Fasteners and Gaskets for Power Plant Service

Anyone who works in the power industry knows how important fasteners, such as nuts, bolts, and rivets, and gaskets are to plant operation. Fasteners provide structural integrity, effectively holding everything together. You couldn’t operate a turbine or generator, or maintain piping systems and pressure vessels, without them. Gaskets, meanwhile, create the seal between mating surfaces, such as flanges (Figure 1), covers, and joints. These seals are essential for containing and preventing the leakage of fluids, such as steam, water, and oil, or gases within the power plant. Proper sealing helps to maintain system pressures, prevent environmental contamination, and ensure the efficient operation of the plant.

1. Bolted flanges are held together with fasteners and kept leak-free with high-quality gaskets. Courtesy: StockSnap / Tim Sullivan

Choosing the Right Fasteners and Gaskets for a Job

The type of power plant, such as nuclear, coal, natural gas, or renewables, can affect gasket and fastener requirements. “Some of the older, traditional models, such as coal, use standard and commodity gaskets and fasteners, whereas, in comparison to nuclear, there’s more regulation and specifications that are associated with the purchase of gaskets and fasteners to ensure a high-quality product,” said Justinn General, engineering manager with Lamons, one of the largest privately held gasket, seal, bolt, and hose assembly manufacturers in the world. General said many renewable energy power facilities are also dependent on standard and commodity gaskets and fasteners, but some are beginning to move toward better alternatives.

There are many factors to consider when selecting gaskets and fasteners for power plant applications. Some of the most critical parameters include temperature, pressure, and medium, that is, what’s inside the pipes. The bolt and joint connection, and how they interact with each other, are also important. General said when gaskets require a very tight seal, then high-strength fasteners are necessary. Engineers must also consider whether the application is going to be pressure cycling or thermal cycling. Furthermore, if the media is corrosive, alloy selection and gasket selection become more important.

Power plants often experience significant vibrations and thermal fluctuations due to the high-speed rotation of turbines, the combustion of fuels, and the transfer of heat. Fasteners and gaskets help to absorb and distribute these stresses, helping prevent damage and failure of critical components. This helps to extend the lifespan of the equipment and maintain reliable power generation.

Often, there is a tradeoff between cost and performance, and the decision on what gaskets and fasteners are used is a compromise. “You have to really understand the criticality of the application and the importance of it not failing,” said General. “When it comes to these high-performance and cannot-fail systems, it usually merits equipment and high-performing gaskets that would give that guarantee of not failing.”

Failure Modes and Solutions

Yet, even when critical factors have been considered and the best materials chosen, gaskets and fasteners can still fail over time. It’s not uncommon for bolted connections to begin leaking a few years after installation. General offered some tips, however, to minimize failure rates.

“Workers must understand the importance of proper lubrication of the studs to ensure a consistent k-factor,” he said. K-factor, also known as the nut factor or torque coefficient, is a dimensionless number that represents the ratio of input torque to the resulting clamp force in a bolted joint. It helps engineers and technicians determine how much torque should be applied to achieve the desired clamping force in a bolted connection. Factors affecting k-factor include things like friction between the bolt threads and nut threads, friction between the nut face and the joint surface, geometry of the threads, material properties of the fasteners and joint, surface finish and coatings, and lubrication.

“It’s also important to use proper instruments and tools that give you the highest accuracy of torque being applied through bolt-up,” continued General. Meanwhile, having proper bolt-up procedures and training workers appropriately should not be overlooked.

When systems are exposed to cycling at high temperatures, it may be worthwhile to use high-recovery gaskets. These are gaskets with the ability to “recover” or return to their original shape more readily than other types after being compressed or exposed to thermal cycling. Lastly, if a plant finds there is a constant problem with leakage from a specific joint or application, that could mean a thorough engineering evaluation is warranted. In such a situation, a better alternative to the existing gasket material could exist and may be worth trying.

Among innovative gasket designs General mentioned was Lamons’ CorruKamm gasket. It utilizes “Kammprofile technology” with a heavy substrate capable of extreme load-bearing properties, combined with a precisely located corrugated pattern that greatly enhances deflection and compression under load. This makes the gasket more forgiving when perfect alignment and parallelism do not exist.

Concerning fasteners, General pointed to load-indicating studs as a significant improvement. He also said performance coatings for fasteners, such as NanoGalv, improve corrosion resistance and thermal degradation, leading to improved outcomes. NanoGalv, made by Modumetal, is a proprietary zinc-nickel coating that the company says “offers superior performance, competitively and with substantial sustainability benefits.”

—Aaron Larson is POWER’s executive editor.