Imagine operating equipment at extreme temperatures exceeding 700°C under intense pressure. What material can ensure safe and stable performance under such demanding conditions? The answer lies in nickel-based alloy steel. With its exceptional creep resistance and high strength, this advanced material has become indispensable for challenging industrial applications.

Nickel-based alloy steel is primarily composed of nickel as the main alloying element, enhanced with additional elements like chromium, molybdenum, and iron to optimize its properties. Compared to conventional steels, it offers several distinct advantages:

• High-Temperature Strength and Creep Resistance: Maintains exceptional strength at elevated temperatures while resisting creep deformation, making it ideal for high-temperature applications.
• Superior Corrosion Resistance: Demonstrates excellent resistance to corrosive environments, including acids, alkalis, and salts, ensuring long-term durability.
• Excellent Weldability: Facilitates the fabrication of complex structural components through reliable welding processes.
• Low-Temperature Performance: Certain grades maintain good toughness even in cryogenic conditions, expanding their application range.

Advanced Ultra-Supercritical technology represents a breakthrough in power generation efficiency and emission reduction. A-USC plants operate with steam parameters exceeding 700°C, demanding materials with extraordinary performance characteristics. Nickel-based alloy steel has become essential for A-USC turbine manufacturing.

Conventional Design: 1000MW A-USC turbines typically employ a TC4F configuration with four casings: a single-flow very high pressure (VHP) casing, high pressure (HP) casing, double-flow intermediate pressure (IP) casing, and two double-flow low pressure (LP) casings. The VHP casing operates at 35MPa pressure.

Modified Design: Some designs combine the VHP and HP casings into a single unit to reduce overall length and material usage, though this compromises some efficiency and rotor stability.

700MW A-USC Design: These turbines typically integrate HP and IP casings. Cooling systems are strategically placed in the VHP casing and between HP/IP casings, with additional cooling for rotor weld joints.

• HP and IP Turbine Blades: The high inlet temperatures and strength requirements make nickel-based alloys the material of choice.
• Rotors: Essential for maintaining strength and creep resistance under extreme conditions.
• Turbine Casings: Selected high-temperature areas of VHP and HP casings utilize nickel-based alloys.

Advanced cooling techniques are employed to maintain component integrity:

• Blade Cooling: Utilizes cooled steam from VHP and HP turbine exhaust
• Rotor Cooling: Specialized cooling of weld joints extends service life

• Production Tubing: Nickel-based alloys provide critical corrosion resistance in high-production wells against H2S, CO2, and chlorides.
• Compressor Housings: Selected for cryogenic applications where conventional materials become brittle.

Materials like Alloy 600 and stainless steel serve as vital structural components in reactors, though stress corrosion cracking (SCC) in high-temperature water environments remains a challenge requiring ongoing research.

The exceptional corrosion resistance makes these alloys ideal for equipment handling aggressive chemical media.

Nickel-based alloy steels are categorized by microstructure and composition:

• Martensitic stainless steels
• Duplex martensitic-ferritic steels
• Austenitic stainless steels
• Nickel-based alloy steels

Tarim Oilfield: Implemented composite-coated corrosion-resistant tubing with AOC-2000T or CK-54 internal coatings to withstand 140°C temperatures and corrosive media including acids, alkalis, salts, Cl-, CO2, and H2S.

Sour Gas Fields: Requires specialized materials or corrosion inhibitors to prevent SCC and electrochemical corrosion in H2S/CO2 environments.

SCC represents a significant failure mechanism for nickel alloys and stainless steels in specific environments. Studies focus on:

• Slip-dissolution/oxidation mechanisms
• Age-related crystalline ordering processes
• Initiation timing and activation energy
• Stress/strain rate effects
• Electrode potential variations

Nickel-based alloy steels continue to enable technological advancements across industries facing extreme operating conditions. Future development will focus on:

• Performance optimization through alloy design
• Advanced manufacturing techniques
• Expanded application engineering
• Enhanced understanding of failure mechanisms

As industrial demands evolve toward higher efficiencies and more challenging environments, these advanced materials will play an increasingly vital role in supporting technological progress while ensuring operational safety and reliability.