Unveiling the crucial factors and coating mitigation of solid particle erosion in steam turbine blade failures: A review

1 Introduction

Steam turbines are essential energy converters in thermal power plants and various industrial applications. They play a crucial role in absorbing the power of steam and converting it into mechanical energy. The turbines are equipped with comprehensively built blades that are divided into low-pressure (LP), medium-pressure (MP), and high-pressure (HP) parts as shown in Figure 1. These sections are specifically engineered to handle different operational requirements based on the varied pressures and temperatures [1]. In the LP section of the steam turbine blades, the design focuses on maximizing efficiency and extracting as much energy from the steam as possible. In the mid section (MP) of the steam turbine blades, the design aims to balance efficiency and durability, as this section experiences relatively HPs and high temperatures. Finally, in the HP section of the steam turbine blades, the design prioritizes strength and resistance to erosion and corrosion, as this section is subjected to the highest pressures and temperatures in the turbine [2]. Every section of the turbine is meticulously designed to achieve the optimal balance between efficiency, durability, and strength, so maximizing its performance.

Figure 1

Rotor of the combined HP-IP and LP sections of a large impulse-type steam. Reproduced from Dick [9].

Among the various difficulties that pose a threat to steam turbine blades, such as fatigue, corrosion, erosion, creep, and thermal stresses, erosion is particularly insidious. The continuous and unrelenting impact of water droplets or solid particles gradually erodes the surfaces of the blades, posing a risk to both the efficiency of airflow and the structural strength. Unlike slower-paced failure mechanisms, erosion accelerates the degradation process, especially in environments rich in moisture or particulate matter. Erosion in steam turbine blades occurs in two main forms: water droplet erosion (WDE) [3], which mostly affects the LP region, and solid particle erosion (SPE), which is a significant concern in HP parts [4]. The erosive effect of solid particles, such as grit or sand transported by the flow of steam, gradually wears away the surfaces of the blades, often resulting in early failure [5]. To address a critical need, there are ongoing research efforts to investigate various materials, coatings, and design alterations that can improve the durability of turbine blades against erosion and corrosion [6,7,8].

A lot of recent research shows that SPE is a big problem for steam turbine blades. The Scopus database reveals a significant corpus of 2,806 papers (2013–2023) dedicated to this subject (Figure 2). However, despite this substantial body of literature, there remains a notable dearth of up-to-date review articles addressing SPE and its implications for steam turbine blade integrity, particularly concerning protective coating strategies. To better illustrate the methodology used in gathering and analyzing this literature, we present Figure 3, which outlines the systematic approach we followed in our review.

Figure 2

Number of publications for SPE between 2013 and 2023 based on Elsevier database.

Figure 3

The flowchart of literature used for the trend on SPE.

In light of this gap in comprehensive reviews, this article aims to address the deficiency by providing a comprehensive overview of SPE-induced failures in steam turbine blades. Section 2 delves into a thorough review of failures in steam turbine blades, while Section 3 focuses on SPE in these blades. Section 4 examines the myriad parameters influencing SPE, including particle properties and impingement conditions. In Section 5, the article scrutinizes materials and protective coatings designed to mitigate SPE, offering detailed insights into their selection and application methods. Section 6 summarizes and discusses the findings from the review. By meticulously dissecting these aspects, this review aims to bridge the existing knowledge gap and shed light on the profound impact of SPE on steam turbine blade performance. Finally, in Section 7, we conclude by identifying the current gaps in understanding and addressing the ramifications of SPE, paving the way for future research endeavors and advancements in turbine blade technology.

2 Failure in steam turbine blade

The blades of steam turbines might fail for a variety of reasons, even though they are essential parts of many industrial applications. The factors that contribute to the degradation of the system include thermal stress, mechanical stress, vibration effects, corrosion, erosion, fatigue, and creep, as shown in Figure 4. Gaining a comprehensive understanding of the complex mechanisms responsible for these failures is crucial to develop efficient mitigation techniques that guarantee consistent turbine performance across time.

Figure 4

Common failure modes in steam turbine blades are depicted: (a) crack localization on last stage LP turbine blades, (b) fracture surface of rotor blade, (c) erosion on HP turbine rotor blade, (d) fractured blade failure in LP last stage, (e) pitting along the leading edge of turbine blade, (f and g) corrosion and fracture on blade surface, and (h) fracture surface of cracked steam turbine blade. Reproduced from [14,15,16,17,18,19].

