Morten Handberg, Principal Consultant at Wind Power LAB, returns to discuss blade damage categorization. From transverse cracks and leading edge erosion to carbon spar cap repairs, he explains what severity levels really mean for operators and why the industry still lacks a universal standard.

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Welcome to Uptime Spotlight, shining Light on Wind. Energy’s brightest innovators. This is the Progress Powering tomorrow.

Morten, welcome back to the program. Thanks, Allen. It’s fantastic to be back again. Boy, we have a lot to discuss and today we’re gonna focus on categorization of damage, which is a super hot topic across the industry. What does a cat five mean? What does a category three mean? What does a category 5.9 I’ve I’ve seen that more recently.

Why do these defect categories matter?

Morten Handberg: Well, it matters a lot because it really tells you as, uh, either an OEM or as an operator, how should you respond to your current blade issue. So you need to have some kind of categorization about what the defect type is and what the severity is. The severity will tell you something about the repairability and [00:01:00] also something about the part of the blade that is affected.

The type of the defect tells you something about what is the origin From an operational point of view, it doesn’t make as much sense in a way because you really just wanna know, can this be repaired or not? You know? And you know, what does it need to repair? That’s what you need, what you really need to focus on as an operator, whether it’s then del elimination, erosion, peeling.

Uh, transverse cracks, it’ll all come down to repairs. It does matter for you because it will tell you an underlying, you know, are there reason why I’m keep seeing all these damages? So that’s why you need to know the category as well. But purely operational. You just need to know what is the severity side know, what does it take to repair it?

Allen Hall: So as the operator, a lot of times they’re getting information from different service providers or even the OEM. They’re getting multiple inputs on what a damage is in terms of a category. Are we getting a lot of conflicting information about this? Because the complaint from [00:02:00] I hear from operators is the OE EMM says this is a category four.

The ISP says is a category five. Who am I to believe right

Morten Handberg: now? Well, there is a lot of, a bit different opinions of that. It almost becomes a religious issue question at some point, but it, it really dives down to that, you know, there is no real standardization in the wind industry. And we’ve been discussing this, uh, I wanna say decades, probably not that much, but at least for the past 11 years I’ve been, been hearing this discussion come up.

Uh, so it’s, it’s something this was just been struggling with, but it also comes down to that. Each OEM have their own origin. Uh, so that also means that they have trended something from aeronautics, from ship building industry, from, you know, uh, from, from some other composite related industry, or maybe not even composite related.

And that means that they are building their own, uh, their own truth about what the different defects are. There is a lot of correlation between them, but there is still a lot of, lot of tweaks [00:03:00] and definitions in between and different nomenclature. That does add a a lot of confusion.

Allen Hall: Okay,

Morten Handberg: so

Allen Hall: that explains, I mean, because there isn’t an industry standard at the moment.

There is talk of an industry standard, but it does seem like from watching from the outside, that Europe generally has one, or operators specifically have one. Uh, EPRI’s been working on one for a little while. Maybe the IEC is working on one, but there isn’t like a universal standard today.

Morten Handberg: There is not a universal standard.

I mean, a lot of, a lot of OEMs or service providers will, will, will claim that they have the standard, they have the definition in wind power lab. We have our own. That we have derived from the industry and in, in general. But there is not an, uh, an industry agreed standard that everyone adheres to. That much is true.

You could say in Europe, a lot of owners have come together, uh, in the Blade Forum, and they have derived, there’s a standard within that. Um, uh, and with a lot of success, they’d written, the [00:04:00] Blade Hamburg I think was very helpful because it was operator driven, um, approach.

Allen Hall: So there is a difference then between defects that are significant and maybe even classified as critical and other defects that may be in the same location on the blade.

How are those determined?

Morten Handberg: The way that I’ve always approached is that I will look at firstly what kind of blades type it is. So how is it structured? Where are the load carrying elements of the blade? That’s very important because you can’t really say on a business V 90 and a Siemens, uh, 3.6 that the defect in the same position will mean the same thing.

