Swift response saves the day after massive turbine failure;
In recent years, the large electric generating plant located south of Boston on the Fore River has had to over come many challenges as it underwent massive upgrades and frequent changes of ownership. Those challenges were driven, in part, by the shifts in energy costs, deregulation and environmental requirements that have roiled the entire utility sector.
Established early in the 20th century by Boston Edison as the coal-burning Edgar Station, the facility had a long history of serving the region and particularly its neighbors, such as the historic Fore River Shipyard, founded by Alexander Graham Bell’s famous business partner, Thomas A. Watson. It was eventually retired in the 1970s due to cost and environmental concerns. However, the plant was reborn with modern technologies when the old site was acquired from Boston Edison by Sithe Energies.
The new owners contracted with Raytheon’s Engineering & Construction Group to build an efficient, state-of-the-art facility. But midway through the project, Raytheon sold the division to another company which quickly went bankrupt. Fortunately for Sithe, Raytheon was contractually obligated to complete the plant – and did – in time for an Exelon subsidiary to buy the plant from Sithe. The combined-cycle facility married natural gas combustion turbines with steam turbines to squeeze the maximum power from the fuel consumed – up to 40 percent more electricity generated for a given amount of heat energy.
But that was by no means the end of the convoluted story. That subsidiary, in turn, ended up in financial difficulties and plant ownership went to US Power Generation, through its subsidiary, Boston Generating Company.
An unfortunate incident
It was during Boston Generating Company’s ownership that the facility faced one of its greatest challenges – the failure of a recently acquired Mitsubishi 501G gas turbine unit (GT11), which threatened to keep the plant offline for more than a year. Fortunately, however, FM Global was able to bring its resources and experience to bear, yielding a happy ending.
The unit consisted of a 17-stage axial compressor, 16-can annular type steam cooled combustors and 4-stage turbine, and was rated at 254 megawatts. The combined-cycle unit also included a heat recovery steam generator (HRSG) with a single high-pressure/intermediate-pressure, and double-flow low-pressure steam turbine. To provide an ‘insurance policy’ against natural gas supply disruption or price spikes, the turbine was also designed to operate on fuel oil when necessary.
After performing without incident for more than five years, on October 20, 2008, GT11 tripped offline due to the operation of a high-temperature relay. That in itself was not exceptional. However, when the building shook and the unit coasted to a stop in a mere eight minutes, compared to the normal 25 minutes, operators were certain they encountered a major mechanical problem.
The severity of the problem was revealed when the casing of the combustion turbine was removed. A row-2 compressor blade had detached, causing extensive component damage downstream. In fact, nearly all the compressor blades and vanes were damaged as was the compressor inner liner. That’s when Boston Generating phoned their account manager at FM Global and explained the problem. FM Global got in the loop as soon as they learned of the loss, ready to support Boston Generating and share advice and experience. Within hours, they had an adjuster on scene along with an experienced field engineer able to provide technical support.
For an insurer, the first order of business when faced with any potential loss is to determine the scope of damages and the potential scale of the problem. That’s followed quickly by thoughts about how to get the insured back in business. Since the turbine generator was of recent vintage and had, by all accounts, been properly maintained, there was no question of considering wear and tear as mitigating matters. With that box checked, it was straight to loss assessment and mitigation.
As technicians delved deeper into the machinery, things began to look even worse. Repair would be challenging. The turbine blades and other hot gas path parts were shipped to Mitsubishi Power Systems at their Orlando Service Center in Florida for examination, nondestructive evaluation, and refurbishment and repair, if or when possible.
FM Global determined that complete, new compressor rotor replacement and a repair of the combustor and turbine section would cost more than US$25 million, not including shipping and installation. Mitsubishi provided an initial estimate for rotor repair of approximately US$18 million for the rotor, blades and the labor, a figure only slightly lower than replacement costs. However, either option was expected to require 12 to 18 months before the unit could be back online. That lag time represented a huge reduction in potential revenue from electricity sales.
