Nickel Alloy 690 Composition , Inconel 690 Chemical Composition Corrosion Resistant

Forged corrosion resistant nickel alloy Inconel 690 round bar for high temperature service

INCONEL® alloy 690 (UNS N06690/W. Nr. 2.4642) is a high-chromium nickel alloy having excellent resistance to many corrosive aqueous media and high temperature atmospheres. In addition to its corrosion resistance, alloy 690 has high strength, good metallurgical stability, and favorable fabrication characteristics.

The chemical composition of INCONEL alloy 690 is listed as below. The substantial chromium content gives the alloy outstanding resistance to oxidizing chemicals and to high-temperature oxidizing gases. The high level of nickel imparts resistance to stress corrosion cracking in chloride-containing environments as well as to sodium hydroxide solutions.

The properties of INCONEL alloy 690 are useful for various applications involving nitric or nitric/hydrofluoric acid solutions. Examples are tail-gas reheaters used in nitric acid production and heating coils and tanks for nitric/hydrofluoric solutions used in pickling of stainless steels and reprocessing of nuclear fuels.

The alloy’s resistance to sulfur-containing gases makes it an attractive material for such applications as coal-gasification units, burners and ducts for processing sulfuric acid, furnaces for petrochemical processing, recuperators, incinerators, and glass vitrification equipment for radioactive waste disposal.

In various types of high-temperature water, alloy 690 displays low corrosion rates and excellent resistance to stress-corrosion cracking. Thus, alloy 690 is widely used for steam generator tubes, baffles, tube sheets, and hardware in nuclear power generation.

Chemical composition, %

Nickel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58.0 min.

Chromium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27.0-31.0

Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.0-11.0

Carbon. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.05 max.

Silicon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.50 max.

Manganese . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.50 max.

Sulfur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.015 max.

Copper. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.50 max.

Mechanical Properties

INCONEL alloy 690 has high strength over a broad range of temperatures. Mechanical properties of the alloy vary with product form and temper. Alloy 690 is normally used in the annealed temper, and strength characteristics described below are representative of annealed material. The usual annealing temperature is approximately 1900°F (1040°C).

Tensile Properties

At room and elevated temperatures, INCONEL alloy 690 displays high yield and ultimate strengths along with good ductility.

Creep and Rupture Properties

INCONEL alloy 690 offers attractive properties for applications involving extended service at elevated temperatures. The alloy has good creep-rupture strength along with metallurgical stability and resistance to high temperature corrosion.

Corrosion Resistance

INCONEL alloy 690 has excellent resistance to corrosion in a broad range of aqueous and high temperature environments. Because of its high chromium content, the alloy is particularly resistant to oxidizing conditions. Alloy 690 also offers excellent resistance to attack by sulfur at high temperatures.

Corrosion by acids

Alloy 690 has good resistance to many oxidizing acid solutions. It is especially useful for handling nitric and nitric/hydrofluoric acids. In nitric acid, laboratory tests have shown the alloy to corrode at rates less than 1 mpy (0.03 mm/a) in concentrations through 70% at room temperature and at 176°F (80°C). In mixtures of nitric and hydrofluoric acids such as those used in pickling of stainless steels and reprocessing of nuclear fuel elements, INCONEL alloy 690 has displayed excellent corrosion resistance.

INCONEL alloy 690 is highly resistant to phosphoric acid at room and moderate temperatures. Laboratory tests have shown the alloy to have corrosion rates of less than 1 mpy (0.03 mm/y) in concentrations of phosphoric acid through 85% at temperatures to 176°F (80°C). At boiling temperatures, alloy 690 is resistant to lower acid concentrations. Tests exposed in boiling acid exhibit general corrosion rates of 30 mpy (0.8 mm/a) in 20% acid and greater than 100 mpy (2.5 mm/a) at higher concentrations.

Stress-corrosion cracking

INCONEL alloy 690 has good resistance to stress-corrosion cracking in many environments including chloride containing solutions, high-temperature water, polythionic acid, and moderate concentrations of sodium hydroxide.

In boiling 45% magnesium chloride, stressed U-bend specimens of alloy 690 did not crack in 30 days of exposure.

Alloy 690 has been tested extensively for resistance to stress-corrosion cracking in high-temperature water such as encountered in nuclear steam generators. The results show the alloy to be highly resistant to cracking in chloride containing water, oxygen-containing water under crevice conditions, and deaerated (oxygen of 0.02 ppm or less) water.

In polythionic acid, stressed U-bends of alloy 690 showed no cracking after exposure for 720 h to a solution that cracked sensitized Type 304 stainless steel within 1 h. The specimens of alloy 690 were tested both in the annealed condition and after being exposed to 600°F (315°C) for up to 1000 h.

The results of stress-corrosion-cracking tests in sodium hydroxide are given in Table 8. The tests were performed on U-bend specimens in nondeaerated sodium hydroxide. Testing at 500°F (260°C) and 610°F (320°C) was done in autoclaves having air in the head space. The results indicate that alloy 690 resists cracking in boiling sodium hydroxide at concentrations up to about 50%. Severe general corrosion occurred at 500°F (260°C) and 610°F (320°C) in concentrations of 30% and greater.

In deaerated 1% sodium hydroxide at 600°F (316°C), U-bend specimens did not crack in 9400 h.

Additional tests in sodium hydroxide were performed on bent-beam specimens stressed at 50%, 90%, and 100% of yield strength (0.2% offset). No cracking occurred in 100 h of exposure to boiling 80% sodium hydroxide.

Oxidation and sulfidation

INCONEL alloy 690 has good resistance to oxidation and sulfidation in high-temperature gaseous environments.

Fabrication

INCONEL alloy 690 is readily fabricated by conventional techniques for high-nickel alloys. In most working operations, alloy 690 exhibits characteristics similar to those of INCONEL alloy 600.

Heating and Pickling

Like other nickel alloys, alloy 690 should be clean before it is heated and should be heated in a low-sulfur atmosphere. Furnace atmospheres for open heating should also be slightly reducing to prevent excessive oxidation of the material.

INCONEL alloy 690 is a solid-solution alloy and is not hardenable by heat treatment. The alloy is normally used in the annealed condition.

Forming

The temperature range for heavy hot forming of INCONEL alloy 690 is 1900 to 2250°F (1040 to 1230°C). Light forming can be done at temperatures down to 1600°F (870°C).

Microstructure

INCONEL alloy 690 is an austenitic, solid-solution alloy with a high degree of metallurgical stability. The alloy has a low solubility for carbon, and its microstructure normally contains carbides. The major carbide present in the alloy is M23C6; the abundance of the phase varies with carbon content and thermal exposure of the material. Other phases normally present are titanium nitrides and carbonitrides. No embrittling intermetallic phases such as sigma phase have been identified in alloy 690.

Available Products and Specifications

INCONEL alloy 690 is available in a wide range of standard mill forms including rod, bar, pipe, tube, and forging.

Alloy 690 is designated as UNS N06690, W. Nr. 2.4642 and ISO NW6690.

Rod, Bar, and Forging - ASTM B / ASME SB 166, ASTM B 564 /ASME SB 564, ASME Code Case N-525, ISO 9723, MIL-DTL-24801

Seamless Pipe and Tube - ASTM B / ASME SB 163, ASTM B 167 / ASME SB 829, ASTM B 829 /ASME SB 829, ASME Code Cases 2083, N- 20, N-525, ISO 6207, MILDTL- 24803

Product size range
Diameter: 100mm - 600mm
Length: on request
 
Production Process