Protecting Turbine Blades From Wear Using High Velocity Oxygen Fuel Coating

Literature Review

Discuss about the Protection Of Turbine Blades From Wearing Using High Velocity Oxygen Fuel Coating.

The erosion, corrosion and wear occur on the moving blades of turbine due to flow of velocity fluid and water droplet at the surface of turbine blades. The water-droplets start as bubbles in small amount and then increase gradually and make turbine blades cooler. This large amount of droplets developed, is converted into liquid, which causes erosion on the surface of turbine blades. These droplets impact the convex surface of the turbine moving blades which enhances the effect of corrosion.  The intensity of wear and tear reduces as corrosion occurs on the surface and make the turbine blades weaker, ultimately failing after few rotations. The corrosion and erosion on the edges of the blades gradually increases with the increase in the volume of the liquid, similarly, reduced liquid volume results in lesser wear and tear. The high-velocity oxygen fuel coating process has been recently developed; however, laser hardening process is the best alternative process for water droplet erosion control. This process creates tensile stress and residual stress on the material.

The high velocity oxygen fuel coating is compressive in nature and that creates the need to develop a reaction of high velocity oxygen fuel spray coating. The high velocity oxygen fuel study indicates the depth of peening effect which could be more than 50 per meter which is much higher than tungsten carbide powder, that obtains compressive stress in the range of around 250 to 450 MPa.

The complete report is demonstrated in different chapters. Chapter (2) discusses about the literature review, research articles and past researches that have been done on the topic (3) chapter 3 discusses about the research methodology and experimental procedures applied to perform research on the given topic. Chapter (4) demonstrates the results as per given methodology and discussion. Chapter (5) discusses about the conclusion obtained from the research and any future scope for the research.

According to this paper, the water droplet erosion property of the high velocity oxygen fuel was sprayed on coating and laser hardened steel such as 12Cr mixed with the steels and titanium alloys used, in order to manufacture turbine blades at the different energy source. According to study and research about the droplet erosion, the round sample which is suggested according to ASTM G73-98 is used.  At the moderate energy level, the high velocity oxygen fuel coating used 12Cr steel which is considerably better than 12Cr and other materials such as 13Cr-Ni steels.  This occur due to mixture of hard carbide particles in the cobalt chrome matrix and is sufficiently hard to absorb shocks. Good carbide materials are considerably harder and have good strength.  As per further research and development, the laser hardened 12Cr steel give the best result, which is followed by 17Cr-4Ni and allows heat treatment process for steel.  According to experimental result, it gives the maximum and adaptive resilience of the materials which plays significant role in the combat droplet erosion.  This erosion test results of all these materials and high velocity oxygen fuel coating with the other impurities and properties are plotted in micrographs and discussed in the results. (Arya, 2013)

Research Methodology

In the power generation company, the inlet cooling is used regularly to cool the turbine inlet air. The gas turbine inlet air is cooled directly, cost-effectively and helps energy saving solution for to raise power output of the entire turbine procedures. This is obtained through the spray water at the gas turbine inlet position.  This results in the liquid erosion of the rotation blades in the turbine compartment such as compressor, service life reduction of the gas turbines. The liquid impingement erosion demonstrates the continuous material loss at the turbine blades surface because of the continued impacts of the liquid drops or water jet condition.  This type of problem was shown in turbine blades and turbine assembly. Therefore, it was essential to find solution because frequent blade replacement is costly, difficult and time consuming for steam turbine and gas turbines.  The design engineer sustainably improved the erosion resistance of turbine and compression blades. There are different tactics in order to protect turbine blades and other component of turbine. There are variety of protection method such as heat treatment process, case or core hardening, laser cladding, chromium carbide and satellite coating. These are the method that can be used to overcome corrosion and wear problems. As more experiments are performed, it will give more accurate result about the objective. This will help to enhance performance of turbine blades and turbine output. (Y. Itoh, 2012)

To determine different method to protect turbine blades from wear using high velocity oxygen fuel coating.

Subproblems

• Selection of suitable materials that overcome wearing and corrosion of the turbine blades.
• Prevention of corrosion and wearing along with the protection of the turbine blades.
• Re-designing or optimization of turbine blades that will prevent corrosion and wearing of the blades.

Hypothesis

We will use different methods in order to protect turbine blades from wearing off, compare those methods and evaluate which method is the best.

Change the velocity in order to reduce wearing and corrosion and thereby increasing the life span of the turbine blades.

Defintion Of Key Terms

HVOF: High velocity oxygen fuel, that is essential in order to provide protection against corrosion and wearing.

Assumptions

• The experimental procedure and obtained data considering error in positive and negative terms in order find the best result of the given situation.
• Neglecting human and environment errors in order to obtain result as per objective.

