7F Rotor Life Management: Top 5 FAQs
You asked - we answered. Here are the top 5 questions you're asking about 7F rotor life management.
YOUR TOP 5 ROTOR PLANNING QUESTIONS—
ANSWERED.
#1: HOW DO I START PLANNING
FOR MY ROTOR’S LIFE?
Hear from Penny Leahy, Senior Product Manager at GE Gas Power
Planning for rotor life management begins with a few questions. In my experience, starting with these four questions are a great way to initiate a dialogue around developing a plan.
One of the most important things we talk to customers about is planning early. Typically, our partnership with operators is the most successful when we start developing the plan three years before reaching the major outage where the rotor solution will be implemented. The first year revolves around understanding the future operational mission of the plant, time frame of the life of the plant, financial imperatives such as asset utilization, depreciation, risk management, then identifying options that most benefit the asset strategy of the plant. The second year is typically spent with customers acquiring various approvals. In the third year GE procures, manufactures, and tests items in preparation for delivery.
Our most forward-looking customers have a maintenance and rotor management plan covering multiple time horizons. For example, sometimes their plan exceeds 10 years and cover many outages cycles. Having a rolling 10-year perspective allows better decision-making throughout the lifecycle of the plant. As the industry changes, the recommended solution may change, too.
It’s not always easy to know where to start with the rotor life planning process, so let’s collaborate to find the optimal solution. Know that even if the future is uncertain or not so well defined, we welcome the challenge.
#2: HOW QUICKLY CAN I GET A ROTOR
IN AN EMERGENCY?
IT’S NOT WHAT YOU’VE PLANNED FOR...
...and certainly not what you want. But during an emergency sometimes you need a rotor—often due to issues that are many times beyond our control (weather and natural disasters, human error, equipment issues, or equipment damage).
But keep in mind, these are expensive inventory items, have specific unit design nuances, and configurations differences are important to understand for safe operation of the gas turbine. Even with these nuances, GE is typically able to work to cover the bulk of the FA fleet with assets in our refurbished rotor pool.
So what can you do?
Let’s go through a step-by-step process:
Our rotor pool: a closer look
GE makes our best effort to hold a safety rotor pool of assets for customers to use in the event of an emergency issue. It can be costly to hold a big inventory, and occasionally the lead times for some of the parts can be significant (for example nickel wheels have over a year lead time!).
We evaluate the size and reliability of each fleet by framesize. This is a general approximation that is mostly driven by the size of the fleet and our experience of needing rotors, as well as knowing that issues outside of our control happen at power plants.
Based on this fleet assessment, we try to hold an appropriate amount of rotors somewhere in our work in process to reduce the lead time of the return to service for operators.
#3: HOW HAVE ENERGY INDUSTRY CHANGES AFFECTED MY ROTOR LIFE?
Hear from Jeff Chann, Power Markets Intelligence Leader at GE Gas Power
Power plants were designed for a 30-year life. But depending on how you ran (starts vs hours) you may need to replace the rotor before your get to 30 years. Or your plant life may be extended beyond the 30.
So if you need a rotor, which is a major capital investment, you’re going to want to look at the new date you’re trying to reach. Ideally, you’d want to match the rotor life to expire right after that date. What’s important is the projected mission of the plant from now until then. Think about the number of starts, the number of hours, capacity factor, etc. Then, it’s an iterative conversation between engineering, operational risk, and finance.
The good news is that we recognize the dilemma and we’re here to help. But as you might expect, every plant is likely to have a different outcome, simply because every plant has different goals in your corporate strategy.
Since the F rotor was initially launched in the mid-90s, there have been many world and industry changes that have caused us to rethink how to operate a gas-powered plant. For example, legislation and influx of renewable power has caused gas power to become a back-up plan or be used to stabilize the grid in some regions.
In other regions, the retirement of coal and nuclear power has increased the burden on gas-powered plants to increase their output and provide more power to the grid. These two shifts in the energy landscape are just a few examples of what has caused GE to rethink how to best service and support power plant operators.
To support operators who need their plant to start more and cycle frequently, we’ve had to work closely with them to really think through this issue, and come up with creative solutions on how to best modify the equipment. We know that operators subsidizing a decline in coal or nuclear generated power have had to push their gas powered plants to the limits of physics by increasing the temperature and using hardware that can provide superior performance.
#4: WHAT FACTORS IMPACT MY ROTOR LIFE AND PERFORMANCE...AND WHAT SHOULD I CONSIDER TO MEET MY PLANT TARGET YEAR AND GOALS?
Hear from Louis Veltre,
7F Gas Turbine Product Manager at GE Gas Power
If I can offer one piece of advice up front, it’s this:
Short-term focus will limit your options during planning.
Typically, we see operators start planning 3 years in advance of needing to install a solution. This allows a lot of flexibility to evaluate different types of options. There are a few factors that influence the timing of needing a rotor solution. The main drivers are the number of hours and starts run per year. As we have seen the 7F gas powered plants moving toward a more cyclic operation, this can move the timing of rotor maintenance in or out in time.
Once the operator understands when a rotor solution is needed, it is helpful to analyze the long-term plans for the plant. In some cases, there may be some uncertainty in this area. However, in other cases the plant target year can be defined as the Power Purchase Agreement term or a plant life extension. Understanding how long you need to run your rotor solution helps you make sure you pick an option that gives you the right amount of rotor life, not too much or too little.
Other things to consider when planning for rotor maintenance include outage window or the need to address multiple gas turbines. Many operators face limitations on outage duration which does not make it easy to send their rotor to the shop for maintenance. In these cases we see most operators do a rotor swap with a new or refurbished rotor. Other times when there are multiple gas turbines to consider we can use a refurbished rotor asset as a seed and rotate it through the fleet of gas turbines.
#5: WHAT HAPPENS TO MY ROTOR WHEN I SEND IT FOR AN OVERHAUL?
30 turbine rotor, 10 compressor rotor and
100 blade design modifications
OVERHAULING A USED ROTOR
From our years of service shop and engineering experience, we’ve developed a thorough set of procedures for overhauling a used F rotor. Our processes are safety-critical and must be completed in a certified shop to avoid damage to plant and personnel if there is an issue with the rotor. Since 1990, there have been over 30 turbine rotor, 10 compressor rotor and 100 blade design modifications made with learnings from the fleet and engineering analytics, so it’s critical to understand the configuration and design of each asset to apply the correct rotor and achieve the highest overall reliability of the rotor after the life extension or swap is performed.
To do a full 7FA rotor life extension, typically it takes 12 weeks of time once the rotor arrives at our service shop assuming there was proper planning. The planning is critical to ensure all the parts and inspection equipment are at the service shop and ready to be used. Over the years this turn-around time has significantly improved.
When the rotor arrives at the certified service shop it undergoes a complete tear-down, is cleaned and inspected. A tear-down is required to ensure that all safety critical areas are inspected properly. Some of the inspections include eddy current testing, ultra-sonic testing and magnetic particle/fluorescent penetrant inspection of various areas of the rotor wheels and shafts. Some places undergo skilled repairs which must be performed with care. Additionally, some components cannot be re-used such as the stage 1 turbine wheel and bolting, among others. All parts and inspections used must be performed by a certified shop to ensure safe operation of the machine.
Once the rotor has been through the GE rotor life extension process, the rotor incorporates the latest latest technology improvements available for those components and is certified for safe operation.
We’ve overhauled over 325 units in the F-class fleet. As these rotors come through the service shops, we’ve observed findings, perform root cause investigations, and incorporated these lessons into our procedures to improve the rotor itself or our processes.
