Corrosion Resistant Special Alloys For Petrochemical Industry Good Workability

Corrosion resistant alloy 31 rod, bar, forging, pipe, plate for petrochemical processing

1 PRODUCT

Corrosion resistant alloy 31 rods, bars, forgings, pipes, plate, wire, sheet, strip etc.

2 EQUIVALENT DESIGNATION

UNS N08031, W.Nr. 1.4562, X1NiCrMoCu32-28-7(DIN), VDM^® Alloy 31, Nicrofer^® 3127 hMo

3 PRODUCT FORM

Sheet

Delivery condition: Hot- or cold-rolled, heat-treated, de-scaled or pickled

Strip

Delivery condition: Cold-rolled, heat-treated, pickled or bright annealed

Rod

Delivery condition: Forged, rolled, drawn, heat-treated, oxidized, de-scaled or pickled, twisted, peeled, ground or pol- ished

Wire

Delivery condition: Drawn bright, ¼ hard to hard, bright annealed in rings, containers, on spools and headstocks

4 APPLICATIONS

Alloy 31 has proven itself to be suitable particularly in the chemical and petrochemical industries, in ore digestion plants, in environmental and marine engineering as well as in oil and gas extraction.

The material is included in the list of the German Federal Institute for Materials Research and Testing (BAM) for transport and storage containers for hazardous goods.

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

5 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.

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

VdTÜV-certification for pressure vessels with operating temperatures from -196 to 550 °C (-320.8 to 1,022 °F)

Certification according to ISO 15156/NACE MR 0175 up to level VI for acid gas applications in the oil and gas industry

ASME approval for pressure vessels up to 800 °F (427 °C)

6 CHEMICAL COMPOSITION (wt%):

7 PHYSICAL PROPERTIES

Density: 8.05 g/cm3 (0.29 lb/in3) at 20°C (68°F)

Melting range: 1330-1370°C (2426-2498°F)

Relative magnetic permeability at 20 °C (68 °F): 1.001

8 MECHANICAL PROPERTIES

Mechanical properties at room temperature according to ASTM B625 (plate, sheet and strip), B649 (bar and wire)

ISO V-notch impact toughness

Average value, room temperature: ≥185J/cm2

Average value, -196°C (-320.8°F): ≥ 140J/cm2

Minimum impact values at room temperature for sheet products according to VdTÜV material data sheet 509.

9 MICROSTRUCTURE

Alloy 31 has a face-centered cubic lattice. The 0.2% nitrogen content stabilizes the austenite and reduces the precipitation rate of intermetallic sigma phases.

10 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). Figure 1 shows the ISO corrosion diagram of Alloy 31 in lightly aerated sulfuric acid of technical purity, determined in immersion tests of at least 120 hours.

Figure 1 ISO corrosion diagram of Alloy 31 in weakly aerated sulfuric acid of technical purity, determined in immersion tests of at least 120 hours.

Under heavy stress from erosion corrosion in the wet digestion process in the production of phosphoric acid, Alloy 31 has proven to be a true alternative to nickel alloys. Tests in chlorine dioxide bleaching plants in the pulp and paper industry have shown that Alloy 31 withstands the harshest operating conditions.

11 HEAT TREATMENT

Solution annealing should take place at temperatures between 1150 and 1180°C (2102 and 2156 °F). The retention time during annealing depends on the semi-finished product thickness and can be calculated as follows:

For thickness d <= 10 mm (0.39 in), the retention time is t = d * 3 min/mm

For thickness d = 10 to 20 mm (0.39-0.79 in), the retention time is t = 30 min + (d – 10 mm) * 2 min/mm

For thickness d > 20 mm (0.79 in), the retention time is t = 50 min + (d – 20 mm) * 1 min/mm

The retention time commences with material temperature equalization; longer times are generally considerably less critical than retention times that are too short.

12 WORKING INSTRUCTION

Hot forming

Alloy 31 should be hot-formed in a temperature range of 1200 to 1050°C (2192 to 1922°F) with subsequent rapid cooling in water or in air. For heating up, workpieces should be placed in a furnace that has been heated up to the maximum hot-forming temperature (solution annealing temperature). Once the furnace has reached its temperature again, the workpieces should remain in the furnace for around 60 minutes per 100 mm (3.94 in) of thickness. After this, they should be removed from the furnace immediately and formed within the temperature range stated above, with reheating necessary once the temperature reaches 1050°C (1922°F). Heat treatment after hot forming is recommended in order to achieve optimal properties.

Cold forming

The workpieces should be in the annealed condition for cold forming. Alloy 31 has a significantly higher work hardening rate than other widely used austenitic stainless steels. This must be taken into account during the design and selection of forming tools and equipment and during the planning of forming processes. Intermediate annealing is necessary for major cold forming work. For cold forming of > 15%, a final solution annealing must be conducted.

Machining

Alloy 31 should be machined in the heat-treated condition. Because of the considerably elevated tendency toward work hardening in comparison with low-alloy austenitic stainless steels, a low cutting speed and a feed level that is not too high should be selected and the cutting tool should be engaged at all times. An adequate depth of cut is important in order to cut below the previously formed strain-hardened zone. Optimum heat dissipation through the use of large quantities of suitable, preferably aqueous, lubricants has considerable influence on a stable machining process.

13 STANDARD SPECIFICATION

14 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.

15 BUSINESS TERM