That’s just not true because they are structured in very different ways. So you really need to look at the plate type just to start with. Then you need to look at, is it in a. In a loaded part of the blade, meaning is it over the, the load carrying part, um, uh, laminates? Is it in a, in a shell area? And you know, what is the approximate distance from the roof?

Is that, that also tells you something [00:05:00] about the general loads in the area. So you know, you need to take that into consideration. Then you also need to look at how much of the blade is actually affected. Is it just surface layers? Is it just coating or is it something that goes, uh, through the entire laminate stack?

And if that is on the, on the beam laminate, you’re in serious trouble. Then it will be a category five. If the beam laminate is vectored. And if you’re lucky enough that your blade is still sitting on the turbine, you should stop it, uh, to avoid a complete BA bait collapse. Uh, so, so you need, so, so that, you know, you can, that, that is very important when you’re doing defect categorizations.

So that means that you need

Allen Hall: internal inspections on top of external

Morten Handberg: inspections. If you see something, uh, that is potentially critical, then yeah, you should do an internal inspection as well to verify whether it’s going through, um, the entire lemonade stack or not. That that’s a, that’s a good, good, good approach.

Um, I would say often, you know, if you see something that is potentially critical, uh, but there is still a possibility that could be repaired. Then I might even also just send up a repair [00:06:00] team, uh, to see, you know, look from the outside how much of the area is actually affected, because that can also pretty quickly give you an indication, do we need to take this blade down or not?

Sometimes you’ll just see it flat out that, okay, this crack is X meters long, it’s over sensitive area of the blade. You know, we need to remove this blade. Uh, maybe when, once it’s down we can determine whether it’s repairable or not, but. We, but it’s not something that’s going to be fixed up tower, so there’s not a lot of need for doing a lot of added, um, add added inspections to verify this, this point.

Allen Hall: Let’s talk about cracks for a moment, because I’ve seen a lot of cracks over the last year on blades and some of them to me look scary because they, they are going transverse and then they take a 90 degree and start moving a different direction. Is there a, a rule of thumb about cracks that are visual on the outside of the blade?

Like if it’s how, if they’re [00:07:00] closer to the root they’re more critical than they’re, if they’re happening further outers or is there not a rule of thumb? You have to understand what the design of the blade is.

Morten Handberg: Well, I mean the general rule of thumb is transfers cracks is a major issue that’s really bad.

That’s, uh, you know, it’s a clear sign, something. Severely structural is going on because the transverse crack does not develop or develop on its own. And more likely not once it starts, you know, then the, uh, the, the strain boundaries on the sides of the cr of the crack means that it requires very little for it to progress.

So even if in a relatively low loaded area with low strain, once you have a, a transverse crack, uh, present there, then it will continue. Uh, and you mentioned that it’s good during a 90 degree. That’s just because it’s doing, it’s, it’s taking the least path of the path of least resistance, because it’ll have got caught through the entire shell.

Then when it reaches the beam, the beam is healthy. It’s very stiff, very rigid laminate. So it’s easier for it to go longitudinal towards the [00:08:00] root because that’s, that, that, that’s how it can progress. That’s where it has the, uh, you know, the, the, the strain, uh, um, the, the strain high, high enough strain that it can actually, uh, develop.

That that’s what it would do. So transverse cracks in general is really bad. Of course, closer to root means it’s more critical. Um, if there is a crack transverse crack, uh, very far out in the tip, I would usually say, you know, in the tip area, five, 10 meter from the tip, I would say, okay, there’s something else going on.

Something non load related. Probably causes, could be a lightning strike, could be an impact damage. That changed the calculation a little bit because then, you know, it’s not a load driven issue. So that might give you some time to, you know, that you can operate with something at least. But again, I, I don’t want to make any general rules that people then didn’t go out and say, well, I did that, so, and, but my blade still broke.

That’s not really how it works. You need to really, you need to, to, uh, look at cracks like that individually. You can’t make a a common rule.

Allen Hall: Another [00:09:00] area, which is under discussion across the industry are surface defects and there are a variety of surface defects. We’re seeing a lot of hail damage this year.

