First published in Bolted #1 2017.
ENERGY. With oceans covering more than 70 per cent of the earth’s surface, wave power is potentially a huge untapped source of renewable energy. The problem is that most wave energy converters are too large and costly to be commercially viable. Swedish company CorPower Ocean could have the answer.
The company’s compact Wave Energy Converter works by oscillating in resonance with waves, amplifying their motion and then converting that energy into power. CorPower Ocean founder, cardiologist Stig Lundbäck, invented the initial concept based on the pumping principles of the human heart. In the same way that a heart uses hydraulically stored energy to form back in place, the Wave Energy Converter uses a pneumatic pre-tension system to pull down the buoy after it has been lifted by a wave.
This allows for a relatively small device to harvest a large amount of energy. It is estimated that one buoy, eight metres in diameter, can generate around 250 kilowatts of power. That is enough electricity for around 200 homes.
“If you look at wave energy potential, somewhere between 10 to 20 percent of global electricity consumption could be provided by wave power,” says Patrik Möller, CEO, CorPower Ocean. “It has the potential to become the most competitive source of renewable energy. It offers five times more energy density than wind and ten times more than solar power. Waves have fewer variations and are more predictable than sun and wind, so you know a few days in advance what the energy flow will be.”
Currently, the Wave Energy Converter is undergoing tests with simulated wave loading, while a full-scale demonstration is being set up to begin in 2017. One of the key challenges has been keeping the buoy small and lightweight, while at the same time strong and durable enough to survive the toughest storms at sea.
This has presented a number of fastening challenges. On the mainframe inside the buoy, CorPower Ocean has elected to use Superbolt tensioners due to their lower torque requirements compared to a single bolt, which makes assembly far more manageable. Superbolt can also guarantee reliability over the buoy’s intended 20-year lifespan. At the base of the buoy, Nord-Lock washers are used, since they can maintain the correct tension over many load cycles over a long period of time.
First published in Bolted #1 2017.
Don’t miss the new Nord-Lock Group video that focuses on the hands-on aspects of our Expansion bolt technology.
The video takes you through an entire Superbolt Expansion bolt installation process, from preparation and positioning to the fitting of the bolts into the holes when aligned.
The video was filmed on location at the EDF hydro electric power station, Usine Électrique de Malgovert, in the beautiful French Alps, where electricity generator giant EDF joined forces with the Nord-Lock Group to install Superbolt on the Malgovert turbines.
“EDF chose Superbolt Expansion bolts to simplify future maintenance. Ease of installation and removal due to the expanding sleeve technology insures against future damage to coupling bolt and coupling holes. There is no longer a need to re-machine holes or replace bolts,” says Steve Brown, expansion bolt specialist with the Nord-Lock Group. “This film is for everyone who wants the optimal bolted coupling, using and making the most of a Superbolt installation.”
First published in Bolted #2 2016.
Cost pressure on the growing wind energy industry makes intensive testing necessary. Consistent research on cost reduction methods is also required to strengthen wind power as an alternative, long-term energy source without subsidies.
Helping clients such as manufacturers of wind turbine generators (WTGs), wind farm operators, suppliers and energy supply companies, the German Fraunhofer Institute IWES (The Fraunhofer Institute for Wind Energy and Energy System Technology) provides industry-related research services and cooperation for a wide range of technical wind energy issues.
“The IWES is an industry institute devoted to the field of wind industry,” explains Hans Kyling, Research Associate for the current BeBen XXL project, which is researching whether business safety requirements can be met using less material.
Running between 2012 and 2017, the project is a collaboration between Fraunhofer IWES, wind turbine manufacturer Suzlon Energy GmbH (which initiated the project) and the Hamburg University of Applied Sciences (HAW). It is funded by the Federal Ministry for Economic Affairs.
The German abbreviation BeBen translates as “accelerated experimental endurance strength verification for large wind turbine components using the example of main shafts.”
