Section
2 Castings for ship and other structural applications
2.1 Scope
2.1.1 The requirements are for carbon, carbon-manganese and alloy steel castings,
intended for ship for worldwide service and other structural applications. The
requirements also consider grades that are intended for fabrication by welding, as well
as grades not intended for welding.
2.1.2 Provision
is made for two quality grades, Normal and Special.
2.1.3 Where it
is proposed to use carbon-manganese steels of higher specified minimum
tensile strength than required by Ch 4, 2.4 Mechanical tests and properties 2.4.3,
or alloy steels, particulars of the chemical composition, mechanical
properties and heat treatment are to be submitted for approval.
2.2 Chemical composition
2.2.1 The chemical composition of ladle samples is to comply with Table 4.2.1 Chemical composition of ladle
samples for carbon and carbon-manganese hull steel castings and Table 4.2.2 Chemical composition of ladle
samples for alloy hull steel castings .
Table 4.2.1 Chemical composition of ladle
samples for carbon and carbon-manganese hull steel castings
Chemical element
|
Qulity
grade
|
Normal
grade
|
Castings for welded
construction
|
Castings for non-welded
construction
|
Special grade
(see Notes 3 and 4)
|
Carbon
|
0,23% max.
|
0,40% max.
|
0,23%
max.
|
Silicon
|
0,60%
max.
|
0,60% max.
|
0,60%
max.
|
Manganese
|
0,50
1,60%
|
0,50-1,60%
|
0,70
1,60%
|
Sulphur
|
0,035%
max.
|
0,035% max.
|
0,035%
max.
|
Phosphorus
|
0,035%
max.
|
0,035% max.
|
0,035%
max.
|
Aluminium -
(acid soluble)
|
|
|
0,015
0,080% (see Notes 1 and 2)
|
Residual
elements:
|
|
|
|
Copper
|
0,30%
max.
|
0,30% max.
|
0,30%
max.
|
Chromium
|
0,30%
max.
|
0,30% max.
|
0,30%
max.
|
Nickel
|
0,40%
max.
|
0,40% max.
|
0,40%
max.
|
Molybdenum
|
0,15%
max.
|
0,15% max.
|
0,15%
max.
|
Total
|
0,80%
max.
|
0,80% max.
|
0,80%
max.
|
Note
1. The total aluminium content may be
determined instead of the acid soluble content, in which case the
total aluminium content is to be 0,020 0,10%.
Note
2. Grain refining elements other than
aluminium may be used subject to special agreement with LR.
Note
3. For the Special grade, the nitrogen
content is to be determined.
Note 4.Special grade is also applicable to
castings for welded construction.
|
2.2.2 For the Special
grade, the product of the aluminium and nitrogen contents is to comply
with the following formula:
2.2.3 For the Special grade, a check chemical analysis on the product or a test
bar is mandatory. The check analysis on the product or test bar is to comply with the
requirements of Table 4.2.3 Mechanical properties for hull steel castings intended for
welding and Table 4.2.4 Mechanical properties for hull steel castings not intended for
welding.
Table 4.2.2 Chemical composition of ladle
samples for alloy hull steel castings
Chemical element
|
Applications
|
Castings for welded
construction
|
Castings for
non-welded construction
|
Carbon
|
Alloying element values are to comply with recognised national/
international standards or designers specifications and shall be agreed
with LR
|
0,45% max.
|
Silicon
|
0,60 & max.
|
Manganese
|
0,50-1,60%
|
Sulphur
|
0,030% max.
|
Phosphorus
|
0,035% max.
|
Residual elements (See
Note):
|
|
Copper
|
0,30% min.
|
Chromium
|
0,40% min.
|
Nickel
|
0,40% min.
|
Molybdenum
|
0,15% min.
|
Total
|
-
|
Note. At least one of
the elements shall comply with the minimum content.
|
2.3 Heat treatment
2.3.1 Castings
are to be supplied:
-
fully annealed; or
-
normalised; or
-
normalised and tempered
at a temperature of not less than 550°C; or
-
quenched and tempered
at a temperature of not less than 550°C.
2.3.2 For larger castings where a coarser
microstructure may be present in heavier thickness, a double austenising
heat treatment may be required to ensure adequate grain refinement.
A coarse microstructure will be indicated by an increased attenuation
of approximately 30 dB/m at 2 MHz during ultrasonic examination.