Uh, that’s getting categorized as lightning damage. And so there’s obviously a different kind of repair going on. Hail versus lightning. Are there some standards regarding surface defects? Uh, the visuals on them? Is there a guideline about

Morten Handberg: it? Well, I mean, uh, some of the, uh, some of the, how do you say, omic couture, some of the, uh, some of the standards, they do provide some guideline to determine which surface kind of surface defect it is, you could say, on the operational points, as long as it’s surface related.

Then the repair methodology is the same, whether it’s peeling, erosion, voids, chipping scratches, the repair is the same. So that in principle does not change anything. But in the reason why it matters is because we need to understand the [00:10:00] underlying issue. So if you have lot of peeling, for instance, it means you have a very low quoting quality, and that is something that is either post post repair related or it’s manufacturing related, depending on the blade, on the age of your blade.

So that’s very important for you to know because if you have peeling somewhere, then more likely than not, you’ll also have have issues with it elsewhere because, you know, tend to, they tend to follow each other, you know, coding quality issues. So that’s a good thing to know for you as an operator that you, this is just one of many, erosion is important, but often gets miscategorized because erosion is a leading edge issue.

Um, so we only see it on the, on the very edge of the leading edge. So approximately 40 millimeter band. That’s typically what we see, and it’s straight on the leading edge. So if someone’s claiming that they see lead, leading edge erosion on the, on the pressure side, shell or ide, shell, it’s miscategorizing because that’s what you, that’s not why they have to have the ring.

Uh, impacts ring can still, still [00:11:00] hit the shells, but when it hits the, the, the shell areas, it will ricochet because it hits it at an angle. Leading edge gets straight on. So it gets the entire impact force and that’s why you get the erosion issue because of, of fatigue essentially. Uh, coding fatigue. So that’s very important.

There is something that you know you can really utilize if you just know that simple fact that it’s always a leading edge, it’s always uniform. It, you can track that. And if you have leading edge erosion in one area, you will have it in the entire wind farm. So you don’t need to do that much inspection to determine your erosion levels, voids, pinholes.

They are manufacturing driven because they are driven by either imperfections in the coating, meaning you have a sand, grain dust, or you had, uh, air inclusions underneath your coating. And they will weaken the structure. And that means that, um, rain effect or other effects causing strain on your coating will accelerate a lot faster.

So they will develop and create these small, um, yeah, uh, how do you [00:12:00] say, small defined holes in your coating. So that’s why it’s important to know. But if you’re running a wind farm 15 years, 10 years down the line. Then it’s more important for you to know that it’s a surface defect and you need to fix it by doing coating repair.

You don’t need to think so much about the, the underlying issue, I would say.

Allen Hall: Okay. I think that’s been miscategorized a number of times. I’ve seen what I would consider to be some sort of paint adhesion issue because it’s sort of mid cord and not near the leading edge, but sometimes it just looks like there’s massive peeling going on and maybe, uh, it’s easy to assume that maybe is erosion.

It’s just a weak adhesion of paint. That that’s what you’re saying?

Morten Handberg: Yeah. If it’s, if it’s midspan, if it’s shell related, then it’s, it’s a, it’s a coating quality related issue. It doesn’t really have anything to do with erosion. Um, you could say erosion. We can, we can, we can, uh, we can look at in, in, in two areas.

So you have the out or third of the leading edge. [00:13:00] That’s where you would have the theoretical leading edge erosion breakdown, because that’s where you have rain impact high enough that it will cause some kind of degradation, but that all of your leading edge will suffer in the same way because the tip speed of the outer four meters of your blade.

Versus the re the other, you know, uh, 10, 12 meters depending on length of your blade. Sometimes it’s a lot longer, but they are getting degraded in a much different way. So the out of pew meters, they can get what’s called structural erosion. So that means that the erosion goes fast enough and it’s progressive enough that you can start to damage the laminate underneath.

You won’t see that further in because the, the impact is just not that great and you will likely not see structural erosion over the lifetime, but the out a few meters, that’s important. And that’s where you need, need to focus your, that that’s where you need to pay attention on what kind of materials you add because that can save you a lot of repair, re, re repair.

