Offshore Oil Gas Production Corrosion Resistant Alloys , High Strength Special Alloys UNS N08825

Corrosion resistant Alloy 825, N08825 for offshore oil-gas production, seawater heat exchanger, piping system

1 PRODUCT

Corrosion resistant Alloy 825, UNS N08825 for offshore oil and gas production, seawater heat exchanger, piping system, sour gas component etc.

Alloy 825 is available as pipe, tube, sheet, strip, plate, round bar, flat bar, forging stock, hexagon and wire, etc.

2 EQUIVALENT DESIGNATION

NiCr21Mo(DIN), W.Nr. 2.4858, NA 16(BS), NiFe30Cr21Mo3(ISO), INCOLOY® Alloy 825, NS142(GB/T)

3 OVERVIEW

Alloy 825 is a titanium stabilized full austenitic nickel-iron-chromium alloy with additions of molybdenum, copper, and titanium. The alloy’s chemical composition is designed to provide exceptional resistance to many corrosive environments. The nickel content is sufficient for resistance to chloride-ion stress-corrosion cracking. The nickel, in conjunction with the molybdenum and copper, also gives outstanding resistance to reducing environments such as those containing sulfuric and phosphoric acids. The molybdenum also aids resistance to pitting and crevice corrosion. The alloy’s chromium content confers resistance to a variety of oxidizing substances such as nitric acid, nitrates and oxidizing salt. The titanium addition serves, with an appropriate heat treatment, to stabilize the alloy against sensitization to intergranular corrosion.

This alloy is characterized by:

• good resistance to stress-corrosion cracking

• satisfactory resistance to pitting and crevice corrosion

• good resistance to oxidising and non-oxidising hot acids

• good mechanical properties at both room and elevated temperatures up to approximately 550˚C (1020˚F)

• permission for pressure-vessel use at wall temperatures up to 425˚C (800˚F)

4 APPLICATION

The resistance of alloy 825 to general and localized corrosion under diverse conditions gives the alloy broad usefulness. Applications include chemical processing, pollution control, oil and gas recovery, acid production, pickling operations, nuclear fuel reprocessing, and handling of radioactive wastes. Applications for alloy 825 are similar to those for Alloy 20.

Typical applications as follows

• Air Pollution Control: Scrubbers

• Chemical Processing Equipment: Acids, Alkalis

• Food Process Equipment

• Nuclear: Fuel reprocessing, fuel element dissolvers, waste handling

• Offshore Oil and Gas Production: seawater heat exchanger, piping system, sour gas components

• Ore Processing: copper refining equipment

• Petroleum Refining: Air-cooled heat exchanger

• Steel Pickling Equipment: Heating coils, tanks, crates, baskets

• Waste Disposal: Injection well piping systems

5 CHEMICAL COMPOSITION

6 PHYSICAL PROPERTIES

(1) Density:8.14 g/cm³ (0.294lb/in³)

(2) Melting point:1370-1400°C (2500-2550°F)

(3) Specific heat: 0.105 Btu/lb•°F(440J/kg•°C)

(4) Curie Temperature: ≤-320°F (-196°C)

(5) Permeability at 200 oersted (15.9 kA/m): 1.005

7 MECHANICAL PROPERTIES

Alloy 825 has good mechanical properties from cryogenic temperatures to moderately high temperatures. Exposure to temperatures above about 1000°F (540°C) can result in microstructural changes (phase formation) that significantly lower ductility and impact strength. For that reason, the alloy is not normally used at temperatures where creep-rupture properties are design factors.

Tensile properties at room temperature are listed in Table below. As indicated, the alloy can be strengthened substantially by cold work.

Alloy 825 has good impact strength at room temperature and retains its strength at cryogenic temperatures.

8 METALLURGICAL STRUCTURE

Alloy 825 has a stable face-centred cubic structure. The chemical composition and optimised annealing treatment ensure that corrosion resistance is not impaired by sensitisation.

9 CORROSION RESISTANCE

The outstanding attribute of Alloy 825 is its high level of corrosion resistance. In both reducing and oxidize environments, the alloy resists general corrosion, pitting, crevice corrosion, intergranular corrosion, and stress-corrosion cracking. Some environments in which Alloy 825 is particularly useful are sulfuric acid, phosphoric acid, sulfur containing flue gases, sour gas and oil wells, and sea water.

