Section
3 Forgings for shafting and machinery
3.1 Scope
3.1.2 Where it is proposed to use alloy steel forgings, particulars of the
chemical composition, mechanical properties and heat treatment are to be submitted for
approval.
3.2 Chemical composition
3.2.1 The chemical composition of ladle samples for carbon, carbon-manganese and
alloy steels is to comply with the following overall limits provided in Table 5.3.1 Chemical composition limits for machinery steel forgings:
Table 5.3.1 Chemical composition limits for machinery steel forgings
| Steel
type
|
Composition in percentage mass by mass maximum, minimum, or
a range as shown
|
| C
|
Si
|
Mn
|
P
|
S
|
Cr
See Note
3
|
Mo
See Note
3
|
Ni
See Note
3
|
Cu
See Note
3
|
Total
residuals
|
| C, C-Mn
|
0,23
Max.
See Notes 1 & 2
|
0,45 Max.
|
0,30-1,50
See Note 6
|
0,035 Max.
|
0,035 Max.
|
0,3 Max.
|
0,15 Max.
|
0,40 Max.
|
0,30 Max.
|
0,85 Max.
|
| Alloy
See
Note 4
|
0,45 Max.
|
0,45 Max.
|
0,30-1,00
|
0,035 Max.
|
0,035 Max.
|
0,40 Min.
See Note 5
|
0,15 Min.
See Note 5
|
0,40 Min.
See Note 5
|
0,30 Max.
|
-
|
Note 1. For welded components, the carbon content
of C and C-Mn steel forgings may be increased above 0,23% maximum,
provided that the carbon equivalent (Ceq) is not more than 0,41%,
calculated using the following formula:
Note 2. The carbon content of C and C-Mn steel
forgings not intended for welded construction may be 0,65
maximum.
Note 3. Elements are considered as residual
elements unless shown as a minimum.
Note 4. Where alloy steel forgings are intended
for welded constructions, the proposed chemical composition is subject
to approval by LR.
Note 5. For alloy steel forgings, one or more of
the elements is to comply with the minimum content.
Note 6. For C and C-Mn steel forgings, the
Manganese content is not less than 3 times the actual carbon content
for components which are not given a post-weld heat treatment.
|
3.3 Heat treatment
3.3.1 Forgings
are to be:
-
fully annealed; or
-
normalised; or
-
normalised and tempered;
or
-
quenched and tempered.
The tempering temperature is to be not less than 550°C.
3.3.2 The delivery condition shall meet the design and application requirements. It is the
manufacturers responsibility to select the appropriate heat treatment method to obtain
the required mechanical properties.
3.4 Mechanical tests
3.4.2 Where a forging
exceeds both 4 tonnes in mass and 3 m in length, a tensile test is
to be taken from each end. These limits refer to the `as forged' mass
and length but exclude the test material.
3.4.3 A batch testing
procedure may be used for hot rolled bars not exceeding 250 mm diameter,
which are intended for the manufacture (by machining operations only)
of straight shafting, bolts, studs and other machinery components
of similar shape. A batch is to consist of either:
-
material from the same
piece provided that, where this is cut into individual lengths, these
are all heat treated together in the same furnace, or
-
bars of the same diameter
and cast, heat treated together in the same furnace and with a total
mass not exceeding 2,5 tonnes.
3.4.6 Forgings may be supplied to any specified minimum tensile strength selected
within the general limits detailed in Table 5.3.2 Mechanical properties for acceptance purposes: carbon, carbon-manganese and
alloy steel forgings for machinery and shafting, except
that for main propulsion shafting forgings the specified minimum tensile strength is to
be as defined in the relevant Rules dealing with design.
Table 5.3.2 Mechanical properties for acceptance purposes: carbon, carbon-manganese and
alloy steel forgings for machinery and shafting
| Steel
style
|
Tensile strength Rm min. N/mm2
|
Yield
stress Re min. N/mm2
|
Elongation A5 min. %
|
Reduction of area Z min. %
|
Hardness
See Note 1 (Brinell)
|
Charpy V-notch impact test
See Notes 2 &
3
|
| Test
temperature (0C)
|
Minimum average energy (J)
|
| Long.
|
Tang.
|
Long.
|
Tang.
|
Long.
|
Tang.
