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Allen Hall discusses the growing issue of blade wrinkles with Morten Handberg, blade expert at Wind Power LAB. They delve into the causes, consequences, and challenges of identifying and repairing these minute deformities that can significantly reduce blade life. Visit https://windpowerlab.com/!
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Allen Hall: Welcome to the special edition of the Uptime Wind Energy podcast. I’m your host, Allen Hall, and if you have been following the news lately, there are several ongoing campaigns by blade manufacturers to deal with wrinkles in their blades. Even though these wrinkles are minute in appearance, these fabric deformities can create weaknesses that reduce blade life.
And as you have seen all over the news, these wrinkles are also expensive to remove and repair. Our guest is Morton Handberg, Chief Blade Specialist and Partner at Wind Power Lab, which is a blade consulting company located in Copenhagen, Denmark. If you haven’t heard Morten on our podcast previously, Morten is our resident blade whisperer.
In our episode today, we’ll be discussing how wrinkles are created, how they produce stresses, and why they are difficult to eliminate during manufacturing. Morten, welcome to the program.
Morten Handberg: Hi Allen,
Allen Hall: it’s nice to be back again. If we can catch up a little bit, you and I talked to each other about Blade Wrinkles several weeks ago now, and that topic has just gotten progressively hotter and hotter.
I thought, now’s the time. To get it out there about what’s happening with wrinkles and why we should care. Now, and at the same time, you sent me some pictures and it would just scare the heck out of me because I thought these wrinkles were relatively small coming from an aerospace background.
Wrinkles don’t tend to be big. In aerospace products, but the wrinkles you showed me are large. And I’m trying to understand like what is the real threat here? Let’s just start there. What’s the real threat. If a wrinkle is in a side of a blade, what does it matter?
Morten Handberg: So it really matters depending on the location of the wrinkle.
So is it in the structural spark cap or in a heavy node, part of the bait, let’s say the root or the transition zone. Then even small wrinkles can actually turn into very large cracks. And it doesn’t really matter what the size is. It’s more, if it’s in an area that allows it to grow into a crack, because as soon as it does that, it will just continue growing at a pace defined by the loading conditions, it can ultimately turn to a blade failure.
Obviously, the larger and more aggressive, the cracking the wrinkles, meaning how how steep the angles are of the wrinkles. So if this is the shape it matters that the wrinkles is shaped like this or like this. Then how much stress it requires for it to develop, because it’s all about the, how much reduction that it creates to the to the underlying blade structure.
If you have changes in the UD laminate and it starts to fold, it means that the strength of the UD laminate is reduced. And then it’s just about a matter of time before it then turns into a structural crack.
Allen Hall: And the defect doesn’t just apply to the plies where the wrinkle is, it applies, it puts additional stress on the plies that are around it?
Is that the loading problem?
Morten Handberg: Yeah, because, if you remove the loading capacity of one area, it has to be taken up by another, right? It doesn’t, the loading doesn’t go away. It just, if you have a wrinkle that starts turning into a crack, it means that all the UD fibers, they are essentially removed from the equation.
They’re not taking up any blade loads anymore. And that then creates more stress to the boundaries of the crack, but it also creates more and more stress to the other laminate areas of the blade, because now they have to take over whatever part is this area of the blade, but this area of the laminate was taken over.
And this is also why some of these cracks can turn into blade failures. Because at a certain point, then then the amount of laminate that’s been removed, that’s not enough for the rest of the blade to, to carry the load anymore. And then it eventually fails.
Allen Hall: What does this look like as the wrinkle progresses into a larger defect?
Is it a delamination that happens? Is it a physical crack? Like you start breaking plies? What does it look like?
Morten Handberg: If you have a wrinkle as I said, it’s like a fold inside the laminate. If the, if that fold is creating a wave like this, then at, on the top of the ridge, you are, you’re consistently, the wrinkle is trying to stretch itself out during operation.
So it’s trying to do like this and that creates a lot of stress on the top part of the ridge. And that’s where you create the crack. But on the lower side where you have the slopes, they are trying to lift they’re lifting themselves out, out of the laminate, essentially, that that’s what’s going on.