Thermal stresses arise due to variations in temperature within turbine parts, resulting in deformation, cracking, and other types of damage. The studies conducted by Kumar and Reddy [10], Azeez [11], and Mukherjee et al. [12] have examined topics such as high-temperature low-cycle fatigue and material characteristics that are important for withstanding thermal stress. The combination of mechanical stress, fluctuating dynamic stresses, and centrifugal forces plays a crucial role in causing blade fatigue and eventual failure. The blade experiences mechanical stresses due to the combined effects of steam pressure, steam temperature, and centrifugal forces caused by rotating movement [13].

Corrosion is a notable risk in steam turbines due to their frequent use of fuels that contain corrosive substances, including sulfur, vanadium, lead, sodium, and other elements [20]. When air or saltwater impurities are present, the presence of these chemicals can cause the formation of alkali metals. These alkali metals then launch highly destructive corrosion attacks on turbine blades, ultimately resulting in failure [21]. The study conducted by Plesiutschnig et al. [22] examined a crack located at the base of the third row of blades in an LP steam turbine. The steam turbine blade was made of Ferritic/Martensitic x20cr13 alloy. The researchers noted that corrosion pits at the root caused stress levels to exceed the yield stress. The primary factor leading to the onset of fatigue cracks was determined to be pitting corrosion. Additionally, crack propagation was attributed to the combined effects of centrifugal load and superimposed bending strain resulting from unstable steam forces.

Fatigue failure, a common reason for blade malfunction, happens when cyclic stresses exceed the fracture toughness of the material. Cano et al. [23] He et al. [18], and Zhao et al. [24] have conducted research to enhance turbine dependability by investigating the fatigue behavior. They have taken into account several elements including material qualities and operating conditions. Krechkovska et al. [25] examined the fatigue fracture of steam turbine rotor blades made of high-alloyed heat-resistant steel 15Kh11MF. The researchers discovered several factors that contribute to early failure, such as severe corrosion-erosion wear, uneven microstructure, and the presence of micro defects in the surface layers. The corrosive impact of the steam-water combination in the phase transition region was also discovered to contribute to the fracture process. The study examined the structural and mechanical condition of various high-alloyed heat-resistant steels in steam turbine rotor blades at different points throughout their operation.

Creep, which refers to the gradual distortion of a material over time when exposed to high temperatures and steady stress, presents an ongoing risk to the integrity of turbines. Gong et al. [26], Mudang et al. [27], and Abdollahzadeh Jamalabadi [28] have conducted research on many elements of creep behavior, such as the impact of heat treatment and material microstructure.

Erosion stands out prominently among the mechanisms affecting steam turbine blades due to its high occurrence rate, as shown in Figure 5. Its impact is particularly pronounced when compared to other common degradation mechanisms such as creep, fatigue, corrosion, thermal stress, and mechanical damage. The evidence is clear from published research and industry data, where erosion consistently emerges as a leading cause of degradation in steam turbine blades. This phenomenon is often attributed to the abrasive action of particles suspended in the steam flow, which can wear away the surface of the blades over time. Erosion, which includes the effects of solid particle impact, corrosion, and mechanical degradation, gradually deteriorates the surfaces of the blades and undermines their performance [29]. Yadav et al. [21] and Thijel et al. [17] emphasize the harmful impact of erosion corrosion on the lifespan and performance of blades and recommend taking proactive maintenance and optimization steps. Thijel et al. [17] examined a fracture in an LP steam turbine blade at an Iraqi refinery. They concluded that the fracture was mainly caused by erosion–corrosion pitting and a decrease in material strength. The study conducted by Yadav et al. [21] investigated the effects of foreign particles on several turbine components, specifically blades. They emphasized that turbine blades play a vital role in turning steam into shaft work. However, erosion and particle deposits can cause defects, resulting in operational problems such as reduced steam flow and increased axial thrust. These issues arise from the poor quality of steam caused by the dissolving of boiler salt.

Figure 5

Distribution of type failure in steam turbine blade from 2013 to 2023.

WDE, alongside SPE, significantly damages steam turbine blades, often leading to critical material loss, particularly on the leading edges, which exhibit rough, eroded surfaces characteristic of WDE, as shown in Figure 3(e). WDE commonly affects LP and MP steam turbine blades, where wet steam conditions result in frequent high-velocity water droplet impacts [30]. The erosion severity increases with larger droplets and higher velocities, following a power-law relationship [31]. To mitigate WDE, advanced coatings like high-velocity oxygen fuel (HVOF) coatings with hard carbide particles and laser surface treatments that enhance surface hardness are commonly employed [32]. Additionally, blade geometry is vital; optimizing design features such as drainage grooves can help reduce erosion effects [3,33]. Given the critical role of WDE in turbine blade degradation, it is equally important to consider SPE, which also poses significant risks to blade integrity and performance. Understanding the interplay between WDE and SPE provides a comprehensive view of the erosion mechanisms affecting turbine blades, setting the stage for a deeper exploration of SPE in the following section.

