every stage of a project, from initiation through to ongoing maintenance and support. AME has a diverse range of inspection services to supply customers with manufacturing and maintenance inspection and testing support.

Our NDT services include Eddy Current Testing (ECT), Ultrasonic Testing (UT), Magnetic Particle Testing (MPT), Dye Penetrant Testing (DPT) and Visual Testing (VT).

For more information on our Perth NDT service enquire directly to speak to an AME specialist on 08 9446 7444.