Is it and that then means that it de bonds from the from the lower from the laminate. What we typically see is that on the lower boundaries of the wrinkle, we create delamination and then on the ridge, we create a crack in the direction of the wrinkle. Wow. Okay.
Allen Hall: So you, depending on where you’re looking, you may see a DLAM or you may see a crack on either side of it, but you probably have both?
Morten Handberg: If you have in a very sensitive area where you have very high loading, maybe one or the other is more than maybe the crack is more. Aggressive than the wrinkle. So the crack will progress faster than the delamination develops. If you’re in a low unloaded zone, then maybe it’s the delamination that is the most prominent one developing.
So you can’t really say that with, for whatever, whenever you see a brinkle or you see a brinkle in development, that. It will be the crack that will be the dominating or it will be the the delamination. But if you’re in the Spark app laminate, then you would cut away the laminate layers before the delamination becomes anything significant.
And then the crack will be the be the measles finger.
Allen Hall: So the blade manufacturers today, when they, if they have blades out in service and they realize that they may have wrinkles, is it easy to detect how, if you’re on a turbine, this blade is on a turbine, can they find wrinkles simply or is there a way to do that?
Or is this get really complicated for them to identify where the wrinkles are? What is normally done when the blade is produced?
Morten Handberg: Is that after the, after it’s been demolded. Either the shell or the full blade, depending on the manufacturer. A QC technician will go through the entirety of the blade on the outside and on the inside and look for waviness or rises in the laminate to see are there any wrinkles here and then get those fixed if they’re outside of factory specification.
Allen Hall: How are they identifying those? Is it an ultrasound? Is it a flashlight? Is it a tap test, what’s involved there?
Morten Handberg: A Tap test wouldn’t make any sense because see, it’s still solid laminate, so there’s no no, no deep bonding that you could detect from a Tap test you can use ultrasonic to see you, you typically do that for the low carrying path of the lathe, for the spark caps.
Not all OEMs are doing that. And that is a problem because often what some of the wrinkles that we see leading to major structural damages or blade failures, Is because the the quality checks at factory were not sufficient. We’re not not carried out in a way that would allow for them.
But skilled quality technicians, they would be able to see them either visually, just by looking at it, by knowing how does a healthy laminate look from a laminate with a distortion. You can also, to some extent, use a you use a light dispersion test by holding over a flashlight over an area and see how the light passes through it.
If there’s any major changes to lemme structure that will show in, in, in that way, but it requires some skill to detect it that way. So again, it’s not something that you would send out any guy on the street and he would be able to find it. You need to know what you want to look for at the factory.
The best way to do it is to use entity but that’s typically only applied to the main load carrying parts of the blade, because that’s what you’re mainly concerned about, but wrinkles can happen anywhere. It’s not something we can say it always at six meters. It’s only on the leading edge. It’s only in the spike gaps.
They can occur anywhere where you have a laminate stack.
Allen Hall: And then, so in the factory, easier to identify because the blade’s sitting there and you can have probably the proper tools, Once you’re in service though, what happens, is it only ultrasonic? For the inner third of
Morten Handberg: the blade, you could still, you can still walk in, do a manual inspection to check if there’s any changes to the, any, if there’s any visible changes in the laminate structure.
Not seeing a damage yet, just by seeing if there’s a, if there, there’s a certain rise in the blade suddenly without any need for it. That typically indicates that there’s a wrinkle in this area. They can either be longitudinal, they can be transverse. Typically longitudinal, they don’t matter as much because they’re in line with the UD fibers.
So the UD fibers are still unidirectional. So it’s really rare that we see longitudinal cracks, wrinkles develop into damages just on their own accord. Transverse wrinkles, they do tend to develop into cracks even the smaller sizes. You have to change the
Allen Hall: structure. Is that because of the compression and tension cycles of the blade goes through every rotation that it’s just putting an immense amount of stress on that one weakness?
Morten Handberg: You’re putting stress on that the laminate is not designed for. It’s not designed for the UD laminate to be bended. And you can have transverse wrinkles. that doesn’t develop into cracks if they’re far enough out in the plate. But you are rolling the dice a little bit because just because it didn’t develop in two years doesn’t mean that it won’t happen ever, you’re just hoping that it doesn’t develop over the lifetime.
