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Datasheet updated

2024-01-11 10:32
(supersedes all previous editions)

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Sanicro® 25 is an austenitic 22Cr25NiWCoCu stainless steel material with excellent high temperature properties, designed for use in advanced pulverized coal fired steam boilers. The grade is characterized by:

  • Very high creep strength
  • High oxidation resistance
  • High structural stability
  • Good fabricability

Standards

  • UNS: S31035
  • EN Number: 1.4990
  • EN Name: X7NiCrWCuCoNb25-23-3-3-2

Product standards
Seamless tube and pipe: ASTM A213, ASTM A312

Approvals

  • European Particular Material Appraisal (PMA)
  • VdTÜV material data sheet 555, 23.10.2018
  • The American Society of Mechanical Engineers (ASME) Boiler and Pressure
  • ASME Code Case 2753-1, Section I and 2752-1, Section VIII Division 1
  • China Pressure Vessel Approval CSCBPV BV-ME-210

Chemical composition (nominal)

Chemical composition (nominal) %
C Si Mn P S Cr Ni W Co Cu Nb N
≤0.1 0.2 0.5 ≤0.025 ≤0.015 22.5 25 3.6 1.5 3.0 0.5 0.23

Applications

The high creep strength of Sanicro® 25 combined with its good corrosion resistance makes it an extremely suitable option for use in superheaters and reheaters in advanced coal fired power boilers. Use in high temperature applications in other types of steam boilers employing different fuel types is also possible. The material has been specifically developed for use at material temperatures up to around 700°C (1300oF).

Corrosion resistance

Hot corrosion

Sanicro® 25 has very good resistance to hot corrosion in a coal ash environment.

Oxidation tests in air, performed as both isothermal tests at 650°C (1202oF) and 750°C (1382oF) for 1000, 2000 and 3000 hours and discontinuous tests with cooling to room temperature after 24, 50, 100, 200, 500, 1000, 1500, 2000 and 3000 hours, show a very low mass rate change.

Oxidation tests in aqueous steam at 600°C (1112oF) and 700°C (1292oF) for 500 and 1000 hours respectively, showed that Sanicro® 25 has very good oxidation resistance.

Bending

The material can be bent at high as well as at low temperatures.

Recommended temperature range for hot bending is 850-1250°C (1560-2280°F) . Following hot bending, solution annealing is needed, unless the bending has been performed at controlled temperatures between 1180°C and 1250°C (2155°F and 2280°F).

Cold-bending should be followed by solution annealing if the cold deformation is >20% or the R/D ratio is ≤2.5, if the service temperature is in the creep range. For best corrosion properties at high temperatures it is recommended that solution annealing should be performed, even at lower degrees of cold forming.

See also the Heat treatment section.

Forms of supply

Sanicro® 25 is supplied as cold pilgered solution annealed and white-pickled seamless tubes, in common reheater and superheater boiler tube dimensions.

The VdTÜV-material datasheet 555, 23.10.2018, applies for outside diameter 25 mm to 114.3 mm and wall thickness 4.5 mm -12.5 mm.

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

1180-1250°C (2155-2280°F) and quenched.

Contact Alleima for advice regarding further heat treatment issues.

Mechanical properties

At 20oC (68oF), annealed condition

Metric units
Proof strength Tensile strength Elong. Hardness Vickers
Rp0.2a Rp1.0a Rm Ab A2"
MPa MPa MPa % %
approx.
≥310 ≥355 ≥680 ≥40 ≥40 185

1 MPa = 1 N/mm2

Imperial units
Proof strength Tensile strength Elong. Hardness Vickers
Rp0.2a Rp1.0a Rm Ab A2"
ksi ksi ksi % %
approx.
≥45.0 ≥50.0 ≥99.0 ≥40 ≥40 185

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

At high temperatures, annealed condition

Metric units
Temperature Proof strength Tensile strength
Rp0.2 Rp1.0 Rm
°C MPa MPa MPa
min min min
100 250 315 625
200 225 255 575
300 210 240 560
400 200 225 550
500 195 215 535
600 180 205 500
700 180 195 455
800
180
195
355
Imperial units
Temperature Proof strength Tensile strength
Rp0.2 Rp1.0 Rm
°F ksi ksi ksi
min min min
200 38.6 45.0 91.1
400 33.0 38.0 84.1
600 29.7 33.9 80.9
800 28.1 31.8 79.2
1000 27.5 30.8 76.4
1200 27.0 29.9 70.1
1400
26.0
28.4
57.9

Impact strength

Due to its austenitic microstructure, Sanicro® 25 has very good impact strength, both at room temperature and at cryogenic temperatures.

Creep rupture strength according to VdTÜV Wb555, 09.2018

Temperature
°C ºF 10 000 h 100 000 h
MPa ksi MPa ksi
500 932 500 72.5 405 58.7
550 1022 380 55.1 325 47.1
600 1112 310 45.0 230 33.4
650 1202 230 33.4 155 22.5
700 1292 145 21.0 95 13.8
750 1382 85 12.3 50 7.3
800 1472 50 7.3 25 3.6

Max allowable stress values according to ASME Code Case 2753-1, Section I and 2752-1, Section VIII Division 1.

