Sandvik SAF 2906™

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Description

Sandvik SAF 2906™ is a high-alloy duplex (austenitic-ferritic) stainless steel with excellent corrosion resistance in caustic environments and environments with chlorides. Sandvik SAF 2906™ characteristics:


  • Excellent resistance to caustic environments, also in the presence of contaminants such as chlorides
  • Excellent resistance to intergranular corrosion
  • Excellent resistance to pitting and crevice corrosion
  • High resistance to stress corrosion cracking (SCC)
  • Good weldability
  • Very high strength. The proof strength is about three times as high as for conventional austenitic stainless steels.

  • More technical information and charts that are relevant to the materials corrosion, mechanical and physical performance are displayed in the figures on the right side of the material page.


    Datasheet URL:

    Sandvik SAF 2906™


    Datasheet updated 2019-12-20 09:57 (supersedes all previous editions)

    Related Standards

    Equivalent Materials

    This material data has been provided by Sandvik Materials Technology.

    All metrics apply to room temperature unless otherwise stated. SI units used unless otherwise stated.
    Equivalent standards are similar to one or more standards provided by the supplier. Some equivalent standards may be stricter whereas others may be outside the bounds of the original standard.

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    Properties

    General

    PropertyValueTemperature

    Density

    7.7 g/cm³

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    23.0 °C

    Mechanical

    PropertyValueTemperatureComment

    Elastic modulus

    200 GPa

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    20.0 °C

    194 GPa

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    100.0 °C

    186 GPa

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    200.0 °C

    180 GPa

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    300.0 °C

    Elongation

    25 %

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    20.0 °C

    min.

    25 %

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    100.0 °C

    min.

    25 %

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    200.0 °C

    min.

    25 %

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    300.0 °C

    min.

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    Tensile strength

    750 - 800 MPa

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    20.0 °C

    min for thickness > 10mm, max for < 10mm

    730 - 750 MPa

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    100.0 °C

    min for thickness > 10mm, max for < 10mm

    700 - 720 MPa

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    200.0 °C

    min for thickness > 10mm, max for < 10mm

    690 - 710 MPa

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    300.0 °C

    min for thickness > 10mm, max for < 10mm

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    Yield strength Rp0.2

    550 - 650 MPa

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    20.0 °C

    min for thickness > 10mm, max for < 10mm

    500 - 550 MPa

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    100.0 °C

    min for thickness > 10mm, max for < 10mm

    430 - 470 MPa

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    200.0 °C

    min for thickness > 10mm, max for < 10mm

    410 MPa

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    300.0 °C

    min for thickness > 10mm, max for < 10mm

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    Thermal

    PropertyValueTemperatureComment

    Coefficient of thermal expansion

    1.15E-5 1/K

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    100.0 °C

    for 30°C to the mentioned temperature

    1.2E-5 1/K

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    200.0 °C

    for 30°C to the mentioned temperature

    1.25E-5 1/K

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    300.0 °C

    for 30°C to the mentioned temperature

    1.25E-5 1/K

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    400.0 °C

    for 30°C to the mentioned temperature

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    Specific heat capacity

    470 J/(kg·K)

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    20.0 °C

    500 J/(kg·K)

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    100.0 °C

    530 J/(kg·K)

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    200.0 °C

    560 J/(kg·K)

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    300.0 °C

    600 J/(kg·K)

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    400.0 °C

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    Thermal conductivity

    13 W/(m·K)

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    20.0 °C

    14 W/(m·K)

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    100.0 °C

    16 W/(m·K)

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    200.0 °C

    18 W/(m·K)

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    300.0 °C

    19 W/(m·K)

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    400.0 °C

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    Electrical

    PropertyValueTemperature

    Electrical resistivity

    8.1E-7 Ω·m

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    23.0 °C

    Chemical properties

    Property

    Carbon

    0.03 %

    max.

    Chromium

    29 %

    Copper

    0.8 %

    max.