So we’ve seen wrinkles develop after 10, 12, 15 years of operation and. Everyone was saying this doesn’t matter. This blade is passed in the warranty. So it doesn’t, it would have developed if it ever was, but that’s just not how it works because it’s it’s, it’s a fatigue as a threshold.
So the blade is designed for, let’s say most plates are designed for 25 years. Then they’re designed for nominal load or nominal load cycle over that 20, 25 years of lifetime. But if you have a wrinkle that weakens the blade in that structure, it means that you’re reducing that, that threshold. How much is, that requires very advanced simulations, but at the end of the day, it is a reduction.
So a wrinkle should always be considered as something that will cause a potential damage down the line. Doesn’t matter if it’s five, 10, 15, 20, or 30 meters from the root. Maybe even 50 for, a 70 meter plate. It’s something that we can’t say exactly how fast or how slow it will develop or at what point in time.
We can just say that it is a weakness and we know that these wrinkles, they can turn into cracks eventually. Okay.
Allen Hall: Let’s, I want to walk back into the factory for a minute. What is creating these wrinkles? Is it the mere fact that the, there’s so many layers of glass and that they’re manually applied and you got people stepping on them as they put these plies down?
Or is it the fact that. We’re making bigger and bigger blades with the same number of people. So there’s just a little bit of a rush. What’s driving the wrinkle issue today?
Morten Handberg: Let’s say wrinkles have always been there. It’s not a new invention. It’s been there as long as we’ve been building things out of composites.
We’ve had wrinkles because it’s just a change in the in the laminates. That’s all it is. So it’s not something you, it’s, it can also happen if you stretch the laminate. You change the uniform structure and you can also create waviness in that way. It’s not wrinkles as we think about them right now, but it’s still a change in the structure that can affect the blade negatively.
The way that they occur can actually have several causes. So one is a quite commonly that when you’re laying up the glass fibers, then and as you lay down these long glass fiber match next to each other then sometimes there’s need just to adjust them a little bit or move them around and that can then create some small folds.
And then as you’re applying more and more glass fiber, if you’re not, if you’re not careful, if you’re not aware, then you can build up a larger and larger waves that then can create this wrinkle. So it’s just by pushing the fiber mats around even slightly can have really big consequences.
And now another cause is the core material that we, that are used in the blade to add thickness, but without adding a lot of weight. These also comes in large sheets that are moved around and adjusted. But if there is a, if there’s a large gap between two sections of ga of core material, that creates a a a separation where there’s no no resin, there’s no fiber.
And then when the blade is cast, then the fiber can actually get stuck down in, into this core gap and then create a wrinkle in that, in, in that way. And it can also be from adding core material adjusters where you change the thickness of the core material in a small area that also creates the, these waves in the structure.
So, there are just really several paths to the same effect, but it is whenever you are creating sort of the space underneath the laminate where you then get a resin rich area then it can, it gets locked into this to this, into this wrinkle. And it’s something that it doesn’t happen after in, in operation, they’re not created after manufacturing, it’s created during manufacturing, and then it’s locked in.
And then we’ll develop over time during during that period of time.
Allen Hall: That’s interesting. So is it, let’s see just some of the discussion as an electrical person, seeing some of the news articles and hearing some of the difficulties that some of the OEMs are having to eliminate wrinkles. Is it ultimately a design to build question that maybe the way that the blade was designed is encouraging wrinkles?
Is that the way to think of it? Because it’s the same, roughly the same manufacturing people doing the same job over and over again.
Morten Handberg: My view on it is that the wrinkle problem has been persisted for decades in the blades. But they’re, but the blades are becoming more sensitive because they’re becoming longer.
They are they are getting more optimized. So you use the materials in a different way where you have less buffer. in your blade to account for deviations inside your blade. So that also means that any manufacturing defect is much more sensitive because you don’t have the same conservatism when designing your blades anymore.
It’s not because your manufacturing method has changed. Not as I see it because that’s still essentially the same way. But the focus on. Quality assurance have not gone up with producing longer and how do you say more optimized plates? And it should be the, it should, the more you optimize it, the more focus you should have on the quality assurance, because you become more, more sensitive to structural damage.
