A little over ten years ago, the Sayano-Shushenskaya hydroelectric dam, once Russia’s largest, failed with catastrophic results. A problematic turbine in the main turbine hall began vibrating rigorously – more so than it ever should. Before long, the turbine cover was displaced and the 1000 ton-rotor rocketed into the air, allowing water to shoot from the shaft at 67,000 gallons per second. The turbine hall folded in on itself like a house of cards.
The failure raised many questions relating to turbomachinery safety control systems. What caused such rigorous vibration in the first place? At what point should an emergency shutdown have occurred? What safety standards might have prevented such a disaster?
Types of Turbomachinery
To understand turbomachinery failure modes, it’s important to point out that turbomachinery comes in all shapes, sizes, and has a variety of interesting applications. Essentially, anything that transfers energy from a fluid to a rotor is a turbine. Anything that transfers energy from a rotor to a fluid, is a pump or a compressor. They can be categorized even further, to whether the flow runs parallel (axial flow) or perpendicular (radial flow) to the axis of rotation. This family of machines also includes fans and wind turbines.
In industrial facilities and power-generating plants, ensuring the constant, safe operation of turbomachinery and compressors is key for safety lifecycle management. But achieving this is not easy. Traditionally, every individual turbomachine function has its own separate safety controller, software, and protection system. This meant it was often difficult to get an overview on turbomachinery performance.
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Fatigue and Corrosion: The Shock Factors
An investigative report in the Russian dam revealed that the turbine which erupted on the morning of the event was to blame for the catastrophe. Not only was the turbine cover missing at least six of its mounting bolts, but of the 49 bolts recovered, 41 of them showed signs of fatigue.
Fatigue is a concern for plant operators dealing with rotating equipment. The same goes for corrosion, which is mainly caused by the repeat fluctuation of a moving metal component. Whether its blades, bearings, or bolts; regular physical inspection during maintenance intervals can reveal even the smallest signs of fatigue or corrosion that can have extreme consequences if left untreated.
Full Speed Ahead – But No More Than That
Overspeed protection is the most crucial aspect in the turbomachinery safety train. The energy that is generated in the rotor can force the turbine apart, if it exceeds a safe operating speed. Therefore, finding the balance between productivity and functional safety is essential.
According to the Sayanogorsk report, a fire at another power station on the same day caused vital communication and automation systems to fail. The report also declared that the company’s vibration monitoring program was “below industry standard” and that predictive maintenance was “not practiced to any great extent.” The then-Prime Minister of Russia, Vladimir Putin declared a nationwide inspection of industrial infrastructure.
All in One
In the past, all safety functions would be built-in to the turbomachinery itself – mechanical shutdown is one example of this. Such a mechanical shutdown would involve numerous logic-solvers and require extra external support, not to mention complex architecture.
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Nowadays, all functions are separated, allowing for greater control and foresight over individual aspects, such as speed and vibration. Monitoring, regulating, and controlling turbomachinery is simpler. Plant operators that opt for a proactive approach to safety, making use of proper diagnostics and monitoring equipment, will also enjoy maximum uptime and machine reliability. This teamed with the international acceptance of functional safety and automation standards – API-670, IEC 61508, and IEC 61511 – will mean that accidents like the one in Sayanogorsk can be avoided in the future.