General Comments

In this paper, the author sets out an ambitious goal: to outline a process for developing a wear test program for roller-type pitch bearings based on aero-elastic simulation data and wind speed measurements. In that respect, it provides a valuable potential contribution to the wind industry, as the only strict design requirement currently stated in IEC 61400-1 relates to the static load capacity; whereas, a much more vague requirement that “…consideration shall be given to the potential effect of insufficient lubrication due to small movement…“ relates to wear. The subject of this paper could indeed one day lead to greatly improved design and/or design verification requirements in IEC 61400-1 or an equivalent standard.

Specific Technical Comments

Line 103: I recommend that the authors have a look at Brinji, O., K. Fallahnezhad, and P.A. Meehan. 2020. “Analytical Model for Predicting False Brinelling in Bearings.” Wear 444–445: 203135. doi: https://www.sciencedirect.com/science/article/pii/S0043164819313699. Additionally, there may be more recent works that cite this (see https://www.sciencedirect.com/science/article/pii/S0043164819313699#section-cited-by), which I would recommend having a quick look at as well. I will admit I have only briefly scanned this work and need more time to digest it myself, but it might change how the sentence at line 103 is written. Having said that, these works relate to false brinelling, rather than the more general “wear” described in line 103. I invite the author’s thoughts here in either agreement or disagreement.

Line 181: I certainly agree that the applied load can overcome the preload such that the roller is in clearance and no longer carries a load, thus Equation (9) is true. However, I have to wonder if this load Q that is set to 0 at this position, then must be carried by the roller opposite (180 degrees) from this position? Is that accounted for in the formulation? Effectively, we have a system of parallel springs that can only carry load in one direction. I invite the author’s thoughts here as well.

Minor Clarifying Comments

Line 20: For the more general wind audience, I recommend adding something like the following “…, which protect the raceway from wear by redistributing the grease in the pitch bearing, as explained…” to this sentence.

Line 29: I recommend adding “…decades, results of several wear tests…”. I also believe many of the sentences in lines 29-54 can/should be made into a single paragraph.

Lines 78-79: I will admit I don’t have experience with this type of bearing, so I don’t know the nomenclature. However, I think it’s a little clearer to say “One of the rings is typically C-shaped and split into two halves, as shown in Figure 1, where the outer ring is split.”

Lines 80: I think it’s a bit clearer to say for the general wind audience “When the blade, pitch bearing, and hub are assembled, the tensioning of the bolts of the c-shaped ring introduces the preload of the rollers.” Alternatively, it is typical that the outer ring is stationary with the hub, so one could say “When the pitch bearing and hub are assembled, …”

Line 85: Again for a more general audience, it might be worthwhile to add “…evaluating wear of the raceways, which are the surfaces of the bearing rings that contact the rolling elements.” It might even be worth it to label the inner ring, outer ring, and raceway surfaces in Figure 1.

Line 96: It feels like the sentence “The appearance of standstill marks has a characteristic undamaged central area” is at first a bit confusing (i.e. a mark that leaves no mark). I think something like “Standstill marks typically occur at the roller ends, often separated by an undamaged central area as shown in Figure 3” is clearer.

Line 131: It appears there are some typos here with the tilde. Same for line 320.