3 SPE in steam turbine blades

SPE presents a significant challenge to the structural integrity and operational efficiency of HP steam turbine blades. Notably, the control valve stems, first-stage stationary blade, and moving blade of the HP turbine, as well as the first-stage stationary blade, moving blade of the intermediate or reheat turbine, and the fin region of these stages, are particularly susceptible to SPE [3]. During operation, steam flowing through the turbines’ HP section commonly carries solid particles such as dust, sand, or other impurities [34]. Upon collision with the blade surface, these particles generate high-speed erosive impacts. The resulting high velocity and energy lead to material removal or wearing away from the blade surface, a process known as erosion [6,35]. Figure 6 displays a schematic diagram illustrating erosion wear caused by the impact of solid particles.

Figure 6

Erosion wear due to SPE. Reproduced from the study of Shitole et al. [36].

3.1 Understanding SPE mechanisms

To effectively address SPE, it is crucial to grasp the underlying mechanisms and contributing factors. Parameters like type of erosive particle, particle size, velocity, impact angle, and material properties exert notable influence on the erosion process [36,37,38,39,40,41]. The investigation findings provide a deeper understanding of the complex dynamics of SPE and offer significant knowledge about how materials function under erosive situations. A study conducted by Laguna-Camacho et al. [37] examined the erosion characteristics of AISI 304, 316, and 420 stainless steels, revealing major differences in their erosion tendencies. AISI 420 had excellent resistance to erosion and exhibited ductile behavior regardless of the impact angle. In contrast, AISI 304 and 316 showed higher rates of erosion and suffered considerable wear damage, including detachment of large fragments and brittle fractures. The study also noted that the diameters of wear scars rose when the impact angles were lower (30 and 45°) but decreased when the angles were higher (60 and 90°), with different forms being detected. In addition, the surface roughness experienced a substantial increase following erosion testing, especially when subjected to normal impact angles of 90°. The study by Shitole et al. [36] examined copper erosion using quartz, silicon carbide (SiC), and alumina particles, focusing on the impact of particle characteristics and impact angles. The highest erosion wear was observed at shallow impact angles of about 30° for quartz and SiC and approximately 22.5° for alumina (Figure 7). Increased particle angularity led to deeper craters and greater mass loss. Dense, angular particles showed significantly higher erosion rates, emphasizing the relationship between particle form and erosion rate. The results from both researchers highlight the significance of comprehending the interaction among material parameters, particle characteristics, and impact angles in forecasting and reducing SPE in engineering applications.

Figure 7

Comparative erosion rates of copper utilizing quartz, SiC, and alumina (d = 362.5 µm, v = 4 m·s⁻¹, c _w = 10%). Source: by Shitole et al. [36].

Additionally, the design of turbine blades and the implementation of protective coatings have a substantial influence on their ability to withstand erosion [42]. A study conducted by Chen et al. [43] discovered significant SPE damage on an IP stage 1 turbine after 6 years. The damage was mostly observed on the fixed blade trailing edge and moving blade leading edge. The analysis uncovered that particles known as “bounce back” were responsible for erosion, specifically on the trailing edge of the fixed blade, due to the centrifugal force propelling them outward. Expanding the axial distance between the fixed and moving blade decreased the extent of this damage. Field inspections conducted after a period of 4 years confirmed these findings (Figure 8). The inspections showed that erosion was reduced at the trailing edge of the fixed blade, but damage on the ledge of the moving blade remained. These findings have contributed to a better understanding of the phenomenon known as SPE and have provided valuable insights for designing turbines that can perform better and last longer.

Figure 8

Compares SPE in steam turbine blades before and after modification using the particle trajectory method. (a) Original IP stage 1 SPE damage (6 years) and (b) modified IP stage 1 SPE damage (4 years). Source: from Chen et al. [43].

4 Solid particle erosion contributing factors

The effects of SPE on steam turbine blade operation have been extensively studied due to its complex nature, involving multiple processes and parameters requiring thorough analysis. Various factors, including particle velocity, size, shape, concentration, and target material properties, significantly influence the rate of material removal and the mechanisms underlying SPE (Figure 9). Table 1 provides a summary of parameters impacting blade life efficiency affected by SPE. Understanding the interaction of these factors is crucial for developing effective strategies to mitigate SPE and extend turbine blade lifespan. It also has been observed that there is a limited amount of experimental research on steam turbine blade performance compared to simulation studies. The majority of publications regarding steam turbine blade analysis are based on simulation results, often utilizing software such as Abaqus or Ansys.

Figure 9

Key contributing factors to SPE on steam turbine blade [47].

