DNV-OS-C201 Structural Design of Offshore Units (WSD method)

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DNV-OS-C201 Structural Design of Offshore Units (WSD method)

Sec.4: Structural Categorisation, Material Selection and Inspection Principles

D: Structural Steel

D300: Selection of structural steel

Sec.4
D 300 Selection of structural steel

Sec.4 D
301   The grade of steel to be used shall in general be related to the service temperature and thickness for the applicable structural category as shown in Table D3.

Sec.4 D
302   Selection of a better steel grade than minimum required in design shall not lead to more stringent requirements in fabrication.

Sec.4 D
303   Grade of steel to be used for thickness less than 10 mm and/or service temperature above 10°C may be specially considered.

Sec.4 D
304   Welded steel plates and sections of thickness exceeding the upper limits for the actual steel grade as given in Table D3 shall be evaluated in each individual case with respect to the fitness for purpose of the weldments. The evaluation should be based on fracture mechanics testing and analysis, e.g. in accordance with BS 7910.

Sec.4 D
305   For structural parts subjected to compressive and/or low tensile stresses, consideration may be given to the use of lower steel grades than stated in Table D3.

Sec.4 D
306   The use of steels with specified minimum yield stress greater than 550 N/mm² (NV550) shall be subject to special consideration for applications where anaerobic environmental conditions such as stagnant water, organically active mud (bacteria) and hydrogen sulphide may predominate.

Sec.4 D
307   Predominantly anaerobic conditions can for this purpose be characterised by a concentration of sulphate reducing bacteria, SRB, in the order of magnitude >10³ SRB/ml (method according to NACE TPC Publication No.3).

Sec.4 D
308   The steels' susceptibility to hydrogen induced stress cracking (HISC) shall be specially considered when used for critical applications (such as jack-up legs and spud cans). See also Sec.10.

Sec.4 D
Table D3 Thickness limitations (mm) of structural steels for different structural categories and service temperatures (°C)
Structural Category Grade ł 10 0 -10 -20 -25 -30
Secondary A
B/BW
D/DW
E/EW
AH/AHW
DH/DHW
EH/EHW
FH
AEH
DEH/DEHW
EEH/EEHW
FEH 35
70
150
150
60
120
150
150
70
150
150
150 30
60
150
150
50
100
150
150
60
150
150
150 25
50
100
150
40
80
150
150
50
100
150
150 20
40
80
150
30
60
150
150
40
80
150
150 15
30
70
120
20
50
120
^*)
30
70
120
^*) 10
20
60
100
15
40
100
^*)
20
60
100
^*)
Primary A
B/BW
D/DW
E/EW
AH/AHW
DH/DHW
EH/EHW
FH
AEH
DEH/DEHW
EEH/EEHW
FEH 30
40
70
150
30
60
120
150
35
70
150
150 20
30
60
150
25
50
100
150
30
60
150
150 10
25
50
100
20
40
80
150
25
50
100
150 N.A.
20
40
80
15
30
60
150
20
40
80
150 N.A.
15
35
70
12.5
25
50
^*)
17.5
35
70
^*) N.A.
10
30
60
10
20
40
^*)
15
30
60
^*)
Special D/DW
E/EW
AH/AHW
DH/DHW
EH/EHW
FH
AEH
DEH/DEHW
EEH/EEHW
FEH 35
70
15
30
60
120
20
35
70
150 30
60
10
25
50
100
15
30
60
150 25
50
N.A.
20
40
80
10
25
50
100 20
40
N.A.
15
30
60
N.A.
20
40
80 17.5
35
N.A.
12.5
25
50
N.A
17.5
35
70 15
30
N.A.
10
20
40
N.A.
15
30
60
^*) For service temperature below -20°C the upper limit for use of this grade must be specially considered.
N.A. = no application

DNV-OS-C201 Structural Design of Offshore Units (WSD method)

Sec.4D 300 Selection of structural steel

Sec.4
D 300 Selection of structural steel