Imperial units Metric units
Metal temperature, ºF Allowable stress, ksi Allowable stress, ksi 1) Metal temperature, ºC Allowable stress, MPa Allowable stress, MPa 1)
75  27.1  27.1  40  184  184 
100  27.1  27.1  65  184  184 
150  26.9  27.1  100  174  184 
200  25.5  27.1  125  167  184 
250  24.3  26.9  150  161  181 
300  23.4  26.3  175  156  179 
350  22.6  25.9  200  152  176 
400  22.0  25.5  225  149  174 
450  21.4  25.2  250  146  173 
500  21.0  25.0  275  143  172 
550  20.6  24.8  300  141  171 
600  20.3  24.7  325  139  170 
650  20.0  24.6  350  138  170 
700  19.7  24.5  375  136 169 
750  19.5  24.4  400  134  168 
800  19.2  24.3  425  133  168 
850  18.9  24.2  450  131  167 
900  18.7  24.0  475  129  166 
950  18.4  23.7  500  128  164 
1000  18.2  23.4  525  126  163 
1050 17.9  23.0  550  125  160 
1100  17.7  22.5  575  123  158 
1150  17.5  21.1  600  122  154 
1200  16.2  16.2  625  120  140 
1250  12.1  12.1  650  111  111 
1300  8.9  8.9  675  85.1  85.1 
1350  6.5  6.5  700  64.4  64.4 
1400  4.9  4.9  725  48.5  48.5 
750 37.1 37.1

1) Due to the relatively low yield strength of these materials, in some cases slightly higher stress values in this column were established at temperatures where slightly greater deformation was acceptable. These stress values are not recommended in applications where small amounts of distortion can cause leakage or malfunction.


Stress values shown in italics are obtained from time-dependent data.
The maximum use temperature is 1382oF (750oC).

Physical properties

Density: 8.32 kg/dm3; 0.29 lb/in3

Thermal conductivity
Temperature, oC W/(m oC) Temperature, oF Btu/(ft h oF)
20 12 68 7
100 13 100 7
200 15 200 7.5
300 16 400 9
400 18 600 10
500 20 800 11
600 22 1000 12
700 23 1200 13
800 25 1400 14.5
900 27 1600 15.5
1000 28 1800 16.5
1100 30 2000 17.5
Specific heat capacity 1)
Temperature, oC J/(kg oC) Temperature, oF Btu/(lb oF)
20 470 68 0.11
100 485 100 0.11
200 500 200 0.12
300 520 400 0.12
400 535 600 0.12
500 555 800 0.13
600 570 1000 0.13
700 585 1200 0.14
800 605 1400 0.14
900 620 1600 0.15
1000 640 1800 0.15
1100 665 2000 0.16

1) Mean values

Resistivity
Temperature, oC µΩm Temperature, oF µΩin.
20 0.98 68 38.6
Thermal expansion 1)
Temperature, oC Per oC Temperature, oF Per oF
 30-100  14.5 86-200  8
 30-200  1.5. 86-400  8.5
 30-300  16 86-600  8.5
 30-400  16 86-800  9
 30-500  16.5 86-1000  9
 30-600  16.5 86-1200  9.5
 30-700  17 86-1400  9.5
 30-800  17 86-1600  9.5
 30-900  17.5 86-1800  10
 30-1000  18 86-2000  10
30-1100 18.5

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

Thermal expansion 1)
Temperature, oC Per oC Temperature, oF Per oF
100-200 16 200-400 8.5
200-300 16.5 400-600 9
300-400 16.5 600-800 9.5
400-500 17 800-1000 10
500-600 18 1000-1200 10.5
600-700 19 1200-1400 11
700-800 19.5 1400-1600 11
800-900 20 1600-1800 11.5
900-1000 21 1800-2000 12
1000-1100 23.5

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

Modulus of elasticity 1)

Temperature, oC MPa Temperature, oF ksi
20 197 68 28.6
100 191 200 27.8
200 183 400 26.5
300 175 600 25.2
400 168 800 24.0
500 160 1000 22.8
600 153 1200 21.6
700 145 1400 20.3
800 137

1) (x103)

Welding

The weldability of Sanicro® 25 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.

In common with all fully austenitic stainless steels, Sanicro® 25 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® 25, 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

TIG/GTAW or MIG/GMAW welding

ISO 18274 S Ni 6617/AWS A5.14 ERNiCrCoMo-1 (e.g. Exaton Ni53, Alloy 617 mod)

MMA/SMAW welding

ISO 14172 E Ni 6117/AWS A5.11 ENiCrCoMo-1

Disclaimer: Recommendations are for guidance only, and the suitability of a material for a specific application can be confirmed only when we know the actual service conditions. Continuous development may necessitate changes in technical data without notice. This datasheet is only valid for Alleima materials.