Sandvik SAF 2507® is a super-duplex (austenitic-ferritic) stainless steel for service in highly corrosive conditions. The grade is characterized by:
- Excellent resistance to stress corrosion cracking (SCC) in chloride-bearing environments
- Excellent resistance to pitting and crevice corrosion
- High resistance to general corrosion
- High resistance to erosion corrosion and corrosion fatigue
- High mechanical strength and correspondingly high breaking loads in its slickline wire product form
- UNS: S32750
- EN Number: 1.4410
- EN Name: X 2 CrNiMoN 25-7-4
- SS: 2328
Chemical composition (nominal) %
Forms of supply
Sandvik SAF 2507® slicklines are supplied cold drawn and degreased, in continuous lengths, without welds, on metallic spools.
|mm||inch||N||lbf||kg/1000 m||lb/1000 ft|
Wire in Sandvik SAF 2507® is tested and certified in accordance with a minimum tensile strength. Proof strength is approximately 90% of the tensile strength. Sandvik SAF 2507® is able, therefore, to resist high loads without permanent set of the wire.
|Diameter||Proof strength, Rp0.2*||Tensile strength, Rm|
|2.083 - 3.556||0.082-0.140||≥1620||≥235||≥1800||≥261|
|3.810 - 4.064||0.150-0.160||≥1530||≥222||≥1700||≥247|
* Rp0.2 corresponds to 0.2% offset yield strength.
Sandvik SAF 2507® is highly resistant to corrosion by organic acids, e.g. experience less than 0.05 mm/year in 10% formic and 50% acetic acid where ASTM 316L has a corrosion rate higher than 0.2 mm/year. Pure formic acid, see Figure 2.
Sandvik SAF 2507® remains resistant even in contaminated acids. Figure 3 and Figure 4 show results from tests of Sandvik SAF 2507® and various stainless steels and nickel alloys in acetic acid contaminated with chlorides which in practice are frequently present in processes.
Practical experience with Sandvik SAF 2507® in organic acids, e.g. in teraphthalic acid plants, has shown that this alloy is highly resistant to this type of environment. The alloy is therefore a competitive alternative to high alloyed austenitics and nickel 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. Figures 5 to 7 show isocorrosion diagrams for sulphuric acid, sulphuric acid contaminated with 2000 ppm chloride ions, and hydrochloric acid, respectively.
Pitting and crevice corrosion
The pitting and crevice corrosion resistance of stainless steel is primarily determined by the content of chromium, molybdenum and nitrogen.
One parameter for comparing the resistance to pitting in chloride environments is the PRE number (Pitting Resistance Equivalent). The PRE is defined as, in weight-% PRE = %Cr + 3.3 x %Mo + 16 x %N
For duplex stainless steels the pitting corrosion resistance is dependent on the PRE value in both the ferrite phase and the austenite phase, so that the phase with the lowest PRE value will be limiting for the actual pitting corrosion resistance. In Sandvik SAF 2507® the PRE value is equal in both phases, which has been achieved by a careful balance of the elements.
The minimum PRE value for Sandvik SAF 2507® wirelines is 42.5.
Stress corrosion cracking
Sandvik SAF 2507® has excellent resistance to chloride induced stress corrosion cracking (SCC). Figure 8 clearly demonstrates that Sandvik SAF 2507® has better SCC resistance in chloride solutions in comparison with several duplex and austenitic alternative grades in the annealed condition.
There were no signs of SCC in Sandvik SAF 2507® up to 1000 ppm Cl-/300°C (572°F) and 10000 ppm Cl-/250°C (482°F).
The super-duplex stainless steel Sandvik SAF 2507® has a higher resistance to SCC in in sour environments in oil and gas production than lower alloyed duplex stainless steels. The partial pressure of hydrogen sulphide should not exceed 3 psi (0.20 bar).
The mechanical properties combined with corrosion resistance give Sandvik SAF 2507® a good resistance to erosion corrosion. Testing in sand containing media has shown that Sandvik SAF 2507® has an erosion corrosion resistance better than corresponding austenitic stainless steels. Figure 9 below shows the relative mass loss rate of the duplex Sandvik SAF 2507® , Sandvik SAF 2205™ and an austenitic 6Mo+N type steel after exposure to synthetic seawater (ASTM D-1141) containing 0.025-0.25% silica sand at a velocity of 8.9-29.3 m/s (average of all tests is shown).
Duplex stainless steels which have a high tensile strength usually have a high fatigue limit and high resistance to both fatigue and corrosion fatigue.
The high fatigue strength of Sandvik SAF 2507 can be explained by its good mechanical properties, while its high resistance to corrosion fatigue has been proven by fatigue testing in corrosive media.
Density: 7.8 g/cm3, 0.28 lb/in3
|Metric units||Imperial units|
|Temperature, °C||J/(kg °C)||Temperature, °F||Btu/(lb °F)|
|Sandvik SAF 2507||14||15||17||18||20|
|Sandvik SAF 2507||8||9||10||11||12|
Sandvik SAF 2507® has a coefficient of thermal expansion close to that of carbon steel. This gives Sandvik SAF 2507® definite design advantages over austenitic stainless steels in equipment comprising of both carbon steel and stainless steel. The values given below are average values in the temperature ranges.
|Sandvik SAF 2507||13.5||14.0||14.0||14.5|
|Sandvik SAF 2507||7.5||7.5||8.0||8.0|
|Figure 1. Thermal expansion, per °C (30-100°C, 86-210 °F).|
|Temperature, °C||μΩm||Temperature, °F||μΩin|
|Temperature, °C||MPa||Temperature, °F||ksi|