Extrasensory inspection

As new technologies make condition monitoring cheaper and more reliable industries are becoming wise to the benefits of having real-time information about the state of their products.

Condition monitoring – the ability to acquire real-time information about a machine’s performance and maintenance needs – is an essential feature of factories and heavy industry.

However, as technology becomes cheaper and companies grow more aware of the benefits of condition monitoring, the approach has been growing in popularity.

Nowadays, among users adding condition monitoring systems into their plans are the marine industry and off-shore wind energy generators.

This movement can be attributed to commercialisation of the technology and the convergence of new techniques being applied in situations where traditional sensors function poorly.

One example, outlined by Markys Cain, principal research scientist, Functional Materials Group, National Physics Laboratory (NPL), was born out of the telecom boom and subsequent bust which resulted in a massive surplus of fibreoptic cables. NPL has been working with the Photonics Cluster, a UK organisation that supports the photonics industry, to establish alternative non-telecom solutions for the fibre optics industry.

Fibreoptic cable can be used to sense strain on large structures such as buildings or bridges. For example, on a bridge, it can be integrated within reinforced composite structures.

The nature and geometry of fibre optic cables allows them to be successfully embedded within load bearing materials.

Cain says it is a mature technology, but the interrogation systems have also improved and become cheaper, making the whole system more viable.

‘I would say that up to about five years ago, the cost of the interrogation system was prohibitive,’ he said.

‘There are now new interrogation systems based on different technology, which makes it cheaper. We can do things quickly using faster electronics that you could not use before.’

According to Cain ‘a perfect example is the off-shore wind turbine industry, which is a big market’. Wind turbine growth has accelerated over the past two years. Denmark already produces 20 per cent of its electricity from wind farms, and the UK is pushing ahead with plans for several offshore farms.

By their very nature and environment (remote, in accessible locations to benefit from the more consistent winds off the coast), offshore wind turbines will benefit highly from condition monitoring technology that will help to maximise efficiency and production.

Among the benefits that Martin Jones, chief executive of Insensys, a Southampton fibre-optic monitoring firm sees for wind turbines are: keeping an eye on the condition of the blades themselves; and, most important, the ability to exercise active blade control, where the angle of the blade is monitored with a view to reducing bearing wear and keeping productivity at a maximum.

This is crucial, as wind shear on an offshore turbine is substantial, with wind speed varying by up to eight knots between the top and bottom of the blade.

One system that operates on LM Glasfibre’s LM 61.5P – the world’s longest wind turbine blade – constantly monitors critical conditions such as load, temperature and damage.

Jones believes the increase in demand for condition monitoring stems from inadequate conventional monitoring technology that fails to deliver consistently.

He explained: ‘If you look at the market, we are making progress in areas where strain gauges,conventional mechanisms orelectronics are unstable or unreliable. I think to a certain extent you have got a convergence of a relatively new technology, the commercialisation of this technology, the prices have come down significantly. And it is being applied where strain gauges just cannot hack it.’

Jones adds: ‘With traditional strain gauges, they are not that robust – one lightning strike and your system has gone. Whereas we have had one of our fibreoptic systems hit by lightning and it was fine.’ With government legislation requiring 10 per cent of UK power to come from renewable sources by 2010, wind-power – especially offshore – will play a significant role in enabling the UK to meet this target.

Airtricity, an Irish, privately-owned wind power generator, is constructing what will beIreland’s largest offshore wind park on the Arklow Bank, off the east coast of Ireland. In December last year, Airtricity was also awarded a lease from the Crown Estate to build and operate a 500MW wind park at GreaterGabbard. The project is located some 26km off the Suffolk coast at Felixstow/Hollesley Bay.

This is one of the 15 successful projects (totalling 7,169 MW) to be granted rights by the Crown Estate in the round two tender. Jones believes the burgeoning offshore market, which cannot rely on conventional technology, has driven the development and commercialisation of the new technology.

He said: ‘The goal for the wind power industry is to reduce the cost of ownership of these turbines, so condition monitoring is a central part of this. To be able to reduce bearing wear and so on makes greateconomic sense.’

