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A Basic Introduction To Inconel 690

What is Inconel 690?

Alloy 690, often known as Inconel 690, is a variant of Inconel alloy 600 with a high chromium content that exhibits exceptional resistance to several oxidizing acids and salts and some resistance to sulfidation at high temperatures. The resilience of hydrofluoric and nitric acid combinations makes them ideal for pickle shop tasks. In steam-generating nuclear reactors for pipework, separators, and weldments, alloy 690 has replaced Inconel alloy 600 due to its greater stress cracking resistance.

Together with Inconel alloy 693, the alloy has recently replaced Inconel alloy 601 as the preferred material for metal-dusting conditions, making it an outstanding engineering material for the newest designs of compact reformers.

There are several different kinds of mechanical property tests, including tension, plain fatigue tests, and hardness tests. Using a bridge-style contact pad and plate-style specimen, the flat-flat contact arrangement is used to conduct the fretting fatigue test. In recent years, the material of preference for commercial nuclear steam generator applications has been 690 Inconel. Weld liquidation cracking and weld solidification resistance has been achieved in filler metal 52.

Nitric or nitric/hydrofluoric acid solutions are used in various applications where Inconel alloy 690’s characteristics come in handy. The alloy is a desirable material for applications such as coal-gasification units, burners, and ducts for processing sulfuric acid, furnaces for petrochemical processing, recuperators, incinerators, and glass vitrification equipment for disposal of radioactive waste due to its resistance to sulfur-containing gases. Examples include heating coils and tanks for nitric/hydrofluoric solutions used in the pickling of stainless steels and the reprocessing of nuclear fuels, as well as tail-gas reheaters used in the manufacturing of nitric acid.



Mechanical Properties of Inconel 690

High strength is present in Inconel alloy 690 throughout a wide temperature range. The alloy’s mechanical characteristics change depending on the product’s shape and temper. Normally, alloy 690 is utilized for its strength and annealed temper qualities. Typically, annealing occurs at a temperature of around 1900°F (1040°C).

Tensile Strength

The Inconel alloy 690 exhibits strong yield and ultimate strengths and good ductility at ambient and hot temperatures. Alloy 690 maintains a significant level of tensile characteristics at high temperatures, with temperatures above 1000°F (540°C) needed to cause noticeable decreases in strength. According to the values provided, tensile characteristics may change with product form and size.

In applications requiring prolonged service at high temperatures, Inconel alloy 690 has appealing qualities. The alloy possesses a good creep-rupture strength along with metallurgical stability and resistance to high-temperature corrosion.

Due to its high degree of metallurgical stability, alloy 690 does not undergo embrittlement after exposure to high temperatures for an extended period. Exposure to key intermediate temperatures for 12,000 hours and more does not materially alter the material’s room temperature tensile characteristics or impact strength.

Corrosion Resistance of Inconel 690

Excellent corrosion resistance is provided by Inconel alloy 690 in a variety of aqueous and high-temperature situations. The alloy is highly resistant to oxidizing environments due to its high chromium concentration. Additionally, alloy 690 provides great resistance to sulfur attack at high temperatures.

Alloy 690 can withstand a variety of oxidizing acid solutions with ease. It is extremely helpful when dealing with nitric and nitric/hydrofluoric acids. According to testing, the alloy corrodes in nitric acid at rates less than 1 mpy (0.03 mm/a) in concentrations up to 70% at room temperature and 176°F (80°C) in concentrations through 70%. Inconel alloy 690 has demonstrated exceptional corrosion resistance in nitric and hydrofluoric acid combinations, such as picking stainless steels and reprocessing nuclear fuel elements.

At normal temperatures, Inconel alloy 690 is extremely resistant to phosphoric acid. According to laboratory studies, the alloy has corrosion rates of less than 1 mpy in phosphoric acid concentrations up to 85% at temperatures as high as 176°F (80°C). Alloy 690 is resistant to weaker acid concentrations at boiling temperatures. Tests on boiling acid show that general corrosion rates are over 100 mpy at higher concentrations and 30 mpy at 20% acid.

In a variety of conditions, including chloride-containing solutions, hot water, polythionic acid, and mild sodium hydroxide concentrations, Inconel alloy 690 has better resistance to stress-corrosion cracking.

