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It would be safe to refer to stainless steel as an ubiquitous material, for the prime reason being the fact that it’s used for a manufacturing a great range of products - cooking utensils, jewellery, medical devices, automotive components, and what not! Most people prefer this material simply because it cannot rust. Contrary to popular belief, however, stainless steel products do rust or corrode, which can make a consumer question the authenticity of the items.

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Advantages Of Some Common NDT Tests

Non destructive testing methods are generally used for controlling the quality of various materials. These techniques help in detecting the presence of internal or surface flaws, or identifying metallurgical condition of materials without disturbing their integrity or suitability for an application in any way. They can be utilised either for individual investigation or checking a material entirely for production quality regulation.

At present, certain methods of non destructive testing in Melbourne are used extensively by various manufacturing industries. They include radiography, dye penetrant testing, ultrasonic flaw detection, magnetic particle inspection and eddy current electromagnetic induction. The suitability of these procedures are often determined by advantages that each offers.

So let’s take a look at the individual advantages of these methods:

Radiography

One of the reasons why radiographic testing has so high demand is because the results of the tests are presented pictorially. In addition to that, there are also permanent records of the procured information and they can be referred to anytime & anywhere. Radiography is appropriate for nearly any material and very effective for thin sections also.

Dye Penetrant Testing

Another popular NDT method, dye penetrating testing, is preferred particularly for its ability to ensure qualitative analysis. It is quite easy to execute and also highly effective for locating surface-breaking fissures in non-ferrous metals. The technique is also aptly suited for automatic testing.

Ultrasonic Flaw Detection

This commonly used non destructive method proves to be very useful when there is a need for testing thickness & length less than or equal to 30 feet. It can easily determine the type, size and position of defects. Being quite portable, it provides extreme sensitivity whenever necessary and can also be absolutely automated. It needs access to just one side of the surface, and consumables are normally not used.

Magnetic Particle Inspection

MPT is yet another easy-to-use quantitative testing method that can be viewed as well as automated. It also allows for using parts of automatic defect recognition like bars and billets, where a unique camera takes images of the defect.

Eddy Current Electromagnetic Induction

Eddy current testing is capable of determining several conditions of any conducting material, including hardness, permeability, composition, conductivity and defects. The information obtained from the test results are usually in easily comprehensible terms.

The above mentioned information comes in handy when there is a need to determine which NDT method would be ideal for a particular application.

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Developed during the 1930s in the United States of America, the magnetic particle testing (MPT) method of non-destructive tests was established to inspect steel components on the production lines. The main principle of MPT is magnetisation of the specimen for producing flux or magnetic lines in it. In case the flux lines encounter a discontinuity (like a crack), they create secondary magnetic poles at its faces. The places where the secondary fields appear on the metal surface can be visualised by spreading magnetic particles or liquid suspension on the surface. Once applied, the particles or suspension get attracted towards the flux leakage, clumping around it to make the flaw visible to human eye.

In a typical MPT, the particles used are generally black or have a coating of fluorescent dye on them for ensuring maximum visibility. The lines of the magnetic flux are normally at right angles in order to give a good indication of the flaw by establishing maximum flux leakage. This factor dictates the selection of an appropriate magnetising technique, which is used in different forms to get an absolute inspection.According to the welding experts providing non destructive testing in Melbourne, an MPT encompasses the following vital steps:

Pre-cleaning of the material

Demagnetisation, in case it has magnetic properties

Background contrasting paint application, if required

Magnetisation of the component

Application of magnetic inks or particle powders

Investigation of the surfaces for visible discontinuities

Demagnetisation, as well as re-magnetisation in case it’s necessary

Recording the defects

Demagnetisation

Cleaning and safeguarding

A defect or discontinuity on a steel component draws in more particles if it crosses a greater number of magnetic lines. As such, the ability to reveal a flaw always depends on its depth, its angle to lines of force and the induced magnetic field strength. Also, the magnetic particle testing method can be used only for ferromagnetic materials like nickel, cobalt and iron. Diamagnetic and paramagnetic materials are incapable of holding an adequate flux for attracting particles and therefore, produce no results with MPT.

The different kinds of electrical currents used for conducting MPT include alternating current (AC), full wave direct current (FWDC) and half wave direct current (HWDC). Out of them, HWDC is probably the best due to its high magnetic penetration ability. Detection of subsurface discontinuities using AC is limited because of the skin effect – tendency of the current to get distributed inside a conductor.

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From time to time, scientists and the welding industry have devised several methods for inspecting the quality of welds after their completion, such as ultrasonic testing, radiography, magnetic particle testing, liquid penetration and so on. Despite of the fact that these techniques are highly advanced and substantially effective at detecting flaws, there are still plenty of manufacturing firms throughout Victoria (and also Australia) that rely heavily on the traditional visual welding inspection technique.

Even in the modern times, the significance of a good old visual welding inspection cannot be ignored. In order to carry out the analysis, a qualified welding inspector usually remains present during the operation. It is his responsibility to make sure that standard quality welds are achieved, particularly by investigating condition of the electrodes, relevant certificates, weather condition, joint preparation, tools & machines used, slag cleaning, current, incomplete welds, etc. These steps cannot be assessed properly without thorough scrutiny by the human eye.

A typical visual welding inspection in Melbourne can help to save a lot when conducted properly, by nullifying the need for re-radiography and repairs. But in order to make that happen, the inspector taking care of the process requires to pay careful attention to every aspect. However, that is generally not a problem because most reputed welding inspectors possess the required qualifications and certification issued by the relevant authority. They are also aware of the necessary international & national standards and codes that they need to observe. For instance, pipeline welds are generally inspected as per API 1104 and so on.

Another vital reason why visual welding inspection has such substantial significance in the manufacturing industry is due to the fact that not all joints are picked for radiography once they have been completed. And any joint not inspected by radiography may have a flaw, which can cause a pipeline or plant operation to fail, ultimately spelling disaster. A faulty joint is incapable of handling the stress triggered by high temperature and pressure of the fluid inside it. But a joint that has been inspected visually is already flawless and can therefore, pose no threat even if not selected for radiographic testing.

Thus, it is clearly evident from the above mentioned information why visual welding inspection is given so much importance even today. Its efficacy cannot be championed even by uber-modern techniques like magnetic particle testing or dye penetration. It can stop weld defects even before they occur.