Section
2 Materials
2.1 General
2.1.1 The
Rules relate in general to the construction of steel ships, although
consideration will be given to the use of other materials.
2.1.3 Materials
for which provision is not made therein or covered by this Section
may be accepted, provided that they comply with an approved specification
and such tests as may be considered necessary.
2.2 Grade of steel
2.2.1 The grade of steel, supply condition and its mechanical properties are to be
indicated on the construction plans.
2.2.2 In order to distinguish between the material grade requirements for
different hull members at varying locations along the ship, material classes are
assigned, as shown in Table 6.2.1 Material classes and
grades. For each class, depending on thickness, the
material grade requirements are not to be lower than those given in Table 6.2.2 Steel grades for normal
operation.
Table 6.2.1 Material classes and
grades
Structural member category
|
Material class/Minimum
grade
|
SECONDARY
|
A1.
|
Longitudinal bulkhead strakes, other
than belonging to the Primary category
|
Class I within
0,4L
R amidships
|
A2.
|
Deck plating exposed to weather, other
than that belonging to the Primary or Special category
|
Grade A/AH outside
0,4L
R amidships
|
A3.
|
Side plating
|
|
PRIMARY
|
B1.
|
Bottom plating, including keel
plate
|
|
B2.
|
Strength deck plating, excluding that
belonging to the Special category
|
Class II within
0,4L
R amidships
|
B3.
|
Continuous longitudinal plating of
strength members above strength deck
|
Grade A/AH outside
0,4L
R amidships
|
B4.
|
Uppermost strake in longitudinal bulkhead
|
|
SPECIAL
|
C1.
|
Sheerstrake (or rounded gunwale) and
stringer plate at strength deck, see Note 1
|
Class III within
0,4L
R amidships
|
C2.
|
Deck strake at longitudinal bulkhead,
see Note 1
|
Class II outside
0,4L
R amidships
|
|
|
Class I outside
0,6L
R amidships
|
C3.
|
Strength deck plating at
corners of large hatch openings
|
Class III within
0,6L
R amidships
|
|
Class II outside
0,6L
R amidships
|
C4.
|
Bilge strake in ships
with double bottom over the full breadth and length less than 150 m
|
Class II within
0,6L
R amidships
|
|
Class I outside
0,6L
R amidships
|
C5.
|
Bilge strake in other ships,
see Note 1
|
Class III within
0,6L
R amidships
|
|
|
Class II outside
0,4L
R amidships
|
|
|
Class I outside 0,6L
R amidships
|
ADDITIONAL MINIMUM
REQUIREMENTS FOR SINGLE STRENGTH DECK SHIPS OF LENGTH GREATER THAN 150
m
|
D1.
|
Longitudinal plating of strength deck where
contributing to the longitudinal strength
|
Grade B/AH within
0,4L
R amidships
|
D2.
|
Continuous longitudinal strength plating of
members above strength deck
|
|
D3.
|
Single side strakes for ships without inner
continuous longitudinal bulkhead(s) between bottom and strength deck
|
|
ADDITIONAL MINIMUM
REQUIREMENTS FOR SHIPS OF LENGTH GREATER THAN 250 m
|
E1.
|
Sheerstrake (or rounded gunwale) and stringer
plate at strength deck, see Note 1
|
Grade E/EH within 0,4L
R amidships
|
E2.
|
Bilge strake, see Note 1
|
Grade D/DH within 0,4L
R amidships
|
Note
1. Single strakes required to be of Class
III or of Grade E/EH and within 0,4L
R amidships are to have breadths not less than 800 +
5L
R mm, but need not be greater than 1800 mm, unless limited
by the geometry of the ship’s design.
Note
2. For strength members not mentioned,
Grade A/AH may be generally used.
Note
3. Steel grade is to correspond to the
as-fitted thickness.