And, uh, down the line, how do you categorize

Allen Hall: leading edge erosion? A lot of [00:14:00] times I see it, uh, from operators. Let’s say it’s, uh, category four because it’s into the fiber. But is it always a structural issue? Is there a lot of loading on the leading edges of these blades where you would have to come back with structural applies to repair it?

Or is it just a aerodynamic shape and does it really depend upon who the OE Em is?

Morten Handberg: Well, I mean, I’ve seen erosion category five as well, and I think it’s a mis misinterpretation. I think it’s, you know, people are trying it to raise awareness that, hey, there was a serious issue with erosion, but it’s a wrong way to use the severities.

Because if we look at severity five, severity five, if you have a critical issue, your blade is about to come down if you don’t do anything. So category five means you need to stop your turbine. Maybe you can repair it, but that really depends on the, uh, on what is damaged by, on, on, on the blade. And you can determine that once you removed it and looked at it on, on, on the ground.

But you need to stop. Category four is a severe structural damage. It’s not something that [00:15:00] is causing an immediate threat, but it’s something that will progress rapidly if you don’t do anything. So here you need to look at the damage itself. So how does it affect the structure and can you operate it curtailed, uh, or can you operate it, uh, or can you operate normally and repair it within a short time window?

That’s what you can use because it’s something that is. Uh, that can, that can develop into an, into an imminent issue if you don’t react to it. Severity three is more for your, is more your annual maintenance schedule. So that is your, your minor structural damages and it’s your erosion issues. So that’s something that there is a severity Three, you need to look at it for next year’s budget.

Severity two means that. Something that’s gradually degradating your coating on the blade, but it’s not something that means anything at this point in time. So one is your coating, is your surface damage or minor surface damage. Pinholes uh, contamination. It’s really light issue, so it’s not something you really need to consider.

So. [00:16:00] Severity ones, you, you really mean that, that it’s, you don’t need to think about this anymore. You know, it’s, it’s not an issue. So erosion will fall typically within severity two to severity four. Severity four being you have a hole in your blade from erosion, basically. Uh, because you can still have structural degradation of deleting it and still being a severity three, because it does not really change your maintenance cycle in any, in any way.

You don’t need to do anything immediate to fix it. Um, so that’s why I would put most of erosion defects in severity three and just say, okay, it’s something we need to plan a leading edge, a leading edge ERO repair campaign next year or the year after, depending on the severity of it. That’s why, how I, I would approach,

Allen Hall: that’s good insight, because I do think a lot of operators, when they do see a hole in the leading edge, think I have to stop this turbine.

But at the same token, I have seen other operators with holes. I could put my fist through. That are continuing to use those blades and they will say, it’s not structural, it’s not [00:17:00] great aerodynamically, but the, we’re still making power here. We’re still making rated power. Even with the hole and the leading edge, it’s not going to progress anymore.

It’s a, it’s a, it’s a progression that we understand. That’s how they describe it. It will get worse, but it’s not gonna get catastrophic worse.

Morten Handberg: I mean, if you run it long enough, at some point, something secondary will happen. Sure. But again, that’s also why we use the severity four category for erosion, where you have severe structural degradation because it does starting to mean something for the integrity of the blade.

It will not mean that it’s coming down right away when you see a hole in the blade from erosion. That’s, that’s the entire purpose of it. But it does it, you use it to raise awareness that there is something you need to look at imminently or at least react to, uh, and make a plan for. You can’t just pull, you can’t just delay it until next year’s, uh, maintenance campaign.

We have an active issue here, so that’s why I think severity four applies to erosion. That has penetrated all structural layers.

Allen Hall: Are there some [00:18:00] blade damages that are just can’t be repaired or, or just have too much difficulty to repair them, that it’s not worth it? And how do you know? How do you understand?

That blade is not repairable versus the one next to it which looks similar, which can be repaired. What goes into that assessment?

Morten Handberg: So one is, is the, is the beam laminate damaged? If it is, then uh, either it comes down to a commercial decision. It’s simply not fixable and, and restoring it in, you know, restoring it back, uh, to original form ship.

