Maximizing Your ROI When Managing a Fleet of Aging Heavy Duty Gas Turbines

Proven to be rugged, reliable, and lasting for decades, gas turbines are the workhorses of the power industry. Some turbines have been operating for years, with decades still to go, however, a significant number of these units will be reaching midlife in the near future.

As these units get older, maximizing their return on investment (ROI) requires a proactive strategy that includes attention and maintenance. Managers must assess various approaches and develop comprehensive plans to optimize performance and extend the life of these assets, all while managing the inherent risks of an aging fleet.

Let's say you want to operate a heavy duty gas turbine for 240,000 hours at 6,000 hours per year for 40 years. When you're coming up on 140,000 hours, chances are low that it will last another 100,000 hours without maintenance. Considering the rotor will likely fail anyway, you won't gain anything by trying to squeeze out a few extra hours. Instead, if the new heavy duty gas turbine will last 144,000 hours, maintenance at any time after 96,000 hours of operation will let the unit operate to 240,000 hours with low risk.

Mitigating Risks

There are specific trade-offs with respect to risks and investments when maximizing ROI. The key is to evaluate this through a number of lenses.

The first issue to consider is the operator's life-cycle view for each specific unit. How long and in what manner was the turbine utilized? The second issue is how the turbine has been operated. If it is located in a hot climate or is subject to a frequent stop/start operating regime, it will be prone to different failure modes than machines run differently in other environments.

OEMs can help provide plant operators insight regarding the potential failure modes that are more consistent with their particular operating profile.

Systems-Thinking Portfolio Approach

Each heavy duty gas turbine in a fleet is deployed with its unique history of run-hours. Consequently, there are ways to optimize the approach to an entire fleet, rather than focusing on isolated units.

Thinking about the fleet as a whole allows you to create a long-term vision. Determine which units need to be upgraded, which units operate base load at all times, and which units are peakers. Then you can put together a plan for how to handle different units.

In such instances, you might save costs by thoroughly upgrading a heavily used base load machine and swapping out and refurbishing its rotor for use in a less frequently deployed peaker unit.

It's best practice to develop a plan leading up to the second major inspection, anywhere from 96,000 hours to 112,000 hours for gas turbines, with a heavy focus on rotors.

Potential Failures

If operators choose to do nothing, they risk experiencing one of three modes of failure, each of them costly or potentially dangerous.

1. Forced Plant Shutdowns

Rotor vibration can force plant shutdown and rotor replacement, which typically involves a 30–45 day outage. It may be less of an issue for an infrequently deployed peaking unit, but it could be quite costly for a base load plant.

2. Lost Components

More critical is if a piece of the rotor comes loose, is sucked through the machine, and takes out the turbine, which could cost $10–20 million to repair as well as lost revenues from 45 days of downtime.

3. Uncontained Incidents

Complete uncontained turbine failure, such as the American Airlines jet engine failure at O'Hare airport in October, is a risk that, though rare, can occur and can be fatal.

As gas turbines and their rotors move into midlife, there is a fairly large sweet spot and, therefore, a dimension of flexibility where managers can act on rotors rather than waiting until the last minute. The savings resulting from proactive maintenance more than justify the investments.