And that’s also why we’re seeing the fatigue damages we’re seeing in the field today, and that a lot of owners are experiencing is because that the, is because that the blades were not thoroughly checked at factory. And if the OEM is saying otherwise, then, you can just look at the defect it’s there and it shouldn’t be there.
You shouldn’t expect to have critical damages or blade failures after one, two, three or five years in operation, it shouldn’t happen. And that means that defects were overlooked that should have been detected and repaired at factory.
Allen Hall: Does that indicate a need to upgrade or to maybe change the way we’re inspecting blades during the manufacturing process, like during the ply layup and plus after the fact once the blade has been cast?
Morten Handberg: It’s a good question. I think that obviously there are ways you could I’m sure there’s ways that you could optimize your manufacturing, but. a good place to start is to increase your focus on quality control. And that’s where you need to start. And then maybe you can implement changes to the manufacturing over time that would reduce your the the frequency of these defects occurring.
But right now with the methods that we’re using for manufacturing, then we need an added focus for quality control. And a number one is to do entity, especially of the structural critical areas. I would say. All the blades should be checked because we know that wrinkles can appear anywhere.
But that need, we need to start with that point that It shouldn’t be possible to produce a 80, 90, 100 meter blade without doing an entity inspection. And then send the blade out in operation, then hope for the best.
Allen Hall: So because the margins are lower, the blades and the blades get longer.
So we learned from our previous designs, we’re making them lighter to. Allowed to be shipped and a lot of other reasons, cost reduction, right? Less weight is less material, which is less cost that then forces. Okay. An improved quality system and maybe even a training system to how we’re going to build these blades.
That seems like a big effort. And it’s, and when watching some of the OEMs go through this cycle, it’s, it seems like it’s taking a long time to rectify the situation. Months and months. Does that make sense why it’s taking so long is because it’s changing so much of the internal systems.
Morten Handberg: But the focus is also has been for a long time on building bigger and longer blades faster and releasing new methods in into production and into the shield because you had to stay ahead of the curve with the other manufacturers and that has taken over some of the.
focus from quality assurance of the blades. So that has been down prioritized in order to opt in order to optimize cost and get the blades longer. Another factor in it is also that we’re introducing carbon more and more inside the blades and glass fiber is a really nice material when it comes to some manufacturing defects, because it has a lot of elasticity.
So it means that it can it can work with them, with the manufacturing defects for a longer period of time. Carbon fiber doesn’t work like that. If you have any change to the carbon fiber, it’s, it because it’s a lot more brittle. It develops into a fatigue damage much faster. So you see a rapid development in the damages for carbon fiber plates than you would for traditional glass fiber plates
Allen Hall: So carbon is less forgiving and we’re seeing more carbon as the blades get longer and that it sounds like some of the carbon Pultrusions are coming from a sub supplier into the system. Does that make sense that at least in some of the discussions I’ve seen it seems like it’s a supplier issue but it’s a composite supplier issue which to me says carbon fiber and if carbon fiber is less forgiving You’re bringing in something that may not have been inspected to the level.
Maybe it should have been And then it gets stuck in a blade and it just magnifies the issue. Is that kind of where this is headed?
Morten Handberg: That, that might be a way to look at, but if the man, if the OEM is putting together the blade, it shouldn’t really matter if they are producing the protrusion or they have a third party.
They should be responsible for making sure that the protrusion is is checked and it’s, and that it’s inspected and making sure that there’s no manufacturing defects in that before installing it in, inside the blades.
Allen Hall: Does it become more critical on the carbon fiber to do an ultrasonic inspection because it’s such a critical load path for the blade?
Morten Handberg: It would develop faster, compared to a glass fiber, but for protrusion, if you’re talking about glass fiber. It’s equally necessary. The severity you could say is almost the same but the how do you say it will develop faster for, yeah, the speed of development is faster.
And yeah, the reduction in strength is also greater with carbon because you’re relying much more on your, on, on the load capacity in carbon compared to glass fiber. It would take longer for the damage to develop, but again, the ultimate consequence would be the same as long as we’re talking about the disbar caps, if it’s glass fiber or carbon fiber.