2.3.3 Following the attachment of handling brackets, all castings are to be
subject to post weld heat treatment at a temperature of not less than 550°C before
delivery.
2.4 Mechanical tests and properties
2.4.1 At least
one tensile test is to be made on material representing each casting
or batch of castings.
2.4.2 Where the casting is of complex design, or where the finished mass exceeds
10 tonnes, two cast on test samples are to be provided from the heaviest section,
located as far as practicable from each other. Where large castings are made from two or
more casts which are not mixed in a ladle prior to pouring, two or more test samples are
required corresponding to the number of casts involved. These are to be integrally cast
at locations as widely separated as possible.
2.4.3 The results of these tensile tests are to comply with the requirements
provided in Table 4.2.3 Mechanical properties for hull
steel castings intended for welding and Table 4.2.4 Mechanical properties for hull
steel castings not intended for welding.
Table 4.2.3 Mechanical properties for hull
steel castings intended for welding
Steel type
|
Specified minimum tensile strength
(N/mm2)
|
Yield stress (N/mm2) min.
|
Elongation on 5, 65 min.
|
Reduction of area (%) min.
|
Charpy V-notch impact test (See
Note)
|
Test
temperature
(°C)
|
Minimum
average energy (J)
|
C, C-Mn
|
400-550
440-590
480-630
520-670
560-710
600-750
|
200
220
240
260
300
320
|
25
22
20
18
15
13
|
40
30
27
25
20
20
|
0
|
27
|
Alloy
|
550-700
|
355
|
18
|
30
|
600-750
|
400
|
16
|
30
|
650-800
|
450
|
14
|
30
|
700-850
|
540
|
12
|
28
|
Note: Special consideration may be given
to alternative requirements for Charpy V-notch impact test, depending on
design and application, and subject to agreement by LR.
|
Table 4.2.4 Mechanical properties for hull
steel castings not intended for welding
Steel type
|
Specified minimum tensile strength
(N/mm2)
|
Yield stress (N/mm2) min.
|
Elongation on 5, 65 min.
|
Reduction of area (%) min.
|
Charpy V-notch impact test (See Note
1)
|
Test
temperature
(°C)
|
Minimum
average energy (J)
|
C, C-Mn
|
400-550
440-590
480-630
520-670
560-710
600-750
|
200
220
240
260
300
320
|
25
22
20
18
15
13
|
40
30
27
25
20
20
|
AT (See Note 2)
|
27
|
Alloy
|
550-700
|
340
|
16
|
35
|
600-750
|
400
|
16
|
35
|
650-800
|
450
|
14
|
32
|
700-850
|
540
|
12
|
28
|
Note 1. Special
consideration may be given to alternative requirements for Charpy
V-notch impact test, depending on design and application, and subject
to agreement by LR.
Note 2. AT refers to
Ambient Temperature (i.e. 23°C±5°C), which is specified in ISO
148-1.
|
2.5 Non-Destructive Examination
2.5.1 Castings used in ship construction for the sternframe, rudder and propeller
shaft supports are to be examined by ultrasonic and magnetic particle methods in
accordance with Ch 4, 1.7 Visual and surface Non-Destructive Examination. The type and extent of Non-Destructive Examination of castings
for other structural applications are to be specially agreed by the Surveyor.
2.5.3 Acceptance levels for visual inspection are to be taken as follows:
-
No cracks, crack-like indications, hot tears or cold shuts are
permitted.
-
Castings are to be free of other injurious indications to the
satisfaction of the Surveyor.
-
Thickness of the remains of sprues or risers should be within casting dimensional
tolerance.
- Additional magnetic particle, liquid penetrant or ultrasonic testing may be required
for a more detailed evaluation of surface irregularities at the request of the
Surveyor. These examinations are in addition to those required by Ch 4, 2.6 Acceptance levels for Non-Destructive Examination of castings.
2.6 Acceptance levels for Non-Destructive
Examination of castings
2.6.1 The following definitions apply to indications associated with magnetic
particle and liquid penetrant testing:
-
Linear indication. An indication with a largest dimension three or more
times its smallest dimension (i.e. l ≥ 3w).
-
Non-linear indication. An indication with a largest dimension less than
three times its smallest dimension (i.e. l < 3w).
