Thermal Power

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Thermal Power

Problem

Steam Turbine Components

A steam turbine is a device that extracts thermal energy from super-heated high velocity pressurized steam and uses it to do mechanical work on a rotating output shaft. In the process blade tips of LP turbine rotor get worn out due to droplet erosion thereby reducing the efficiency of rotor. Also solids contained in dirty steam cause wear on critical components such as rotor and stator blades, sealing areas and other zones subjected to the steam flow. Also the bearing journals of rotors are subjected to sliding wear due to rotation at high RPM. The entire steam turbine system consist of a series of valve component assemblies of which many areas are subjected to severe abrasive, corrosive and erosive wear. Premature failure of any of these components will not only lead to heavy downtime and maintenance costs but also prove to be fatal.

Boiler Tubes

Boiler tubes consist of a series of tubes that contain high pressure flowing water which is heated externally by fire. Boiler tubes are subjected to temperatures which make them more vulnerable to erosion from abrasive soot emitted from burning of coal. Continuous bombardment leads to reduction in wall thickness that eventually leads to failure

Solution

Steam Turbine Components - High Temperature Wear, Erosion and Corrosion Resistant Coatings

Components coming in contact with steam at high temperatures and subjected to impact loads and erosion can be coated with Chrome Carbide based Cermets like PIC DC12, PIC DC07 etc. and Cobalt super-alloys like PIC C21, PIC C52, PIC C53, PIC C54 etc. These coatings exhibit high temperature oxidation endurance and they prolong the operational life of critical components by enhancing wear and high temperature erosion properties. Carbide coatings are deposited with robotic controlled HP-HVOF process to get uniform coating deposition and further impregnated with special sealant to achieve dense coating. Cobalt based weld overlays are deposited with automated and controlled GTAW and PTAW process. These weld overlays are qualified for WPS, WPQ and PQR as per requirements of BHEL and NTPC. Our coatings find various applications on steam turbine components as listed below :
  • HP Turbine Blades for erosion resistance
  • LP Turbine Blades to combat droplet erosion
  • Steam Control Valve componen
  • Abradable coatings for Turbine Casings for better clearance control & prevent steam leakage
  • Insulating washers for thermal and electrical insulation
  • Babbitt coating for bearing bush
We have complete in-house capabilities for supply of coated valve components as per customer specification. These components are manufactured to precision on our heavy duty calibrated CNC and Grinding machines. We have successfully supplied completely manufactured valve components for multiple projects through BHEL, NTPC and other multinational OEM’s. Few of these components are listed below :
  • Diffusers
  • Valve Spindle with Cone
  • Valve Cone
  • Valve Cone Extension
  • Valve Seats
  • Guide Bush
  • Angle Rings
  • Contour Rings
  • Insulating Washers etc.
Coating Properties PIC C52 PIC C53 PIC DC07 PIC DC12
Process GTAW/PTAW GTAW/PTAW HVOF HVOF
Bonding Metallurgical Metallurgical Mechanical Mechanical
Micro Hardness (HRc) 28 - 36 42 - 48 72 - 74 68 - 72
Coating Application High Temperature Oxidation and Impact Resistance Erosion and Corrosion Resistance Erosion and Corrosion Resistance High Temperature Abrasion and Corrosion Resistance
Max Temperature (°C) < 600 < 600 < 700 < 850
Surface Finish < 1.6 Ra µm < 1.6 Ra µm < 0.8 Ra µm < 0.8 Ra µm

Wear and Corrosion Resistant Coatings on Rotor Bearing Journals

We offer ceramic and carbide based coatings on rotor bearing journals to combat sliding wear and corrosion at high operating RPM’s. Our PIC B02 coating deposited with Atmospheric Plasma Spray process and impregnated with special sealer offer good resistance to abrasive and corrosive wear. Our PIC DC09 coating deposited with HP-HVOF process produces very dense and homogeneous coatings and offer excellent resistance to abrasive and sliding wear. These coatings are ground and super-finished to achieve the desired dimensions and surface finish. The coating and grinding process is carried out under controlled conditions and with necessary precautions to ensure that the run-out of journal areas is maintained within 0.01mm.
Coating Properties PIC DC09 PIC B02
Process HVOF Plasma
Bonding Mechanical Mechanical
Micro Hardness (HRc) 72 - 74 68 - 72
Coating Application Abrasion and Sliding Wear Resistance Abrasion and Corrosion Resistance
Max Temperature (°C) < 450 < 540
Surface Finish < 0.4 Ra µm

Boiler Tubes

We offer TRIBODEX M range of coatings specifically developed for combating erosion in boiler tubes with negligible effect on the heat transfer efficiency of the tubes. TRIBODEX M coatings could extend life of boiler tubes by 3 – 4x in comparison to uncoated tubes. TRIBODEX M range of coatings can be deposited using different processes based on the application requirements.
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