“The term lightweight construction is a bit exaggerated,” Kyling points out, “because we don’t really build light, we just build lighter.”
All wind industry OEMs (Original Equipment Manufacturers) will potentially benefit from positive project results. If certification guidelines are adjusted accordingly, it will improve cost-effectiveness, as it won’t be necessary to oversize WTG components.
In addition to the main project goal, the suitability of high-tensile cast iron as a substitute for expensive forged material is also being investigated and validated. Kyling says: “We are conducting an accelerated service life test by altering some of the parameters, for instance using a higher rotation speed than during normal WTG operation, thus putting greater stress on the main shaft through a heavier rotor.”
Another thing that makes the project innovative is the creation of a so-called Wöhler curve, which determines the vibration resistance of a material or a component – especially a very large one. The automotive industry generally uses vibration resistance tests for much smaller components. For cost reasons, even the aerospace industry usually conducts tests on significantly smaller components.
Despite the huge dimensions of the WTG main shaft, the working space for bolted joints is quite limited, which can make installation and maintenance difficult – even risky.
“We created a split form of test rig,” Kyling says. “There is a steel structure, which is connected to the foundation, and an upper steel structure, which is connected to the test specimen.”
Typically, both these applications are very hard to access. The structure is designed for load-flow optimisation, which means that the bolts are sometimes placed in hard-to-reach places with little room for maneuvering the tools. Apart from the tight spaces, Kyling stresses other challenges: “The loss in pre-load should be as low as possible, and very high forces must be countered.”
These challenges were a major reason for selecting Nord-Lock products. Superbolt tensioners contribute to the safety of the project, not only because they make it possible to work in confined spaces, but also because they allow for use of lighter tools. Handling hydraulic equipment in these situations could compromise the technicians’ safety.
Superbolt tensioners are used between the two upper steel components and between the steel structure and foundation. Eight size-M80 tensioners are used in the project, along with 28 smaller M56 tensioners. Even with the large M80 Superbolt tensioners, there are still 2.8 MN (meganewtons) of force to be reckoned with, but Superbolt multi-jackbolt tensioners can handle it.
Apart from the actual parts, the BeBen XXL project also benefits from the Nord-Lock wind energy industry experience. Positioning is key to success in this market, “Because there’s always the cost pressure,” Kyling says.
Nord-Lock sales engineer Tobias Klanck says that, “As a highly qualified supplier for the wind energy industry, we are glad that the growth trend in this segment is continuing. This holds especially true for weak-wind turbines. Making full use of the existing wind, they are well suited to many locations worldwide.”
Going forward, Kyling says about wind turbine construction that, “There are still many challenges to overcome.” One of them is the use of increasingly large rotor blades. Regarding the drivetrain, there is the problem of using cast shafts instead of forged ones to keep costs down for large volumes. As there is no general drivetrain concept, bearings are another challenge for WTG manufacturers in order to meet to be competitive.
Technical insights: Products for all conditions
The Nord-Lock Group premium product range is very attractive to the wind energy industry, as it meets the tough requirements of wind turbine operators. Nord-Lock products are perfect for securing bolted joints in wind turbines that must be able to withstand enormous pressures under extreme conditions. They also provide practically maintenance-free operation.
Nord-Lock washers protect from bolt loosening due to vibration and dynamic loads, using tension instead of friction, thus reducing the risk of production failures or property damage. X-series washers offer extra safety since they, in addition to the same wedge-locking effect as original wedge-locking washers, can compensate for relaxation and settlements. They also handle dynamic loads dependably, especially in new turbines with increasingly high performance.
Superbolt tensioners are a superior choice for wind turbines. Replacing conventional nuts and bolts, they increase the lifespan of bolted joints and require only hand tools to tighten the joints. They are ideally used in the drivetrain, before and after the gearbox, at the housing and footing screws, all of which are continuously subjected to great forces.
