A sound way to detect defects

A 100+ metre wind turbine tower is made up of 30 or more massive ring sections held together by more than 25km of welding. At present inspecting welds on a big structure like this and correcting any flaws is a slow and laborious process.

“Our only option is to grind flaws out and do big repair welds; not just unsightly but costly and time consuming,” said Dr Alan Thompson, manager of welding technology for Long Products at Tata Steel Europe.

Tata, TÜV Rheinland Sonovation and the Nuclear AMRC (Advanced Manufacturing Research Centre) came together to find a solution for this problem – in response to an Innovate UK competition to find improved manufacturing solutions for offshore wind energy structures

Putting welding to the test

Innovate UK funded a feasibility study to explore whether non-destructive testing (NDT) could be carried out during high temperature welding  – looking at two areas, offshore energy and nuclear applications, where real-time testing to assure the quality and integrity of welding could bring real benefits.

Offshore wind turbines are largely constructed from massive steel pipes welded together from multiple ring sessions – not just the visible tower, but also the below-water structure that supports it and anchors it to the seabed. Real-time inspection to ensure the welds can stand up to the harsh conditions offshore not only boosts safety but considerably cuts the time and costs of reworking.

Similarly, in nuclear applications, being able to test welding during the high temperature process would confirm their integrity and enable flaws to be corrected immediately – important in an industry where safety is absolutely paramount.

The result of the study is an innovative, proven NDT process, which tests for flaws during the welding process, reducing time and money spent on repairs and improving not just aesthetics but build integrity and safety.

Integrating a sound solution

The consortium’s solution was to integrate defect testing equipment – based on sound wave technology using ultrasonic transmitters and receivers – into an existing welding rig. The system was designed with heat-resistant probes and a cooling system to enable it to work at high temperatures (up to 450°C) and adaptive controls to adjust the speed and feed of welding.

The prototype was tested on a submerged arc weld around a large cylinder. Probes bounce sound waves across welds allowing its internal structure to be seen, with flaws showing up in the reflected sound waves.

“We were concerned that the intensity of high temperature welding would prevent us from detecting the signal or damage the equipment, but in fact the trials went very smoothly,” said John Crossley, NDT Lead at the Nuclear AMRC.

“With conventional ultrasound equipment, we can only inspect welds at temperatures of up to 50°C,” commented Bjorn Snijders, Sonovation’s lead engineer on the project.

“The beauty of this technique is that flaws show up immediately in the image. You can see the length and height very accurately, enabling depth to be easily calculated,” John commented.

The importance of being adaptable

As well as detecting imperfections in welds in real time at high temperatures, the system’s adaptive controls enable welds to be filled uniformly and at greater speed despite variations in size.

“We get a high completion rate so we don’t need to add partial weld runs. Non destructive, real-time testing is a true breakthrough. It will save companies considerable amounts of time and money correcting flaws,” said Alan.

Reassuring the public

A proven NDT procedure for high temperature welding not only reduces costs and saves time, it also plays an important role in assuring build safety and integrity – particularly important for a civil engineering industry building ever bigger and more complex structures.

“We need to be doing more to reassure people that the structures we build are subject to stringent measures to ensure their quality and safety,” Bjorn noted.

“Posting weld testing results on the internet would be one step towards showing the public how the structures they live next to are built, how they are approved for quality and safety and who’s responsible for signing off each step of the process.”

Real gains from a real-time solution

“Engineering is a long-term game. You need to have a solid body of proven results from studies to convince people to invest large amounts money in your technology,” Alan commented.

The results of the feasibility study are a significant move forward towards NDT testing of welds at high temperatures. The next step is to move to a production-level test bed that offers more detailed analysis, such as how soon defects can be detected.

One particularly exciting finding from the study was that the adaptive controls on the new equipment could increase the speed of the welding process five-fold.  However, consortium members know that achieving these potential gains will require more advanced equipment, further development and a much higher level of familiarity with the process.

Sonovation is considering its next move, either providing machines with an NDT rig under license, or building and marketing an NDT welding machine themselves – possibly in partnership with a welding equipment manufacturer.

With the help of Innovate UK and Nuclear AMRC, this technology has an exciting future – although it may take a while for industry to notice it.

“We wouldn’t have been in a position to do this research without Innovate UK support and the facilities of the Nuclear ARMC. They make it possible for companies like us to work on projects that deliver real benefits but that aren’t central to our manufacturing base,” he concluded.

The Companies

TÜV Rheinland Sonovation provides a range of material testing and measurement consultancy to industry, especially in non-destructive testing (NDT). Tata Steel Europe makes and supports the use of steel for a range of industrial applications.

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