Water-droplet erosion behavior of high-velocity oxygen-fuel-sprayed coatings for steam turbine blades

The water-droplet erosion of low-pressure steam turbine blades under wet steam environments can alter the vibration characteristics of the blade, and lead to its premature failure. Using high-velocity oxygen-fuel (HVOF) sprayed water-droplet erosion resistant coating is beneficial in preventing the erosion failure, while the erosion behavior of such coatings is still not revealed so far. Here, we examined the water-droplet erosion resistance of Cr3C2–25NiCr and WC–10Co–4Cr HVOF sprayed coatings using a pulsed water jet device with different impingement angles. Combined with microscopic characterization, indentation, and adhesion tests, we found that: (1) both of the coatings exhibited a similar three-stage erosion behavior, from the formation of discrete erosion surface cavities and continuous grooves to the broadening and deepening of the groove, (2) the erosion rate accelerates with the increasing impingement angle of the water jet; besides, the impingement angle had a nonlinear effect on the cumulative mass loss, and 30° sample exhibited the smallest mass loss per unit area (3) an improvement in the interfacial adhesion strength, fracture toughness, and hardness of the coating enhanced the water-droplet erosion resistance. These results provide guidance pertaining to the engineering application of water erosion protective coatings on steam turbine blades.

Development of a new type of automatic magnetic particle inspection wall-climbing robot

In the paper, a permanent magnet adsorption wall-climbing robot using magnetic particle detection technology for crack detection is introduced, which solves the problems of low efficiency of traditional manual detection and long detection time. According to the working environment of the detection system and the detection functions that need to be completed, the body structure of the robot is designed, the overall size of the robot is smaller than the distance between two steam turbine blades, so it can achieve the crack detection function of large steam turbine blades, and the stability and force analysis of the robot are carried out, and the adsorption conditions that meet the conditions of no sliding and overturning are obtained. In the paper, we use the magnetic circuit method to design a miniature excitation device for robotic applications and use the simulation software Ansoft-Maxwell to verify its feasibility. In the final experiment, it can be shown that the robot designed can achieve a series of functions such as magnetic particle inspection and image acquisition. There is a good prospect for the inspection of turbine blades.

Enhancing Thermal Properties of Steam Turbine Blades by Coating with Nanomaterials

Heat resistant coatings are considered for the external surface Low-Pressure Steam Turbines (LPST). 410 stainless steel covered with nano heat resistant coatings consists of a heat resistant connecting layer enhanced by nanoparticles. A commercial paint was modified by using 20%wt of (titanium dioxide (TiO2) - aluminum oxide (Al2O3)) with different concentrations range (25,50,75wt% of TiO2) layers. These nano-coatings paints were airbrushed onto the surface of specimens of steam turbine blades. The test rig and experimental apparatus have been fabricated and collected to accomplish the thermal tests. The samples were subjected to heat resistance and a temperature test approximately similar to the steam turbine's operation condition temperature. The test results are used to choose the nano-coating layer with a concentration that ensures a composition's highest protective properties. The test sample with concentration (paint-(75% Al2O3+25% TiO2)) showed the highest thermal properties compares with the other cases.

The Influence of Thermocyclic Treatment on the Structure and Mechanical Properties of Pseudo-Alpha Titanium Alloys for Steam Turbine Blades

The influence of thermal cycling treatment of pseudo-α-titanium alloys OT4 and VT20 on their structural and substructural characteristics, as well as their mechanical properties is considered. A significant change in structural characteristics is established. This contributes to an increase in the strength properties of alloys with satisfactory ductility and high-temperature strength.

CORROSION RESISTANCE OF REINFORCED LAYERS OF 15Х11МФ STEEL STEAM TURBINE BLADES

The reliability of the vane apparatus of steam turbines largely determines the operation of the turbine as a whole. The results of scientific research indicate that the surface operation of the blades in the wet-steam flow is caused by a combination of corrosion and drip erosion. The presence of chemical elements and compounds in the working fluid intensifies the process of blade wear. The pH value of the working environment, which can fluctuate significantly during operation, has a significant effect on the wear characteristics. The influence of methods of strengthening the leading edges of steam turbine blades made of steel is analyzed 15H11MF on corrosion resistance. Corrosion tests of blade samples were carried out, the inlet edges of which were strengthened in three ways: high current amplification, electrospark alloying with T15K6 alloy, electrospark alloying with steel 15H11MF. According to the results of the tests, the layer strengthened by hardening by high-frequency currents has the lowest corrosion rate, the layer strengthened by electrospark alloying with T15K6 hard alloy has the highest. The corrosion rate of the layer reinforced by electrospark alloying of steel 15H11MF is 2.1 less than that of the layer reinforced with T15K6 alloy.

Study of wear mechanism of contact surfaces of steam turbine blades made of titanium VT6 alloy

The contact surfaces of the banding shelves of adjacent steam turbine blades made of titanium VT6 alloy after operation are studied by fractography, micro-X-ray and microstructural analysis and determination of mechanical properties. The different types of destruction of the contact surfaces are analyzed and explained. It is shown that the reason for intensive abrasion of the turbine blades' binding meshes is violation of the welding mode in the station conditions.