Malloy Wind Solves Gearbox Bearing Mysteries

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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https://www.windaustralia.com 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?