Note
4. Plating materials for sternframes
supporting the rudder and propeller boss, rudders, rudder horns and
shaft brackets are, in general, not to be of lower grades than
corresponding to Class II. For rudder and rudder body plates subjected
to stress concentrations (e.g. in way of lower support of semispade
rudders or at upper part of spade rudders) Class III is to be
applied.
Note
5. RAS seating and support structure are
to be of Grade D/DH for t ≤ 20 mm and Grade E/EH for t
> 20 mm. For ships operating in cold weather RAS seating and
support structure are to be of Grade E/EH.
Note
6. Corner inserts in way of complex
openings such as for lifts and side doors which may impinge on the
deck plating or stringer plate are to be of Grade D/DH for t ≤
20 mm and Grade E/EH for t > 20 mm.
Note
7. The material class used for
reinforcement and the quality of material (i.e. whether mild or higher
tensile steel) used for welded attachments, such as waterway bars and
bilge keels, is to be similar to that of the hull envelope plating in
way. Where attachments are made to rounded gunwale plates, special
consideration will be given to the required grade of steel, taking
account of the intended structural arrangements and attachment
details.
Note
8. The material class for deck plating,
sheerstrake and upper strake of longitudinal bulkhead within
0,4L
R amidships is also to be applied at structural breaks of
the superstructure, irrespective of position.
Note
9. Engine seat top plates outside
0,6L
R amidships may be Grade A/AH. Steel grade requirement for
top plates within 0,6L
R amidships will be specially considered.
|
Table 6.2.2 Steel grades for normal
operation
Thickness, in mm
|
Material Class
|
I
|
II
|
III
|
Mild
steel
|
H.T.
steel
|
Mild
steel
|
H.T.
steel
|
Mild
steel
|
H.T. steel
|
≤10
|
A
|
AH
|
A
|
AH
|
A
|
AH
|
10-15
|
A
|
AH
|
A
|
AH
|
A
|
AH
|
15-20
|
A
|
AH
|
A
|
AH
|
B
|
AH
|
20-25
|
A
|
AH
|
B
|
AH
|
D
|
DH
|
25-30
|
A
|
AH
|
D
|
DH
|
D
|
DH
|
30-35
|
B
|
AH
|
D
|
DH
|
E
|
EH
|
35-40
|
B
|
AH
|
D
|
DH
|
E
|
EH
|
40-45
|
D
|
DH
|
E
|
EH
|
E
|
EH
|
45-50
|
D
|
DH
|
E
|
EH
|
E
|
EH
|
2.2.5 Ships operating in certain environmental conditions, and those where
operational requirements may lead to a risk of impact damage, or ships with military
notations, may require higher toughness grades.
2.2.6 Where a ship has the notations FDA, ESA or RSA, the
toughness requirements for steel will be specially considered on the basis of fatigue
crack limitation and subsequent propagation through the structure.
2.2.7 Where tee or cruciform connections employ full penetration welds and the
plate material, is subject to significant strains in a direction perpendicular to the
rolled surfaces, it is recommended that consideration be given to the use of special
plate material with specified through thickness properties, and tested in accordance
with Ch 3, 8 Plates with specified through thickness properties of the Rules for Materials. The plan should indicate the
material grade followed by the letter Z (e.g. DZ, DHZ).
2.3 Refrigerated spaces
2.3.1 Where
the minimum design temperature of the steel falls below 0°C in
refrigerated spaces, the grade of steel for the following items is
to comply, in general, with the requirements of Table 6.2.3 Grades of steel for refrigerated
spaces with a minimum design temperature below 0 Degrees C:
- Deck plating.
- Webs of deck girders.
- Longitudinal bulkhead strakes attached to deck.