    Iron

    Balance

    Manganese

    1 %

    Molybdenum

    2.3 %

    Nickel

    7 %

    Nitrogen

    0.35 %

    Phosphorus

    0.03 %

    max.

    Silicon

    0.3 %

    Sulfur

    0.015 %

    max.

    Technological properties

    Property
    Application areas

    Typical applications for Sandvik SAF 2906™ are:

  • Caustic soda production: the material is suitable for use in piping systems from the cells up to the evaporation plant. It is also an excellent choice for very aggressive conditions, such as the evaporator tubes, in both diaphragm and membrane process.
  • Alumina production: heat exchanger tubes and piping in the digestion of alumina
  • Environments where high resistance to pitting and crevice corrosion is required
  • Cold Forming

    The force needed for bending Sandvik SAF 2906™ is higher than that for standard austenitic stainless steels which is a natural consequence of the higher yield strength.

    Compliance

    Approvals:

  • Approved by the American Society of Mechanical Engineers (ASME) for use in accordance with ASME Boiler and Pressure Vessel Code, Section VIII, div. 1 and 2.
  • PED (Pressure Equipment Directive) PED 2014/68/EU and AD2000 Merkblatt W2: Particular Material Appraisal (PMA), Austenitic-ferritic steel Sandvik SAF 2906.
  • Corrosion properties

    Caustic environment: Sandvik SAF 2906™ has, owing to its high chromium content, a very good resistance in caustic environments. For pure caustic soda, the performance of Sandvik SAF 2906™ can be observed in the iso-corrosion diagram (0.1 mm/year), see Figure 1. In the production of caustic soda, however, impurities in the form of chlorides and chlorates are present. Usually in the caustic soda manufacturing process Ni200 or high nickel alloys are used, especially in critical equipment such as the evaporators.


    Results of corrosion tests in sodium hydroxide (NaOH) containing different amounts of sodium chloride (NaCl) and sodium chlorate (NaClO₃ ), similar to the content found in the evaporation plants of diaphragm and membrane processes, are presented in Table 1, 2 and Figure 2. The results clearly indicate the good performance of Sandvik SAF 2906™ in caustic environments.


    Table 1. Performance in caustic environments - Diaphragm process

    GradeEnvironmentTemperature, °C (°F)Corrosion rate

    mm/year
    Sandvik SAF 290610% NaOH, 2% NaCl, 800 ppm ClO₃⁻
    100 (212)< 0.01
    Boiling< 0.01
    50% NaOH, 7% NaCl, 800 ppm ClO₃⁻100 (212)< 0.01
    Boiling0.016
    Sanicro 2810% NaOH, 2% NaCl, 800 ppm ClO₃⁻100 (212)< 0.01
    Boiling< 0.01
    50% NaOH, 7% NaCl, 800 ppm ClO₃⁻100 (212)< 0.01
    Boiling0.34
    Ni20010% NaOH, 2% NaCl, 800 ppm ClO₃⁻100 (212)< 0.01
    Boiling< 0.01
    50% NaOH, 7% NaCl, 800 ppm ClO₃⁻100 (212)< 0.01
    Boiling0.15


    Table 2. Performance in caustic environments - Membrane process

    GradeEnvironmentTemperatureCorrosion rate

    mm/year
    Sandvik SAF 290632%NaOH + 30 ppm Cl⁻
    + 20 ppm NaClO₃
    Boiling< 0.01
    50%NaOH + 30 ppm Cl⁻
    + 20 ppm NaClO₃
    Boiling< 0.01
    Ni20032%NaOH + 30 ppm Cl⁻
    + 20 ppm NaClO₃
    Boiling< 0.01
    50%NaOH + 30 ppm Cl⁻
    + 20 ppm NaClO₃
    Boiling< 0.01


    Pitting and crevice corrosion: Sandvik SAF 2906™ has a carefully balanced composition with a high content of chromium and nitrogen and a moderate amount of molybdenum. This gives the material a high resistance to localized corrosion caused by chlorides. An index for comparing pitting corrosion resistance is the PRE number (Pitting Resistance Equivalent).


