Detecting these defects is challenging as they are often invisible to the human eye.
So how do you see the invisible, in accurate and safe ways to prevent new tragedies?
It is a race against time that first takes us to Madrid, in Spain.
Researchers here are trying to detect tiny, millimetric defects in the mock-up of a nozzle, a crucial, sensitive component of a nuclear reactor.
The nozzle helps to control the flow of water that cools the reactor.
“This the inner surface of the vessel. Inside here is the nuclear reactor. Here in this region there is the nozzle that we need to inspect. In this weld there are a number of defects, that either they are so thin that we can’t see them with naked eyes or that they have been buried inside the volume of the material,” says Dimos Liaptsis, Coordinator, NozzleInspect project
Meanwhile with similar urgency, in Hamburg, Germany, researchers from another European Union Research Project face a different problem, detecting invisible defaults in key compounds of a ship, built and monitored at this shipyard.
“Here you can see a so-called, ‘ finstabiliser’, which is a large fin to stabilise big ships by minimising its movements on high seas, so that sailing in rough weather will be more comfortable,” explains Uwe Ewert, Radiology engineer, BAM.
Back to Madrid where scientists think they have found a solution to inspect inside the thick layer of low carbon steel of the nozzle mock-up. A robotic arm equipped with ultrasounds.
“The reason that an automated system is being required to inspect this particular nozzle, is because outside here there is a high radiation area,” points out Dimos Liaptsis.
Giannis Roditis a mechanical engineer with Cereteth explains: “Operators just need 2 to 3 minutes to install the robot on the nozzle. It is clamped. And then the operators can move outside the inspection area, that is protected with a concrete wall. So they won’t be exposed to the radiation from the reactor.”
In Hamburg, the problem is different and so are the solutions. Here researchers are testing a brand new prototype of high energy digital radiography to see what can’t be seen with the naked eye.
“The question is are there are any air bubbles inside the iron casting of the fin? These air bubbles could disturb how it works, and they pose a certain risk, the fin could even break up. So to find out more about these bubbles, we are making a high energy, 7.5 mega-electrovolt digital radiography of the fin,” explains Uwe Ewert.
Back in Madrid. The robotic arm is sending the ultrasound beams. Structural faults are identified, measured and catalogued in real time.
Dimos Liaptsis explains: “By using these data, we can identify any defects, and then we can characterise them. They can be either cracks, or porosity, or other defaults inside the material.
‘This is for instance a cracking. In this case the crack is 21 mm in height and 44 mm in length. So it is fairly a big crack. So we are going to provide this information to the operator of the plant -they are the final users of this technology. And they will do their calculations.
‘They will have to decide if this crack needs to be repaired just after the inspection or if they can wait until the next inspection to monitor if the cracks increase further.”
In Hamburg, the digital x-ray equipment can be tested on just about any part of a ship even on some industrial installations of the shipyard itself.
Uwe Ewert says: “We are now sending radiation through the finstabiliser. On the other side of it we have placed digital storage plate systems, something completely new to the market. They are highly sensitive and it takes less radiation time to get a clear picture of the interior of the monitored part. Digital radiography is far more effective than classical film radiography.”
Tests done in the real shipyard are then analysed in Berlin, in a research institute that helped to develop the prototype.
Its developers say they are impressed not just by its accurate performance but also by its ecological footprint.
Subash Sood is the Chairman/Electronic & communication engineer at CIT.
“With digital radiography, we have eliminated the use of chemicals, the use of X-ray films, as well as the physical storage requirements under controlled conditions. All these constraints have been minimised to a normal office-type environment, where all the digital records are kept in electronic media,” he explains.
Both prototypes have been successfully tested. And what do the final users think?
In Madrid, engineer Carlos Gavilán supervises the inspection of nozzle components in nuclear reactors.
Carlos Julián Gavilán is a Mining engineer with Iberdrola:
“With this prototype, we have improved the accuracy of our monitoring of nuclear nozzles. That means our calculations about life span and deterioration rate of these nozzles are much more accurate. It takes less time to install this monitoring robot, so our inspection workers receive lower radiation doses,” he says.
“In future the operators could be entirely removed from the whole installation procedure. I think that is the ultimate goal,” explains Giannis Roditis.
And back to Hamburg, the shipyard’s managing director, Uwe Cohrs has already some ideas about the future uses of the digital X-ray equipment that has just been tested.
“Take for instance the elevator right behind me. Before we could just try to detect surface flaws or cracks. Now, with digital radiography, we can already plan to find or detect flaws or cracks in its inner structure.
‘And that is an advantage from a economical point of view. With classical radiation monitoring we could just see defaults linked to the use and deterioration of a given ship part.
‘With digital radiography we can prevent unwanted structural defaults during the construction of that same part. Predicting eventual structural defaults will help to reduce maintenance costs,” he says.
And these prototypes, researchers say, are just the iceberg tips of a brand new generation of innovative monitoring systems that soon will allow us to see what can’t be seen, in real-time, faster, more accurate, and in a more environmentally friendly way.