Weldable fine-grain structural steels for pressure vessels

Usage

These fine-grain structural steel grades are characterized by a minimum yield strength of 275 - 460 MPa, by good weldability and high resistance to brittle cracking. These grades are used above all for manufacturing vessels for pressurized gas (LPG, butane and propane tanks), pressure vessels, steam boiler parts, pressure piping, compressors etc.

The following special grades are available for extraordinary applications:

  • P...NL1 and P...NL2 or P...ML1 and P...ML2 for application temperatures below -20 °C;
  • P...NH for operating temperatures of up to 400 °C.

The user of these steel grades must make sure that his calculation, design and processing methods are appropriate for the material. The welding technique used must be suitable for the intended application and comply with the state-of-the-art.

The fine-grain structural steel grades rolled under normalized conditions offer good cold-forming and hot-forming properties without negatively affecting the material properties. These steel grades are therefore also suitable for cold-bordering and cold-flanging as well as for cold-bending and cold-folding, considering the bending radii according to DIN 6935 for a steel grade of corresponding strength. With cold-forming above 5% or hot-forming outside of the temperature range of 850 - 1.000 °C as well as after excess times, the steels rolled under normalized conditions should be subsequently normalized at 900 - 950 °C. The holding time after temperature equalization should be approx. 1 minute per millimeter of plate thickness.

Standards

Europe Material no. DE FR IT GB US Salzgitter Flachstahl FK1)
EN 10028-3 DIN 17103 2) NFA 36-205, 36-207 UNI 7382 BS 1501 ASTM
P275NH 1.0487 WStE 285 - Fe E 285 KW 224-400 B A 516 Gr. 60 SB 29 F W A
P275NL1 1.0488 - - Fe E 285 KT 224-400 A A 516 Gr. 60 SB 29 FK A
P275NL2 1.1104 EStE 285 - - 224-400 A - SB 29 F TT A
P355N 1.0562 StE 355 A 510 AP Fe E 355 KG 225-490 A A 516 Gr. 70 SB 36 F G B
P355NH 1.0565 WStE 355 A 510 AP Fe E 355 KW 225-490 B A 516 Gr. 70 SB 36 F W B
P355NL1 1.0566 TStE 355 A510 FP Fe E 355 KT 225-490 A A 516 Gr. 70 SB 36 F K B
P355NL2 1.1106 EStE 355 - - 225-490 A A 707 SB 36 F TT B
EN 10028-5
P355M 1.8821 - - - - - SB 36 TM G B
P355ML1 1.8832 - - - - - SB 36 TM K B
P355ML2 1.8833 - - - - - SB 36 TM TT B
P420M 1.8824 - - - - - SB 42 TM G C
P420ML1 1.8835 - - - - - SB 42 TM K C
P420ML2 1.8828 - - - - - SB 42 TM TT C
P460M 1.8826 - - - - - SB 46 TM G C
P460ML1 1.8837 - - - - - SB 46 TM K C
P460ML2 1.8831 - - - - - SB 46 TM TT C
  1. FK = Tensile strength class, see dimensions
  2. invalid standard

Chemical composition in percent by weight [%] (Heat analysis)

Grade C Si Mn P S N Ni Ti V Nb CE1)
max. max. max. max. max. max. max. max. max. max.
P275NH2)3) 0.16 0.40 0,804) - 1,50 0.025 0.010 0.012 0.50 0,035) 0,055) 0,055) 0.40
P275NL12)3) 0.16 0.40 0,804) - 1,50 0.025 0.008 0.012 0.50 0,035) 0,055) 0,055) 0.40
P275NL22)3) 0.16 0.40 0,804) - 1,50 0.020 0.005 0.012 0.50 0,035) 0,055) 0,055) 0.40
P355N2)3) 0.18 0.50 1,10 - 1,70 0.025 0.010 0.012 0.50 0,036) 0,106) 0,056) 0.43
P355NH2)3) 0.18 0.50 1,10 - 1,70 0.025 0.010 0.012 0.50 0,036) 0,106) 0,056) 0.43
P355NL12)3) 0.18 0.50 1,10 - 1,70 0.025 0.008 0.012 0.50 0,036) 0,106) 0,056) 0.43
P355NL22)3) 0.18 0.50 1,10 - 1,70 0.020 0.005 0.012 0.50 0,036) 0,106) 0,056) 0.43
P355M7)8) 0.14 0.50 ≤ 1,60 0.025 0.010 0.015 0.50 0,059) 0,109) 0,059) 0.39
P355ML17)8) 0.14 0.50 ≤ 1,60 0.020 0.008 0.015 0.50 0,059) 0,109) 0,059) 0.39
P355ML27)8) 0.14 0.50 ≤ 1,60 0.020 0.005 0.015 0.50 0,059) 0,109) 0,059) 0.39
P420M7)8) 0.16 0.50 ≤ 1,70 0.025 0.010 0,0207) 0.50 0,059) 0,109) 0,059) 0,4310)
P420ML17)8) 0.16 0.50 ≤ 1,70 0.020 0.008 0,0207) 0.50 0,059) 0,109) 0,059) 0,4310)
P420ML27)8) 0.16 0.50 ≤ 1,70 0.020 0.005 0,0207) 0.50 0,059) 0,109) 0,059) 0,4310)
P460M7)8) 0.16 0.60 ≤ 1,70 0.025 0.010 0,0207) 0.50 0,059) 0,109) 0,059) 0,4511)
P460ML17)8) 0.16 0.60 ≤ 1,70 0.020 0.008 0,0207) 0.50 0,059) 0,109) 0,059) 0,4511)
P460ML27)8) 0.16 0.60 ≤ 1,70 0.020 0.005 0,0207) 0.50 0,059) 0,109) 0,059) 0,4511)
  1. A max. carbon equivalent   
    CE = C + Mn/6 + (Cr + Mo + V)/5 + (Cu + Ni)/15   
    can be agreed upon.
  2. Cr ≤ 0.30 %, Cu ≤ 0.30%, Mo ≤ 0.08 % 
  3. Altotal ≥ 0.020% 
    If N is additionally fixed by means of Nb, Ti or V, the minimum Al content is not determined.
    If N is only fixed with Al, then: Al/N ≥ 2.
  4. For thicknesses < 6.0 mm, a minimum content for Mn 0.60% is permitted.
  5. Nb + V + Ti ≤ 0.05%
  6. Nb + V + Ti ≤ 0.12%
  7. The minimum value for Altotal does not apply if sufficient amounts of other nitrogen-fixing elements are present.
  8. Mo ≤ 0.20%(Cr + Cu + Mo) ≤ 0.60%
  9. Nb + V + Ti ≤ 0.15%
  10. For thicknesses > 16 mm, a maximum carbon equivalent of 0.45% is acceptable, if agreed upon ordering.
  11. For thicknesses > 16 mm, a maximum carbon equivalent of 0.46% is acceptable, if agreed upon ordering.

