In high-speed rotating equipment such as steam turbines, gas turbines and compressors, the leading edge of a blade is one of the most critical surfaces in the entire system. It is the first point of contact with the incoming flow of air, steam or fluid, and as such it experiences the highest mechanical and environmental stresses.
When these systems operate in wet or fogged environments, this leading edge is exposed to high-velocity water droplets that repeatedly impact the blade surface. Over time, this repeated impact can cause a destructive phenomenon known as leading edge erosion, or more specifically water droplet erosion (WDE).
Understanding how this process occurs, why it accelerates equipment degradation and how it can be prevented is essential for engineers seeking to improve turbine efficiency, extend component life and reduce costly maintenance cycles.
Leading edge erosion is the gradual removal or deformation of material from the front edge of turbine or compressor blades caused by repeated impacts from water droplets, solid particles or cavitation effects.
In wet operating environments, the dominant mechanism is water droplet erosion (WDE). This occurs when droplets travelling at very high velocities strike the blade surface repeatedly, producing shock waves and stress concentrations within the material.
The leading edge is particularly vulnerable because:
Over time, these repeated impacts damage the blade surface, causing roughening, pitting and material loss. This damage increases aerodynamic drag, reduces turbine efficiency and ultimately requires blade repair or replacement.
Leading edge erosion is commonly observed in several high-energy systems.
In steam turbines, the expansion of steam causes condensation as pressure drops. Water droplets form within the flow and strike the rotating blades, particularly in the last rows of low-pressure stages, where droplet size and velocity are highest.
Gas turbine systems often use inlet fogging to increase air mass flow and improve efficiency. However, water droplets from fogging systems can impact compressor blades, producing erosion on the leading edges.
High-speed compressors and flow equipment may experience erosion from:
In these cases, leading edge erosion can occur on impellers, vanes and compressor blades
Water droplet erosion is a complex fatigue-driven erosion process caused by repeated high-velocity droplet impacts. When a droplet travelling at high speed strikes a metal surface, several events occur simultaneously.
Upon impact, a high-pressure shock wave travels through the droplet and into the metal surface. This produces an extremely high localised stress field, even though the droplet itself is soft compared with the metal surface.
The droplet spreads rapidly across the surface, creating lateral jetting with velocities up to ten times the droplet’s impact velocity. These jets can tear away surface asperities and propagate microcracks in the material.
Repeated impacts cause:
Eventually these cracks intersect, causing pieces of material to detach from the surface.
Once cracks propagate sufficiently, small fragments of the surface detach, creating pits and cavities. These defects then act as stress concentrators, accelerating further erosion and creating a positive feedback loop.
Whilst erosion may initially appear superficial, it can rapidly degrade turbine performance and reliability. Even small increases in blade surface roughness can significantly increase drag and reduce aerodynamic efficiency. This is because the aerodynamic profile of turbine blades is designed with precise tolerances. Surface damage disrupts airflow and reduces turbine efficiency. In severe cases, erosion can cause measurable losses in turbine power output.
As erosion progresses, the required maintenance cycles increase in parallel. Blades require regular polishing, repair, replacement. These interventions increase maintenance costs and often require shutdowns. In power generation or aviation systems, these shutdowns can be extremely costly.
In advanced stages, erosion can also cause deep pits and cracks. These defects can eventually propagate into structural failures, especially under cyclic loading conditions.
Engineers have traditionally used several approaches to protect turbine blades from erosion.
Thermal spray coatings such as HVOF tungsten carbide are widely used but suffer from several issues:
Cobalt-based alloys such as Stellite are sometimes brazed onto blade edges. However these solutions introduce challenges including:
One of the most effective ways to prevent leading edge erosion is through advanced protective coatings. Hardide’s nanostructured CVD tungsten carbide coatings provide a unique combination of hardness, toughness and a pore-free microstructure, enabling exceptional resistance to repeated droplet impacts.
Deposited atom-by-atom from the gas phase, the coating forms a uniform protective layer on complex blade geometries. Independent testing has shown that Hardide coatings can withstand high-velocity water droplet impacts for significantly longer than uncoated materials and traditional hardfacing solutions, dramatically extending turbine blade life, maintaining aerodynamic performance and reducing maintenance cycles in wet or fogged operating environments.
Download our guide below to find out more about CVD’s capabilities to protect components against erosion.