Three ideas for more reliable turbines

 

Reliable equipment is needed to decrease turbine costs and downtime. Large amounts of time and resources are often spent on finding methods to reduce the risks of large components failing. Turbine gearboxes are one such example. However, more often than not, it is the small components such as seals and bolts that are central to reliability, performance, and ultimately, profitability. UK-based James Walker has identified at least three options that can help the industry overcome these problems.

Reducing the risks of bolt failure
Some 90 to 95% of all bolted-joint failures are caused by insufficient bolt tension on installation. So to improve reliability and reduce equipment failures, it is essential that correct tension is generated at installation and maintained throughout the life of the bolt. Traditional tightening procedures, such as torque and hydraulic tensioning, measure the effort applied but not the tension generated across the bolted joint. Hence, torques is not an adequate measure of correct bolt tension.

Advanced bolt tension technologies can reduce the risks of bolt failure by accurately measuring tension across bolted joints. The company says its RotaBolt offers accurate installation to within ±5% of the customer’s specified design tension. This reduces the risk of bolts loosening in operation due to factors such as vibration or thermal cycling. Additionally, the tension-control fasteners allow monitoring any loss of tension across the bolt by a simple tactile or visual check requiring no specialist expertise or tools. This technology can reduce the risks of equipment failure while also improving safety and significantly reducing maintenance costs.

Reducing the risks of seal failure
Poor seal performance lets lubricants leak, compromise performance and accelerate equipment failure. As more wind farms are installed in challenging environments, rapid on-site seal replacement with the minimum of disassembly is essential to minimise the loss of energy production. However, retrofitting such components is a vital consideration often absent in seal design.

Seal manufarturers have developed on-site joining technology to fit the wind industry. For example, Walkersele OSJ-2 is an on-site jointed seal concept from James Walker that can replace a typical turbine main shaft seal in less than 30 min without major disassembly. On-site joined seals offer the same integrity, life, and performance as the seal fitted during manufacture by an OEM. Timely seal replacement will help to reduce the risks of equipment failure.

Vibration elimination
Shaft and blade vibration can cause fatigue and ultimately, the premature failure of turbine components. To improve performance and reduce maintenance requirements, vibration must be minimised or eliminated.

Vibration control reduces the risks of equipment failure. Companies such as James Walker Tiflex have developed vibration attenuation and structural isolators. A range of machinery mounting options, foundation pads, and structural bearings can isolate structures from plant vibration and equipment from structural disturbance. Many years of sound and vibration attenuation engineering experience and state of the art research let’s Tiflex provide tailored solutions to specific turbine, tower resonance, and vibration problems.

“As demand for energy grows, technology in the wind industry must improve equipment reliability”, said Keith Tripp, marketing director of James Walker. “Recent activity has focused upon maintaining the reliability of large components. However, smaller components are also important and should not be overlooked. Investment in technology that reduces the risks of equipment failure will in turn reduce the costs of maintenance and improve the long term reliability of renewable-energy generation.”

James Walter Group
www.jameswalker.biz/windenergy

Hydraulic bolt tensioners

The Tentec Aero WTB is a range of hydraulic bolt tensioning tools to suit most wind turbine bolting applications. All WTB Tensioning tools have capacity to generate the specified proof load requirements as detailed in EN ISO 898-1:1999 and ASTM A490M for grade 10.9 Bolts. These tensioners have been designed with rapid tensioning in mind and offer a safe, reliable, and consistent method to simultaneously tension many bolts.

Tentec
www.tentec.net

Thread locker holds bolts and zinc protects them

Bolts take a lot of attention in most machinery and more so in the always-slightly-moving wind turbines. Two recent products provide ways to hold them fast and then protect them.

A high-viscosity, primerless, red threadlocker, intended for use in a wide range of heavy duty industrial applications, cures even on fasteners treated with thread lubricants and anti-corrosion and protection fluids without cleaning.  Henkel Corp. introduced its Loctite 263 Threadlocker, (www.useloctite.com) a high-strength, single-component anaerobic threadlocker intended to permanently lock and seal threaded fasteners up to one-inch in diameter

When confined in the absence of air between close-fitting metal surfaces, the anaerobic treadlocker is said to rapidly fix and cure. The company says the material performs equally well on active and passive metal surfaces including stainless steel and plated material without the use of a primer.

Once fully cured and in service, the material prevents fasteners from loosening and leakage caused by shock and vibration. It withstands temperatures to 360ºF.  The material is said to provide excellent resistance to a variety of industrial fluids and solvents, ensuring a leak-free seal of the threaded assembly. Localized heat and hand tools are required to disassemble treated fasteners.

To protect fasteners, A chrome-free, inorganic zinc-rich fastener coating provides a thin silver coat and superior product performance in a single layer, according to it manufacturer. Magni 501(www.themagnigroup.com)  is engineered as a replacement coating for zinc plating and trivalent passivation. A few features includes exceptional corrosion resistance , no hydrogen embrittlement concerns, and consistent torque tension relationship. Other features include a resistant to automotive fuels and fluids, excellent adhesion, cost-competitive, paintable, and there is no waste treatment needed. It’s also RoHS, WEE, ELV and REACH compliant.