Boltight hydraulic tools offer reliable and precise pre-tensioning for all critical bolt connections, both for construction and maintenance. Applications include tower-field connections, as well as frames, bearings, foundations and rotor blades.
M80 MULTI-JACKBOLT TENSIONER
FACTS: The BeBen XXL research project
Customer: The Fraunhofer IWES industry institute.
Location: Bremerhaven, Germany.
Project: The BeBen XXL research project, running 2012–2017.
Project goal: To determine if it is possible to reduce or change the material use for large wind turbine shafts.
Nord-Lock products: Superbolt M56 and M80 Multi-jackbolt tensioners
First published in Bolted #2 2016.
Couplings are as old as industrialisation itself with even early simple machines, such as cotton mills and windmills, needing some way of connecting shafts. However, ever since the invention of the steam turbine back in 1884, shaft couplings have become essential in the power generation and shipping industries. As both turbines and shipping vessels have increased in size, so too has the amount of power and torque that needs to be transmitted. This in turn has greatly increased the demands on shafts and couplings, and in the case of bolted couplings, on the bolts themselves.
“In the power generation and marine industries, couplings have always been there and they really haven’t evolved much,” says Martin Walsh, an engineer with over 30 years experience working with large-scale bolted couplings. “If you look at a coupling from 60-70 years ago, it is pretty much the same design and concept as today. However, the engineering behind them has evolved a lot. Bolts in particular is an area where couplings have become a lot more sophisticated and this has allowed smaller couplings to transmit more torque.”
One of the most important functions of a bolted coupling is to maintain shaft alignment. In marine applications, where shafts typically turn at low speed, any misalignment will cause vibration, which in turn puts unnecessary loading on the bearings. In power generation applications, where rotation can be as high as 3,600 rpm, even the slightest vibration or uneven loading is unacceptable and would severely limit the turbine’s ability to run at full power. For this reason, a lot of time and resources are invested in optimising shaft alignment.
“Once you’ve achieved the alignment, then the bolts need to hold it as it was set and maintain that alignment in service,” says Walsh. “At some point in the future, you will take those bolts out and disconnect the shaft. When you put it back together, you want it back to exactly where it was before because you’ve already invested a lot in getting the alignment right.”
For many years the most common bolting solution was standard through bolts, which are relatively cheap and readily available. A bolt is simply inserted through the bore and tightened with nuts on either end to create a friction connection. But the amount of torque that can be transmitted through friction is severely limited and excessive torque can lead to slippage and misalignment. The resulting micro movements and uneven loading can then lead to damaged bolts and bores. The coupling therefore needs to be rebuilt and shaft alignment re-established.
In theory, fitted bolts, which fill the bore, can offer greater torque capacity, since torque is then driven through direct shear across the cross-section of the bolt. In practice it is difficult to achieve a truly fitted bolt, since the bolt’s diameter will reduce as it is tightened. This creates a gap between the bolt and the bore, leading to the same problems of slippage and bolt failure.
This need to establish and maintain shaft alignment, even after a coupling has been dissembled and reassembled again, has led to the increased use of expanding sleeve bolts. Since expanding sleeve bolts expand into the bore, they can ensure a truly fitted bolt and a far more even load distribution. This eliminates movement and slippage, so that shaft alignment should automatically be re-established once the expanding sleeve bolts are reinstalled.
“The expanding sleeve bolt has probably been the biggest single advance in accuracy over the past 30 years,” says Steve Brown, Global Product Manager – Expansion Bolts, Nord-Lock. “They offer many pros and little in the way of cons – ease of installation, accuracy of fit, ease of removal, regaining of alignment and with correctly prepared holes, regaining of concentricity and re-usability.”
A key factor driving the development of bolted couplings has been the evolution in engineering analysis. “70-80 years ago, couplings and bolts were over-engineered and bigger than they needed to be, as engineers erred on the side of caution,” says Walsh. “It was a situation that existed in many industries because the ability to do sophisticated calculations and simulations was not available.”