-
Aligned indication. Three or more indications in a line, separated by 2 mm
or less edge-to-edge, which results in a unique indication defined as follows:
- Non-linear indications form an alignment when the distance
between indications is less than 2 mm and at least three indications are
aligned. An alignment of indications is considered to be a unique indication
and its length is equal to the overall length of the alignment.
- Linear indications form an alignment when the distance between
two indications is smaller than the length of the longest indication.
-
Open indication. An indication visible after removal of the magnetic
particles or that can be detected by the use of contrast liquid penetrant
testing.
-
Non-open indication. An indication that is not visually detectable after
removal of the magnetic particles or that cannot be detected by the use of
contrast liquid penetrant testing.
-
Relevant indication. An indication that is caused by a condition or type of
discontinuity that requires evaluation. Only indications which have any dimension
greater than 1,5 mm are to be considered relevant for the categorisation of
indications.
2.6.2 For the purpose of evaluating indications, the surface is to be divided into
reference band length of 150 mm for Level MT1/PT1 and into reference areas of 22500
mm2 for Level MT2/PT2. The band length and/or area is to be taken in the
most unfavourable location relative to the indications being evaluated.
2.6.4 Acceptance criteria for ultrasonic testing are shown in Table 4.2.6 Ultrasonic Acceptance Criteria for
steel castings Using DGS or DAC system as UT1 and UT2. Discontinuities within the
examined zones interpreted to be cracks, cold shuts or hot tears are not acceptable.
Table 4.2.5 Acceptance criteria for surface
inspection evaluation
Quality
level
|
Maximum number of
indications
|
Type of
indication
|
Maximum number of
each type
|
Maximum dimension
of single indication, mm (see Note 2)
|
MT1/PT1
|
4 in
150 mm length
|
Non-linear
|
4 (see Note
1)
|
5
|
Linear
|
4 (see Note
1)
|
3
|
Aligned
|
4 (see Note
1)
|
3
|
MT2/PT2
|
20 in
22500 mm2 area
|
Non-linear
|
10
|
7
|
Linear
|
6
|
5
|
Aligned
|
6
|
5
|
Note 1. Minimum of 30 mm (measured in any direction) between relevant
indications.
Note 2. In weld repairs, the maximum dimension is 2 mm.
|
Table 4.2.6 Ultrasonic Acceptance Criteria for
steel castings Using DGS or DAC system
Quality level
|
Allowable disc shape according to DGS,
mm (see Note 1)
or
Diameter of FBH
according to
DAC curve, mm (see Notes 2 &
3)
|
Maximum number of indications to be registered
(see Note 4)
|
Allowable size of all relevant indications, mm
(see Notes 5 & 6)
|
UT1
|
>6
|
0
|
0
|
UT2
|
1215
>15
|
5
0
|
50
0
|
Note
1. DGS Distance Gain Size.
Note
2. DAC Distance Amplitude Correction.
Note
3. The corresponding DAC level to each of the Flat Bottom Hole
(FBH) reflectors is at 100% DAC.
Note
4. Grouped in an area measuring 300 x 300 mm.
Note
5. Measured on the scanning surface.
Note
6. The measured indication is regarded as the longest dimension,
as measured in the scanning process.
|
2.6.8 Parts which are welded are to be examined by the same method as at the
initial inspection as well as by additional methods as required by the Surveyor.
2.6.9 The maximum number of indications to be recorded and the maximum length of indications
permissible for quality Level UT2 apply to normal probes.
2.6.10 For quality Level UT2, any discontinuity producing a signal amplitude in excess of the
15 mm DAC curve is to be regarded as unacceptable.
2.6.11 Any signal between 12 mm FBH + 15 mm FBH curve is to be evaluated for length of
defect.
2.6.12 For near surface testing, to an approximate depth of 25 mm, a twin crystal 0° - normal
beam - probe should be used, plus a single crystal 0° probe, beyond a depth of 25 mm,
for the remaining volume.
2.6.14 DGS and DAC methods may be used for determining sensitivity. The DAC method for normal
beam probes may be based on a 6 mm diameter reflector or FBH. A DAC curve is to be
produced using reference blocks containing 6 mm FBH reflectors over a range
representative of the inspection thickness, after adjustment for transfer and
attenuation losses.
2.6.15 For quality Level UT1, any discontinuity producing a signal amplitude in excess of the 6
mm DAC curve is unacceptable.
|