Faster and better
By then, FM Global had brought in an accounting team to meet with the financial and accounting people at Boston Generating with the goal of determining how much power the station had generated, how much revenue was earned on that electricity, and the likely financial impact of protracted downtime. Although the plant’s operating profile changed from season to season and varied with demand (factors such as extremely hot or cold weather figured into calculations), they came up with an estimate that, on average, each week of downtime cost the facility about half a million dollars in lost revenue.
That was a big number and it got everyone’s attention. Clearly, time was of the essence and anything that could be done to shorten the time needed for recovery should be considered.
Then, the turbine manufacturer identified an available compressor rotor in Japan. The complete replacement rotor with blades was available and could be shipped within a month, saving approximately 15 months in downtime, though the manufacturer would need to alter the coupling section of the compressor rotor assembly to fit the specific unit in place at Boston Generating. With those modifications, the total cost came to US$11 million. Distance was still the challenge. Shipping via sea and land would require at least six weeks. To shorten that time period, it was proposed to airlift the compressor rotor – something only a handful of airfreight companies could do. That responsibility was expedited and accomplished, and the giant Russian Antonov aircraft, operated by Volga-Dnepr Airlines, was summoned, loaded and sent on its way.
But nothing is ever simple. The shipping container in which the compressor rotor was packed was designed to keep corrosive salt air away from sensitive components on a long, sea-level voyage. For that reason, it was airtight. However, as the Antonov climbed to operating altitude, the drop in air pressure in its unpressurized cargo bay made the container burst, causing consternation for the crew, who opted to land immediately in Russia.
Although the only apparent damage to the aircraft turned out to be displaced insulation, a ‘better safe than sorry’ attitude prevailed and a substitute aircraft was summoned, the compressor rotor was transferred, and the component again went airborne, bound for Portsmouth International Airport, near Boston.
Once safely on the ground, the aircraft was met by a local trucking firm specializing in extra bulky and heavy loads. Their job was to navigate the remaining miles to Boston Generating.
When components came on-site and repairs got under way in earnest, a few more surprises were discovered. Debris from the original point of failure had permeated other parts of the system. That meant additional removal of debris and cleaning the air ducts from compressor to coolers. Furthermore, there was heat damage to the power (combustion) portions of the turbine. Fortuitously, Boston Generating determined that they had a complete set of refurbished power section blades, which had been purchased for future installation at the company’s sister facility north of Boston.
FM Global’s adjusters provided an onsite clerk to monitor day-to-day repair activities as they progressed. Ultimately, repair of GT11 was expedited by approximately 45 days by the use of airfreight instead of shipment by sea. The use of parts scheduled for another unit owned by the company further reduced the period by several months. That meant the time period from determination of loss to resumption of commercial availability was a mere 129 days.
Evaluating the incident
FM Global Senior Engineering Specialist Daniel Farnham explains that it was possible the loss could have been prevented. Analysis of the failed blade showed there had been a pre-incident defect (stress due to a minor dent). Since the plant utilized very good preventive maintenance programs and had qualified operators, it might have been possible to spot the blade problem.
Still, given the extent of damage in the incident, this evidence of prior blade damage was not considered conclusory. Farnham also notes that combustion turbines are especially prone to failure. The combination of high operating temperatures and speeds and shifting duty cycles (more warm-ups and cooldowns than in a continuous-duty scenario) could have contributed to the failure.
On the other hand, the operator exhibited good contingency planning – stocking of spare parts – which significantly reduced the forced outage downtime.
Today, the plant is operating effectively. The facility was sold to Calpine in November 2014 and is now called the Fore River Energy Center. It continues to sell power into the competitive wholesale markets administered by ISO-New England, an independent, not-for-profit corporation responsible for keeping electricity flowing across the region.
This article first appeared in Reason magazine Issue 2, 2016, which you can read here