When Should You Do Your Next Major Turbine Outage?

Executive summary

John Latcovich, Hartford Steam Boiler

How can you decide and justify the right time between major outages for steam turbine generators? A proven approach is to have your steam turbines and generators analyzed by Hartford Steam Boiler's proprietary risk-based programs. TOOP (Turbine Outage Optimization Program) and STRAP (Steam Turbine Risk Assessment Program) can help predict when outages should occur. These unique programs optimize and prioritize steam turbine and generator overhaul interval, maintenance and upgrade decisions. 

Risk and Reliability

The programs utilize reliability and risk factors that were developed by pooling the cumulative knowledge and experience of HSB and leading members of the power generation, manufacturing, engineering consulting and repair industries. By using that experience and data, HSB established the attributes that are important and necessary to achieve a longer time interval between major turbine and generator outages. Those attributes were converted into risk modifying factors to view turbine and generator risks in terms of design, history, operation, inspection and monitoring.

How the Programs Work

For each risk model, the systems, subsystems and components are defined for the steam turbine and generator. For instance: a typical steam turbine generator evaluated by TOOP looks at high-pressure, intermediate-pressure and low-pressure turbines and the generator. Within each section, the risk model defines failure mechanisms, probabilities of failure and consequences of failure for each component. Detailed questionnaires account for differences between units and the information is used to modify risk levels based on the risk modifying factors developed by HSB and its industry teams.

Longer Outage Intervals

HSB's TOOP and STRAP programs have analyzed 138 turbines and 93 generators. The units have included nine different turbine and generator original equipment manufacturers, sizes from 590 SHP to 890 MW, dates of manufacture from 1946 to 1992 and operating times from 12,000 hours to 54 years. There is no guarantee that every unit will achieve a longer outage interval, but more than 80 percent of the units analyzed by HSB have one or more outage levels of turbine sections or generators increased by one to five years.

What the Programs Can Do For You

The TOOP and STRAP programs can help plants in all industries to:

  • Safely defer or extend the time between major outages
  • Reduce steam turbine and generator total risk and improve reliability/availability
  • Focus plant efforts on the most important areas (highest risks)
  • Tailor major outage work scopes to concentrate on the areas of highest risk to minimize outage costs and time
  • Utilize/evaluate as a corporate standard for objective benchmarking, risk assessment, and outage planning for prioritizing corporate resources and budgets
  • Save your company money

About the Author

John Latcovich is Hartford Steam Boiler’s Fleet Manager for Rotating Equipment. He has more than 27 years experience with rotating machinery and works with HSB inspection specialists and clients on rotating equipment technical, operational and maintenance issues.

 

The full article

When Should You Do Your Next Major Turbine Outage?

Introduction

HSB’s analysis tools, TOOP (Turbine Outage Optimization Program) and STRAP (Steam Turbine RiskAssessment Program), can help predict when outages should occur, allowing your equipment to run longer between scheduled shutdowns. These unique risk-based programs optimize and prioritize steam turbine and generator overhaul interval, maintenance, and upgrade decisions. 

Determining the time between major outages for steam turbine generators can be a difficult decision. You cannot afford to do major steam turbine-generator outages too frequently. If you wait too long, you may have to undertake an unplanned outage to perform major repairs. Meanwhile, your insurance company wants to know what justification you have to safely defer an outage. How do you decide and justify the right interval to schedule your major outages?

A proven approach is to have your steam turbines and generator analyzed by Hartford Steam Boiler’s proprietary risk-based analysis programs TOOP (Turbine Outage Optimization Program) or STRAP (Steam Turbine Risk Assessment Program). These programs were developed by HSB in the mid-to-late 1990s to objectively and independently assess the risk of steam turbines and generators to run longer times between major outages.

Reliability and Risk Factors

HSB with leading members of the power generation, manufacturing, engineering consulting and repair industries pooled their cumulative knowledge and experience to develop reliability and risk factors for steam turbine and generators. That experience and data was leveraged to establish what attributes are important and necessary to achieve a longer time interval between major outages. Those attributes were converted into risk modifying factors to view turbine and generator risks on a holistic basis — design, history, operation, inspection and monitoring. This information was constructed into turbine and generator risk models based on the Risk Based Inspection Guideline methodologies of the American Society of Mechanical Engineers (ASME).

The TOOP risk model was tailored for multiple case steam turbines and generators utilized in power production applications. STRAP was tailored for manufacturing applications where the steam turbine was heavily integrated into the manufacturing processes such as in the refinery, petrochemical, chemical products, and pulp and paper industries.

How the Programs Work

For each of the risk models, the systems, subsystems and components are defined for the steam turbine and generator. A typical steam turbine generator evaluated by TOOP is indicated in Figure 1. In this case, there are three turbine sections (high pressure (HP), intermediate pressure (IP), low pressure (LP) turbines) and the generator.

