Sandvik 2RE10: Premium Austenitic Stainless Steel for Superior Corrosion Resistance

Sandvik 2RE10 is very suitable for heat exchanger tube and pipe in processes that treat nitric acid, for example, the manufacture of nitric acid, acrylic fibres, ammonium nitrate and the reprocessing of nuclear reactor fuel. Extensive practical experience in such applications has confirmed the superiority of Sandvik 2RE10 over standard steels such as ASTM 304L and ASTM 329.

Tail gas preheaters: The main reason for highly corrosive conditions in tail gas preheaters is that droplets of nitric acid are entrained in the tail gas from the absorption tower. When this gas enters the heater, the droplets settle on the hot tube wall and start boiling. The temperature of the heating medium, usually hot process gas or steam, can be very high. In this type of condition, ASTM 304L tends to have a short service life. Tubes and tube sheets manufactured in Sandvik 2RE10 are recommended for a long service life.

Cooler/condensers: In cooler/condensers, corrosion is normally encountered at the inlet end, where the first condensate is formed. If reboiling of the first condensate occurs, the corrosive conditions become very severe, leading to the kind of attack illustrated in figure 5. This typical corrosion problem can be detected easily. By upgrading to Sandvik 2RE10 the service life will be substantially longer than, for example, ASTM 304L.

Approvals: ASME Code Case 2591. Section VIII, Division 1

The excellent formability of Sandvik 2RE10 permits cold bending to very small bending radii. Cold working does not impair resistance to general and intergranular corrosion. Annealing is not normally necessary after cold bending. If, however, tubes have been cold worked and are to be used under conditions where stress corrosion cracking (SCC) is liable to occur, stress relieving is recommended. See under 'Heat treatment'.

General corrosion: General corrosion: Sandvik 2RE10 was developed to combat corrosion problems in nitric acid service. Thanks to its high chromium and low impurity contents it has considerably better resistance to nitric acid than steels of type ASTM 304L, as illustrated by the isocorrosion diagram, figure 1. In such applications Sandvik 2RE10 is far superior to ASTM 304L, ASTM 321 and ASTM 329.The corrosion rates of these grades in 65% nitric acid (Huey test) are compared in figure 2.

Sandvik 3R12 is the Sandvik version of ASTM 304L. Results are presented from tests of solution annealed material (the delivery condition) and also material in a sensitized 650°C (1202°F) for 1 h condition. ASTM 329 was sensitized at 650°C (1202°F ) for only 5 min.

Stress corrosion cracking (SCC): The higher nickel content makes Sandvik 2RE10 slightly more resistant to stress corrosion cracking (SCC) than conventional austenitic stainless steels, such as ASTM 304L.

Intergranular corrosion: Sandvik 2RE10 is highly resistant to intergranular corrosion even after long-term sensitization. Figure 3 shows the results of Huey testing (boiling in 65% nitric acid for 5x48 h) sensitized specimens of Sandvik 2RE10 and a steel of type ASTM 304L. The low tendency for sensitization is an advantage in complicated welding operations.

In delivery testing, by means of the Huey test, the guaranteed maximum corrosion rate for Sandvik 2RE10 is 0.12 mm/year (5 mpy) in the solution annealed condition, and 0.20 mm/year (8 mpy) after sensitization at 675°C (1250°F). Even lower values can be guaranteed by agreement in certain cases. Figure 3 demonstrates that sensitization does not increase the corrosion rate greatly in Huey testing, whereas the corrosion rate for ASTM 304L increases significantly.

Pitting corrosion: Sandvik 2RE10 has considerably higher pitting corrosion resistance than ASTM 304L and is also superior to ASTM 329, as illustrated by figure 4.

Tubes are delivered in the heat treated condition. If another heat treatment is needed, due to further processing, the following is recommended.

Stress relieving: 850–950°C (1560–1740°F), 10–15 minutes, rapid cooling in air. Alternatively 1000–1050°C (1830–1920°F), about 1 minute, rapid cooling in air.

Solution annealing: 1000–1100°C (1830–2010°F), 5–20 minutes, rapid cooling in air or water.

Forms of supply:

Tube and pipe are supplied in dimensions up to 80 mm (3.15 in.) outside diameter in the solution annealed and white-pickled or in the bright annealed condition.

Sandvik 2RE10 is also supplied in forms of:

The weldability of Sandvik 2RE10 is good. Suitable methods of fusion welding are manual metal-arc welding (MMA/SMAW) and gas-shielded arc welding, with the TIG/GTAW method as first choice.

In common with all fully austenitic stainless steels, Sandvik 2RE10 has low thermal conductivity and high thermal expansion. Welding plans should therefore be carefully selected in advance, so that distortions of the welded joint are minimized. If residual stresses are a concern, solution annealing can be performed after welding.

For Sandvik 2RE10, heat-input of <1.0 kJ/mm and interpass temperature of <100°C (210°F) are recommended. A string bead welding technique should be used.

Recommended filler metals:

• TIG/GTAW or MIG/GMAW welding
  • 25.20.L (e.g. Exaton 25.20.L)
  • ISO 14343 S 25 22 2 N L (e.g. Exaton 25.22.2.LMn)
• MMA/SMAW welding
  • ISO 3581 E 25 22 2 N L B (e.g. Exaton 25.22.2.LMnB)
  • ISO 14343 S 25 22 2 N L wire or strip electrodes are recommended for overlay welding of tube sheets and high-pressure vessels in cases where corrosion resistance, equal to that of Sandvik 2RE10, is required.