Show notes
From mysterious white etching cracks to cutting-edge material innovations, Malloy Wind's expert Cory Mittleider reveals the complex world of gearbox bearing failures that plague wind turbines. Learn why traditional monitoring may not be enough and what operators need to know about the latest solutions to keep their gearboxes running reliably. Read the EPRI article Cory references: https://restservice.epri.com/publicdownload/000000003002021422/0/Product
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Welcome to Uptime Spotlight, shining light on wind energy's brightest innovators. This is the progress powering tomorrow.
Allen Hall: Welcome back to the Uptime Wind Energy Podcast Spotlight, where we tackle the technical challenges and innovations in wind energy. I'm your host, Allen Hall, joined by my co host, Joel Saxum.
We're excited to welcome back one of our most popular guests, Cory Mittleider from Malloy Wind. In his previous appearance, Cory shared his expertise on main bearing failures. And many of you reached out asking for a deep dive into gearbox bearings. Today, Cory returns to do exactly that. As Malloy's business unit manager, he and his team have diagnosed and solved countless gearbox bearing issues across different turbine platforms.
Having spent over 15 years in power transmission, Cory has become a specialist in understanding why these critical components fail and, more importantly, how to prevent those failures through better bearing selection and maintenance practices. Cory, welcome to the Uptime Wind Energy Podcast Spotlight.
Thanks for having me again. All right, so we've got a lot of requests to hear about gearbox, bearing, and what the issues are with those bearings. Gearboxes is something I know a little bit about. But you're the expert. I hear a lot of complaining from the field. What is happening to gearbox bearings at the minute?
Cory Mittleider: Sure. Gearbox bearings has been an interesting one for me. So when I started in wind in 2011, it was generator bearings and gearbox bearings is where I started learning about this stuff. A lot of the generator stuff was electrical fluting damage. That's pretty well figured out how to avoid that.
The gearbox one was a little more complex than that. And I don't know if you've heard of. NREL's Drivetrain Reliability Conference that's happened for the last 12 plus years now. That's a recurring topic for the last every single year, right? Is gearbox bearing failures. A lot of the conversation that started back in the day and is still going on is around what they call white etching cracking or white etching failures.
And back, in say, 11 and 12, A lot of the conversation was around was around that. It was around, the oils in the gearboxes. It was around coatings and bearing types and how they could affect the bearing itself to improve the life. And, specifically when it comes to gearbox bearings That was really hard back in the, the service providers and the operators themselves weren't used to having to replace gearbox bearings.
They maybe weren't even planning on having to replace gearbox bearings, right? But they started to see these problems. They started to get their head around the scope and how to identify them early and started to dig into it. There's been a lot of investigations from bearing manufacturers, from third parties, from operators.
into those failures for over a decade now.
Allen Hall: I remember looking into some of the early gearbox issues and you're talking about some of the failures I am actually familiar with. Those had a lot to do with just sort of basic fundamentals of like lubrication and loading, which were not obvious at the time.
Have we overcome some of those sort of basic bearing issues, or do they still exist out in the field?
Cory Mittleider: I started going to this drivetrain reliability conference in 2015. So I was a couple years later than the initials. But some of the earliest things I remember was slip occurring, right?
From typically I think the scenario that was presented on was high speed low load scenario. Yep. Such as bringing a turbine online, and I remember a chart very vividly from NREL's outfitting of the high speed bearings on their test 1 5, right? The rollers should be rolling at 400 RPM, but their only roll, or the cajun roller assembly should have been going 400 RPM.
But it was only going 100 RPM meaning there was a ton of slip, a differential speed between the rollers and the inner ring raceway surface. There was some, oils that got fingers pointed at them for essentially being readily available to, to release hydrogen ions. And as we look back at wet etching cracking and the information that's been collected over the years and investigated I think most people agree that hydrogen embrittlement is a big factor in that, um, there's certainly components of material cleanliness that are involved in that conversation as well.
It's a lot of investigation there. And to answer your question, is it still happening? I've got this report from an organization called EPRI. I found it on their website. It's called Wind Turbine Gearbox Reliability Assessment. And they have listed what is it, seven points that lead to most of the gearbox related issues.
related failures and I'll just read them off. It's high contract stresses leading to pitting and spalling, bearing race slippage, macro pitting due to skidding and bearing slippage, wear due to inadequate lubrication, race cracking due to white etching formation, low quality materials and material defects or inclusions.
and improper bearing design leading to non uniform stresses or loads. And this was published December of 2021, right? So this is a couple years old, but it's pretty, pretty recent from an accumulation of data, having time to digest and put out a report. This is pretty recent. And when I look at some other things in here that are really interesting 42 percent of gearbox related downtime is from high speed and intermediate bearings.
The other 58 percent is gearing related or maybe some of the other stages, but 42 percent are from high speed and intermediate bearings from those failure modes that I described. So the takeaway in my mind, as much as that's something to be aware of and watch out for if it's high speed and intermediate bearings, those often are replaced up tower.
So you can do that scopal work up tower. Another thing that's also in the report they're talking about that uptower scope of work costs somewhere between 15, 000 and 70, 000, right? So you can guess the sooner you catch that, you're monitoring your CMS, you're looking for inner ring defects or cracked inner ring or whatever, maybe sometimes outer rings falling as well.
If you can catch that sooner, get that replaced sooner, there's less debris generated, there's less additional ancillary components that need to be replaced or serviced. And that keeps it closer to that 15, 000 Scope of work,
Joel Saxum: of course, right? Let me ask you a question about that then. So to find that early enough, we're usually always talking CMS, right?
And we know there's a CMS usually from the factory. If it's a Vesta, whatever they, if they're doing an FSA, they're monitoring that from afar. But there is aftermarket CMS for drivetrain monitoring that, like Onyx Insight comes to mind and there's a couple of other brands out there, of course, would you recommend?
Cause this is a conversation we just had not too long ago with a bunch of people about blades and other reliability things. Would you recommend someone to shadow monitor a like a drivetrain CMS, even though they're maybe they're. Full service, agreement already has one. Do you think that's smart?
Do you think that's a good spend on money?
Cory Mittleider: Unfortunately what I've heard is it seems like no matter the application, gearbox, blade bearings, anything I've heard quite a few operators say that when they got to the end of warranty period or end of service agreement periods, they didn't know what happened.
They didn't know if X component had been replaced at all, or if it had been replaced five times. I guess I would certainly encourage operators to do everything they can to understand their own equipment. Is that making sure they get the reports from the people that are currently hired to service that?
Maybe it's as simple as that. Maybe those are behind the wall, and they don't get access to those. And there probably is some merit in understanding or maybe even say, shadow monitoring or double checking some things on their own to understand their asset. Ultimately it's their asset.
And They'd be best off to know what's going on with it. Yeah.
Joel Saxum: So let me ask you another question. With all of the, and this is monitoring inspection related. So to, to catch problems early. So CMS is one tool, right? Another tool is like an Uptower Borescope inspection. Of course, to me, end of warranty is an absolute must to have a third party come in and look at the, do a bore scope inspections, end of warranty.
Is there any other times that you recommend that, or do you recommend that to do every year like we do blade inspections, or what does that look like for you?