Alloy 690 UNS N06690: Properties and Applications in High-Temperature Environments

# Alloy 690 UNS N06690: Properties and Applications in High-Temperature Environments

## Introduction to Alloy 690 UNS N06690

Alloy 690 UNS N06690 is a nickel-chromium-iron alloy that has gained significant attention in industries requiring high-temperature resistance and excellent corrosion properties. This advanced material is specifically designed to withstand extreme environments, making it a preferred choice for critical applications in power generation, chemical processing, and nuclear industries.

## Chemical Composition and Key Properties

The chemical composition of Alloy 690 plays a crucial role in its exceptional performance:

– Nickel (Ni): 58-63%
– Chromium (Cr): 27-31%
– Iron (Fe): 7-11%
– Carbon (C): ≤0.05%
– Manganese (Mn): ≤0.50%
– Silicon (Si): ≤0.50%
– Sulfur (S): ≤0.015%
– Copper (Cu): ≤0.50%

This carefully balanced composition results in several outstanding properties:

– Excellent resistance to stress corrosion cracking
– High resistance to oxidation and carburization
– Good mechanical properties at elevated temperatures
– Superior resistance to intergranular attack
– Excellent fabricability and weldability

## Mechanical Properties at Various Temperatures

Alloy 690 maintains its mechanical integrity across a wide temperature range:

Temperature (°C) | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%)

Room Temp | 586-758 | 241-345 | 30-45
315 | 517-689 | 193-310 | 25-40
538 | 483-655 | 172-276 | 20-35
649 | 448-620 | 152-241 | 15-30

## Applications in High-Temperature Environments

### 1. Nuclear Power Industry

Alloy 690 has become the material of choice for steam generator tubing in pressurized water reactors (PWRs). Its superior resistance to stress corrosion cracking in primary water environments makes it ideal for this critical application. The alloy is also used in:

– Reactor vessel head penetrations
– Control rod drive mechanisms
– Nuclear waste containers

### 2. Chemical Processing

The chemical industry extensively uses Alloy 690 for equipment exposed to highly corrosive environments:

– Heat exchangers and condensers
– Reaction vessels and piping systems
– Flue gas desulfurization systems
– Sulfuric and nitric acid production equipment

### 3. Power Generation

In conventional and advanced power plants, Alloy 690 finds applications in:

– Superheater and reheater tubing
– Boiler components
– Gas turbine combustors
– High-temperature heat exchangers

## Fabrication and Welding Considerations

While Alloy 690 offers excellent fabricability, certain considerations should be noted:

– Hot working should be performed between 871-1177°C (1600-2150°F)
– Cold working requires intermediate annealing
– Recommended welding methods include GTAW, GMAW, and SMAW
– Post-weld heat treatment may be necessary for certain applications
– Proper cleaning is essential to prevent contamination

## Comparison with Similar Alloys

Alloy 690 offers several advantages over similar nickel-based alloys:

– Superior stress corrosion cracking resistance compared to Alloy 600
– Better high-temperature strength than Alloy 800
– More cost-effective than some cobalt-based superalloys
– Better oxidation resistance than many stainless steels at high temperatures

## Future Trends and Developments

As industries push for higher efficiency and longer component life, Alloy 690 continues to evolve:

– Development of optimized heat treatments for specific applications
– Improved welding techniques to enhance joint integrity
– Research into nano-structured versions for enhanced properties
– Expanded use in next-generation nuclear reactors
– Applications in emerging clean energy technologies

Alloy 690 UNS