Sandvik SAF 2707 HD™

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Description

Sandvik SAF 2707 HD™ is a high-alloy duplex (austenitic-ferritic) stainless steel for service in highly corrosive conditions. The grade is particularly suited for use in aggressive acidic and chloride containing environments. Sandvik SAF 2707 HD™ characteristics:


  • Excellent resistance to pitting and crevice corrosion
  • Excellent resistance to stress corrosion cracking (SCC) in chloride containing environments
  • High resistance to general corrosion in acidic environments
  • Excellent resistance to erosion corrosion
  • Excellent corrosion fatigue properties
  • Extremely high mechanical strength
  • Physical properties that offer design advantages
  • Good weldability

  • 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 2707 HD™


    Datasheet updated 2019-12-20 09:55 (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

    PropertyTemperatureValue

    Density

    23.0 °C

    7.8 g/cm³

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    Mechanical

    PropertyTemperatureValueComment

    Elastic modulus

    20.0 °C

    197 GPa

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    100.0 °C

    189 GPa

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    200.0 °C

    178 GPa

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    300.0 °C

    168 GPa

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    Elongation

    23.0 °C

    25 %

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    min.

    Elongation A2

    23.0 °C

    25 %

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    min.

    Hardness, Rockwell C

    23.0 °C

    34 [-]

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    max.

    Tensile strength

    20.0 °C

    920 - 1100 MPa

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    50.0 °C

    900 MPa

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    100.0 °C

    850 MPa

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    150.0 °C

    840 MPa

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    200.0 °C

    830 MPa

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    250.0 °C

    810 MPa

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    300.0 °C

    790 MPa

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    Yield strength Rp0.1

    20.0 °C

    800 MPa

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    min.

    50.0 °C

    760 MPa

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    min.

    100.0 °C

    670 MPa

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    min.

    150.0 °C

    640 MPa

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    min.

    200.0 °C

    590 MPa

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    min.

    250.0 °C

    570 MPa

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    min.

    300.0 °C

    560 MPa

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    min.

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    Yield strength Rp0.2

    20.0 °C

    700 MPa

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    min.

    50.0 °C

    645 MPa

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    min.

    100.0 °C

    600 MPa

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    min.

    150.0 °C

    560 MPa

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    min.

    200.0 °C

    540 MPa

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    min.

    250.0 °C

    510 MPa

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    min.

    300.0 °C

    500 MPa

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    min.

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    Thermal

    PropertyTemperatureValueComment

    Coefficient of thermal expansion

    100.0 °C

    1.25E-5 1/K

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    for 30°C to the mentioned temperature

    200.0 °C

    1.3E-5 1/K

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    for 30°C to the mentioned temperature

    300.0 °C

    1.4E-5 1/K

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    for 30°C to the mentioned temperature

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    Specific heat capacity

    20.0 °C

    470 J/(kg·K)

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    100.0 °C

    495 J/(kg·K)

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    200.0 °C

    530 J/(kg·K)

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    300.0 °C

    560 J/(kg·K)

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    400.0 °C

    590 J/(kg·K)

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    Thermal conductivity

    20.0 °C

    12 W/(m·K)

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    100.0 °C

    14 W/(m·K)

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    200.0 °C

    16 W/(m·K)

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    300.0 °C

    18 W/(m·K)

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    400.0 °C

    19 W/(m·K)

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    Electrical

    PropertyTemperatureValue

    Electrical resistivity

    23.0 °C

    7.5E-7 Ω·m

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    Chemical properties

    PropertyValueComment

    Carbon

    0.03 %

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    max.

    Chromium

    27 %

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    Cobalt

    1 %

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    Iron

    Balance

    Manganese

    1.5 %

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    max.

    Molybdenum

    4.8 %

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    Nickel

    6.5 %

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    Nitrogen

    0.4 %

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    Phosphorus

    0.04 %

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    max.

    Silicon

    0.5 %

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    max.

    Sulfur

    0.01 %

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    max.

    Technological properties

    Property
    Application areas

    Typical applications for Sandvik SAF 2707 HD™ are tubular heat exchangers operating in process industries, such as oil refineries, petrochemical and chemical plants.

    Cold Forming

    The force needed for bending Sandvik SAF 2707 HD™ is higher than that for standard austenitic stainless steels, which is a natural consequence of higher proof strength. However, cold bending can be carried out with normal bending methods, and owing to its good ductility, Sandvik SAF 2707 HD™ can be bent to very close bending radii. Normally, there is no need for subsequent heat treatment. Heat treatment, if any, should be carried out by solution or resistance annealing. For pressure vessel applications using cold bent tubes, special conditions may apply regarding the minimum bending radii allowed without subsequent heat treatment.

    Compliance

    Approvals:

  • ASME Code Case 2586-1.
  • Particular Material Appraisal (PMA), austenitic-ferritic steel Sandvik SAF 2707HD™ (seamless tube): PED (Pressure Equipment Directive) 2014/68/EU and AD2000.
  • Corrosion properties

    General corrosion: Sandvik SAF 2707 HD™ is highly resistant to organic acid corrosion, e.g. formic acid and acetic acid, see Figures 2 to 5. It also remains resistant in contaminated acid. The alloy is, therefore, a competitive alternative to high alloyed austenitic stainless steels and Ni-base alloys in applications where standard austenitic stainless steels corrode at a high rate.