4.4 Erosive particles

Understanding the specific characteristics of erosive particles like quartz, SiC, alumina, salt, and iron oxide is crucial for minimizing erosion rates, as different particles exhibit varying erosion rates [36,37,48,49]. Factors such as material composition, size, and shape significantly contribute to erosion rates. For instance, alumina particles generally result in higher erosion rates compared to SiC and quartz [36,37]. Figure 10 illustrates a range of particle materials, shapes, and sizes used in investigating SPE. The study by Shitole et al. [36] delves into the impact of different solid particles on the erosion of ductile materials, particularly focusing on copper. Utilizing a slurry pot tester, it investigates erosion caused by quartz, SiC, and alumina particles across various impact angles (30–90°), revealing that maximum erosion occurs at shallow angles, notably 30° for quartz and SiC, and 22.5° for alumina. Moreover, the study underscores the influence of particle angularity on erosion rates, with denser and more angular particles exhibiting higher erosion rates, thereby emphasizing the critical role of particle shape in erosion behavior.

Figure 10

Particle materials and shapes of SPE used in studies. (a) 500 µm sand [50], (b) 150 µm semirounded sand [36,51], (c) 300 µm sharp sand [36], (d) SiC [37], (e) quartz [36], (f) alumina [36], (g) 150 µm glass beads [51], (h) 50 µm Al₂O₃ [52], and (i) 50 µm SiO₂ [52]. Reproduced from [36,37,50,51,52].

5 Coating technology for SPE mitigation

SPE poses a significant challenge across various industries, from aerospace to energy and manufacturing. To effectively prevent this erosion, it is necessary to use resistant coatings and materials [53,54,55,56,57]. These coatings must withstand high-speed impacts and minimize material loss, making advanced coating technologies essential.

Among these technologies, nanocomposite coatings, particularly those based on graphene, show potential for improving erosion resistance [58,59,60,61,62]. Furthermore, current research is exploring self-healing coatings and enhanced ceramic materials, which have the potential to make significant advancements in reducing erosive particle damage [63,64]. By investing in the research and implementation of these advanced coating technologies, it is possible to greatly extend the lifespan and improve the performance of essential components when faced with SPE difficulties.

Recent studies have specifically focused on creating advanced coatings that possess enhanced adhesion, hardness, and erosion resistance. These coatings aim to enhance the durability of turbine blades when exposed to challenging operating conditions. A comprehensive compilation of studies regarding coating treatments on SPE, as summarized in Table 2, provides valuable insights into key parameters such as coating process, material, substrate, thickness, erosive particle characteristics, test conditions, and observed outcomes. This compilation is a useful resource for researchers and practitioners who are working to improve coatings for the purpose of reducing erosive wear.

5.4 Enhancing erosion resistance through advanced and alternative coating technologies

The review highlights the efficacy of coating technology in mitigating erosion rates, particularly SPE, across various materials, notably in aerospace, automotive, and marine industries. Advanced techniques like thermal spray coatings and advanced polymer coatings show promising results in reducing erosion impact on components and structures. These technologies not only shield against erosive forces but also enhance overall durability and lifespan. Furthermore, ongoing research and development in coating technology continuously advances erosion resistance, promising even more effective solutions in the future.

The study by Alajmi and Ramulu [83] aimed to evaluate various coatings, particularly graphene-based ones, for their ability to reduce erosion, specifically SPE. It investigated the effects of coating type, layering, and particle impact angle on wear resistance. Results showed that different coatings alter material wear rates; for example, a single layer of H-146 graphene reduced wear by up to 19%. Increasing layers, such as using two layers of polyurethane, improved wear reduction by up to 38%. Coatings with smoother surfaces exhibited superior resistance to SPE, as illustrated in Figure 11. Graphene-based coatings, particularly when used in single layers or combined with polyurethane, have shown potential for enhancing erosion resistance. In previous studies, improvements of up to 19% in material removal and 8% reduction in erosion depth have been observed with single-layer graphene coatings. Multilayer systems, such as those combining polyurethane and graphene, demonstrated even better performance under certain conditions, with up to 13% improvement in material removal and 16% reduction in scar depth. However, in this study, the level of protection observed was comparable to uncoated samples, suggesting that further optimization or testing may be required to achieve more substantial improvements. The study emphasized that particle impact angle and duration influence coating effectiveness, underscoring the importance of considering operational conditions when selecting coatings.

Figure 11

Optical photograph of typical erosion scar shape for uncoated and different coated specimens. Reproduced from Alajmi and Ramulu [83].

