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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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....
