Chemical composition (nominal) %

Forms of supply

Seamless tube and pipe

Tube and pipe are normally supplied in the solution annealed and white-pickled condition. Small sizes, e.g. heat exchanger tubes, can also be supplied in the bright-annealed condition. The principal size range is shown in figure 1.

Figure 1. Principal size range for seamless tube and pipe.

Other forms of supply

Welding consumables

Mechanical properties

At 20 °C (68 °F)

1 MPa = 1 N/mm2
a) Rp0.2 and Rp1.0 correspond to 0.2% and 1.0 % offset yield strength, respectively.
b) Based on L0 = 5.65 ÖS0 where L0 is the original gauge length and S0 the original cross-section area.

At high temperatures

Creep strength

Sanicro 70 has a creep strength which is comparable to that of AISI tp 310 (UNS S31008).

Physical properties

Density: 8.4 g/cm3, 0.30 lb/in3

Scaling temperature in air: 1175 °C, 2145 °F

Corrosion resistance

General corrosion

Sanicro 70 has approximately the same resistance to organic and inorganic acids as steel of the AISI 304 type. Its resistance to sodium hydroxide is very good even at high concentrations and temperatures.

Pitting

Resistance to pitting is equal to that of steel of the AISI 304 type.

Stress corrosion cracking

Sanicro 70 has very good resistance to stress corrosion cracking, particularly in chloride-bearing solution.

Gas corrosion

Sanicro 70 has very good oxidation resistance. It can be used in:

• Air up to 1175°C (2145°F)
• Up to 800°C (1470°F)
• Dry chlorine and hydrogen chloride up to about 550°C (1020°F)
• Synthesis gas (ammonia synthesis) up to 600°C (1110°F). The resistance to nitrogen absorption, e.g. cracked ammonia at high temperatures, is very good.

Due to high nickel content the material should not be uses in reducing, sulphurous atmospheres (containing hydrogen sulphide) at temperatures above 550°C (1020°F).

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

800-875°C (1470-1920°F), 10-15 minutes, cooling air.

Solution annealing

950-1050°C (1740-1920°F), 5-30 minutes, rapid cooling in air or water.

Welding

The waldability of Sanicro 70 is good. Suitable fusion-welding methods are manual metal-arc welding (MMA) and gas-shielded arc welding, with the TIG and MIG methods as first choice. Preheating and post-weld heat treatment are normally not necessary.

The welding of high-nickel materials calls for high standards of cleanliness. Joint surfaces and filler metals must be free from grease, dirt, colour (pigments) and other impurities. If necessary, the welding zone shall be cleaned with a suitable solvent, e.g. acetone or alcohol.

Since Sanicro 70 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 joints can be kept under control.

The welding of fully austenitic steels often entails the risk of hot-cracking in the weld metal, particularly if the weldment is under constraint. To reduce the cracking risk, the welding should be carried out with lowest practical heat input, <1.0 kJ/mm and interpass temperature <150°C.

Recommended filler metals for:
MIG and TIG: Sanicro 72HP or Sanicro 68HP (wire electrodes and filler wire/rods).
MMA: Sanicro 71or Sanicro 69 (covered electrodes).

Bending

Heat treatment 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 stress relieving or solution annealing.

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

Applications

Sanicro 70 has good resistance to chlorine and hydrogen chloride at high temperatures and can therefore be used in the production of chlorinated hydrocarbons, e.g. in the oxychlorination reactor and the cracking furnace in vinylchloride plants.

Sanicro 70 can also be used in wet corrosive conditions, where austenitic 18Cr/8Ni steels would be susceptible to stress corrosion cracking.