Table 6.2.3 Grades of steel for refrigerated
spaces with a minimum design temperature below 0 Degrees C
Minimum
design temperature, in oC
|
Thickness, in mm
|
Grades of
steel
|
0 to
-10
|
t ≤12,5
|
B/AH
|
12,5 < t ≤ 25,5
|
D/DH
|
t > 25,5
|
E/EH
|
< –10 to –25
|
t ≤ 12,5
|
D/DH
|
t > 12,5
|
E/EH
|
<
–25 to –40
|
t ≤ 12,5
|
E/EH
|
t > 12,5
|
FH/LT-FH (see also
Ch 3, 6 Carbon–manganese and nickel alloy steels for low temperature service)
|
2.3.2 Unless
a temperature gradient calculation is carried out to assess the design
temperature in the items defined in Vol 1, Pt 6, Ch 6, 2.3 Refrigerated spaces 2.3.1, the temperature to which the steel deck may be subjected
is to be assessed as shown in Table 6.2.4 Assessment of deck
temperature
Table 6.2.4 Assessment of deck
temperature
Arrangement
|
Deck
temperature
|
(1) Deck not
covered with insulation in the refrigerated space
|
Temperature
of the refrigerated space
|
(2) Deck
covered with insulation in the refrigerated space and not insulated on the
other side
|
Temperature
of the space on the uninsulated side
|
(3) Deck covered with
insulation on both sides (a) Temperature difference not
greater than 11oC
(b) Temperature
difference greater than 11oC but not greater than
33oC (c) Temperature difference greater than
33oC
|
Mean of the temperatures of the spaces
above and below the deck Mean of the temperatures of the
spaces above and below the deck less 3oC Deck
temperature will be specially assessed
|
Note Where one of the internal spaces concerned is not
refrigerated, the temperature of the space is to be taken as
5oC.
|
2.4 Ships operating in cold weather conditions
2.4.2 The specified design air temperature is to be selected by the Owner based on the lowest
mean daily average temperature (MDAT) for the area and period of operations considered
in the Concept of Operations.
where
Mean |
= |
statistical mean over a minimum of 20 years |
Average |
= |
average during one day and one night |
Lowest |
= |
lowest during the year |
MDHT |
= |
Mean Daily High Temperature |
MDAT |
= |
Mean Daily Average Temperature |
MDLT |
= |
Mean Daily Low Temperature |
2.4.3 Unless otherwise specified, all ships designed for sea area SA1 are
to be designed for a lowest mean daily average design air temperature of –30°C MDAT or
lower. However, where agreed, materials for SA1 ships not intended for operations
in cold weather conditions may be based on requirements for normal service for higher
design air temperatures (-10°C MDAT or higher).
2.4.6 For ships where a Polar Service Temperature (PST) is to be assigned, note that the PST
is taken as 13°C lower than the design air temperature, i.e. if the design air
temperature is -12°C MDAT, then the PST for the application of the Polar Code is -25°C
(-12°C MDAT minus 13°C).
Table 6.2.5 Material classes and grades for
structures exposed to low temperatures
Structural member category
|
Material class
|
SECONDARY
|
A1.
|
Deck plating exposed to
weather, other than that belonging to the Primary or Special
category
|
Class I
|
A2.
|
Side plating above the
Cold Waterline (CWL), see Note 4
|
|
A3.
|
Transverse bulkheads above CWL,
see Note 4
|
|
PRIMARY
|
B1.
|
Strength deck plating,
excluding that belonging to the Special category, see Note 1
|
Class II within 0,4L
R amidships
|
B2.
|
Continuous longitudinal
members above strength deck
|
Class I outside
0,4L
R amidships
|
B3.
|
Longitudinal bulkhead
above CWL, see Note 4
|
|
SPECIAL
|
C1.
|
Sheerstrake (or rounded
gunwale) and stringer plate at strength deck, see Note 2
|
Class III within 0,4L
R amidships
|
C2.
|
Deck strake at longitudinal
bulkhead, see Note 3
|
Class II outside 0,4L
R amidships
|
Note
1 Plating at the corners of deck
openings, superstructure ends and other structural discontinuity is to
be specially considered. The requirements of Class III are to be
applied in positions where high local stresses may occur but the
material is not to be less than Grade E/EH.
