Sanicro 41 Cold‑Worked Nickel Alloy: Superior Corrosion Resistance & Welding Performance

Sanicro® 41 is particularly suited for use in heat exchangers for crude oil and oil refineries, especially where high concentrations of hydrogen sulphide and chloride are present.

Approvals:

The excellent formability of Sanicro® 41 enables the material to be cold bent to extremely small radii. Annealing after bending is not normally necessary.

General corrosion: Sanicro® 41 possesses excellent resistance to corrosion. The material is far superior to molybdenum alloyed steels such as AISI 316L, particularly when exposed to non-oxidizing media such as sulfuric acid or phosphoric acid. It also has satisfactory resistance to highly oxidizing agents such as nitric acid. Sanicro® 41 has significantly better corrosion resistance in formic acid than standard austenitic stainless steels.

The results of corrosion tests in nitric acid are tabulated below. Resistance to sulfuric acid is illustrated in Figure 1. It should be noted that the corrosiveness of sulfuric acid depends on the oxygen content. Sulfuric acid in contact with air is, therefore, more corrosive than deaerated acid.

Pitting and crevice corrosion:Corrosion tests carried out in sodium chloride solutions indicate that the resistance of Sanicro® 41 to pitting and crevice corrosion is superior to that of AISI 316- a result of the higher chromium and molybdenum contents of the material. Critical pitting temperatures (CPT) for the two grades in 3% sodium chloride solutions at different pH values are plotted in Figure 2.

Stress corrosion cracking:The high nickel content of the material promotes excellent resistance to stress corrosion cracking induced by both chlorides and alkalis. The results of stress corrosion cracking tests in 40 % calcium chloride are shown in Figure 3.

Sanicro® 41 displays excellent resistance to stress corrosion cracking in sour environments. Tests carried out at the Nickel Development Institute (NIDI), concluded that Sanicro® 41 could be used in sour environments up to 260°C with H₂S contents corresponding to a partial pressure of up to 10000 psi, in the absence of elementary sulfur. The material also shows some immunity to all concentrations of CO2, according to NIDI. Sanicro 41 is used in the oil and gas industry in environments up to 200°C (392°F), a 60 psi partial pressure of H₂S and with chlorides present.

According to ISO 15156/NACE MR0175 it is acceptable for use in the cold worked and annealed condition with no environmental limits in respect of partial pressures of H₂S or elemental sulfur.

Intergranular corrosion: Even in the heaviest sizes, Sanicro® 41 can be welded without the risk of carbide precipitation causing intergranular corrosion. This is due, in part, to the low carbon content of the material, but also to the fact that it is titanium stabilized.

Tubes are delivered in the heat treated condition. If additional heat treatment is needed due to further processing, the following is recommended.

Solution annealing: 1000-1100°C (1830-2010°F), 5-10 minutes, rapid cooling in air or water.

Forms of supply:

Seamless tube and pipe- finishes and dimensions: Heat exchanger tubing, straight or bent to specification, with or without heat treatment of bends, can be supplied. Seamless tube and pipe in Sanicro® 41 can be supplied in dimensions up to 260 mm (10") outside diameter. The delivery condition is solution annealed and either white pickled or bright annealed.

Materials for oil and gas production

Cold worked seamless tube and pipe:

Size range:

The weldability of Sanicro® 41 is good. Suitable methods of fusion welding are manual metal-arc welding (MMA/SMAW) and gas-shielded arc welding, with the TIG/GTAW method as first choice.

Since the material has low thermal conductivity and high thermal expansion. Welding plans should therefore be carefully selected in advance, so that distortions of the welded joint are minimized. If residual stresses are a concern, solution annealing can be performed after welding.

For Sanicro® 41, heat-input of <1.0 kJ/mm and interpass temperature of <100°C (210°F) are recommended. A string bead welding technique should be used.

Recommended filler metals for temperature

• TIG/GTAW or MIG/GMAW welding
  • ISO 18274 S Ni 8065/AWS A5.14 ERNiFeCr-1 (e.g. Exaton Sanicro 41 Cu)
  • ISO 14343 S 27 31 4 Cu L/AWS A5.9 ER383 (e.g. Exaton 27.31.4.LCu)
• MMA/SMAW welding
  • ISO 14172 E Ni 8025, E Ni 8165
  • ISO 3581 E 27 31 4 Cu L R/AWS A5.4 E383-16 (e.g. Exaton 27.31.4.LCuR)

Overlay welding: