by Andrew Brooks
NDT comes out of the cold–and cuts data volumes down to size
As a method of product inspection, non-destructive testing (NDT) has obvious advantages. Aside from the fact that whatever is tested isn’t expended in the process, saving money and time, NDT is steadily becoming more portable and user-friendly, enhancing its suitability for inline, in-process applications.
That said, NDT is still applied mostly in the field, where parts and components in active service are checked to see whether they need repair or replacement. The oil and gas and aerospace sectors are particularly heavy users. But for manufacturers and job shops, automation is making it increasingly practical to apply NDT inside the four walls.
The five most commonly used NDT methods are ultrasonic (UT), magnetic-particle, liquid penetrant, remote visual inspection, eddy-current testing and radiography, says John Zirnhelt, P.Eng., principal of Ponteca Inc., a welding and NDT service provider. “We’re adding to that now, but we’re also adding technology to the existing methods. For example, the principles of digital cameras are now being applied to radiographic cameras. Filmless radiography is a big advancing field, whereas it used to be film-based. Film hasn’t been totally replaced yet, but this is one of the big trends.”
One of the most important trends in NDT, as in many other fields, is computerization. “The instrumentation has become a lot faster and that’s made a lot of things possible now that weren’t possible 20 or 40 years ago,” Zirnhelt says. “Speeding up the process of inspecting the equipment, but speeding up the process of handling the data as well.”
Automation hasn’t changed the equipment itself all that much, says Peter Detmers, vice president of Mitutoyo Canada. “The parameters for measurement are the same. The automation functionality allows more measurements, which allows greater throughput, especially where 100 per cent inspection is required.”
Jérôme-Alexandre Lavoie, product manager for Creaform, agrees, noting that the goal isn’t so much to automate data acquisition but to automate data analysis.
“Three-dimensional scanning generates a lot of data–close to half a million data points per second,” Lavoie says. “It can be intimidating for people to learn how to get the information they need from that. That’s the main reason we’ve developed our software for NDT. We want to make it easier for pipeline engineers to extract the information.”
Automation is ‘external’ to the devices in another way. In markets such as oil and gas, companies use NDT methods to scan inside pipelines and other structures, where conventional 3D scanning can’t reach. Ultrasonic and phased array are a couple of the preferred methods, Lavoie says, with the added touch that the probe is often mounted on a robot or a gantry machine in order to get at hard-to-reach places.
“When you work with those technologies, you have to keep the probe very perpendicular to the surface that you are measuring. Otherwise the amplitude of the signal goes down very quickly and you can’t get a good reading.” The path for the robot or gantry machine can be drawn based on the CAD model of the part, but there’s generally enough of a difference between the model and the part that the path still doesn’t produce accurate results.
“We’ve worked with different companies, like Zetec and others, to directly give users a 3D scan–an STL [stereolithography] file with a triangulated surface of the physical part that they can use to do the simulation and extract the right path,” Lavoie says.
The operators who do the NDT measurements are usually being challenged to get the data as quickly as possible without compromising accuracy. That’s where the handheld 3D scanner becomes an NDT tool, Lavoie says. Scans can be done quickly and accurately, almost irrespective of the operator’s skill level. But there’s a downside.
“At the end of the day you have all that data, but you still have to decide if the asset needs to be repaired, replaced or left as is,” Lavoie says. “That decision-making process is complex enough when you’re using manual tools, but it’s even more complex when you have so much data and you’re not used to working with that volume of information.”
This dilemma has led to demand for highly specialized software. “People are looking to have application-based software that’s very specific – one shape, one code, one result that needs to be produced,” Lavoie says. “We want to have all that data processed with almost a single button click, so you can get the results you need without having to do large amounts of data processing.”
While most NDT activity still occurs in the field, manufacturing operations can also bring it in-house. The question is what is the threshold at which this becomes practical.
“Think of a ball bearing manufacturer, where when the ball bearings come off the line and they’re sorted electronically by eddy current NDT,” Zirnhelt says. “They go through a little coil and if there are any flaws it sends a signal and the line’s shut down until they rectify the problem. So I’m thinking big companies, like Linamar–they’d be using that.”
What about job shops? In most cases, the best alternative is to contract out to a service provider.
“If you develop an NDT specialist in-house, you have to provide a career path and invest in training and retention,” Zirnhelt says. “And the small guy usually just doesn’t have enough work. But a contractor has his people working in the field 100 per cent of the time. For them it’s just another two-day job; they’re only in for that contract.”
When looking for an NDT contractor, price should never be the main consideration, Zirnhelt says. “Look for company reputation. Too often you get people offering their services–but they have little or no experience.”
Look for continuity. “Don’t hire somebody where you get one guy coming in one day and someone else the next,” Zirnhelt says. “Make sure you’re going to get one or two technicians over the long term, so they get to know your products and processes.”
Certification is also high on the list. The national certification program is managed by Natural Resources Canada in accordance with the Canadian General Standards Board CAN/CGSB-48.9712-2014 Standard (Qualification and Certification of Non-Destructive Testing Personnel).
“That’s a pretty well established standard, so anyone who’s looking for an NDT inspector should look for that,” Zirnhelt says. SMT