WPE

 

 

A better coating for wind power bolts

Andrew R. Pfeifer, Metal Coatings International Inc., Chardon, Ohio, metal-coatings.com

Since the 1970s, users of high strength ASTM A490 bolts were prohibited from using metallic coatings. The main reason for this restriction was the possibility of early fracture due to hydrogen embrittlement. Following research presented to ASTM Committee F16 on Fasteners and the Research Council on Structural Connections (RCSC), the metallic coating DACROMET was added to the A490 specification as the only approved coating (2008) and is scheduled to be inlcuded in the next publication of the RCSC spec (2010).

The coating, manufactured by Metal Coatings International, was evaluated according to the test method prescribed in the IFI-144 standard, “Industrial Fasteners Institute – Test Evaluation Procedures for Coating Qualification Intended for Use on High-Strength Structural Bolts”. The objective of the investigation was to verify that the structural integrity of high-strength structural fasteners was not compromised with the use of a metallic coating.

Extensive testing was conducted on two separate lots of 1-in. diameter ASTM A490 bolts supplied by two manufacturers. The test bolts were coated with DACROMET by an industrial facility under normal operating conditions (cleaning by alkaline wash, mechanical blast only, no acid pickling or electrolysis), while samples of uncoated bolts from each lot were retained for baseline results.

Results confirmed that the coating does not cause internal hydrogen embrittlement nor does it promote environmental hydrogen embrittlement (evidenced by the fact that there was no loss in the strength of the coated bolts following installation and exposure to corrosion testing). These are the most significant findings of the investigation because they address the primary concern that led to the prohibition of metallic coatings in the first place.

Other notable results from this study include:

Corrosion protection – Continuous salt spray and cyclic corrosion testing showed the superior protection offered by the coating, especially when compared to hot dip and mechanical galvanizing.

Thickness – The coating (~ 9 microns) was significantly thinner than the galvanizing methods.

Assembly – The coated hardware assembled according to industry requirements without use of a supplemental wax or lubricant.

This study correlates to the wind market on several levels. For instance:

• A490 bolts (or equivalents) are used throughout most turbine structures. Part manufacturers were previously restricted from supplying these bolts with a coating, but this research provides them confidence in supplying the approved finish.
• Studs used in towers, nacelles, and blades use materials similar to the A490 bolts, presenting a potential for embrittlement. To meet durability requirements in the most stable manner, the approved coating (or the chrome-free alternative GEOMET) should be used to protect these studs.
• Turbines located on the coastline or in off-shore applications will be exposed to highly corrosive elements. Conventional finishes may not provide the degree of protection required for various components.

Structural-bolting industries have embraced coatings on fasteners and hardware to protect their structures. For the wind industry, the approved coating should be well received because it will help it meet life expectancy of the growing off-shore wind farms, which are likely to receive maintenance visits less frequently than similar land-based facilities. As the wind industry continues refining its performance requirements, thin-film corrosion protective coatings will find wider use, thereby extending the life of its structures and ensuring this green technology endures.

How small tools generate big bolt tension

A Superbolt or multi-jackbolt tensioner is a direct replacement for hex nuts, covered nuts, and bolts. They spin onto existing bolt or stud and provide a better way to bolt up the joint. Multi-jackbolt tensioners consist of a hardened washer which protects equipment and provides a hardened, flat surface for the jackbolts to “push” against. A nut body spins onto the existing bolt or stud and seats against the washer hand tight (Superbolt nut bodies are typically round). Jackbolts then thread through the nut body and are used to tighten the joint in pure tension. Mechanics then tighten the jackbolts using ordinary hand tools.

Superbolt tensioners are useful when tightening a nut greater than 1-in. diameter, and more so as the size of the nuts and bolts increase with the load needed to properly tighten them rises. Multi-jackbolt tensioners eliminate time consuming and unsafe bolting equipment such as sledgehammers, hydraulic wrenches, and stud heaters. Only simple hand tools are needed for any size tensioner.

Superbolt Tensioners come in a variety of sizes and configurations. Many stocked items are available and a large shop can quickly handle custom jobs.

A brief tour of a bolt factory

All raw materials used to manufacturer products at AA Anchor Bolt Inc, Northville, Mich., is melted and manufactured in the U.S. by certified steel mills. The company inventories over 600,000 lb of material which allows for quick turnarounds. Threading capabilities range from ¼ to 5 in. The company manufacturers rolled and cut threaded products as well as threaded rod in different grades. The company also saws, shears, chamfers, and threads rebar. It has 18 Landis cut threaders, single and double spindled, along with 12 flat-die thread roller and seven cylindrical-thread rollers. Bending capacity ranges from ¼ to 3 in.