Delimitations

• The material used in powder form to perform the experiment.
• Ratio of the fuel and oxygen varies at every experimental process.

This research uses experimental methods. Two methods used for this research are “erosion of turbine and compression blades” and “liquid impingement erosion of compression blades”. Other methods are discussed in order to demonstrate the research about preventing the turbine blades from wearing using high velocity oxygen fuel. The research methods such as “Heat treatment process”, “HVAF tungsten carbide”, “Laser Clad Stellite”, “HVOF Stellite” “HVAF cemented carbides” are used with lower, moderate and higher rate of water droplet resistance process. (RHYS-JONES, 2011)

Results and Discussion

Table. 1 experimental data of HVOF with coating

Table. 2 experimental data of HVOF without coating

Table.3 Comparison of hardness of the blades without HVOF and with HVOF

As shown in above table, both the data obtained from the experimental procedure varies as changes in condition such as with and without flow. The results show that the flow of methane and oxygen changes with the changing conditions. Table 3 compares the hardness of the blades with experiments clearly showing that the hardness of blades with HVOF is better than the hardness of blades without HVOF.

The experiment has been performed with two-powder material such as Si and.It used Diamond Jet 2500 high velocity oxygen fuel spraying equipment along with the three cathode ASP gun which was operated through six axis robots manipulated according to the direction and situation requirement. The HVOF gas burner allocated through the convergent nozzle provided lower particle velocities and there was considerable time to compare with the convergent-divergent nozzle. The HVOF process uses methane gas during which, The HVOF feeding position and the ratio of methane and oxygen ratios varies according to the distance of the gun.  Therefore, the rate of the flow of methane differed such as 190, 220, 230 etc. and the flow of the oxygen remained constant. The equipment obtained a maximum value of 390. The ferrite stainless steel was used at the beginning of the experimental procedure with powder coating. Further, the alumina grit blasted with the approximate particle size of around 40 to 120 m and it was used under the pressure of 3 bars and velocity of 20 m/s reacting with the average roughness size of 3.9 to 4.1 m (K.Gupta, 2014).

In order to evaluate the effect of oxygen and methane flow rates, it is required to measure the area specific weight and average roughness of the coating, under observation. The correlation between the ASW and roughness values of the as-sprayed coatings was obtained and so was the optimum value of ASW for the coating with the minimum roughness and this occurred accordingly. It is sensible that the high ASW has low roughness mixture of the coating to the well molten, compressed and bonded particles, that interprets to translate with the high particle temperature and velocities spread by the combustion of the fuel and oxygen mixture. The molecular will remain in the non-molten or partially molten state and become unstable and a cause of reduction in the ASW, further that will lead to an increase in the roughness of the surface finish. For an easy operation and a smooth outcome, the rough surface of the HVOF should be sprayed with the molten and non-molten particle of the individual material. (S.Prakash, 2015)

The actual correction between the ASW and the roughness value of the coatings sprayed was obtained. The maximum ASW was obtained through the coating with the minimum value of roughness that worked as an indirect method of analysis. It is considerable to assign the maximum value of ASW with the low roughness value of the coating to the well molten and flattered and bounded particles, that will translate to the high particle temperature and high velocity delivered through the combustion of the oxygen and other flammable mixture.

Conclusion

Prevention of turbine blades from the wearing off due to high velocity oxygen fuel coating required the usage of HVOF process. The above methodology and experimental procedure concludes with the fact that the turbine blades are affected due to corrosion and wearing off because of various factors. These factors need to be kept in mind for the construction of turbine blades that can resist such damage. The heat treatment process, laser clad stellite, HVOF stellite, HVOF cemented carbide, HVAF tungsten carbide, are the methods can be used to overcome corrosion and wearing of the blades.

Future work:

• The optimization technique used to overcome force droplet issue.
• Heat treatment process used to resist wearing and hard material such as tungsten or carbide used for the same.

References

Arya, B. M. (2013). Abrasive and erosive wear characteristics of plasma nitriding and HVOF coatings: their application in hydro turbines. Wear, 354-360.

K.Gupta, J. T.-M. (2014). Protective coatings in the gas turbine engine. Surface and Coatings Technology, 1-9.

RHYS-JONES, T. (2011). THERMALLY SPRAYED COATING SYSTEMS FOR SURFACE PROTECTION AND CLEARANCE CONTROL APPLICATIONS IN AERO ENGINES. Metallurgical Coatings and Thin Films , 402-415.

S.Prakash, T. S. (2015). Hot corrosion of some superalloys and role of high-velocity oxy-fuel spray coatings—a review. Surface and Coatings Technology, 441-446.

Itoh, M. S. (2012). Characteristics of MCrAlY Coatings Sprayed by High Velocity Oxygen-Fuel Spraying System. Journal of Engineering for Gas Turbines and Power , 43-49.

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