Non-destructive testing – a hidden world
For many, they are the unsung heroes of engineering: technicians who perform non-destructive testing (NDT) to ensure our safety and the integrity of components that are present in all walks of life.
Argyll-Ruane Ltd (ARL) is the leading name in the vital and far-reaching industry of NDT. Recently acquired by the Institution of Mechanical Engineers, ARL offers worldwide practical and theoretical training and examinations in NDT to all industry sectors including oil, gas, nuclear, rail, aerospace and automotive. The company also runs bespoke training and testing for a range of industry leaders.
Andy Kular has been working with Argyll-Ruane for over 13 years as centre manager and training coordinator at ARL’s Halesowen base in the West Midlands. His NDT background is in radiography for aerospace and general engineering, and he now delivers training in radiography, magnetic and penetrant testing. He’s keen to raise awareness of the vital work of NDT technicians, and to show how they are driven by issues of safety, maintenance and prolonging the service life of the machines and components that they test. In Andy’s experience, NDT is an essential part of every aspect of engineering.
What is NDT?
According to the British Institute of Non-destructive Testing (BINDT) it is: “The branch of engineering concerned with all methods of detecting and evaluating flaws in materials. The essential feature of NDT is that the test process itself produces no deleterious effects on the material or structure under test.”
NDT is important in guaranteeing safe operation as well as in quality control and assessing plant life. It ranges from simple techniques such as visual examination of surfaces, through the well established methods of radiography, ultrasonic testing, dye-penetrative testing and magnetic particle crack-detection, to new and specialised methods, such as the measurement of Barkhausen noise and positron annihilation.
Andy Kular explains that as well as various kinds of testing, there are different certifications. “It’s vital that testers are qualified and certified. All of our courses cover theory and practical, whether they are conducted onsite or offsite. Usually, our clients attend a course for initial certification, with recertification required after the prescribed interval. Many people certify in one field of inspection and return at another stage in their careers to learn other methods.”
NDT at every stage
Planning is the key to successful NDT. From the creation of a part, at every stage of its role in an element of machinery or plant, and throughout it’s service, NDT is vital.
Andy says, “It all starts with the manufacture of components. At the initial stages, a casting, for example, or a machined part, will need testing. But at every step in the part’s employment, it must undergo further tests and checks.”
Rail tracks are the obvious example: on any train journey we can see maintenance staff beside the tracks. Their responsibilities are to ensure shearing, distortion or corrosion hasn’t occurred, which could lead to accidents or delay. In some areas, specially designed trains perform this function, picking up and recording signs of defects as they travel along the tracks but NDT trained technicians will perform the majority of the work.
The pregnancy test
Components and parts rely on NDT to ensure efficient and safe operation. As with the human body, if there’s something wrong on the inside, it isn’t necessarily visible on the outside and the implications could be life-threatening.
A perfect non-engineering example of NDT – the crucial aspect of which is that, in carrying out checks, no disruption or distress is caused to the part tested – is the regular ultrasound appointments that a woman undergoes during pregnancy. Ultrasound is used to check the development of the foetus and detect any abnormalities. It is a perfect method, therefore, for checking, in a safe environment and at key stages, the development of the child without detrimental effect on the mother or baby.
It’s a principle that underpins all NDT methods: structured, timed testing which does not disrupt the smooth running of a process, but which does flag up problems if they are present but not necessarily visible.
Moving with the times
NDT methods have kept up with technological advances and made the work of technicians more streamlined and effective. Conventional methods, such as radiography and ultrasonics, have until recently been conducted using analogue equipment; now digital and computerised methods are in place. Ultrasound and advanced methods of ultrasonic testing are growing in applications and ARL promotes use of the most up-to-date inspection methods, such as TOFD (which stands for Time of Flight Diffraction) and Phased Array. TOFD uses two ultrasonic transducers, one transmitting and one receiving, while PA uses an array of ultrasonic transducers. Both are advanced testing methods that require extensive computer power and training above that of conventional level 2 certification.
Andy explains how one method of testing alone, for surface and subsurface (internal) flaws within a given component, is never enough. “For critical parts, there’s a minimum requirement for two separate inspections to be carried out. An example is a dye-penetrant that can only detect surface-breaking defects, so we need to carry out ultrasound or radiography tests for possible internal abnormalities. It’s double-checking and backing up: the goal is ensuring product quality and safety,” he says.
NDT and the global reach
ARL has three centres in South Yorkshire and one the West Midlands but NDT is, of course, practised globally. ARL works in partnership with operations in locations such as Greece, Malaysia, Kazakhstan, South Africa, Saudi Arabia and across a range of engineering sectors.
Bespoke training for NDT has been in place for many years. ARL operates Level 3 consultancy services, advising companies in specific and niche areas. Andy explains: “For example, a company we routinely work with makes turbine blades and they require internal checks for quality control and assurance purposes. Our advisory capability is provided in the form of an annual contract. This covers document and procedural changes, which come about in line with changes or amendments to international standards and practices, as well as pre-audit support on site. Our support and advice is pivotal to the company’s NDT procedures throughout the manufacturing process. Turbine blades must also be tested before being put into service, and whilst in service they are continually monitored for fatigue, cracking, and wear and tear.”
“Other companies, supplying parts to major aerospace manufacturers, might require support when changing written practices, for example, or approving new operating procedures, or in the certification of personnel.”
Getting into NDT
Andy started working in NDT when a chance request from a friend led to a short placement as a radiography assistant. He has worked in radiography testing and training for 15 years now. He says: “My recommendation, for anyone who has an interest in going into NDT as a novice, is to attend an NDT appreciation course. This is an introduction to a variety of methods and gives an eye-opening insight into what NDT is all about. Candidates can then choose which path to take: testing, training or even consultancy. We are seeing an increase in attendance on this course as it is valuable for engineers or managers who specify NDT, to know about what methods are available, as well as their advantages and limitations.”
ARL runs such introductory courses and, as a member of the BINDT committee for membership, qualification and education, Andy affirms that outreach is playing a part in recruiting a new generation. “BINDT is working with colleges and universities to express the importance of NDT in the modern world - this is one of our strategic objectives.”
Find out more
The Institution acquired ARL in November 2012 and is actively recruiting consultant NDT trainers. Could you become a consultant?
The Unseen World of NDT is short film, made by BINDT, which provides an introduction to the ways in which NDT affects all our lives. View it at: http://www.bindt.org/home/video.html