Similarly, the study by Padmini et al. [84] demonstrates the superior erosion resistance of Inconel 738-coated specimens compared to uncoated T11 steel at 700°C, particularly evident at 30 and 90° impact angles. Coated specimens show up to three times higher erosion resistance, emphasizing the protective benefits of Inconel 738 spray coating in high-temperature environments, such as power plants. The study underscores the coating potential to enhance the durability of critical components like turbines and boiler tubes against SPE. The deposited coating exhibits a defect-free interface, dense structure, and higher hardness, essential for improved erosion resistance against SPE. High-temperature SPE tests reveal that the IN 738 coating outperforms T11 steel, with erosion resistance higher at 30° impact angles but lower at normal impacts due to severe oxide layer fragmentation. Figure 12 provides visual evidence of the eroded surface morphology, illustrating the coatings’ effectiveness in mitigating erosion at various impact angles.

Figure 12

Erosion morphology of IN 738 coating at 700°C: (a and b) 30°, (c–e) 90° impact, and (f) EDX analysis. Source: by Padmini et al. [84].

Additionally, the study by Yang and McKellar [85] investigated nanolayered and multilayered coatings, particularly CrAlTiN (CrN/AlTiN) and CrAlTiN-AlTiN, for their effectiveness in mitigating erosion damage to engine components. These coatings, with tailored hardness and toughness, significantly outperformed the baseline CrN coating in erosion resistance. The nanolayered CrAlTiN coatings exhibited erosion rates as low as 25 and 16% of the CrN baseline at 30 and 90°, respectively, while the multilayered CrAlTiN-AlTiN coating demonstrated even lower erosion rates. The study aimed to evaluate how altering layer architectures affected erosion resistance, with findings indicating that increasing the number of smaller layers enhanced coating strength against SPE. This research underscores the significant protective impact of layered coatings on engine parts exposed to abrasive wear, offering insights into optimizing coating composition for enhanced durability and performance in erosion-prone environments.

Prasanna et al. [86] investigated the efficacy of HVOF coatings in mitigating erosion in turbine alloys. They tested Stellite-6, alumina-CoCrAlTaY, and Cr₃C₂-NiCrNiCrAlY coatings on titanium alloy, cobalt-based superalloy, and special steel substrates, subjecting them to silica sand particles at varying angles and velocities. Stellite-6 showed the lowest wear rate, especially at a 30° impact angle, highlighting its superior resistance to damage. The study emphasizes the importance of coating selection based on operational conditions, with HVOF coatings offering promising protection against erosive wear, potentially prolonging turbine part lifespan.

Matikainen et al. [68] compared Cr₃C₂-based coatings sprayed via HVOF and HVAF methods for abrasion, dry particle erosion, and cavitation erosion resistance. Coatings with higher carbide content exhibited lower erosion rates, particularly evident at a 90° impact angle, emphasizing resistance to particle penetration. HVAF-sprayed coatings outperformed HVOF-sprayed ones, being harder, tougher, and more resistant to various wear types. Cr₃C₂-50NiCrMoNb coatings excelled in resisting cavitation erosion, while Cr₃C₂-37WC-18NiCoCr coatings balanced wear resistance and toughness well. The study duration for erosion testing was 6 h for each sample. Figure 13 illustrates significantly higher resistance of HVAF sprayed coatings, especially CW and W coatings, attributed to higher particle velocities resulting in increased peening and lower carbide dissolution, reducing the formation of brittle heterogeneous coating structures and poor interlamellar bonding.

Figure 13

Maximum erosion rates after cavitation erosion test. Source: Matikainen et al. [68].

Chemical vapor deposition (CVD) is emerging as a highly effective alternative coating technology for addressing both SPE and WDE. CVD coatings are recognized for their ability to form uniform, dense, and adherent layers on complex geometries, making them particularly suitable for turbine blades and other intricate components. For instance, CVD W/WC coatings, composed of WC nanoparticles in a metal tungsten matrix, have demonstrated remarkable fracture toughness and high hardness [87,88], providing exceptional protection against both WDE and SPE. Testing has shown that these coatings significantly outperform uncoated samples and traditional protective materials, exhibiting negligible damage even after prolonged exposure to erosive conditions [89].

While CVD coatings offer substantial benefits, it is worth noting that previous reviews have highlighted a limited number of studies specifically applying CVD technology for SPE protection. Research on the application of CVD coatings for SPE has been relatively scarce compared to their use in WDE, suggesting a gap in the literature that could benefit from further exploration [90]. Despite this, the available evidence underscores the potential of CVD coatings in enhancing the durability and performance of metal components across various industrial applications. The uniform, pore-free nature of CVD coatings contributes to their effectiveness against the impacts of solid particles, thereby extending the service life of the equipment. Additionally, CVD-grown graphene coatings have been shown to enhance corrosion resistance significantly, further broadening the protective capabilities of CVD technology [91].

