Incoloy 825 – Properties, Applications, Fabrication, Machinability and Weldability of Incoloy 825 by Austral Wright Metals

Topics Covered

Background

Incoloy 825

Pressure Vessels

Applications of Aluminium Incoloy 825
Chemical Composition of Incoloy Alloy 825

Tensile Properties of Incoloy Alloy 825

Corrosion Resistance

Fabrication

Machinability

Welding

Welding Consumables

Heat Treatment

ASTM Product Specifications

Equivalent Grade Designations

Background

Incoloy alloy 825 is a nickel iron chromium alloy with additions of molybdenum, copper and titanium, with exceptional resistance to many aggressive corrosion environments.

Incoloy 825

Incoloy 825 is highly resistant to corrosion. It has a high nickel content, sufficient to resist chloride ion stress corrosion cracking, and a very stable austenite structure. The levels of molybdenum and copper enable the alloy to resist reducing agents and acids. Chromium gives resistance to oxidising conditions, such as nitric acid solutions, nitrates and oxidising salts. The alloy is titanium stabilised to resist pitting and intergranular attack after fabrication, particularly welding, which includes heating in the critical sensitisation temperature range (650°C – 760°C).

Alloy 825 offers exceptional resistance to corrosion by sulphuric and phosphoric acids and is often the most cost effective alloy in sulphuric acid service.

Austral Wright Metals can supply this alloy as plate, sheet, strip, bar, rod, wire, tube, pipe, fittings, fasteners.

Pressure Vessels

Incoloy 825 is approved for pressure vessel operating temperatures up to 525°C (AS1210, AS4041), 538°C (ASME Boiler & Pressure Vessel Code, Sections I, III, VIII, IX, Cases 1936, N-188). Brittle phases may form in alloy 825 at temperatures above ~ 540°C, so it is not normally used at these temperatures, where creep-rupture properties would be design factors.

Applications of Incoloy 825

Typical Applications of Incoloy Alloy 825 include:

         Sulphuric acid piping and vessels

         Phosphoric acid evaporators

         Pickling tank heaters, pickling tanks and equipment

         Chemical process equipment

         Propellor shafts

         Tank trucks

         Calorifiers

         Electrostatic precipitator electrodes

         Hot vessels for food, water and seawater,

         ammonium sulphate vessels

         Expansion bellows

         Marine exhaust systems

         Power station ash hoppers

Chemical Composition of Incoloy Alloy 825

Table 1. Chemical composition of Incoloy Alloy 825 (ASTM B163 – Heat exchanger tube)

Element

%

Element

%

Nickel

38.0 – 46.0

Carbon

0.05 max

Chromium

19.5 – 23.5

Manganese

1.0 max

Molybdenum

2.5 – 3.5

Sulfur

0.03 max

Copper

1.5 – 3.0

Silicon

0.5 max

Titanium

0.6 – 1.2

Aluminium

0.2 max

Iron

22.0 min (~33%)

 

 

Tensile Properties of Incoloy Alloy 825

Table 2. Typical room temperature tensile properties (not for design. Consult the relevant material or product specification for design values)

Form

Condition

0.2% Proof Stress
MPa

Tensile Strength
MPa

Elong
%

Tube

Annealed

440

770

35

Tube

Cold drawn

880

1000

15

Bar

Annealed

325

690

45

Plate

Annealed

340

660

45

Sheet

Annealed

420

760

39

Figure 1. High temperature tensile properties of annealed Incoloy 825 bar.

Corrosion Resistance

The outstanding property of Incoloy 825 is its corrosion resistance. In reducing & oxidising conditions, Incoloy 825 resists general corrosion, pitting & crevice corrosion, intergranular corrosion and stress corrosion cracking. It is particularly useful in sulphuric & phosphoric acids, sulphur containing flue gases, sour gas and oil wells and sea water.

Figure 2. Isocorrosion chart in laboratory pure sulphuric acid.

Fabrication

Incoloy 825 can be readily hot or cold worked. Hot working should be in the range 870 – 1180°C, finishing at 870 – 980°C. For maximum corrosion resistance hot worked parts should be stabilise annealed before use. The alloy is easier to cold form than stainless steels.

Machinability

Incoloy 825 is classed as a ‘C’ alloy, and is reasonably easy to machine.

Welding

The alloy is readily weldable by the normal processes (GMAW (MIG), GTAW (TIG), SMAW (manual), SAW). The joint must be clean to avoid contamination of the weld pool.

Welding Consumables

Table 5. A guide to welding consumables to be used with Incoloy Alloy 825 under various conditions.

 

Normal Service

Higher Strength

Best Corrosion Resistance

Welding electrode

Inconel WE 112

Inconel WE 112

Inconel WE 112

Filler metal

Inconel FM 625

Inconel FM 625

Inconel FM 625

Flux cored wire

Inco Cored 625DH

Inco Cored 625DH

Inco Cored 625DH

Heat Treatment

Incoloy 825 is stabilise annealed at 940°C. The softest structure is obtained at 980°C. Sections heavier than sheet, strip and wire should be quenched to avoid sensitisation.

Please consult Austral Wright Metals for specific advice on your application.

ASTM Product Specifications

Table 6. ASM specifications for Incoloy Alloy 825.

Specification

Title

B163

Seamless Nickel and Nickel Alloy Condenser and Heat-Exchanger Tubes

B423

Nickel-Iron-Chromium-Molybdenum-Copper Alloy (UNS N08825 and N08221)* Seamless Pipe and Tube

B424

Ni-Fe-Cr-Mo-Cu Alloy (UNS N08825 and UNS N08221)* Plate, Sheet, and Strip

B425 

Ni-Fe-Cr-Mo-Cu Alloy (UNS N08825)

B704

Welded UNS N06625 and UNS N08825 Alloy Tubes

B705

Nickel-Alloy (UNS N06625 and N08825) Welded Pipe

B751

General Requirements for Nickel and Nickel Alloy Welded Tube

Equivalent Grade Designations

Table 7. Other international grades that are equivalent to Incoloy Alloy 825.

Country

Body

Designation

USA 

UNS

N08825

France 

AFNOR

NC 21 FeDU

GB

BS

NA 16

Germany

DIN

NiCr21Mo

Germany

Werkstoff

Nr 2.4858

 

Source: Austral Wright Metals

 

For more information on this source please visit Austral Wright.

 

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