Chemical composition (nominal) %

Forms of supply

Materials for oil and gas production

Cold worked seamless tube and pipe

For production tubing, casing, liner, and coupling stock for downhole oil and gas applications, Sanicro 28 is supplied cold worked with high strength properties. (Sanicro 28-110ksi, -125ksi)

Full details on sizes, finishes and mechanical properties are available on request.
Email: stmo.smt@sandvik.com

Mechanical properties

At 20°C (68°F)

1 MPa = 1 N/mm²
a) R_p0.2 correspond to 0.2% offset yield strength.

At high temperatures

Cold-worked Sanicro 28 also displays very good mechanical properties at higher temperatures. Further information is available on request. Email:stmo.smt@sandvik.com

*) Approximate yield strength at temperature is received by multiplying the corresponding de-rating factor and yield strength at 20^oC (68^oF).

Impact strength

Due to its austenitic microstructure, Sanicro 28 has very good impact strength, both at room temperature and at lower temperatures. Tests have demonstrated that the steel readily fulfills the requirements in accordance with ISO 13680 (min. 40 J at -10^oC (50^oF)).

Physical properties

Physical properties of cold-worked Sanicro 28.

Density: 8.0 g/cm³, 0.29 lb/in³

Metric units Imperial units

1) Mean values in temperature ranges (×10^-6)

1) (×10³)

Poisson´s ratio

The Poisson's ratio is 0.29 for Sanicro 28 at room temperature.

Corrosion resistance

Pitting corrosion

Sanicro 28 can withstand high temperatures in aggressive environments without pitting. A recognised method of ranking a material's susceptibility to localized corrosion is by means of the PRE number (Pitting Resistance Equivalent). This PRE number is based on the contents of chromium, molybdenum and nitrogen in the alloy according to the following formula:
PRE = %Cr + 3.3 × %Mo + 16 × %N

A PRE number is the relative measure of a material's ability of preventing pitting corrosion in chloride containing environments. Sanicro 28 has a minimum PRE number of 38, which confirms its high resistance to pitting corrosion when chlorides are present.

Potentiostatic tests based on ASTM G150 on cold-worked Sanicro 28 in solutions with different chloride concentrations and different pH values are presented in Figure 1 and Figure 2, respectively. In these tests the critical pitting temperature (CPT) is determined in oxidizing conditions at the potential of +600 eV versus SCE. However, the conditions in the well are significantly less oxidizing, resulting in actual CPT values in the wells being higher than those presented in the figures.

Figure 1. Critical pitting temperature (CPT) as a function of chloride concentration for cold-worked Sanicro 28. The potential was +600 mV vs. SCE.

Figure 2. Critical pitting temperature (CPT) as a function of pH for cold worked Sanicro 28 in a 3% Cl^- solution. The potential was +600 mV vs. SCE.

Stress corrosion cracking

Environmental assisted cracking, especially in the presence of hydrogen sulphide (H₂S), is one of the more serious forms of corrosion in sour environments. Failure of tubing by environmental assisted cracking can occur rapidly without any warning. For that reason, the prevention of this form of corrosion must be considered when selecting tubing materials for sour wells.

Sanicro 28 possesses very good resistance to environmental assisted cracking in conditions where hydrogen sulphide is present together with chlorides. The high corrosion resistance of Sanicro 28 has been proven by laboratory tests and confirmed in actual production environments.

Figure 3 presents the results of constant load tests according to NACE TM0177-2005 at different temperatures and partial pressures of hydrogen sulphide. In some cases, the limitation are those of the test equipment and not the material.

Figure 3: Constant load tests of cold-worked Sanicro 28 at 100% of the actual yield strength. The concentration of NaCl in the brine is 15% and the partial pressure of CO₂ is 1000 psi. The grey line represents the approved environments according to NACE MR0175/ISO 15156-3 for the 4c type materials.

Stress corrosion cracking tests have also been performed in the presence of elemental sulfur. Cold worked Sanicro 28 tube with an R_p0.2 value of 889 MPa (129 ksi) has been tested. The tests were performed, according to NACE TM0177-2005, with tensile specimens stressed to 100% of the actual yield strength.

Heat treatment

Tubes for downhole oil and gas applications are delivered in the high strength, cold worked condition. They are not annealed after cold working.

Fabrication

Sanicro 28 tubes are supplied in the cold worked condition and are intended for use with threaded connections.

Applications

Sanicro 28 is used for high strength downhole production tubing, casing, and liners in sour gas wells. This includes environments with high temperatures, high partial pressures of CO₂ and H₂S, and high chloride concentrations.