And there’s also the, the, uh, the, ever, ever, ever, ever, ever, uh, returning element of carbon fiber, because carbon fiber adds another level of complexity repairs, because you’re so dependent on the pristine quality of the carbon for it to, to, for, to utilize the, the, uh, mechanical strength of carbon. And if you, if you don’t apply it in the right way, then you can create some high stress zones.

Where, you know, the [00:19:00] cure is as bad as the disease really. So that’s why you have to be extra careful with carbon repairs. But they can be done. But it, you know, it really comes down to a commercial decision then. So in principle, unless the blade is deformed, uh, or, or, or damaged in such a way that you have to remove a large part of the s shell lemonade in a loaded area, then most things they can, in principle, be repaired.

It’s just a matter of is the, is the cost of the repair. Cheaper than the cost of a new blade. And that calculation might, you know, depend on are there any, any spare blades available? Is this blade, uh, still in production? And if I don’t repair this, then I don’t have any blade for my turbine and then I can’t operate anymore.

That also changed the calculus right along quite a lot, so I think. For a lot of damages. It, it’s more of a, it’s often more of a commercial decision rather than a technical, because ca glass fiber is very forgiving. You can repair a lot, even if it’s really severe. I mean, I’ve seen blade repairs that took [00:20:00] 3000 hours, but it was deemed worthwhile because you couldn’t get a, a bare blade.

And in most other cases, that would’ve been been scrapped, you know, without, you know, without blinking. Um, so, so, you know, if you really want to, you could repair it. In a lot of cases,

Allen Hall: how difficult is it to repair carbon protrusions, because it does seem like when they manufacture those protrusions, there’s a lot of quality control going into it.

The fibers have to be in the right direction all the time, and they’re really compacted in there. They’re tight, tight block of carbon that you’re purchasing and sliding into into this blade. Are they really repairable in sections or is it you have to take out the whole length of a pultrusion and replace it?

I’m, I’m trying to understand the difficulty here because there’s a lot of operators in the United States now that have some portion of their fleet is carbon spar cap, not a lot of it, but some of it. How [00:21:00] difficult is that to repair?

Morten Handberg: Well, it’s difficult enough that a lot of OEMs, they will say if you have a damage to the carbon, it’s a non-repairable defect.

That is to a large extent the general rule. Um, there are, there are, uh, there are ways and some of it is replacement of the protrusion. Um, other, another method is, is to do a vacuum infusion lamination. I’ve also seen some repairs with success where, uh, glass fiber is utilized instead of carbon fiber. So you reply, so you, you, um, you calculate the mechanical strength of the carbon.

And then replace that with an equal amount, you know, strength wise of glass fiber. The problem is you are to a degree playing with little bit with fire because you are then changing the structure of the blade. You are increasing the thickness and thereby you are changing the stiffness. So it’s, you have to be really [00:22:00] careful, uh, it’s possible.

And uh, again. All if all other options are out and you want this blade really to get up and running again because it’s your only option. Maybe it’s worthwhile to, to investigate, but it requires a lot of insight in and also a little bit of, uh, how do you say, uh, you don’t, you shouldn’t be too risk adverse if you go down that that route, but, but again, it is possible.

It is technically possible. But it’s something you do for the outer, uh, outer areas of the blade where you have less loads and you’re less sensitive.

Allen Hall: Can those carbon repairs be done up tower or are they always done with the rotor set or the blade drop down to ground?

Morten Handberg: I know some carbon repairs have been done up tower, but in general it’s down tower also, just because if you have damage to your carbon, it means you have a severe structural issue.

So you wouldn’t generally try to do it that well, I would, not in general, but, but the, the, the cases I’ve seen that, that has been downturn repairs. Yeah.

Allen Hall: Do you think about the categories differently? If it includes carbon [00:23:00] as a structural element?

Morten Handberg: No, because carbon is part of the load carrying laminate. If you’re to the load carrying laminate, then it becomes a four or five immediately.

