Sanicro 41 (Tube and pipe, seamless)

Chemical composition (nominal) %

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:
For production tubing and casing in oil and gas production, Sanicro 41 is supplied cold worked with high strength properties (Sanicro 41-110).

Size range:
Outside diameter: 2 3/8" - 7" (60.33-177.8 mm)
Wall thickness: 0.190"-0.590" (4.83-14.99 mm)

Mechanical properties

At 20 ^oC
Metric units

Condition	Proof strength	Tensile strength	Elongation	Hardness
	Rp0.21)	Rm	A2"	HRB
	MPa	MPa	%
	min.	min.	min.	max.
Cold finished	241	586	30	90
Hot finished	172	517	30	90

At 68 ^oF
Imperial units

Condition	Proof strength	Tensile strength	Elongation	Hardness
	Rp0.21)	Rm	A2"	HRB
	ksi	ksi	%
	min.	min.	min.	max.
Cold finished	35	86	30	90
Hot finished	25	75	30	90

1) Corresponds to 0.2 % offset yield strength
At high temperatures
The alloy, UNS N08825, is approved under ASME Pressure Vessel Code, div. 1, Section VIII for use up to 538 ^oC (1000 ^oF).
Metric units

Temperature	Proof strength
	Rp0.2
oC	MPa
	min
100	215
200	200
300	185
400	175
500	170

Imperial units

Temperature	Proof strength
	Rp0.2
oF	ksi
	min
210	31.1
390	29.0
570	26.8
750	25.4
930	24.7

Physical properties

Density: 8.1 g/cm³, 0.30 lb/in³

Metric units, Imperial units

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

Corrosion resistance

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 sulphuric 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 sulphuric acid is illustrated in Figure 1. It should be noted that the corrosiveness of sulphuric acid depends on the oxygen content. Sulphuric acid in contact with air is, therefore, more corrosive than deaerated acid.

Table 1. General corrosion resistance of Sanicro 41 in nitric acid.

Figure 1. Isocorrosion diagram for Sanicro 41 and AISI 316L in deaerated sulphuric acid. The curves represent a corrosion rate of 0.1 mm/year (4 mpy).

Weight-% H₂SO₄

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.

Figure 2. Critical pitting temperatures for Sanicro 41 and AISI 316 in 3 % NaCl solutions at different pH values.

pH

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^oC with H₂S contents corresponding to a partial pressure of up to 10000 psi, in the absence of elementary sulphur. 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^oC (392^oF), 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 sulphur.

Figure 3. Results of stress corrosion cracking tests in 40 % CaCl₂ at 100 ^oC (210 ^oF), pH=6.5.

Stress/tensile strength at 100^oC (210 ^oF)

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.

Heat treatment

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 ^oC (1830-2010 ^oF), 5-10 minutes, rapid cooling in air or water.

Welding

Sanicro 41 has good weldability. Suitable methods of fusion welding are manual metal-arc welding, MMA, tungsten inert gas welding,TIG, and metal inert gas welding, MIG. Preheating and post-weld heat treatment are not normally necessary.

The standard of cleanliness required, when welding fully austenitic stainless steels, is particularly demanding. Joint surfaces and filler metals must be free from grease, paint and other contaminants. The weld zone should be cleaned, as required, using a suitable solvent such as acetone or alcohol.

Sanicro 41, like other austenitic materials, has a high coefficient of thermal expansion. Welding should, therefore, be carried out with low heat input, using well-prepared welding procedures to control distortion of the welded construction.

Since fully austenitic materials are sensitive to hot cracking, welding should be carried out using the lowest practical heat input, <1.0kJ/mm and an interpass temperature of < 100°C (212^oF).

The recommended filler metal for TIG and MIG welding is Sandvik 27.31.4.LCu. For both TIG and MIG/MAG welding, pure argon should be used as the shielding gas. For MIG/MAG welding, pulsed current is suggested. For manual metal-arc welding MMA, Sandvik 27.31.4.LCuR is recommended.

Bending

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

Applications

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.