Alloy 31

Material

Alloy 31, UNS N08031, W.Nr. 1.4562

Overview

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.

Character

    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

Application

    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

Chemical composition

Material Fe Ni Cu Cr Mo N
Alloy 31 Balance 30.0-32.0 1.0-1.4 26.0-28.0 6.0-7.0 0.15-0.25
Material C Mn Si P S
Alloy 31 ≤0.015 ≤2.0 ≤0.30 ≤0.020 ≤0.010

Mechanical property

Alloy 31 in the solution annealed condition as per ASTM B622

Material Tensile strength
ksi (MPa)		 Yield strength at
0.2 offset ksi (MPa)		 Elongation in 2”
% min.
N08031 ≥94 (650) ≥40 (276) ≥40

Corrosion resistance

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).

Available Process

Cold worked and bright annealed

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

Common Tests

  • ◎ Chemical composition
  • ◎ Tension
  • ◎ Hardness
  • ◎ Flaring
  • ◎ Flange
  • ◎ Flattening
  • ◎ Micro structure
  • ◎ Hydrostatic
  • ◎ NDT
  • ◎ Intergranular Corrosion
  • ◎ Surface condition
  • ◎ Shape and dimension
  • ◎ Positive Material Identification

Product forms

Capillary tube

  • ◎ OD 0.30 ~ 3.0 mm
  • ◎ WT 0.05 ~ 0.5 mm

Precision seamless tube

  • ◎ OD 3.0 ~ 89 mm
  • ◎ WT 0.10 ~ 10.0 mm

HP / UHP BA+ tube

  • ◎ OD 3.0 ~ 76 mm
  • ◎ WT 0.10 ~ 10.0 mm

Service

  • ◎ Precision cutting
  • ◎ Tube surface treatment, like ID surface super mirror polishing, best level could reach Ra0.0015um
  • ◎ Tube deep processing, like coiling, bending, end forming, body forming, laser processing, various needles processing, built to drawing and sample, etc.