Thirty days of exposure to boiling 45% magnesium chloride did not cause strained alloy 690 U-bend specimens to break. For its ability to withstand stress-corrosion cracking in high-temperature water, such as that found in nuclear steam generators, alloy 690 has undergone rigorous testing. An experiment’s findings show that the alloy is very resistant to cracking in water that contains chloride, water that contains oxygen when it is present in crevices, and deaerated water.

Stressed U-bends of alloy 690 in polythionic acid demonstrated no cracking after being exposed for 720 hours to a solution that immediately cracked sensitized Type 304 stainless steel.

Fabrication of Inconel 690

Heating and Pickling: 

Alloy 690 should be cleaned before heating, like other nickel alloys, and cooked in a low-sulfur environment. To prevent excessive material oxidation, furnace atmospheres for open heating should also be somewhat lowered. As a solid-solution alloy, Inconel alloy 690 cannot be heat treated to become harder. The alloy is often utilized in its annealed state.


Excellent weldability is exhibited by Inconel alloy 690. Using Inconel Filler Metal 52 and Inconel Welding Electrode 152, alloy 690 parts are linked to another alloy 690 parts. These welding products’ deposits closely resemble the alloy 690 base metal in composition. Inconel Welding, Electrode 182, Filler Metal 82, and Inco-weld Alloy 690 can be joined to carbon steel, stainless steel, and most dissimilar nickel-chromium iron-nickel chromium alloys using a welding electrode. Nitric and hydrofluoric acid mixtures, frequently used in alloy pickling operations, should be considered when welding alloy 690 components for use in highly corrosive aqueous environments. Inconel Filler Metal 625 and Inconel Welding Electrode 112 should also be considered. Inconel 690 should be machined afterward.


Austenitic solid-solution alloy Inconel alloy 690 has a high level of metallurgical stability. The alloy’s microstructure typically comprises carbides and has poor carbon solubility. The main carbide found in the alloy is M23C6, and its abundance fluctuates depending on the amount of carbon and how much heat the material has been exposed to. Titanium nitrides and carbonitrides are other typical phases. Alloy 690 does not contain embrittling intermetallic phases, such as the sigma phase.


1900 to 2250°F (1040 to 1230°C) is the thermal gradient for heavy hot forming of Inconel alloy 690. The alloy behaves similarly to Inconel alloy 600 when cold-formed. The forces needed for alloy 690, however, are a little higher. It is possible to generate light at temperatures as low as 1600°F (870°C).

What are Inconel 690 Plates and Sheets? 

In pressurized water reactors, Inconel 690 plate and sheets fail to tube. Therefore they are highly suggested for big commercial utilization, with the six commercially available tubes and ten experimentally developed alloys tested with varying amounts of carbon, titanium, and aluminum. These kinds of plates and sheets are filled with various combinations of the significant consequences and other elements at varying pressures, as well as to be selected by the research-assisted customer. Use optional electron microscopy and other microstructure characterization techniques to fully understand the effects of the composition while also managing the heat treatment at various temperatures.

All chosen Inconel 690 Plate had their stress corrosion resistance tested alongside samples in an environment containing pure water, sodium hydroxide, and other chemicals at regulated temperatures. With the aid of susceptibility, it can effectively withstand an intergranular attack connected to the alloy’s aluminum content and thermal treatment.



As a result, as the amount of aluminum increases, the resistance to IGA begins to diminish. To correlate the effects of chromium depletion, heat treatment and compositions used in the corrosion investigation were first investigated over a specialized scanning transmission. The results demonstrated that the alloy’s degree of depletion and corrosion resistance were affected in diverse ways by the special thermal temperatures and times. It has a basic crack below that is visible at low-stress levels and lower loading cycle heights when under fretting conditions. Then it can suffer damage, as seen in fossil and nuclear power plants and in airplanes, cars, and petroleum chemical factories. Here, Inconel 690 is mixed in high concentrations with an alloy of chromium and nickel, which has exceptional resistance to both corrosive environments and high temperatures. As a result, it can be employed extensively in the chemical and nuclear power industries. There are several different kinds of mechanical property tests, including tension, plain fatigue tests, and hardness tests. Using a bridge-style contact pad and plate-style specimen, the flat-flat contact arrangement is used to conduct the fretting fatigue test. Using the available information, one can see that the strength of worrying fatigue decreases by 43% compared to simple strength. It is predicted that using the alloy in industries will be the greatest option. In recent years, the material of preference for commercial nuclear steam generator applications has been 690 Inconel. Weld liquidation cracking and weld solidification resistance has been achieved in filler metal 52.

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