Sandvik 8R40 (Tube and pipe, seamless)

Chemical composition (nominal) %

Forms of supply

Seamless tube and pipe - Finishes and dimensions

Seamless tube and pipe in 8R40 is suplied in dimensions up to 260 mm outside diameter in the solution-annealed and white-pickled condition or in the bright-annealed condition.

Other forms of supply

• Wire electrodes and filler wire/rods
• Covered electrodes
  

Mechanical properties

For tube and pipe with wall thicknesses greater than 10 mm (0.4 in.) the proof strength may fall short of the stated values by about 10 MPa (1.4 ksi).

At 20°C (68°F)

1 MPa = N/mm²
1) R_p0.2 and R_p1.0 correspond to 0.2% offset and 1.0% offset yield strength, respectively.
2) Based on L₀ = 5.65 √S₀ where L₀ is the original gauge length and S₀ the original cross-section area.

Impact strength

Due to its austenitic microstructure, Sandvik 8R40 has very good impact strength both at room temperature and at cryogenic temperatures.

Tests have demonstrated that the steel fulfils the requirements (60 J (44 ft-lb) at -196 ^oC (-320 ^oF)) according to the European standards prEN 13445-2 (UFPV-2) and prEN 10216-5.

At high temperatures

Physical properties

Density: 7.9 g/cm³, 0.29 lb/in³

1) Mean values in temperature ranges (x10^-6)

1) (x10³)

Corrosion resistance

Sandvik 8R40 has with some limitations (nitric acid) the same resistance as the unstabilised steel AISI 304, i.e. the material has good resistance in:

• Organic acids at moderate temperatures
• Salt solutions, e.g. sulphates, sulphides and sulphites
• Caustic environments at moderate temperatures

Sandvik 8R40 is generally used at temperatures above 500 °C (930 °F), however, where wet corrosion is not relevant.

Intergranular corrosion

The stabilisation with niobium gives Sandvik 8R40 good resistance to intergranular corrosion.

Pitting and crevice corrosion

The steel may be sensitive to pitting and crevice corrosion even in solutions of relatively low chloride content.

Stress corrosion cracking

Austenitic steels are susceptible to stress corrosion cracking. This may occur at temperatures above about 60°C (140°F), if the steel is subject to tensile stresses and at the same time comes into contact with certain solutions, particularly those containing chlorides. Such service conditions should therefore be avoided. Conditions when plants are shut down must also be considered as the condensates which are then formed can develop a chloride content that leads to both stress corrosion cracking and pitting.

Gas corrosion

Sandvik 8R40 can be used in

• Air up to 850°C (1560°F)
• Steam up to 750°C (1380°F)
• Synthesis gas (ammonia synthesis) up to about 550°C (1020°F)

Creep behaviour should also be taken into account when using the steel in the creep range.

In flue gases containing sulphur, the corrosion resistance is reduced. In such environments this steel can be used at temperatures up to 600-750°C (1110-1380°F) depending on service conditions. Factors to consider are whether the atmosphere is oxidising or reducing, i.e. the oxygen content, and whether impurities such as sodium and vanadium are present.

Heat treatment

The tubes are delivered in heat treated condition. If another heat treatment is needed after further processing the following is recommended:

Stress relieving

850-950°C (1560-1740°F), 10- 15 minutes, cooling in air.

Solution annealing

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

Welding

The weldability of Sandvik 8R40 is good. Suitable welding methods are manual metal-arc welding with covered electrodes and gasshielded arc welding with the TIG and MIG methods as first choice. Preheating and post-weld heat treatment are not normally necessary.

Since the material has low thermal conductivity and high thermal expansion, welding must be carried out with a low heat input and with welding plans well thought out in advance so that the deformation of the welded joint can be kept under control. If, despite these precautions, it is foreseen that the residual stresses might impair the function of the weldment, we recommend that the entire structure be stress-relieved. See under "Heat treatment".

As filler material for gas-shielded arc welding we recommend wire electrodes and rods Sandvik 19.9.NbSi or 19.9.Nb. In manual metal-arc welding covered electrodes Sandvik 19.9.NbR are recommended. Flux-cored electrode Sandvik 19.9.NbT can also be used.

Bending

Annealing after cold bending is not normally necessary, but this point must be decided with regard to the degree of bending and the operating conditions. Heat treatment, if any, should take the form of slress-relieving or solution annealing, see under "Heat treatment".

Hot bending is carried out at 1100-850°C (2010-1560°F) and should be followed by solution annealing.

Applications

Sandvik 8R40 is used for superheater-tubes in steam powerplants.

It is also frequently used for cooling tubes in ammonia converters, because of its good resistance to nitrogen absorption and good corrosion resistance.
With its good hot-strength, and good resistance to hydrogen sulphide and intergranular corrosion, Sandvik 8R40 is a suitable material for furnace tubes in refineries. Furnace tubing used in vinyl chloride production is another example of applications in which this steel is often used.