Now many OEMs have the ability to test the affects of temperature, different materials and operation conditions using computer modelling and simulations. Due to the complexity of rotating couplings, the finite element method (FEM) is becoming increasingly common for identifying weak points and torque tolerance of specific installations. Shear tests have also been used successfully to demonstrate the physical limitations of different bolting solutions.
“There is still scope for further analysis and it would be helpful to see exactly how the newer design of bolts with expanding sleeves compare to the older bolts when it comes to transmitting higher torque,” adds Walsh. “Having a full FE analysis could be a significant advantage since it shows the potential for reducing the number of bolts and size of the coupling, particularly in industries such as wind turbines, where they tend to avoid bolted couplings due to space restrictions.”
The need to design smarter and smaller couplings will continue to be important as turbines and shipping vessels keep on growing in size and output, and need to transmit even more torque.
C.A. PARSONS ”TURBINIA”
In 1884, British engineer Sir Charles Algernon Parsons invented the first steam turbine.
His first model only generated 7.5 kW of electricity, but it demonstrated huge potential for generating electricity and for powering ships. In 1893, the Parsons Marine Steam Turbine Company was set up and in order to demonstrate the capabilities of the new technology, began developing the experiential vessel Turbinia.
The new ship was equipped with three axial-flow turbines fitted to three shafts, with each shaft driving three propellers. On completion in 1894, the Turbinia was the fastest ship in the world reaching speeds of up to 34 knots (63 km/h) – in comparison the Royal Navy’s fastest vessels could only reach 27 knots.
In 1897, the Turbinia turned up unannounced to the Navy Review for Queen Victoria’s Diamond Jubilee, and in front of royalty and senior Navy figures, it was able to clearly demonstrate its superiority in speed and power. Within two years, Parson’s turbines were adopted by the Royal Navy and shortly afterwards used to power transatlantic passenger ships.
Sir Charles Algernon Parsons’ designs also saw steam turbines quickly scaled up, making it possible to generate cheap and plentiful electricity. In 1899 the first megawatt turbine was built in a power generation plant in Germany, and within Parsons’ lifetime, his invention was adapted by all major power stations in the world.
LET’S STICK TOGETHER
The need to assemble components in bolted joints goes way back. For long the through bolt was the standard threaded fastener. It is inserted through the bore and tightened with nuts on either end to create a friction connection. Excessive torque may lead to slippage and misalignment, which in turn can lead to damaged bolts and bores.
The expanding sleeve bolt is a more recent invention, which overcomes these problems. It expands into the bore and ensures a truly fitted bolt along with more even load distribution. It also simplifies installation and removal as well as retrofitting.
Find out more:
The September issue of Bolted magazine is out now! Prepare yourself on a reading journey to explore interesting cases and insights from the world of bolt securing.
In this issue, our theme article focuses on coupling challenges. Couplings are essential in the power generation and shipping industries, and are arguably the most demanding of all bolting applications. Learn what the bolting experts have to say about couplings.
Engineers from the Nord-Lock Group answer questions on how to get the most out of your fasteners and cover the key advantages of hydraulic tensioning.
We witness the largest public works project in California’s history, where Boltight tensioners are installed on the San Francisco-Oakland Bay Bridge. We then move on to Oman to find out how broadcasting antennas owned by the BBC are being secured against windstorms. Last but not least, we ride on the time machine as we simulate 20 years of wear and tear on a wind turbine in just a fraction of that time.
We are glad to inform that Bolted is now available in Korean language! Bolted magazine are published in 8 languages, download them now:
Want to receive your complimentary copy of the Bolted magazine? Subscribe here now!
The Nord-Lock Group has been serving the Power Generation industry for many years, providing safe and secure bolting solutions. At the recent Power-Gen Europe exhibition in Milan (Italy), we presented our extensive range of bolting technologies, which includes Nord-Lock wedge-locking solutions, Superbolt multi-jackbolt tensioning and Boltight hydraulic tensioning. Our bolting experts provided live demonstrations of the different technologies and engaged in technical discussions with our visitors.
