Taking the judgement on whether it’s safe to continue operating plant or equipment that has reached the end of its design life involves some tough calls and stringent work by engineers. Continuing to operate a nuclear power station – such as reactor one at Oldbury, the operating life of which has been extended three times since 2008 – is a prime example of where a detailed analysis of the structural characteristics and components is necessary before the go-ahead can be given to keep the plant running.
One of the things engineers will have been looking out for at Oldbury and many other
nuclear power stations around the world is what is known as “residual stress” – stresses left over in components after their manufacture. Sometimes residual stresses are welcome – as in the case of safety glass, where many residual stresses are deliberately included to stop the glass shattering into big, jagged shards and instead produce many small, safer, granular chunks. But often they are a pernicious phenomenon, producing cracks in components that may threaten their integrity and fitness for purpose.
Detecting residual stresses and helping engineers to monitor their effects on plant is the business of Veqter, a small spin-out from the University of Bristol that is making big waves in the international nuclear sector, and some other industries too. Managing director Dr Ed Kingston explains: “Anything that’s manufactured has residual stresses in it. They are known as residual stresses because they are left over from the manufacturing process.”
He adds: “Those stresses can have a greater impact than the pressure caused by liquid flowing through a pipe in, say, a nuclear reactor. In order to manufacture a reactor pressure vessel, for example, the easiest and most useful joining technique is to get all the pieces of steel and weld them together. As they are joining, they are putting residual stresses in there.”
Veqter uses a technique known as deep-hole drilling to detect residual stresses and the cracks that might result from them. It is an area where companies already carry out simulations but computers have yet to supersede physical measurement. Kingston says: “The only hard-and-fast way to determine residual stresses, which can be difficult to predict, is to measure them, and that’s where we come in.” The deep-hole drilling technique is known as a semi-invasive mechanical strain relief technology because the strain of the component is measured during stress relief from the removal of a small amount of material.
Veqter’s first clients in the early days of the business were British Energy and Airbus, for which it carried out work on quality control for wing spars on the A380 aircraft. Veqter claims it is the worldwide leader in deep-hole drilling, a technology that it brought to market first but has not patented. “We haven’t patented the technology because it’s not really patentable,” says Kingston, “it’s know-how.” He adds that Veqter is some distance in front of any competitors who might wish to develop the same technology. “We want to grow to be the global leader in residual stress measurement,” he says. The company also offers other measurement techniques, such as synchrotron X-ray and neutron diffraction.
Veqter has been heavily involved in work in both the US and Japanese nuclear sectors. Nuclear reactor downtime can be very expensive, so the onus is on utilities to try to address problems such as residual stresses before they cause cracking of components or worse. Mitigation processes against residual stress are common in the nuclear industry in the US. These include overlay procedures, which involve putting a belt around the component in question, such as a pipe. Kingston says: “What the belt does is it stresses the pipe, but turns the stresses where the crack is on the interior diameter into compressive stresses. That can stop the crack from growing.
“We will help companies measure these stresses so that they can prove to the safety authorities that they’ve done the measurements of stresses and they can use those measurements to predict how fast the crack will grow.”
Physical testing may be used in tandem with finite element analysis to make the predictions. Typically it would be carried out on mock-ups of a reactor component thus preventing exposure to harmful radiation levels. Recently Veqter has helped British Energy prove the benefits of the weld overlay process and how it might be applied at Sizewell B should the need arise. Kingston says: "British Energy pre-emptively ran a large research project with Westinghouse in the US as the main overlay contractor. And they used us to confirm the beneficial transformation of residual stresses."
One project that was shelved by a Japanese company following the tsunami was to develop deep-hole drilling technology that could be used in irradiated areas rather than on mock-ups. “Radiation damage can occur to the materials and material properties can change, so no one really knows what’s going on in the irradiated state,” Kingston explains. “We worked on a project for Japan to develop an automatic remotely controlled machine with a 50m umbilical cord so it could carry out work in a radiation zone.
“Normally, although we control our machines and log data by computer, they are manual in the sense that the tooling and fixtures are changed over by hand. That’s no good for an irradiated environment so we developed this new machine.” The work dropped by the Japanese firm will be taken up by the Electric Power Research Institute in the US, which carries out not-for-profit research on behalf of utilities, says Kingston.
Veqter was started with a £6,000 competition win but has funded itself since it was spun out of the University of Bristol. There are no venture-capital firms in the background demanding exponential growth, and the company is owned by three shareholders: Kingston, his colleague – and fellow Bristol academic – David Smith, and one other minority shareholder.
“The approach has been to start small and grow gradually,” says Kingston. “The university’s been good to us but now it is getting exposure to people it might not otherwise have had.” The fact that Veqter counts major OEMs and utilities among its customer base has been due to Kingston and his nine colleagues working the conference circuit hard and developing research proposals and presenting papers. Typically, he says, Veqter develops relationships with research engineers and scientists at its clients.
The firm may have started small but Kingston’s ambitions are clear. “We’re academics at heart. We want to push back the frontiers of science and do things that nobody else can do so we’re way ahead of the game.
“And part of our success is that we really get a buzz out of our technology.”
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