In the context of nanotechnology, recent advancements in nanocomposite coatings, particularly those incorporating boron carbide (B₄C) nanoparticles, have shown promise in improving erosion resistance. Studies have demonstrated that the addition of nano-sized B₄C particles to aluminum matrix composites enhances hardness and tensile strength, which are critical properties for resisting erosion [92]. These findings align with the broader trend of utilizing nanotechnology to develop coatings with superior mechanical and corrosion-resistant properties, further supporting the potential of advanced coatings in mitigating SPE and WDE challenges.

6 Summary discussion

Steam turbines play a vital role in energy conversion, with meticulously designed blades spanning LP, MP, and HP sections to optimize efficiency, durability, and strength. Despite this, threats like fatigue, corrosion, and erosion, particularly SPE, pose significant challenges, hastening blade degradation. SPE prevalent in HP regions gradually wears down blades, necessitating ongoing research on materials and coatings for protection. From 2013 to 2023, there has been a significant growth in research related to erosion, as evidenced by the steady rise in publications, which increased by approximately 133%. In 2013, the field produced around 150 publications, and by 2023, this number had surged to 350. This growth highlights the growing interest and relevance of erosion studies.

The blades of steam turbines are susceptible to various failure modes, including thermal stress, mechanical stress, vibration effects, corrosion, erosion, fatigue, and creep. Thermal stress, induced by temperature variations, can lead to deformation and cracking, while mechanical stress from steam pressure and centrifugal forces contributes to blade fatigue. Additionally, corrosion, often triggered by corrosive fuel elements, can result in alkali metal formation and subsequent blade corrosion. Fatigue failure occurs when cyclic stresses exceed material fracture toughness, exacerbated by factors like material quality and operating conditions. Creep, the gradual distortion of materials under high temperatures and stress poses ongoing risks. Erosion, prominently affecting turbine blades, results from the abrasive action of suspended particles in steam flow, leading to surface deterioration and performance loss. Notably, erosion emerges as a leading degradation mechanism, alongside erosion corrosion, underlining the importance of proactive maintenance and optimization efforts to mitigate blade failures and ensure turbine performance reliability.

SPE poses a significant threat to HP steam turbine blades, particularly in regions like control valve stems and first-stage blades. During operation, solid particles carried by steam collide with blade surfaces, leading to erosion. Understanding SPE mechanisms is critical, with factors like particle type, size, velocity, and impact angle influencing erosion. Research by Laguna-Camacho et al. [37] and Shitole et al. [36] highlights material behaviors under erosive conditions, emphasizing the importance of particle characteristics and impact angles. Additionally, turbine blade design and protective coatings significantly impact erosion resistance, as demonstrated in studies by Chen et al. [43] and Leyzerovich [46]. Materials like steel, especially when treated, exhibit enhanced resistance to erosion, while advanced computational modeling optimizes blade designs for better performance. The complexities of SPE warrant thorough investigation to develop effective mitigation strategies and enhance turbine longevity and efficiency.

SPE significantly impacts the operation of steam turbine blades, influenced by multiple factors, including particle velocity, impact angle, substrate material, type of erosive particle, and temperature. Higher particle velocities generally correlate with increased erosion rates, emphasizing the need to minimize these velocities during turbine operation. Additionally, the angle of particle impact is a pivotal factor in determining the severity of erosion. Particles striking at near-normal angles (90°) tend to generate substantial material removal compared to those impacting at shallower angles (less than 30°). At near-normal angles, the particles deliver a more direct force to the surface, leading to increased material displacement and, thus, a higher erosion rate. Conversely, at shallow angles, particles may merely graze the surface, resulting in less significant damage [74,98]. The relationship between impact angle and erosion is influenced by particle size: smaller particles at shallower angles result in lower erosion rates, while larger particles at steeper angles cause more significant damage. However, this relationship can vary depending on the material type for instance, in ductile materials, maximum erosion often occurs at shallow angles (30°), while in brittle materials, near-normal angles (90°) typically lead to more significant damage. Higher temperatures correlate with accelerated erosion rates, highlighting the significance of addressing temperature effects.

The impact of temperature on erosion further complicates this relationship, as it is primarily associated with metal softening at elevated temperatures [99]. In steam turbines, components are routinely exposed to high thermal conditions, causing metals to undergo a reduction in hardness due to phase changes and thermal activation of dislocation movement. This softening increases the susceptibility to erosion, as the material can deform more readily under the impact of eroding particles. Consequently, the wear rate of the material may increase significantly, making it more vulnerable to damage during operation. Materials with superior hardness and resistance, such as AISI 420 stainless steel, exhibit lower erosion rates compared to softer materials like copper [37]. This phenomenon underscores the importance of optimizing impact angles and considering temperature as a critical factor in erosion studies, especially for materials used in high-temperature applications like steam turbines [100].