“Power-Gen Europe is a big international event and we are glad to represent the Nord-Lock Group in presenting our range of innovative bolting solutions that have been widely used within this industry”, said Luca Gheddo, General Manager of Nord-Lock Italy.
The main highlight of this exhibition was the Boltight hydraulic tensioning system. Boltight hydraulic tensioners are designed and manufactured for all sectors of the Power Generation industry. The solutions are frequently utilized for critical bolting operations during construction and maintenance of turbine casings, piping, pumps and valves. Boltight tools are used on wind turbine bolting applications, from foundation and tower bolting to blade, nacelle and hub / gearbox bolting. Other common applications include nuclear reactor and generator bolting.
View the video interview from Power-Gen Europe with our experts to know more about Boltight:
First published in Bolted #1 2016.
Energy. Offshore wind turbines are an increasingly common sight as the world moves towards more sustainable forms of energy production. But these standard horizontal axis turbines have a number of drawbacks, such as being expensive to build and install because of the way they work, and because they are fixed to the seafloor.
But Swedish company SeaTwirl has taken a different approach to generating wind power at sea that promises easier construction, installation and maintenance, which in turn means lower lifecycle costs and lower energy costs.
“SeaTwirl has a simple robust design with few moving parts,” says Gabriel Strängberg, managing director of SeaTwirl. “It can be placed in deeper water with good wind conditions. SeaTwirl is built for the ocean.”
SeaTwirl’s vertical axis turbine is fixed on an underwater gravity-based structure that reaches deep down under the surface. The full body then rotates as one piece. Strängberg explains: “The vertical axis makes the wind turbine rotate regardless of wind direction. A horizontal axis turbine must be aimed to catch the wind. That kind of yaw mechanism is not needed in the SeaTwirl turbine.”
SeaTwirl AB was founded in 2012, but traces its history back to 2006 when inventor Daniel Ehrnberg wondered how water could be used as a bearing. After some small-scale testing, the first large prototype was launched in 2011. The second prototype, off Lysekil on Sweden’s west coast, started producing energy in July 2015.
Nord-Lock has taken on a crucial role with the SeaTwirl prototypes, delivering both Nord-Lock wedge-locking washers and Superbolt tensioners.
Strängberg says: “We chose Superbolts to easily achieve a high preload in the joints and to simplify the assembly process.”
Other prototypes are currently being tested and SeaTwirl’s turbines are expected to be commercially available around 2021.
First published in Bolted #1 2016.
Customer: EPFL (École Polytechnique Fédérale de Lausanne)
Item: Flywheel pulse synchronous generator
Production: Swiss Plasma Center
Capacity: 254.40 MW
With fossil fuels running out and the need to reduce greenhouse gases continuously growing, fusion power could potentially be the answer to the world’s long-term energy concerns. The Swiss Plasma Center – part of the world renowned university École Polytechnique Fédérale de Lausanne (EPFL) – is one of the institutions at the forefront of the worldwide development of this new energy source.
One of the key components of its research is the TCV tokamak, an experimental magnetic-confinement fusion reactor. To deliver the requested energy, a synchronous generator and its flywheel are accelerated up to 3,600 RPM. During the experiment the energy is extracted leading to a fast deceleration of the rotating group. This process, which is undertaken around 3,000 times a year, puts tremendous pressure on the generator’s coupling and bolts.
In the past, the Swiss Plasma Center had experienced problems with vertical, horizontal and axial vibrations. With RPM as high as 3,600, the vibrations can be very dangerous to the coupling and the whole generator.
However after consulting Nord-Lock engineers, who assisted with calculations and designs, Superbolt Expansion bolts have since been installed.
The main advantage of the Expansion bolts is that they allow for precise and reproducible alignment of the coupling flanges during assembly, and as a result, reduce the need for demanding balancing of the shaft line.