Table 9-1 Resistance to Laboratory Sulfuric Acid Solutions

Stress-corrosion cracking resistance

The high nickel content of Alloy 825 provides superb resistance to chloride stress-corrosion cracking. However, in the extremely severe boiling magnesium chloride test, the alloy will crack after long exposure in a percentage of samples. Alloy 825 performs much better in less severe laboratory tests. The following table summaries the alloys performance.

Table 9-2 Resistance to Chloride Stress Corrosion Cracking

Mixed - A portion of the samples tested failed in the 2000 hour of test. This is an indication of a high level of resistance.

Pitting resistance

The chromium and molybdenum content of Alloy 825 provides a high level of resistance to chloride pitting. For this reason the alloy can be utilized in high chloride environments such as seawater. It can be used primarily in applications where some pitting can be tolerated. It is superior to conventional stainless steels such as 316L, however, in seawater applications Alloy 825 does not provide the same levels of resistance as SSC-6MO (UNS N08367) or Alloy 625 (UNS N06625).

Crevice corrosion resistance

Table 9-3 Resistance to chloride pitting and crevice corrosion

*ASTM Procedure G-48, 10% Ferric Chloride

Intergranular corrosion resistance

Table 9-4 Resistance to Intergranular Corrosion

9 WORKING INSTRUCTION

Alloy 825 products are heat treated during manufacturing at the mill to develop the optimum combination of stabilization, corrosion resistance, mechanical properties, and formability. To maintain these properties during fabrication, subsequent anneals should be performed between 1700 to 1800°F (930 to 980°C) followed by rapid air cooling or water quenching. Heat treatment in the lower end of the range is acceptable for stabilization. However, annealing at temperatures in the higher end of this range may be preferred for softness and grain structure for forming and deep-drawing while maintaining corrosion resistance. Quenching is usually not necessary for parts of thin cross section (e.g., sheet, strip and wire), but may be desired to avoid sensitization in products of heavier cross section.

Hot forming

The hot-working range for Alloy 825 is 1600 to 2150°F (870 to 1180°C). For optimum corrosion resistance, final hot working should be done at temperatures between 1600 and 1800°F (870 and 980°C).

Cooling after hot working should be air cool or faster. Heavy sections may become sensitized during cooling from the hot-working temperature, and therefore be subject to intergranular corrosion in certain media. A stabilizing anneal (see above) restores resistance to corrosion. If material is to be welded or subjected to further thermal treatment and subsequently exposed to an environment that may cause intergranular corrosion, the stabilizing anneal should be performed regardless of cooling rate from the hot-working temperature.

Annealing

To develop the optimum combination of stabilization, corrosion resistance, mechanical properties, and formability, subsequent anneals after hot forming should be performed between 1700 to 1800°F (930 to 980°C) followed by rapid air cooling or water quenching.

Cold forming

Cold forming properties and practices are essentially the same for Alloy 825 as for Alloy 600. Although work-hardening rate is somewhat less than for the common grades of austenitic stainless steels, it is still relatively high. Forming equipment should be well powered and strongly built to compensate for the increase in yield strength with plastic deformation.

Machining

All standard machining operations are readily performed on Alloy 825. The alloy normally has optimum machining characteristics in the annealed temper.

10 COMPETITIVE ADVANTAGE

(1) More than 50 years experience of research and develop in high temperature alloy, corrosion resistance alloy, precision alloy, refractory alloy, rare metal and precious metal material and products.
(2) 6 state key laboratories and calibration center.
(3) Patented technologies.
(4) Excellent performance

11 STANDARD SPECIFICATION

Alloy 825 is listed in NACE MR0175 for oil and gas service.

Rod, Bar, Wire and Forging Stock

BS 3076 NA16

ASTM B425 / ASME SB425

ASTM B564 / ASME SB564

ASME Code Case N-572

VdTÜV 432

Plate, Sheet and Strip

BS 3072 NA16

BS 3073 NA16

ASTM B424 / ASME SB424

ASTM B906 / ASME SB906

VdTÜV 432

Pipe and Tube

BS 3074 NA16

ASTM B163 / ASME SB163

ASTM B423 / ASME SB423

ASTM B704 / ASME SB704

ASTM B705 / ASME SB705

ASTM B751 / ASME SB751

ASTM B775 / ASME SB775

ASTM B829 / ASME SB829

ASME Code Case 1936

VdTÜV 432

Others

ASTM B366 / ASME SB366

DIN 17744

12 BUSINESS TERM