We provide high-performance coating manufacturing for important components of large power stations (green energy, hydropower stations, thermal power generation, nuclear power stations, wind power generation and other power stations). We provide laser cladding coating manufacturing services for direct repair on-site, as well as accepting customers to send parts that need to be repaired to our factory and then perform coating manufacturing for customers. At the same time, we can also provide customers with customized solutions for a complete set of repair equipment to meet the various demanding conditions of customers. At present, our technical level is at the leading level in the industry, and our independently developed laser cladding technology, process and equipment have been unanimously praised by customers. So far, our company has more than dozens of cooperation experiences with large power stations.

Ⅰ Key components that require surface repair

1. Generator core components

1.1 Bearings: Due to long-term high-load operation, wear, cracks or sand holes are prone to occur. They need to be repaired by scratching, polishing or thermal spraying to ensure the contact point density (1-2 guide bearings/cm²) and non-contact area (≤15%).

1.2 Thrust head and mirror plate: The thrust head mating surface must be smooth and burr-free, and the mirror plate surface finish must reach ▽10 or above (equivalent to Ra≤0.1μm). After repair, the dimensional accuracy and fit clearance requirements must be met.

1.3 Cooler: Copper tube leakage must be blocked, and the number of one-way blocked tubes shall not exceed 1/5 of the total number. The pressure test requires 0.35MPa/30 minutes without leakage.

2. Steam turbine and rotor system

2.1 High/medium pressure rotor and low pressure rotor: focus on repairing the shaft neck, speed regulating stage impeller root and other parts, and detect cracks through ultrasonic flaw detection and surface flaw detection. The hardness deviation must be controlled within the same circumference ≤30HB and the same busbar ≤40HB.

2.2 Blades and connectors: The blade surface must be free of cracks and scratches. The tie rod holes and belt parts must be checked regularly. The last stage blades must be inspected every overhaul.

2.3 Baffles and nozzles: The surface must be free of cracks or collision marks. After repair, it must meet the DL/T438-2000 standard.

3. High temperature and high pressure system components

3.1 High temperature bolts (≥32mm): used to fasten high temperature components (such as cylinders). Creep damage and thread wear must be checked. After repair, it must meet the DL/T439-2006 standard.

3.2 Cylinder and main valve castings: surface cracks, slag inclusions and other defects need to be repaired. The first inspection shall be carried out after 50,000 hours of operation, and the subsequent period shall be 50,000 hours.

4. Auxiliary equipment

4.1 Brakes and brake cabinets: Pistons, cylinders and gates need to be repaired for wear or burn marks. Gates need to be replaced when the loss thickness exceeds 1/4 of the original.

4.2 Oil tank and oil distributor: cleanliness requires no impurities. After installation, wind test and pressure test are required to ensure sealing.

Ⅱ Quality standards and key requirements involved

1. Mechanical properties and surface treatment standards

1.1 Bearing scraping requirements: contact point density (1-2 guide bearings/cm²), non-contact area (≤15%), surface roughness Ra≤1.6μm.

1.2 Laser cladding repair (GB/T 41477-2022): Applicable to components such as rotor blades. The bonding strength of the repair layer must reach more than 90% of the raw material, and the fatigue life must meet the working conditions.

1.3 Ultrasonic flaw detection (DL/T438-2000): used to detect internal defects such as rotors and blades. After repair, there must be no excessive cracks or pores.

2. Pressure resistance and sealing standards

2.1 Cooler pressure test: 0.35MPa/30 minutes without leakage, pipe blockage ratio ≤20%.

2.2 Oil tank sealing: after installation, it must pass wind test and pressure test, and the bolts must be tightened without loosening.

3. Material and heat treatment standards

3.1 High-temperature alloy parts (such as GH4169): The chemical composition must comply with GB/T 5307-2004, and after repair, it must pass the salt spray test (GJB 150.11A-2009) to verify corrosion resistance.

3.2 Hardness control (JB/T1265-2002): The hardness deviation of the rotor repair area must be controlled within 30HB (circumferential) and 40HB (axial).

4. Nondestructive testing and metallographic analysis

4.1 Penetrant testing (HB/Z 61): Used to check for surface microcracks, and there must be no continuous linear defects after repair.

4.2 Metallographic inspection: High-temperature components (such as rotors) need to detect organizational changes to prevent intergranular corrosion caused by overheating.

Ⅲ Repair process and quality control points

1. Pretreatment:

1.1 Mechanical cleaning (sandblasting, shot blasting) to remove the oxide layer, chemical cleaning (pickling, degreasing) to ensure no oil stains.

2. Repair technology selection:

2.1 Laser cladding: For high-precision components (such as blades), the range of the heat-affected zone needs to be controlled.

2.2 Electroplating/chemical plating: restore the wear resistance of the journal, and the coating thickness must be uniform (such as chrome plating ≥ 50μm).

3. Post-processing and acceptance:

3.1 Passivation treatment improves corrosion resistance, verified by salt spray test.

3.2 Dimension re-measurement and non-destructive testing (such as ultrasonic and magnetic particle testing) to ensure compliance with tolerance and defect standards.

