NR 490, Sec 2
8 Bureau Veritas January 2018
3 Steel and aluminium alloys materials
and connections
3.1 General requirements
3.1.1 This Article defines the main characteristics to take
into account for steels and aluminium alloys within the
scope of the determination of the hull scantling as defined
in the present Rules.
3.1.2 Materials with different characteristics may be con-
sidered, provided their specification (manufacture, chemi-
cal composition, mechanical properties, welding,...) is
submitted to the Society for approval.
3.1.3 Testing and manufacturing process
Materials are to be tested in compliance with the applicable
requirements of NR216 Materials and Welding.
The requirements of this Section presume that welding and
other cold or hot manufacturing processes (parent material
types and welding, preheating, heat treatment after weld-
ing,...) are carried out in compliance with current sound
working practice and the applicable requirements of NR216
Materials and Welding.
3.2 Steel structures
3.2.1 Steels for hull structures, forgings and castings
The characteristics of steels to be used in the construction of
ships are to comply with the applicable requirements of
NR216 Materials and Welding.
3.2.2 Mechanical characteristics
The mechanical characteristics of steels are to comply with
the requirements of NR467 Steel Ships, Pt B, Ch 4, Sec 1,
and in particular the:
• grade of steel to be used for the various strength mem-
bers of the structure
• steels for forging and casting.
Tab 2 gives for information the mechanical properties of
steels currently used in the construction of ships.
Higher strength steels other than those indicated in Tab 2
are considered by the Society on a case-by-case basis.
When steels with a minimum specified yield stress R
eH
other
than 235 N/mm
2
are used, hull scantlings are to be deter-
mined by taking into account the material factor k defined
in [3.2.3].
3.2.3 Material factor k for scantlings of structural
members
The value of the material factor k to be introduced into for-
mulae to check structures given in this Section is a function
of the minimum yield stress R
eH
value specified for the steel
to be used.
Tab 3 shows the values of the material factor k to be taken
depending on the R
eH
value of the various high strength
steels for hull structures for which R
eH
390 N/mm
2
.
The use of steels for which R
eH
> 355 N/mm
2
will be con-
sidered in each separate case by the Society, which may
stipulate special acceptance conditions.
If, for special structures, the use of steels for which
R
eH
< 235 N/mm
2
, has been accepted by the Society, the
material factor is to be determined by:
k = 235 / R
eH
In the case where the use of steels with R
eH
values which are
intermediate between those indicated in Tab 3 is allowed,
the values of the material factor k may be determined by
means of linear interpolation.
3.2.4 Welding
The requirements for the scantling and joint design of
welded connection of ships built in steel materials are
defined in NR600, Chapter 6, Section 2.
Table 2 : Mechanical characteristics
Table 3 : k factor
3.3 Aluminium alloy structures
3.3.1 Aluminium alloys for hull structures, forgings
and castings
The characteristics of aluminium alloys to be used in the
construction and their testing process are to comply with
the applicable requirements of the following Rules:
• NR216 Materials and Welding
• NR561 Aluminium Ships.
The list of aluminium alloys given in Tab 4 and Tab 5 for
information only is not exhaustive. Other aluminium alloys
may be considered, provided the specification (manufac-
ture, chemical composition, temper, mechanical properties,
welding, etc.) and the scope of application be submitted to
the Society for review.
Unless otherwise specified, the Young’s modulus for alu-
minium alloys is equal to 70000 N/mm
2
and the Poisson’s
ratio equal to 0,33.
Steel grades
t 100 mm
Minimum yield
stress R
eH
,
in N/mm
2
Ultimate minimum
tensile strength R
m
,
in N/mm
2
A-B-D-E 235 400 - 520
AH32-DH32-EH32
FH32
315 440 - 590
AH36-DH36-EH36
FH36
355 490 - 620
AH40-DH40-EH40
FH40
390 510 - 650
Note 1:
Refer to NR216 Materials and Welding, Ch 2, Sec 1, [2].
R
eH
(N/mm
2
)
k
235
315
355
390
1,00
0,78
0,72
0,70