February 2002
PLANNING FOR OUTAGE SEASON
In today's world, an outage may be as soon as next month. Scheduling an outage has become a fine art.
Once upon a time, plant maintenance personnel could rely on the good-old-fashioned rule of thumb to schedule a maintenance outage. Unless there was a specific cause for alarm, a turbine could be shut down on a regular scheduled basis for maintenance. For major maintenance, the plant could shut down for five or six weeks. Repairs were done, plant went back online, everybody lived happily ever after.
Then came the two-headed ogre of cost containment and deregulation to put an end to that fairy tale. Now, with outages costing an utility an average of $1 million a day in lost revenue, plant engineers find themselves pushed to extend the length of time between outages without running the risk of equipment breakdown and an unplanned outage. For Gas Turbines, the key word is risk. In today's competitive market, outage scheduling becomes a form of risk management.
According to the American Society of Mechanical Engineers' Risk-Based Inspection Guidelines, the first steps in assessing risk are defining the various components and sub systems, their failure modes and the consequences of failure. The last item here is critical. Without a clear understanding of the price of failure, operators cannot develop a rational plan for maintenance schedules. In this case, consequences are obviously the cost of repairs or replacements, but also the cost of lost generating time. Repair cost could be dwarfed by the cost of unscheduled down time.
The only way to project failure rates and consequences is by using data - the more data the better. Here, operators can tap into the company's data, the manufacturer's data, industry data and traditional reliability analyses. As with all data, the closer the data matches real-time operating conditions, the more valuable it becomes. One option open to plant personnel is also one which many avoid using: comparing data with operators in other plants using the same equipment. The reason for this reluctance is obvious: such data can be considered proprietary, akin to a business secret. However, if done appropriately, the sharing of data between operators of the same equipment can often provide a much more practical guide to potential failures than even the manufacturer's fleet data.
All of this data gathering goes to answering one essential question. "When was the last time I was at this operating point and what happened" Once that question is answered, plant personnel can make an informed decision as to when to schedule an outage or a borescope inspection of the unit. The decision, however, is dependant on another question. "How willing or how capable are we to perform condition-based monitoring"
Condition-based monitoring may be the holy grail of plant operations and maintenance. Essentially it means closely monitoring the condition of a turbine and shutting it down only as conditions warrant.
"Operators need to take ownership of their equipment," said Tony Thornton, vice president of Turbine Technology Services, a division of Sermatech Power Solutions. "It's no longer good enough to rely on other people's data. The key to an intelligent approach to scheduling an outage is to base the schedule on your own real world experience. For example, the needs of a plant in an industrial area may be very different from the requirements of a plant in a more rural area. The environment can have a distinct impact on a turbine, a factor not accounted for in average data."
As plant operators move more into a condition-based monitoring scheme, the time frame for actually scheduling the outage shortens. This means operators must be prepared in advanced. Rather than knowing an outage will be scheduled a year down the road, the outage may be required in the next month. The upshot is the operator needs to have a close working relationship with vendors who do the work and supply the parts.
According to Thornton, operators should consider developing long-term alliance with vendors where prices and a menu of services are negotiated in advanced. How to choose the vendor, however, is a matter of the operator doing his homework. For instance, quotes can be obtained for a tier of services - minor, medium and major repairs. By getting a variety of quotes on those services from different vendors, the operator can judge the market value of the services. In other words, if the quotes are in the same general price range, then the operator can most likely be assured the vendors are offering fair prices.
Being assured of fair pricing is crucial for the simple reason that the scope of work cannot necessarily be predicted in advance. No one can precisely predict what will be found once the turbine is opened. The best the operator can do is use his best judgement that the vendor will charge reasonable prices for additional work.
Along with comparing prices, operators would do well to actually visit vendor's shop. What looks good on paper can change when translated into the real-life environment. Along with an actual visit to the shop, references are essential. Operators should determine if the vendor is actually capable of doing the work, supplying the parts, etc within the required quality and time frame. Generally, paying more for quality workmanship and strong engineering support will result in significant long-term savings for the equipment operator. This is not an area to "go cheap" since the costs of an unplanned outage or reduced component life generally dwarf the cost of a component.
Typically, operators think of an outage as involving the turbine. However, an outage also provides the best time to perform maintenance on the other parts of the system. In negotiating contracts and getting quotes, operators should obtain agreements on all of the equipment that may need repair of maintenance.
Structuring the quotes is an art in itself. Should the request for the quote assume one vendor does all the work, or should the different aspects be given to different vendors Perhaps the best way to tell is to ask for different quotes from the same vendor, i.e. ask for a quote for the whole project and a quote for the separate components. That way, the operator can get a better sense of the cost-effective method. Once the vendors have been selected, meetings should be scheduled before and after the outage along with pre- and post-operating measurements.
Once the preparatory work is done, operators are still faced with the decision of timing. Inevitably, that means data collection and analysis using an appropriate system. A wide variety of systems are now available and refinements seem to flourish every month. for instance, Chicago-based Industrial Peer-to-Peer developed a system called eDNA. This system captures, archives and time-stamps mountains of historical and real-time data from power and industrial plant equipment and systems operations sources, including heat rates, fuels cost, transmission information, inlet coolers, gas turbine levels and duct burner fuel flows. According to John Kalanik president of InStep Software, "The historical data can be used in conjunction with the software calculation functions to identify developing situations in equipment. The data can be fed into other programs to create a real-time picture of how the specific turbine is operating."
Kalanik went on to describe a situation with a client that can serve as a model for the contemporary plant engineer's life. The company wanted to turn each unit in the plant into a cost center. That meant operations personnel were expected not only to make operation's decisions, but also make those decisions as financial decisions. Replace, or rebuild, schedule an outage or prolong the time, these were all financial decisions as well as technical decisions. From a financial point of view, data collection and software systems can also help pinpoint the best time for a scheduled outage. By tracking power demand and the price of energy, operators can make an informed judgement as to when an outage will cause the least damage to the bottom line.
In the current economic climate, outage scheduling demands the informed use of data. Perhaps the most important step in planning for an outage is the development of the plant's own data in order to establish realistic criteria. As Sermatech's Thornton said, "The challenge to the plant operator is to take control of your own destiny."
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