Metal surface repair in large power stations requires the selection of processes for different working conditions, and strictly follows national standards (such as GB/T 41477), industry standards (such as DL/T438) and equipment manufacturer specifications. Key control points include surface roughness, mechanical properties, sealing and corrosion resistance, combined with non-destructive testing and metallographic analysis to ensure repair reliability. For more details, please refer to the “Generator Overhaul Project and Quality Standards” and the overhaul standards for thermal power units.

Commonly used metal powder types and their characteristics

Ⅰ. Nickel-based alloy powder

1. Inconel 625 (nickel-chromium-molybdenum-niobium alloy)

Composition: Ni (≥58%), Cr (20-23%), Mo (8-10%), Nb (3-4%)

Performance effect:

High temperature resistance: can work for a long time below 800℃, with excellent anti-oxidation performance.

Corrosion resistance: resistant to seawater, acidic gas (such as H₂S) and chloride corrosion.

High strength: The hardness of the cladding layer can reach HRC 25-30, and the bonding strength is high (≥400MPa).

Typical applications: gas turbine blades, offshore platform pipelines, nuclear power plant heat exchangers.

2. Hastelloy C276 (Hastelloy alloy)
Composition: Ni (balance), Cr (14-17%), Mo (15-17%), W (3-4.5%)

Performance effect:

Strong corrosion resistance: Tolerant to concentrated sulfuric acid, hydrochloric acid and chloride ion-containing media.

High temperature oxidation resistance: The maximum operating temperature can reach 1200℃ (short term).

Typical applications: Inner wall of chemical reactor, flue gas desulfurization system components.

3. NiCrBSi (Nickel-chromium-boron-silicon self-fluxing alloy)
Composition: Ni (70-80%), Cr (10-15%), B (2-4%), Si (3-5%)

Performance effect:

Wear resistance: Hardness reaches HRC 50-60, suitable for high friction conditions.

Self-fluxing: Good fluidity, dense cladding layer without pores.

Typical applications: Shaft parts, gear tooth surface, mold repair.

Ⅱ Cobalt-based alloy powder

1. Stellite 6 (Stellite alloy)

Composition: Co (remainder), Cr (28-32%), W (4-6%), C (1.0-1.7%)

Performance effect:

Super wear resistance: hardness HRC 40-50, resistance to adhesive wear and abrasive wear.

High temperature resistance: still maintain high strength at 800-1000℃.

Typical applications: turbine valve sealing surface, aircraft engine turbine blades.

2. Tribaloy T-800 (Cobalt-Molybdenum-Silicon Alloy)

Composition: Co (remainder), Mo (28-32%), Si (2-3%), Cr (17-19%)

Performance effect:

Low friction coefficient: excellent self-lubricating performance, suitable for dry friction environment.

Heat shock resistance: better thermal fatigue resistance than traditional cobalt-based alloys.

Typical applications: high temperature bearings, internal combustion engine valve seat rings.

Ⅲ Iron-based alloy powder

1. 316L stainless steel powder

Composition: Fe (balance), Cr (16-18%), Ni (10-14%), Mo (2-3%)

Performance effect:

Corrosion resistance: anti-pitting and stress corrosion, suitable for acidic environment.

Economical: lower cost than nickel-based/cobalt-based alloys.

Typical applications: pump body, valve, food processing equipment.

2. FeCrNiMoB (iron-based wear-resistant alloy)

Composition: Fe (balance), Cr (15-20%), Ni (5-10%), Mo (2-4%), B (1-2%)

Performance effect:

Wear resistance and corrosion resistance: hardness HRC 45-55, suitable for medium corrosion environment.

Typical applications: mining machinery gears, hydraulic rods.

Ⅳ Ceramic reinforced composite powder

1. WC-Co (tungsten carbide cobalt composite material)

Composition: WC (80-90%), Co (10-20%)

Performance effect:

Ultra-high hardness: The hardness of the cladding layer can reach HRC 60-70, and the wear resistance is improved by 3-5 times.

Impact resistance: Cobalt bonding phase enhances toughness.

Typical applications: drill bits, tool edges, roller surfaces.

2. Cr3C2-NiCr (chromium carbide nickel-chromium composite material)

Composition: Cr3C2 (70-75%), Ni (20-25%), Cr (remainder)

Performance effect:

High temperature wear resistance: stable wear resistance below 800℃.

Oxidation resistance: suitable for high temperature corrosion environments containing sulfur and chlorine.

Typical applications: boiler pipes, hot blast furnace linings.

Others:

Quality control standards
Coating bonding strength: According to GB/T 41477-2022, the tensile strength must be ≥ 90% of the raw material.
Hardness test: Use Vickers hardness tester (GB/T 4340.1-2009) to verify the target hardness.
Corrosion resistance test: Pitting test according to ASTM G48, or salt spray test (ISO 9227).
Metallographic analysis: Check that the cladding layer has no pores and cracks (porosity ≤ 2%).

The selection of alloy powder for laser cladding repair needs to comprehensively consider the substrate matching, working environment and cost-effectiveness:
Nickel-based alloy: suitable for high temperature and strong corrosion in the aerospace and energy fields;
Cobalt-based alloy: specializes in extreme wear resistance and high temperature conditions;
Iron-based alloy: suitable for low-cost, medium-performance industrial parts;
Ceramic composite materials: used for ultra-hard and wear-resistant mines and tool repairs.
In practical applications, process parameters (such as laser power and scanning speed) need to be optimized to ensure that the cladding layer performance meets the standards.

Alloy Powder Selection Guidelines