Note
2 Not to be less than Grade E/EH within
0,4LR amidships in ships with length exceeding 250 m.
Note
3 In ships with breadth exceeding 70 m at
least three deck strakes are to be Class III.
Note
4 The Cold Waterline (CWL) is to be taken
as 0,3 m below the minimum design Ballast Waterline (BWL).
|
Table 6.2.6 Materials for Class I for low air temperatures
Thickness, in mm
|
Design air temperature
|
-11°C to -15°C
|
-16°C to -25°C
|
-26°C to -35°C
|
-36°C to -45°C
|
-46°C to -55°C
|
MS
|
HT
|
MS
|
HT
|
MS
|
HT
|
MS
|
HT
|
MS
|
HT
|
≤10
|
A
|
AH
|
A
|
AH
|
B
|
AH
|
D
|
DH
|
D
|
DH
|
10-15
|
A
|
AH
|
B
|
AH
|
D
|
DH
|
D
|
DH
|
D
|
DH
|
15-20
|
A
|
AH
|
B
|
AH
|
D
|
DH
|
D
|
DH
|
E
|
EH
|
20-25
|
B
|
AH
|
D
|
DH
|
D
|
DH
|
D
|
DH
|
E
|
EH
|
25-30
|
B
|
AH
|
D
|
DH
|
D
|
DH
|
E
|
EH
|
E
|
EH
|
30-35
|
D
|
DH
|
D
|
DH
|
D
|
DH
|
E
|
EH
|
E
|
EH
|
35-45
|
D
|
DH
|
D
|
DH
|
E
|
EH
|
E
|
EH
|
-
|
FH
|
45-50
|
D
|
DH
|
E
|
EH
|
E
|
EH
|
-
|
FH
|
-
|
FH
|
Note . MS and HT are defined as Mild Steel and High Tensile Steel
respectively.
|
Table 6.2.7 Materials for Class II for low air temperatures
Thickness, in mm
|
Design air temperature
|
-11°C to -15°C
|
-16°C to -25°C
|
-26°C to -35°C
|
-36°C to -45°C
|
-46°C to -55°C
|
MS
|
HT
|
MS
|
HT
|
MS
|
HT
|
MS
|
HT
|
MS
|
HT
|
≤10
|
A
|
AH
|
B
|
AH
|
D
|
DH
|
D
|
DH
|
E
|
EH
|
10-20
|
B
|
AH
|
D
|
DH
|
D
|
DH
|
E
|
EH
|
E
|
EH
|
20-30
|
D
|
DH
|
D
|
DH
|
E
|
EH
|
E
|
EH
|
-
|
FH
|
30-40
|
D
|
DH
|
E
|
EH
|
E
|
EH
|
-
|
FH
|
-
|
FH
|
40-45
|
E
|
EH
|
E
|
EH
|
-
|
FH
|
-
|
FH
|
-
|
FH
|
45-50
|
E
|
EH
|
E
|
EH
|
-
|
FH
|
-
|
FH
|
-
|
FH
|
Note . MS and HT are defined as Mild Steel and High Tensile Steel
respectively.
|
Table 6.2.8 Materials for Class III for low air temperatures
Thickness, in mm
|
Design air temperature
|
-11°C to -15°C
|
-16°C to -25°C
|
-26°C to -35°C
|
-36°C to -45°C
|
-46°C to -55°C
|
MS
|
HT
|
MS
|
HT
|
MS
|
HT
|
MS
|
HT
|
MS
|
HT
|
≤10
|
B
|
AH
|
D
|
DH
|
D
|
DH
|
E
|
EH
|
E
|
EH
|
10-20
|
D
|
DH
|
D
|
DH
|
E
|
EH
|
E
|
EH
|
-
|
FH
|
20-25
|
D
|
DH
|
E
|
EH
|
E
|
EH
|
E
|
EH
|
-
|
FH
|
25-30
|
D
|
DH
|
E
|
EH
|
E
|
EH
|
-
|
FH
|
-
|
FH
|
30-35
|
E
|
EH
|
E
|
EH
|
-
|
FH
|
-
|
FH
|
-
|
FH
|
35-40
|
E
|
EH
|
E
|
EH
|
-
|
FH
|
-
|
FH
|
-
|
FH
|
40-50
|
E
|
EH
|
-
|
FH
|
-
|
FH
|
-
|
FH
|
-
|
FH
|
Note . MS and HT are defined as Mild Steel and High Tensile Steel
respectively.
