Incoloy 825 – Properties, Applications, Fabrication, Machinability and Weldability of 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)

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)

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.

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.

Equivalent Grade Designations

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

This information has been sourced, reviewed and adapted from materials provided by Austral Wright Metals - Ferrous, Non-Ferrous and High Performance Alloys.

For more information on this source, please visit Austral Wright Metals - Ferrous, Non-Ferrous and High Performance Alloys.