    Resistance to inorganic acids is comparable to, or even better than that of high alloy austenitic stainless steels in certain concentration ranges.


    Figure 6 shows an isocorrosion diagram for sulphuric acid, where the resistance of Sandvik SAF 2707 HD™ in up to 50% H₂SO₄ exceeds the resistance of Sandvik SAF 2507® and 316L.


    Pitting and crevice corrosion: The pitting and crevice corrosion resistance of stainless steel is primarily determined by the content of chromium, molybdenum and nitrogen. An index for comparing the resistance to pitting and crevice corrosion in chloride environments is the PRE number (Pitting Resistance Equivalent). The PRE is defined as, in weight % : PRE=%Cr + 3.3x%Mo + 16x%N. The minimum PRE value for SAF 2707 HD™ is 48.


    One of the most severe pitting corrosion tests, applied to stainless steels, is ASTM G48 i.e. exposure to 6% FeCl₃. In a modified version of the ASTM G48A test, the sample is exposed for periods of 24 hours. When pits are detected, together with a substantial weight loss (> 5 mg), the test is interrupted. Otherwise, the temperature is increased by 5°C (9°F) and the test continued with the same sample.


    The corrosion resistance of Sandvik SAF 2707 HD™ in oxidizing chloride solutions is illustrated by critical pitting temperature (CPT), determined in a "Green-Death" solution (1% FeCl₃ + 1%CuCl₂ + 11% H₂SO₄ + 1.2%HCl).


    The crevice corrosion test was performed in 6% FeCl₃ 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 values obtained and a comparison with Sandvik SAF 2507 are given in Figure 7. All test results show significantly higher values for Sandvik SAF 2707 HD™ than for Sandvik SAF 2507®.


    Potentiostatic tests in solutions with different chloride contents are reported in Figure 8. The CPT value for Sandvik SAF 2707 HD™ is significantly better than for Sandvik SAF 2507® in highly concentrated chloride solutions. Figure 9 shows the effect of increased acidity. Sandvik SAF 2707 HD™ shows higher CPT values than austenitic stainless steels of the 6Mo+N type, especially at low pH values. In both cases the applied potential is 600mV vs SCE, a very high value compared with that which could be expected in natural, unchlorinated seawater, resulting in lower critical temperatures compared with most practical service conditions.


    Full scale extended heat exchanger tests in chlorinated natural seawater heated to two different temperatures. The very good pitting corrosion results in laboratory tests have also been verified in full scale extended heat exchanger tests in chlorinated natural seawater. The residual chlorine content was 0.5 ppm.


    Model heat exchangers and heat exchanger tubing in Sandvik SAF 2707 HD™ and Sandvik SAF 2507®, welded into UNS S32750 tube sheets and SAF 2205 welded into a UNS S32205 tube sheet were tested for 6 months at each temperature. The inlet temperature of the seawater was 35°C with a seawater flow rate inside the tubes of 1 m/s. Heat was applied from the shell side with external heating elements and thus a heat flux through the tubes was achieved. As the results in the table show, no pitting was observed on Sandvik SAF 2707 HD™ when the tube skin temperature on the seawater side was 70°C, after tubes were heated from the outside at a temperature of 105°C. At this temperature Sandvik SAF 2507® experienced pitting, but passed at 50°C. Sandvik SAF 2205™ was attacked by pitting at both temperatures.


    GradePRET(skin-out)/T(skin-in),°C
    65/50105/70
    Sandvik SAF 2707 HD≥48No AttackNo Attack
    Sandvik SAF 2507≥42.5No AttackPitting
    Sandvik SAF 2205≥35PittingPitting


    Stress corrosion cracking: The stress corrosion cracking resistance of Sandvik SAF 2707 HD™ in chloride environments is excellent.


    SCC resistance of Sandvik SAF 2707 HD™ in chloride solutions at high temperatures is illustrated in Figure 10. In these tests, there were no signs of SCC up to 1000 ppm Cl-/300°C (572°F) and 10000 ppm Cl-/250°C (482°F).

    Expanding

    Compared to austenitic stainless steels, Sandvik SAF 2707 HD™ has higher proof and tensile strengths. This must be kept in mind when expanding tubes into tubesheets. Normal expanding methods can be used, but the expansion requires higher initial force and should be undertaken in a one-step operation. If the service conditions include a high chloride concentration, tube to tubesheet joints should generally be welded, in order to reduce the risk of crevice corrosion.

    Heat Treatment

    Tubes are normally delivered in the heat treated condition. If additional heat treatment is needed due to further processing, solution annealing is recommended. Please contact Sandvik for further information.

    Machining

    Being a dual phase material (austenitic-ferritic), Sandvik SAF 2707 HD™ will present a different tool wear profile from that of austenitic stainless steels. The cutting data (speed and feed) must, therefore, be lower than that recommended for austenitic grades. Further information is available on request.

    Other

    Forms of supply:

    Seamless tubes in Sandvik SAF 2707 HD™ can be supplied in typical heat exchanger tube dimensions. Tubes are generally delivered solution annealed, with a pickled or light ground surface condition.

    Welding

    The weldability of Sandvik SAF 2707 HD™ 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 2707 HD™, heat input of 0.2-1.5 kJ/mm and interpass temperature of <100°C (210°F) are recommended.


    Recommended filler metals:

  • GTAW/TIG welding
  • Exaton 27.7.5.L