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Alloy 31

Alloy 31, UNS N08031, W.Nr. 1.4562

Alloy 31 is an iron-nickel-chromium-molybdenum alloy with the addition of nitrogen. The alloy closes the gap between high alloyed austenitic special stainless steels and nickel alloys. 

Alloy 31 is characterized by:

Outstanding corrosion resistance in alkaline and acidic halide-containing media

Excellent resistance to sulfuric acid, even in highly concentrated form

Excellent resistance to corrosion and erosion in phosphoric acid media

Outstanding resistance to surface corrosion and local corrosion in chlorine dioxide bleaching plants in paper production

Excellent resistance in reducing and oxidizing media as well as in boiling azeotropic nitric acid

Good workability and weldability

Typical application for Alloy 31 are:

Components for flue gas desulfurization plants

Plants for the production of phosphoric acid via the wet digestion process

Pipes and heat exchangers for sulfuric acids contaminated with chlorides

Pipes containing ocean water and brackish water, condensers and chillers

Pickling plants for sulfuric acid as well as nitric-hydrofluoric acid

Treatment of sulfuric acids from waste

Evaporation and crystallization of salts

Components for the cellulose and paper industry

Digestion of ores, e.g. in HIPAL (high-pressure acid leach) plants for the digestion of laterite ores

Mineral oil production and refineries

Organic acids and ester synthesis

Fine chemicals

Strain-hardened transport and feed pipes as well as slicklines, wirelines and flowlines in the transport of oil and gas

Alloy 31 in the solution annealed condition as per ASTM B622

Optimal corrosion resistance is only ensured if the material is used in a solution annealed, clean and metallic bright condition. The chemical composition of Alloy 31 is designed to enable the achievement of a high corrosion resistance in halide containing media. At the same time, the material has excellent resistance in pure and contaminated sulfuric acid over a broad range of concentrations and temperatures up to 80°C (176°F).

The resistance to inter-crystalline corrosion (IC) was determined both according to ASTM G28, method A, and according to SEP 1877 II. Alloy 31 becomes sensitized only after prolonged exposure. The resistance to pitting was determined via potential measurements and through testing according to ASTM G48 under staged temperature increases and the use of the same samples.

Alloy 31 is suitable only for applications in organic chemistry and for processes in which hydrochloric acid occurs only in low concentrations below 5% and this only at room temperature or slightly elevated temperatures. This is clearly shown by the ISO corrosion diagram in hydrochloric acid and by other investigations at room temperature as well as with acid concentrations in the range of 10% to 30%, which yielded erosive corrosion rates of up to 0.5 mm/year (0.02 in/year).

(1) Hot formed, annealed, descaled

(2) Cold worked and bright annealed

(3) Cold worked, bright annealed, polished (MP, EP, CP etc.)

(1) Hot formed, annealed, descaled

(2) Cold worked and bright annealed

(3) Cold worked, bright annealed, polished (MP, EP, CP etc.)

Chemical composition

Tension

Hardness

Flaring

Flange

Flattening

Micro structure

Hydrostatic

NDT

Intergranular Corrosion

Surface condition

Shape and dimension

Positive Material Identification