Additionally, understanding the characteristics of erosive particles like SiC, quartz, and alumina is crucial for minimizing erosion rates. The choice of erosive particles and material samples in numerous research may not correctly represent actual circumstances for steam turbines, resulting in distorted outcomes and deceptive trends. Softer metals such as copper, which exhibit greater ductility, do not undergo the brittle failures observed in harder turbine materials, resulting in lower erosion rates at 90° impact angles, in contrast to turbine blades fabricated from materials like stainless steel [31,101]. Likewise, the employment of excessively hard particles such as alumina or SiC, which are improbable in turbine environments, skews the significance of results, as actual turbines are majorly subjected to particles like quartz or iron oxides [31,41,101]. Inappropriate material selections can substantially affect erosion predictions and trends, resulting in an inaccurate depiction of SPE during actual turbine operations. Consequently, research employing more realistic mixtures of erosive particles and tougher metals, such as stainless steel in conjunction with quartz or iron oxides, will more accurately replicate actual turbine settings and provide more dependable insights for minimizing SPE [3,31,41,101]. Optimizing these parameters is vital for minimizing erosion rates in turbine blades and preserving turbine component integrity and performance.

Figure 14 illustrates the distribution of publication years for studies related to SPE in steam turbine blades. It highlights specific data points such as substrate material, erosive particle, particle size, particle flow rate, temperature, impact speed, and angle. Each bar color on the graph represents parameter studies on SPE. The presence of specific materials used as substrate material and erosive particles is indicated by color-coding in light yellow and light green, respectively, within each bar. This visualization provides insights into the temporal distribution of research efforts in the field of SPE in steam turbine blades and highlights the variability in parameters across different publication years. Between 2013 and 2015, experiment-based studies accounted for approximately 30% of the research. In contrast, from 2020 to 2023, simulation and computational data approaches became dominant, comprising around 70% of the studies. The parameters of impingement angle and impact speed emerged as key research focuses from 2013 to 2023, underscoring their crucial role in understanding erosive wear mechanisms across both experimental and simulation-based investigations. The graph integrates computational data, highlighting the limited number of publications based on experimental studies compared to the more frequent occurrence of simulation-based studies. While computational models are powerful tools, they may not always capture the full complexity of real-world scenarios due to simplifications and assumptions made during model development. By comparing these two approaches, existing gaps in the literature can be addressed while acknowledging the strengths and limitations inherent in each method. This integrated perspective enhances understanding of erosion in steam turbine applications and informs future research directions.

Figure 14

Distribution of research on SPE factors in steam turbine blades (2013–2023).

Recent advancements in coating technologies offer promising solutions for mitigating SPE in various industries, including aerospace, energy, and manufacturing. Coating compositions vary widely, ranging from YPSZ to boride coatings, with application methods including APS, HVOF spraying, and plasma-enhanced magnetron sputtering (PVD). These coatings exhibit diverse erosion resistance properties influenced by factors such as material hardness, porosity, microstructure, and resistance to cracking. Experimental conditions simulate operational environments, with studies examining parameters like particle size, impact angle, substrate material, and temperature to optimize erosion resistance. Notably, coatings with higher ceramic or carbide content, applied using techniques like HVAF spraying or cathodic arc ion plating, show promise in achieving optimal erosion resistance. Additionally, layered coatings, such as CrAlTiN and CrAlTiN-AlTiN, demonstrate superior erosion resistance compared to baseline coatings. Overall, investing in advanced coating technologies holds significant potential for extending component lifespan and enhancing performance in the face of SPE challenges across diverse industrial sectors.

The graph from Figure 15 illustrates various coating processes and parameters investigated from 2013 to 2023, revealing key trends and gaps in research. From 2014 to 2023, thermal spray processes dominated coating studies, representing about 50% of the research, while PVD accounted for roughly 30%. Coatings designed for extreme conditions comprised around 20% of the studies, particularly increasing in prominence post-2018, highlighting the growing demand for advanced coatings in harsh environments.

Figure 15

Coating process distribution analysis for SPE (2013–2023).

Thermal spray processes, specifically HVOF, APS, and HVAF, are thoroughly researched and often used for materials such as stainless steels and titanium alloys. Processes such as cathodic arc deposition and AIP, which are part of the PVD techniques, are commonly used. These processes often involve the use of materials like YPSZ and TiAlN, which are frequently studied. Coatings for extreme conditions, such as TBC and environmental barrier coatings, focus on materials like SiC and Inconel alloys. Current nanotechnology research emphasizes the use of graphene-based coatings, demonstrating a growing preference for advanced materials. While APS, HVOF, and PVD remain promising techniques for developing erosion-resistant coatings, addressing their limitations is crucial for optimizing their application. Furthermore, CVD coatings, particularly those made from W/WC and graphene, present an advantageous alternative that warrants further exploration, especially in the context of SPE, to provide robust protection against mechanical and chemical degradation in demanding environments.