    The PRE is defined as, in weight-PRE = %Cr + 3.3 x %Mo + 16 x %N A very severe test for pitting or crevice corrosion is the ASTM G48 test, i.e. immersion in 6% FeCl₃. Results for pitting test according to modified method A, as well as crevice corrosion testing according to method B, are presented in Table 3. The crevice corrosion test was performed with a crevice specified in the MTI-2 procedure, where an artificial crevice is mounted on the sample with a torque of 0.28 Nm. The critical pitting temperature (CPT) and the critical crevice temperature (CCT) are the temperatures where pitting or crevice corrosion starts to develop on the material.


    Table 3. PRE, CPT and CCT values

    GradePRE (min.)CPT, °C (°F)CCT, °C (°F)
    Sandvik SAF 290641.575 (167)42.5 (109)
    Sandvik SAF 250742.580 (176)50 (122)
    Sandvik SAF 22053530 (86)18 (64)
    ASTM 316L26<10 (50)<10 (50)


    Potentiostatic tests in solutions with different chloride contents are reported in Figure 3. Figure 4 shows the effect of increased acidity. In both cases the applied high potential, 600 mV SCE, corresponds to very harsh conditions, thus resulting in conservative data with a lower critical temperature compared with most practical situations.


    Stress corrosion cracking (SCC): Sandvik SAF 2906™ has excellent resistance to chloride induced stress corrosion cracking (SCC). The resistance of various alloys to stress corrosion cracking (SCC) determined by constant load testing in aerated 40% CaCl₂ , pH 1.5, at 100°C (210°F), (modified ASTM G36 method) is shown in Figure 5.


    Nitric acid: Due to its balance of chromium and molybdenum, Sandvik SAF 2906™ presents good resistance to nitric acid. The iso- corrosion diagram, see Figure 6, shows the performance of the material compared to Sandvik 2RE10, a high purity austenitic grade widely used for nitric acid.

    Expanding

    Compared with austenitic stainless steels, Sandvik SAF 2906™ has a higher proof and tensile strength. This must be kept in mind when expanding tubes into tubesheets. Normal methods can be used, but the expansion requires higher initial force and should be undertaken in a one step operation. As a general rule, tube to tubesheet joints should be welded to ensure a leak free joint.

    Heat Treatment

    The tubes are normally delivered in the heat treated condition. If additional heat treatment is needed after further processing, the following is recommended.

    Solution annealing: 1040-1080°C (1900-1980°F), rapid cooling in air or water.

    Machining

    Being a dual phase material (austenitic-ferritic) Sandvik SAF 2906™ will present a different wear picture from that of a single phase material like Sandvik 2RE69. The cutting speed must therefore be lower than that recommended for austenitic grades. Further information is available on request.

    Other

    Forms of supply:

    Sandvik SAF 2906™ can be supplied as seamless tube and pipe. Tubes can be supplied straight or U-bent.


    Other forms of supply:


  • Fittings and flanges
  • Plate, sheet and strip
  • Bar steel
  • Forged products
  • Welding

    The weldability of Sandvik SAF 2906™ is good. Welding must be carried out without preheating and subsequent heat treatment is normally not necessary. Suitable method of fusion welding is gas tungsten arc welding GTAW/TIG with shielding gas of Ar+2% N₂. For tube to tubesheet welding, it is recommended to use Ar+3% N₂ as shielding gas to have proper weld metal structure.


    For Sandvik SAF 2906™, heat input of 0.2-1.5 kJ/mm and interpass temperature of <150°C (300°F) are recommended.


    Recommended filler metals:

  • GTAW/TIG welding
  • Exaton 29.8.2.L wire or strip electrodes are recommended for overlay welding of tubesheets and high-pressure vessels in cases where corrosion resistance, equal to that of Sandvik SAF 2906™, is required.