What's the worst thing that could go wrong with your steam turbine?

A blade failure is probably one of the worst nightmares a power plant manager or owner could face—and the most significant level is a Last Stage blade failure, which poses the greatest risks for human safety and equipment damage. The full impact of such a blade failure depends on the location and severity of the damage, the secondary consequences, and the time it takes to get the unit back to service. And most moving blade damage cannot be repaired onsite, so they require downtime of 3 weeks to 6 months—depending on whether the necessary blades are available or need to be ordered. This can result in a huge generation loss and may result into heavy penalties for producers who have a committed power purchase agreement.

So why do blade failures happen?

They are often caused by stress corrosion crack initiations and propagation by low cycle fatigue (LCF), which can happen especially on wet stages and blades operating at high levels of stress. For this reason, these blades are designed and manufactured with the highest possible precision and they undergo a series of quality examinations before introduction to service. The design and precision of the machining also influences the frequency band the blade passes through, so a blade’s condition is the result of a combination of design and operation parameters within OEM guidelines. If the operating and maintenance of the turbine isn’t aligned with OEM standards, deviations can occur—in water chemistry, vacuum levels or wetness fractions—that could have adverse effects on blade health. In total, my team and I have observed 20+ Chinese OEM units that have steam turbine blade failures due to cracks and erosion.

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Customers often ask: “When will I know that my blade is going to fail? How can I prevent it from happening?”

Here’s one tip: If you notice an increased vibration in the unit, that could be an indication of an underlying issue. If left unchecked, this could cause the unit to trip—and the blade could even break apart from the unit, creating a dangerous situation for nearby equipment and people.

We have worked with customers to identify the fault before a failure happens by conducting an investigation on-site as part of a planned outage. How quickly we can detect the failure depends on level of recorded data our team is able to access. But failures most often happen on L-0, L-1 and L-2 blades, so it’s good to keep a close eye on those.

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Let’s say a blade failure in your Chinese OEM steam turbine results in a forced outage. What happens next?

The GE team has extensive experience across OEM and other OEM fleets for critical blade repairs and supply through re-engineering. The first thing we would do is get our on-site support team to the site quickly. From there, we would work with customers to identify the root cause of the issue, using 3D scans to take measurements. Depending on the results of the investigation, we can either repair and or re-engineer the blades.

When re-engineering a blade, we start by developing tailored manufacturing documentation and then introduce material or design improvements. It then goes through GE’s quality assurance program before being delivered to the customer.

Recently we worked with a customer in Saudi Arabia that operates a fleet of Chinese OEM steam turbines. We went to their site immediately after they contacted us about a blade failure and performed a measurement on the broken blades. Based on our fleet knowledge, we suggested that the customer also inspect another LP rotor for any last stage blade issues. As expected, there were cracks in the blades. After measuring the blades and performing a root cause analysis, we were able to re-engineer the blades according to our design expertise and offer the customer new and improved blades.

Be proactive and check your fleet!

This is what I advise all plant owners of Chinese OEM steam turbines and generators. Don’t wait for a failure to occur! If you have a Chinese OEM turbine, you might already be experiencing one or more of these issues. If not, you probably will soon.

Get in touch, and let’s work together!

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