Cain agrees: ‘It all comes down to cost. It’s about scheduled maintenance compared to timed maintenance. You really don’t want to take something offline to check its integrity when in fact it is fine. When a structure fails or is approaching failure, you can measure changes in property of that structure of strain, stress or temperature.’

This is the key to condition monitoring – rather than fix it once it has failed, it’s a preventative measure based on actual knowledge of the structure. Improved structural knowledge is being sought in a number of different environments. Japan, for example, is constructing a countrywide network to monitor buildings.

When an earthquake occurs, it will be possible to immediately assess which buildings are damaged or need repairs. Cain and Jones both single out bridges as an area where the widest possible applications of sensor and structural monitoring is being used, especially in Canada.

The new Interstate 10 bridge in Las Cruces, New Mexico, is one of the first to incorporate fibreoptic technology, with 120 fibre optic sensors embedded in each of the bridge’s six 90-tonne concrete beams. The sensors, made by a Swiss company called Smartec receive light from fibreoptic lines laid within the concrete.

As the beams are stressed, the properties of light change. These changes are picked up by the sensors and the data is collected and analysed, allowing engineers to address potential problems before they become serious and costly.

The marine industry has also approached NPL expressing an interest in condition monitoring with regard to hull corrosion and engine performance. In shipping, when engines are running for a long period, any extra performance that can be gained will substantially reduce costs.

Jim Vaughn, managing director of Kistler, a UK manufacturer of accelerometers which are used in condition and vibration monitoring agrees: ‘This only happens when there is significant payback. On a ship engine, if you are going to get a few extra per cent performance or fuel economy, then on an oil tanker for example you are going to get vast payback.’

Kistler now has a range of pressure sensors that are used to continously monitor ship engine performance, an operation which had always been done once every three months.

Vaughn explained: ‘What we are seeing now is a trend to monitor the performance of the engine on a continuous basis. That is something that has been waiting for suitable sensor technology. For an engine that is running 24 hours a day, seven days a week, the sensor has to last longer than the engine does. That has really only happened over the last year.’

Vaughn is not sure such technology will progress into the automotive industry. He points out that engines already feature numerous emission sensors and mechanically, are now built to standards that negate continuous monitoring on economic grounds.

Cain agrees, although he suggests the adoption of condition monitoring by the sector is some way off because of financial constraints rather than a lack of technology. ‘Automotive companies are interested, but only if you provide them with a solution for five cents,’ he said.

Kistler has also applied its technology to monitor pumps in the gas pipeline industry. And Insensys has been working with the oil industry to develop systems to monitor riser pipes against fatigue and vibration caused by current vortexing.

Georgia Tech spin-off, Atlanta-based Radatec, meanwhile, has made a technological advance with its newly-developed, non-contact displacement sensor that could transform the world ofcondition monitoring. Scheduled for commercial release later this summer, Radatec’s sensors measure motion by sending a continuous microwave signal towards a vibrating or rotating object.

This signal is reflected back to a radio receiver in the sensor which compares the transmitted signal with the received one. Radatec’s business development manager Dave Burgess said the technology could be used to provide real-time information about mechanical components in areas that defeated traditional technology. This will cut out the need to shut down heavy equipment and instead allow operators to ‘virtually’ view the inside of complex machinery.

Burgess explained that the capacitive, eddy current or laser-based sensors typically used in condition monitoring applications do not work in hot, dirty or contaminated areas.In contrast, the microwave technology is unaffected by contaminants such as oil, dust and carbon deposits. It is also immune to electromagnetic interference and can operate at temperatures up to 2,500 degrees F.

Testing with industrial partners began earlier this year. One customer is using the technology to monitor a hydroelectric generator at a Georgia dam, while another is trying it in a monitoring system in high-speed diesel electric locomotives in the US.

These improvements are boosting the potential of condition monitoring and making it more accessible to a wide range of end-use applications. A predicted 17 per cent increase in offshore oil and gas exploration over the next 12 months will ensure this technology is used by even more companies as it becomes readily available.

‘I believe very strongly there is a massive increase in condition monitoring of structures, irrespective of what those structures are. The context of intelligent structure is something I think everyone can see the benefit of, but the technology up till now hasn’t been up to date. I think that has changed over the last 12 to 18 months,’ said Jones.

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