Allen Hall: That would help explain some of the early failures that I think the industry is seeing is maybe it’s in the carbon. That would make a lot of sense from a mechanical standpoint, right? Because yeah, you’re right, you’re using carbon to cut the weight out. And because it’s a stronger fiber, if there’s a problem in the carbon, look out, it’s going to show up pretty fast.
Morten Handberg: The only safe way to, to check it is through entity. Because if she, the ring, if the wrinkle is small enough, it wouldn’t show up in a visual check. Or, and so it’s the only. Only safe way
Allen Hall: to do it. What does a repair look like to fix a wrinkle in a carbon spar cap, let’s say, or a fiberglass shell?
What are we talking about here? Are we talking about days, weeks, months to fix some of these things? Particularly where it’s a highly loaded area?
Morten Handberg: If we’re talking about the spar cap, we’re talking about weeks or months, if the blade is repairable at all, because you need to remove so many layers and you have such a so many iterations of buildup to restore the blade.
That, in a lot of cases it would be deemed a replacement plate. And most damages, they can be repaired. Assuming they have not developed into a large a crack that, that that has affected the majority of a shell. Then most damages, most wrinkles, they can be repaired if they’re outside of the spark cap area.
Yeah. I would say if they haven’t given up, I would even go so far as to say, I would assume all of them.
Allen Hall: And then if I, if now, once those blades get out in service and say they’ve missed the quality inspection and you have this wrinkle, depending on where it is. What is, what are you as an OEM, are the OEMs reaching out to those customers to say, hey, this blade mold, this blade factory had this issue, we need to track this, is that what’s happening in industry right now?
Is there, is just a follow up happening to say, hey, be aware of this, or is it more aggressive? Like we need to stop turbines.
Morten Handberg: We have seen a lot of cases where if the OEM recognized that they have a they have an issue on multiple blades within the same batch, that they reach out to the owners with this particular blade type and then stop turbines, if they see that this.
This blade serial have high likelihood of issues, then it would stop that, or they would say, okay, inspect keep it running, but it will inspect. within a short timeframe. So we have seen cases like that that where the OEMs have taken a proactive approach because they’ve recognized after the fact that they had a large issue with their blades but I would say as an owner if you see a blade where you recognize that this is an issue with wrinkles, I would recommend that if the OEM has, haven’t taken any action and they don’t seem like they’re going to that, then you have to take action because Otherwise it, the problem can escalate and require a lot of downtime, a lot of replacements and a lot of repairs if you’re not proactive on, on, on your own.
And yeah, if it’s something that is something where it’s expected to be in the Spark app laminates, we would recommend doing an entity inspection. If it’s something that looks like it’s in the shell laminates internal, externally, we would An intern inspection can be a really good place to start just to see, are there any visible signs of blade defects.
Allen Hall: And then from the insurance side and insurance is become more and more of a factor in the operation of a wind farm. Is, are the insurance companies starting to step in a little bit and force the operators to go look and to be proactive about this?
Morten Handberg: We’ve seen them ask questions to owners whether they have taken any steps, but it hasn’t gone to so far that they are pending the the insurance renewal on them doing inspections for it.
But but again, if this is a problem that will persist then that could be a likely outcome that, you know, if you haven’t. Stand your own check of your own plates, then that would be that, that, that could affect the the policy.
Allen Hall: Alright, Morten, this issue is still in its infancy.
I think there’s a lot more coming up about blade wrinkles worldwide. Obviously there’s a lot of concern by operators, if they have a blade that has wrinkles or they’re starting to experience some failures, they should probably be reaching out to Wind Power LAB. How do they do that?
Morten Handberg: You can reach us on winpowerlab.com or reach out to us via LinkedIn. Or you can also find me on LinkedIn and reach out to me directly.
Allen Hall: And we’ll pull all the contact information in the show notes. You can get ahold of Morten directly and to Wind Power LAB because blade wrinkles have really grown into a massive issue and it’s time to put some resources to stop them.
And Morten, this has been so great to have you back on the podcast. We love having you on. Everybody, our blade whisperer, Morten Handberg, thank you for being on the podcast.
Morten Handberg: Thank you. Thanks for having me.
