HRSG User's Group: Improving steam-plant reliability, durability and profitability    

Case Studies of Major Losses at Combined-Cycle Projects

Robert Sansone, Power Gen & Construction Practice, LLC

Modern steam turbines have redundant levels of protection from catastrophic overspeed, so overspeed accidents don’t happen in today’s modern times, right?

WRONG! Overspeed accidents still happen in today’s power industry! This presentation stunned the audience with its details of recent overspeed accidents that completely destroyed the turbines, along with other equipment nearby (fig 1).

Figure 1: Recent overspeed accidents prove the need for better maintenance and testing of our protection systems.

The presentation began with a riveting video of one of the accidents, captured in real-time by the plant’s security camera, and graciously provided by Sansone’s client for the training of HRSG users. Sansone then explained what he and his fellow investigators determined were the causes of these accidents, and the measures that plant operators and owners should take to prevent such a major loss at their plants. The cause: these plants weren’t testing their overspeed-protection systems properly. 

“And we find that to be true at many combined-cycle plants,” Sansone warned, whether they have the mechanical (Fig 2), or the newer, electronic types of devices.

Figure 2: The testing is needed on mechanical systems, like this one, and on newer, electronic systems.

Sansone blames this improper testing on a lack of training for both the O & M crews manning the plants, and the insurance representatives inspecting their policy-holders’ facilities. “Insurance reps are indispensable to our industry,” Sansone said. He continued, “Some of them are well-trained, experienced folks who provide sound risk-management advice to their policy-holders. The problem is that when the occasional untrained rep shows up in your plant, he or she leaves your plant with a serious risk-exposure.” 

Specifically, many folks who think they’re protected from overspeed are overlooking: 

    1. The role that the generator output breaker has to play in preventing overspeed 
    2. The need for sequential testing 
    3. The need to visually verify the travel of the control valve and other critical valves—such as the non-return valves on the extraction lines.

At that point, an HRSG user in the crowd shot up his hand and asked, “I can see how overlooking those first two things would mess up overspeed-protection, but what do the non-return valves have to do with it?” Sansone responded, “Great question! And you’re not the only one who doesn’t get this point about the non-return valves. The non-return valves are absolutely critical for this safety system, because entrained steam in the piping can exacerbate the overspeed during testing.”

In his concluding remarks, Sansone advised plant owners and operators to not only review the technical requirements in their OEM manuals for all of the protection systems in their plants, but to also look beyond the technical requirements, and to pay close attention to the cause of 90 percent of all accidents: The Human Element. The human element— inter-personal communication, leadership, and training, and so on—often gets dismissed as “touchy-feely fluff,” but its importance in the ‘hard’ business of science and engineering has been proved time and again during industrial accidents.

Consider the following infamous accidents, where inadequate training of personnel— not a technology failure— caused or at least exacerbated the accident:

    • The meltdown of Three Mile Island Unit two, where poorly trained operators failed to recognize the early indications of a jammed safety valve, which allowed that minor incident to cascade into the headline-grabbing accident that stopped the entire US nuclear-power industry dead in its tracks. Ever since this accident—March 1979—not a single new nuclear power plant has been licensed for commercial operation in the USA.
    • The RMS Titanic’s horrific loss of life, which could have been cut in-half, if the crew had been trained on launching their lifeboats. When the Titanic was found at the bottom of the ocean decades after its sinking, 12 of her lifeboats were still cradled in their davits, attached to the ship. These 12 boats would have held nearly 800 people. 
    • The grounding of the Exxon Valdez, where an inexperienced Third Mate conned the tanker smack into a reef, spilling 11 million gallons of crude oil into Prince William Sound.
    • The Chernobyl nuclear disaster, where poorly trained workers violated the procedures for low-load operations. This disaster immediately killed two workers, and 29 more died in the days following the accident from acute radiation exposure. Note that the long-term death toll and environmental impact of this accident have been hotly debated in the decades since.

Recall for a moment all of these infamous accidents, and contrast them with the following successes where the human element–and proper training — saved the day:

    • The US Nuclear Navy’s perfect operating record: which most maritime experts attribute to the intense, year-long training of its crews before they even step foot on their ship.
    • Neil Armstrong’s first lunar landing: which actually was a near-disaster, when a computer failed in the critical moments of the lunar descent. While Houston Control gasped when they heard the alarm, Armstrong calmly flipped a switch to take manual control, and went flying over the lunar surface in visual search of a safe landing spot. Almost nobody knows about this behind-the-scene near-disaster, but the entire world knows what came next: Across millions of black-and-white TV sets came Armstrong’s re-assuring transmission, “Houston, this is Tranquility Base. The Eagle has landed.” That was an act of great bravery, to be sure, but it also was a testament to Armstrong’s years of Navy pilot training, where he was taught that when all hell breaks loose, you must keep your wits about you, and turn to the most powerful computer ever made—the well-trained human mind. 

All of these examples show us that the ‘Human Element’ is as important to technological success as the lube-oil temperature is to steam-turbine operation.