|
2.4.7 All
bulwarks, spurn-waters, unlagged gas turbine intake structures, side
screens, tie down points, etc. are to be constructed of steel of equivalent
toughness to that of the material to which they are attached.
2.4.10 Structure
attached to and within a distance of 2,0 m within unheated spaces
and 0,75 m for heated spaces of the exposed boundary plating is to
be of the same material grade as that of the exposed plating, but
the grade may be adjusted depending on the material thickness of the
attached structure.
Table 6.2.9 Steel grades for rudder horn,
shaft brackets and stem for ships intended to navigate in Arctic or Antarctic
conditions
Item
|
Condition
|
Construction
|
Steel grade(2)(3)
|
f < 25(1)
|
f ≥ 25(1)
|
Rudder horn
|
Fully immersed
|
Cast
steel
|
Carbon
manganese steel Grade 400
|
Carbon manganese steel
Grade 400
|
Fabricated
|
Grade
EH
|
Grade EH
|
Periodically immersed or
exposed
|
Cast
steel
|
Carbon
manganese steel Grade 460
|
2 1/4 Ni
steel or equivalent
|
Fabricated
|
Grade
FH
|
1 1/2 Ni
steel or equivalent
|
Shaft brackets
|
Fully immersed
|
Cast
steel
|
Special
Grade
|
Special Grade
|
Fabricated
|
Class
B/AH
|
Class B/AH
|
Periodically immersed or
exposed
|
Cast
steel
|
Carbon
manganese steel Grade 400
|
Carbon manganese steel
Grade 460
|
Fabricated
|
Class
II
|
Grade FH
|
Stem including adjacent
strake of shell plating
|
Fully immersed
|
Fabricated
|
Class
B/AH
|
Class B/AH
|
Cast
steel
|
Carbon
manganese steel Grade 400
|
Carbon manganese steel
Grade 400
|
Periodically immersed or
exposed
|
Fabricated
|
Class
II
|
Class II
|
Cast
steel
|
2 1/4 Ni
steel
|
2 1/4 Ni steel
|
Rudder stock
|
|
Forged
|
see
Ch 5, 2.4 Mechanical tests of the Rules for Materials
|
Cast
steel
|
Carbon manganese steel grade
400
|
Note
1.
f =
Note where
P
o is the maximum propulsion shaft power, in kW, for which
the machinery is classed
Δ is displacement, in tonnes, at Ice Load Waterline or
Deepest Ice Operation Waterline when floating in water of relative
density of 1,0.
|
2.5 Mechanical properties for design
2.5.1 The
scantlings determined within this Part of the Rules assume that mild
steel has the following mechanical properties:
|
N/mm2
|
Yield
strength (minimum)
|
235
|
Tensile
strength
|
400–490
|
Modulus of elasticity
|
200 x 103
|
2.5.2 Steels
having a minimum yield stress not less than 265 N/mm2 are
regarded as higher tensile steels.
2.5.4 For
the application of the requirements of Vol 1, Pt 6, Ch 6, 2.5 Mechanical properties for design 2.5.3 special consideration will be given to steel where σ
o ≥ 390 N/mm2. Where such steel grades are used
in areas which are subject to fatigue loading the structural details
are to be verified using fatigue design assessment methods.
|