Most Welded Superalloys in Power Generation: Inconel 617, 625, 718 & Hastelloy X
Most Commonly Welded Superalloys in Power Generation
In the power generation industry, where components face prolonged exposure to high temperatures, pressure, and corrosive environments, the selection of weldable superalloys is critical for fabrication, assembly, and repair. The most commonly welded alloys are chosen for their balance of high-temperature performance, environmental resistance, and—crucially—weldability.
Nickel-Based Alloys: The Workhorses
Nickel-based superalloys dominate due to their superior creep and oxidation resistance.
Inconel 617: A premier choice for advanced ultra-supercritical (USC) coal and gas turbine components like combustors and transition ducts. Its excellent high-temperature strength and oxidation resistance up to 1100°C make it ideal, and it is considered one of the more weldable advanced alloys.
Inconel 625: Widely used for its outstanding corrosion and fatigue resistance. It is commonly welded for pipework, heat exchanger shells, and as a cladding or overlay material due to its good weldability and resistance to post-weld cracking. Its strength comes from solid solution strengthening rather than precipitation hardening, simplifying the welding process.
Inconel 718: While more common in aerospace, it is also used in power generation for high-strength components like turbine discs and blades. Its weldability is good for a precipitation-hardened alloy, but it requires strict control to avoid strain-age cracking and must be followed by a specific post-weld heat treatment.
Inconel 738 / 939: These are widely used for first and second-stage turbine blades and vanes due to their high strength and coating compatibility. Their weldability is more challenging due to high aluminum and titanium content, making them prone to cracking. They are primarily welded during repair operations using highly specialized techniques.
Cobalt-Based and Solid-Solution Strengthened Alloys
Hastelloy X: A nickel-chromium-iron-molybdenum alloy known for its exceptional oxidation resistance and strength at high temperatures. It is extensively welded for combustors, burners, and afterburner components. Its solid-solution strengthened nature gives it good weldability.
Haynes 230: A popular alternative to Hastelloy X, offering similar oxidation resistance and long-term thermal stability. It is commonly welded for similar applications.
Stellite 6: A cobalt-based alloy rarely used for structural components but extensively welded as a hard-facing overlay. It is applied to valve seats, turbine blade shrouds, and other components subject to severe wear, galling, and erosion at high temperatures.
Stainless Steels for Lower-Temperature Sections
316/316L Stainless Steel: While not a superalloy, this austenitic stainless is a backbone material for piping, heat exchangers, and structural parts in less extreme sections of power plants. Its excellent weldability makes it one of the most frequently welded materials in the entire industry.
Key Considerations for Welding in Power Generation
The choice of alloy is dictated by the specific service conditions within the plant, from the hottest sections of the gas turbine to the high-pressure steam turbine and boiler systems. Successful superalloy welding in this sector invariably requires:
Precise Filler Metal Selection: Using matching or over-alloyed filler metals to ensure corrosion resistance and strength.
Strict Control of Heat Input: To minimize segregation and cracking in the heat-affected zone.
Mandatory Post-Weld Heat Treatment (PWHT) and HIP: To relieve stresses, restore microstructure, and heal defects for long-term component reliability under creep conditions.
In summary, the most commonly welded superalloys in power generation—Inconel 617, 625, 718, and Hastelloy X—are selected for their proven performance in extreme environments and their relative weldability, which enables the fabrication and repair of critical plant infrastructure.
