In Melbourne, as well as elsewhere in Australia, examination & qualification of welding inspection personnel is regulated by the Welding Technology Institute of Australia (WTIA). When a weld inspector becomes certified, it implies that he or she possesses a wealth of knowledge on various aspects, including:
- Welding codes as well as contract requisites
- Metallurgy, that is, corrosion resistance, ductility, strength, fatigue life, etc.
- Fundamentals of cutting, welding and joining processes & equipment
- Weld defects, reasons and remedies
- Procedure as well as performance qualification testing
- Test documentation such as WPQs, PQRs, etc.
- Fundamentals of NDT (non destructive testing) methods like ultrasonic testing, radiography, dye penetrant testing, eddy current, magnetic particle, and so on
- Pertinent drawings and symbols
Besides that, a certified individual also has the obvious ability of performing visual inspection.
If you are a newbie in the manufacturing industry and wondering why you need to hire a certified welding inspector, bear in mind that such a professional generally has a lot of experience in addition to weld-related knowledge. He or she can ensure that every phase of any project is conducted as per applicable specifications and codes.
Welding has a wide range of variables that consist of – arc current & voltage, travel speed, polarity, wire feed speed, joint geometry, base metal chemistry, position, filler metal chemistry, tensile strength, fracture toughness, hardness, ductility – and a neverending list. With the presence of all these interdependent variables, having a scientific quality control for welding is absolutely vital. And that is where the certified inspectors come in. A program proceeded with under the guidance of a licensed expert would ensure code compliance and systemic regulation of variables. Moreover, it is a very prudent business move to control the quality of manufacturing processes.
Throughout Australia, a number of high-profile industries, including those of the Aerospace, Oil & Gas, Defense, Energy, Transportation and Construction, necessitate certified inspectors. This is because stakes are generally high in such industries and aftermath of even a single failure can spell catastrophe. Presence of a certified welding inspector on site not only ensures compliance with code requirements, but also prevent weld failures.
Prior to the commencement of production welding processes, it is absolutely imperative to engage a certified welding inspector in advance. The professional would be entrusted with a number of responsibilities, including testing activities, setup before production, and so on. These kind of activities usually take some weeks for completing, and should be reviewed & approved before initiation of client’s production procedures.
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
- 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.
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.