Figure 1 – Typical TOOP Steam Turbine Generator  

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Within these sections, the major systems, subsystems and components are defined in the risk model along with the applicable failure mechanisms, probabilities of failure and consequences of failure (repair/replacement costs or lost production time) for each component. To account for differences between units, the programs utilize a detailed questionnaire that modifies the risk levels of the unit based on the risk modifying factors developed by HSB and its industry teams. The program uses the questionnaire responses to modify (raise or lower) the baseline component failure probabilities and consequences based on the specifics of the unit being analyzed. From the completed questionnaire and the failure probabilities and consequences included in the programs, the risk values are calculated by component, subsystem and the total system.

Viewing Risks - the Crystal Ball

Because the risk values in the program are calculated at the component level, it is possible to look inside the unit to determine where and what are the highest risks and what total risk for the unit for comparison or benchmarking with other units. This is what the TOOP and STRAP programs do. Figure 2, Table 1 and Figure 3 show the TOOP results for an actual IP turbine. In Figure 2 the highest risk components are identified in descending order. Table 1 indicates which failure mechanisms are driving the risk levels. Figure 3 compares the total risk level of the unit analyzed (Unit 100) with all other IP turbines analyzed by HSB.

What does all this mean and how does it relate to the crystal ball? From Figure 2, you can expect that future problems will most likely occur to turbine blade airfoils and blade shrouds, as these are the highest risk components. From Table 1 you can expect that foreign object damage (FOD) and erosion will be the risk drivers for the blade airfoils, while FOD, erosion and rubbing/distortion will be the risk drivers for the blade shrouds.

Because the programs identify the highest risk components and failure mechanisms, you can tailor your maintenance and inspections to concentrate on these areas to minimize the risk of failure and extend the time between major outages. Such actions could include frequent borescope inspections of the airfoils for FOD and erosion damage, more frequent inspections of the steam strainer for debris to prevent FOD damage, and more care in starting the unit to avoid blade tip shroud rubs.

While the risks inside the machine tell you where to concentrate your efforts, the time between outage also depends on what the total risk levels are. In Figure 3, the risk level of Unit 100 is relatively low compared to the other IP turbines analyzed by TOOP. From just a pictorial view, you would expect that turbines (or generators) with lower risk levels should be capable of running longer between outages. That is precisely the case. The turbine and generator risk levels are converted to time between outages by algorithms in the programs.

An example of the results is shown in Table 2. The time between outage is calculated for an actual turbine generator that has three turbine sections (HP, IP, and LP). To facilitate the time between outages, HSB has adopted an equivalent operating hour (EOH) formula for the number of hours, starts and overspeed tests that a unit accumulates during operation. Table 2 indicates the EOH between major outages as well as the calendar time between major outages based on yearly profile provided by the owner.

Do They Really Work?

Since introduction, Hartford Steam Boiler's TOOP and STRAP programs have achieved objective/consistent risk levels and risk distributions regardless of original equipment manufacturers (OEM), operating hours, size, or year of manufacture based on the 138 turbines and 93 generators analyzed to date. The engineering modifying factors utilized in the programs have been calibrated with units of all kinds. The risk model and associated risk levels have been grounded with units that have run longer outage intervals.

The units analyzed have included nine different turbine and generator OEM's, sizes from 590 SHP to 890 MW, dates of manufacture from 1946 to 1992, and operating times from 12,000 hours to 54 years. While there is no guarantee that every unit will achieve a longer outage interval, more than 80 percent of the units analyzed have one or more of their turbine section or generator outage intervals increased by one to five years.

 

 Figure 2 – IP Turbine Risk Ranking by Component 

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Table 1 – IP Turbine Risk Ranking by Component and Failure Mechanism 

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Figure 3 – IP Turbine Risk Ranking/Benchmarking Comparison  

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Table 2 – Calculated EOH/Time Between Major Outages  

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What Can These Programs Do For You?

Since the programs were introduced, the programs have and continue to accomplish the following for plants in all industries:

  • Safely defer or extend the time between major outages
  • Reduce steam turbine and generator total risk and improve reliability/availability
  • Focus plant efforts on the most important areas (highest risks)
  • Tailor major outage work scopes to concentrate on the areas of highest risk to minimize outage costs and time
  • Utilize/evaluate as a corporate standard for objective benchmarking, risk assessment, and outage planning for prioritizing corporate resources and budgets
  • Save your company money

Summary

Assessing risk to the next major turbine outage has become an even more challenging task when you factor in such issues as employee downsizing, aging equipment and reduced operating and maintenance budgets. New approaches are needed to respond to these sweeping changes across all industries. The use of HSB’s risk-based analysis tools meets the needs of industry concerns today — combining the technical and reliability factors of equipment with financial consequences so that limited company resources can be applied to the equipment with the most need.

About the Author

John Latcovich is Hartford Steam Boiler’s Fleet Manager for Rotating Equipment. He has more than 27 years experience with rotating machinery and works with HSB inspection specialists and clients on rotating equipment technical, operational and maintenance issues.

 

Disclaimer statement:

All recommendations are general guidelines and are not intended to be exhaustive or complete, nor are they designed to replace information or instructions from the manufacturer of your equipment. Contact your equipment service representative or manufacturer with specific questions.

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