Essential factors for optimal performance include the type of coating material, the thickness of the coating, and the size of the particles. Impact speed, substrate, erosive particle, temperature, and angle are also studied, though less frequently. Studies have shown a substantial surge after 2015, indicating a rising interest in this particular topic. Contributions from various authors are noted across the years. Processes like HPCS and plasma-enhanced magnetron sputtering are not adequately represented. Although the coating material and thickness have been extensively researched, there is a need for more complete research on characteristics such as impact speed and erosive particles. Further investigation is necessary for advanced applications such as environmental barrier coatings and boride coatings. Finally, incorporating more recent research would guarantee the inclusion of the most current improvements. This review emphasizes the wide range of research conducted on coating processes and factors, while also identifying certain areas that require more exploration to improve industrial coating solutions.

The novelty of this article lies in its key contributions to the field of SPE in steam turbine blades. It highlights a 133% rise in erosion-related research from 2013 to 2023, reflecting the growing importance of this topic. The article critically evaluates the inappropriate selection of materials and particles in many studies, advocating for more realistic combinations, such as stainless steel with quartz or iron oxide, to improve erosion predictions. Additionally, it compares experimental and computational approaches, outlining their strengths and limitations. Finally, it identifies research gaps in coating technologies, emphasizing the need for further exploration of CVD coatings and underrepresented processes like HPCS. These insights provide guidance for future research to enhance turbine blade durability.

7 Conclusions and future direction

SPE is more complex than it may appear at first glance. Addressing SPE in steam turbine blades requires a multidisciplinary approach, integrating insights from material science, fluid dynamics, and engineering design. By staying abreast of advancements in materials, coatings, and design methodologies, turbine maintenance and operation practices can be optimized to mitigate the adverse effects of SPE, thereby prolonging turbine lifespan and improving overall performance. For the past decades, hundreds of brilliant researchers have engaged vigorously in erosion science. After reviewing the resulting body of research, several reflections on the past and future of erosion research can be made:

1. The failure of steam turbine blades can stem from a multitude of factors including thermal stress, mechanical stress, corrosion, erosion, fatigue, and creep. These issues arise from the harsh operating conditions turbines endure, exacerbated by corrosive substances in fuels and abrasive particles in steam flow. Research emphasizes the detrimental impact of erosion, erosion–corrosion, and fatigue on blade integrity and performance, highlighting the urgent need for proactive maintenance and optimization strategies to ensure consistent turbine operation over time.

2. SPE poses a significant threat to HP steam turbine blades, impacting both structural integrity and operational efficiency. Understanding SPE mechanisms, including particle characteristics, impact angles, and material properties, is crucial for effective mitigation. Research highlights the importance of material selection, design optimization, and protective coatings in enhancing erosion resistance. By comprehensively addressing these factors, turbine lifespan can be prolonged, and operational performance optimized, ensuring reliable and efficient turbine operation.

3. The effects of SPE on steam turbine blades are influenced by factors such as particle velocity, impact angle, substrate material, type of erosive particle, and temperature. Lower particle velocities, higher impact angles, materials with superior hardness, and erosion-resistant particles like SiC help minimize erosion rates. Maintaining optimal temperatures further mitigates SPE damage. Understanding and optimizing these parameters are essential for effective SPE mitigation, ensuring prolonged turbine lifespan and enhanced operational efficiency. Future research should capitalize on advancements in computational modeling, materials science, and interdisciplinary approaches to enhance erosion-resistant materials and coatings. Emphasizing sustainability and efficiency, there is potential to explore eco-friendly materials and coatings, particularly for renewable energy technologies. Interdisciplinary collaboration and innovative technologies will continue to advance SPE research and develop robust mitigation strategies for various engineering applications.

4. Thermal spray processes such as HVOF, APS, and HVAF are extensively researched for materials like stainless steels and titanium alloys, while PVD techniques like cathodic arc deposition and AIP often use YPSZ and TiAlN. Coatings for extreme conditions focus on SiC and Inconel alloys, with a growing emphasis on graphene-based coatings in nanotechnology. Key performance factors include coating material, thickness, and particle size, though impact speed, substrate, erosive particle, temperature, and angle related to SPE are less studied. Comprehensive research on impact speed, erosive particles, and advanced applications like environmental barriers and boride coatings is needed, along with incorporating recent studies to capture the latest advancements.