Um, so, uh, so I would say the same rule applies because ag again, it’s a very rough scale, but it applied, but it gives you a sense of where, you know, what is the urgency, which is what I think we in generally need. And I like the more simple model because it’s more applicable to the general industry and it’s easier for, uh, you know, it’s easier to, to implement.

Um. And it is easier to understand than if you have a too too gradual, uh, scale because it’s difficult for the people who are sitting and assessing to determine if, uh, you know, what, what category it is. And it’s difficult for the people who have to read the report afterwards. And it’s also about, you know, what is the purpose?

And in general, I would say, well, this, the defect categorization, the severe categorization is to determine can this be repaired or not? That’s what we use it [00:24:00] for. So that, that, that’s how we, it should be applied.

Allen Hall: Is the industry going to have a universal standard? Soon. Is that possible? Or is this really gonna be country by country, region by region?

How we think about blade defects and blade repairs?

Morten Handberg: I think that. Given the, uh, the, how do you say, the individual interests in having their own model from the different OEMs or service providers? I think the, when they’re choosing a pope, they have an easy task ahead of them, you know, deciding that. Then we have the agreeing on an on inte standard and on plate.

Allen Hall: Pope is currently an American, so that tells you something. The world has shifted. There is still hope. Maybe there is still hope because it, it is a very difficult problem and I hear a lot of conflicting opinions about it and they’re not wrong. The opinions I hear when they’re explained to me, they have a rationale as to why.

They’re calling something a cat four versus a cat three. [00:25:00] It all makes sense, but when you get two engineers in the room, they’re rarely are going to agree. So I’m just thinking maybe, maybe there isn’t a, a yeah, maybe there isn’t a time where we’re all gonna come together.

Morten Handberg: I think that, you know, it’s, it’s also about what are you willing to accept and what are you willing to s.

You know, as an OEM, as a blade engineer, as a service provider, in order to make common agreement. Because I think if we were willing to, you know, set aside differences, um, and then agree on, okay, what is the, what, what is that, what is the, the ma the industry needs and what, what fulfills the purpose? We could agree tomorrow, but that’s not where we are, uh, at the moment.

So, so I don’t see that happening anytime soon. But yes, there, there was a way to do an in to make an international standard. Um, for blades and I, I would say maybe it’s, if the IC made, made, made one, then maybe that that could, uh, that could fix it. Uh, maybe if, uh, they’re starting to become more [00:26:00]focused from governments, uh, and you know, that it wind industry becomes recognized as critical infrastructure.

That then there is a requirement for international standards on what are defects, to make it easier to determine what is critical or not, so that proper reaction can be made. That will also help it. But again, as long as it’s only about late experts having to agree with each other and that’s the only then, then we’re, then we will not get to a point where we’re going to agree on, on everything.

No.

Allen Hall: Wow. This is a continual discussion about blade defects and categorization and Morton. I really appreciate. You’re giving us your thoughts about it because I trust you one and two, you’re on the leading edge of what the industry is thinking. So it’s very good to get you in here and explain where categorization is and, and two operators that are listening to this podcast understand you’re probably getting a lot of different opinions about categorization.

You need to sit down and figure it out for yourself, or reach out to Morton who can explain what you should be thinking and how you should be [00:27:00]thinking about this problem. Morton, how do people get ahold of you to learn more?

Morten Handberg: Easiest way is to reach out to me on LinkedIn. Um, I have a very active profile there.

You can always write me and I’ll always write, write, write it back. You can also write to me on my company email, m me h@windpowerapp.com. Um, those are the two easiest way to get, uh, get in, in, uh, get in touch me. And I would say, as an owner, what you need to know. Is it a structural issue or is a surface issue you have?

And then plan your repairs from there. That is, that is the. Basic, yeah, that, that you need to have, and then forget about the others, the other side of it, you know, if it’s one defect type or another, that’s not necessarily what’s going to help you. It’s all about getting the blades repaired. And, uh, and the turbine up and running again.

That should be the focus.

Allen Hall: Absolutely. Morton, we love having you on the podcast. Thank you so much for joining us. It’s good to be here. See [00:28:00] you.

Morten Handberg Decodes Blade Damage Categories

The Uptime Wind Energy Podcast