Mechanical properties1)

Grade Min. yield strength2) [MPa] Tensile strength [MPa] Min. total elongation [%]
e ≤ 16 e > 16
P275NH 275 265 390 - 510 24
P275NL1 275 265 390 - 510 24
P275NL2 275 265 390 - 510 24
P355N 355 345 490 - 630 22
P355NH 355 345 490 - 630 22
P355NL1 355 345 490 - 630 22
P355NL2 355 345 490 - 630 22
P355M 355 355 450 - 610 22
P355ML1 355 355 450 - 610 22
P355ML2 355 355 450 - 610 22
P420M 420 400 500 - 660 19
P420ML1 420 400 500 - 660 19
P420ML2 420 400 500 - 660 19
P460M 460 440 530 - 720 17
P460ML1 460 440 530 - 720 17
P460ML2 460 440 530 - 720 17
  1. Transverse samples
  2. e = Nominal thickness in mm

Notch impact energy

Grade Position of samples Minimum value of notch impact energy1) in J at a test temperature in °C of
longitudinal -50 -40 -20 0 20
P...N - - 45 65 75
P...NH - - 45 65 75
P...NL1 30 40 50 70 80
P...NL2 2) 42 45 55 75 85
transverse -50 -40 -20 0 20
P...N - - 30 40 50
P...NH - - 30 40 50
P...NL1 - 27 35 50 60
P...NL2 2) 27 30 40 60 70
P...M - - 27 40 60
P...ML1 - 27 40 60 -
P...ML2 27 40 60 80 -
  1. Average values of 3 samples; one individual value may fall short of the required minimum value by not more than 30 %. The sample width shall equal the product thickness if the latter is between 6 and 10 mm, the tests being performed using samples which are similar to Charpy-V samples. The values specified in the table above are to be reduced proportionally to the sample width.
  2. The values are determined by simulative annealed samples. The customer is responsible for the adjustment of the values by the final heat treatment.

Yield point at elevated temperature

In addition to the properties of the basic grade, the heat-resisting grades P...NH offer the following minimum yield point at elevated temperature values in transverse direction.

Grade Yield point at elevated temperature Rp0,2 in MPa at a test temperature in °C of 1)
50 100 150 200 250 300 350 400
e ≤ 16 e > 16 e ≤ 16 e > 16 e ≤ 16 e > 16 e ≤ 16 e > 16 e ≤ 16 e > 16 e ≤ 16 e > 16 e ≤ 16 e > 16 e ≤ 16 e > 16
P275NH 266 256 250 241 232 223 213 205 195 188 179 173 166 160 156 150
P355NH 343 334 323 314 299 291 275 267 252 245 232 225 214 208 202 196
  1. e = Nominal thickness in mm

Welding

The fine-grain structural steel grades of this series can be perfectly welded both manually and using automatic equipment by means of all known welding processes. However, the quality of the weld joint depends on the welding process, the welding conditions and the selection of the correct filler metals.

The welding wires and electrodes approved in this strength category must be used as filler metals. Basic coated electrodes are recommended for manual welding. In general, pre-heating prior to welding or torch-cutting is not necessary. At outside temperatures below +5 °C, pre-heating to approx. 150 °C should be carried out. Subsequent normalized or stress relief annealing with the grades rolled under normalized conditions is required only if called for in the regulations or if operating and manufacturing conditions make a reduction of the residual welding stresses appear useful. The thermo-mechanically rolled steels are not suitable for normalizing; stress relief annealing is possible. With stress relief annealing at 530 - 580 °C, the holding time should be 2 minutes per millimeter of plate thickness, not fall short of 30 minutes and not significantly exceed 60 minutes. Excessively high annealing temperatures or excessively long annealing times bear the risk of reducing the strength values to below the condition of delivery. In addition to this, the guidelines for processing these steel grades according to Stahl-Eisen-Werkstoffblatt’ (Iron and steel material sheet) 088 must be observed.

Condition of delivery, scope of testing and certificate

The steel grades P275NH - P355NL2 are delivered in a condition obtained by normalized rolling. The steel grades P355M - P460ML2 are delivered in a thermomechanically rolled condition. The provisions of DIN EN 10028-2 and -5 shall apply for delivery and inspection.

Certificates according to DIN EN 10204 can be supplied as follows: IT, DUN, FAX, e-mail, paper.