Weldable fine-grain structural steels for pressure vessels

Usage

These fine-grain structural steel grades are characterised 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 pressurised 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 normalised 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 coldforming 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 normalised conditions should be subsequently normalised at 900 - 950 °C. The holding time after temperature equalisation should be approx. 1 minute per millimetre of plate thickness. 

Standards
Europe
Material no.
D
F
I
GB
USA
Salzgitter Flachstahl
FK1)
EN 10028-3
DIN 17103
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
P275NH
1.0488
-
-
Fe E 285 KT
224-400 A
A 516 Gr. 60
SB 29 F K
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
A 510 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

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
0.35)
0.055)
0.055)
0.40
P275NL12)3)
0.16
0.40
0.804) - 1.50
0.025
0.008
0.012
0.50
0.35)
0.055)
0.055)
0.40
P275NL22)3)
0.16
0.40
0.804) - 1.50
0.020
0.005
0.012
0.50
0.35)
0.055)
0.055)
0.40
P355N2)3)
0.18
0.50
1.10 - 1.70
0.025
0.010
0.012
0.50
0.36)
0.106)
0.056)
0.43
P355NH2)3)
0.18
0.50
1.10 - 1.70
0.025
0.010
0.012
0.50
0.36)
0.106)
0.056)
0.43
P355NL12)3)
0.18
0.50
1.10 - 1.70
0.025
0.008
0.012
0.50
0.36)
0.106)
0.056)
0.43
P355NL22)3)
0.18
0.50
1.10 - 1.70
0.020
0.005
0.012
0.50
0.36)
0.106)
0.056)
0.43
P355m7)8)
0.14
0.50
≤ 1.60
0.025
0.010
0.015
0.50
0.59)
0.109)
0.059)
0.39
P355ML17)8)
0.14
0.50
≤ 1.60
0.020
0.008
0.015
0.50
0.59)
0.109)
0.059)
0.39
P355ML27)8)
0.14
0.50
≤ 1,60
0.020
0.005
0.015
0.50
0.59)
0.109)
0.059)
0.39
P420M7)8)
0.16
0.50
≤ 1.70
0.025
0.010
0.0207)
0.50
0.59)
0.109)
0.059)
0.4310)
P420ML17)8)
0.16
0.50
≤ 1.70
0.020
0.008
0.0207)
0.50
0.59)
0.109)
0.059)
0.4310)
P420ML27)8)
0,16
0.50
≤ 1.70
0.020
0.005
0.0207)
0.50
0.59)
0.109)
0.059)
0.4310)
P460M7)8)
0.16
0.60
≤ 1.70
0.025
0.010
0.0207)
0.50
0.59)
0.109)
0.059)
0.4511)
P460ML17)8)
0.16
0.60
≤ 1.70
0.020
0.008
0.0207)
0.50
0.59)
0.109)
0.059)
0.4511)
P460ML27)8)
0.16
0.60
≤ 1.70
0.020
0.005
0.0207)
0.50
0.59)
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) Al total ≥ 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, aminimum 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 properties 1)
Grade
Min. yield strength2)
Tensile strength
Min. total elongation
MPa
MPa
%
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 natch 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 reponsible 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 normalised or stress relief annealing with the grades rolled under normalised 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 millimetre 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 normalised 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.

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