|
| C
and C-Mn
|
360-480
|
180
|
28
|
20
|
50
|
35
|
-
|
AT
See Note 4
|
27
|
18
|
| 400-550
|
200
|
26
|
19
|
50
|
35
|
110-150
|
| 440-590
|
220
|
24
|
18
|
50
|
35
|
125-160
|
| 480-630
|
240
|
22
|
16
|
45
|
30
|
135-175
|
| 520-670
|
260
|
21
|
15
|
45
|
30
|
150-185
|
| 560-710
|
280
|
20
|
14
|
40
|
27
|
160-200
|
| 600-750
|
300
|
18
|
13
|
40
|
27
|
175-215
|
| 640-790
|
320
|
17
|
12
|
40
|
27
|
185-230
|
| 680-830
|
340
|
16
|
12
|
35
|
24
|
200-240
|
| 720-870
|
360
|
15
|
11
|
35
|
24
|
210-250
|
| 760-910
|
380
|
14
|
10
|
35
|
24
|
225-265
|
| Alloy
|
600-750
|
360
|
18
|
14
|
50
|
35
|
175-215
|
| 700-850
|
420
|
16
|
12
|
45
|
30
|
205-245
|
| 800-950
|
480
|
14
|
10
|
40
|
27
|
235-275
|
| 900-1100
|
630
|
13
|
9
|
40
|
27
|
260-320
|
| 1000-1200
|
700
|
12
|
8
|
35
|
24
|
290-365
|
| 1100-1300
|
770
|
11
|
7
|
35
|
24
|
320-385
|
|
Note 1. The hardness values are typical and are
given for information purposes only.
Note 2. Special consideration may be given to
alternative requirements for Charpy V-notch test, depending on design
and application, and subject to agreement by LR.
Note 3. For ships with ice class notation:
Materials used for machinery exposed to sea water temperature, such as
screwshafts, propeller shafts and shaft bolts, intended for ships with
ice class notation 1AS FS(+), IAS FS, 1A FS(+), 1A FS, 1B FS(+), 1B
FS, 1C FS(+) and 1C FS. Charpy V-notch impact testing is to be carried
out for all steel types at 10°C and the average energy value is to be
minimum 20J (longitudinal test). One individual value may be less than
the required average value provided that it is not less than 70% of
this average value.
Note 4. AT refers to Ambient Temperature (i.e.
23°Cą5°C), which is specified in ISO 148-1.
|
3.4.8 Where more
than one tensile test is taken from a forging, the variation in tensile
strength is not to exceed the following:
| Specified minimum tensile strength
N/mm2
|
Difference in tensile strength
N/mm2
|
| <600
|
70
|
| ≥600 <900
|
100
|
| ≥900
|
120
|
3.5 Non-Destructive Examination
3.5.1 Magnetic particle or liquid penetrant testing (where appropriate) is to be
carried out on forgings for main propulsion shafting (including propeller shafts,
intermediate shafts, and thrust shafts with minimum diameter not less than 200 mm), on
all connecting rod and tie rod forgings and on the following components:
Cylinder heads (when intended for engines having a bore diameter larger
than 300 mm) Piston crowns (when intended for engines having a bore
diameter larger than 400 mm) Piston rods (when intended for engines
having a bore diameter larger than 400 mm) Turbocharger shaft and rotor
(when required by the relevant Rules dealing with engine design and
construction) When intended for engines having a bore diameter larger
than 300 mm, bolts and studs for:
- Cylinder heads
- Crossheads
- Connecting rod bearings
- Main bearings
- Crankshafts
- Tie rods
- Holding down bolts
- Propeller blades
- Propeller bosses
Regardless of the above, bolts and studs which are subjected to dynamic
loading (for example, but not limited to, cylinder head bolts, tie rods, crankpin bolts,
main bearing bolts, engine holding down bolts, propeller blade fastening bolts, coupling
bolts for crankshafts) and have a diameter of 50 mm or greater are to be subjected to
surface examinations.
3.5.2 The bores of hollow propeller shafts are to be visually for imperfections uncovered by
the machining operation; relevant indications shall be assessed using the accept/reject
criteria stated in Table 5.2.3 Steel forgings surface
inspection.
3.5.4 Surface inspection acceptance criteria are to be in accordance with Ch 5, 2.5 Non-Destructive Examination. Other
acceptance criteria may be applied, providing they meet these minimum criteria, and are
to the satisfaction of the Surveyor.
3.5.5 Ultrasonic testing is to be carried out in accordance with Ch 5, 2.5 Non-Destructive Examination on
the following items unless otherwise agreed with LR:
-
Shafts having a finished diameter of 200 mm or larger when intended
for main propulsion or other essential services.
-
All piston crowns
-
All cylinder heads.
-
Piston rods for engines having a bore diameter greater than 400
mm.
-
Connecting rods
-
Turbocharger shaft and rotor (when required by the relevant Rules
dealing with design and construction).
-
Bolts and studs (as listed in Ch 5, 3.5 Non-Destructive Examination 3.5.1) for engines having a bore diameter
greater than 300 mm.
The areas to be tested are shown in Figure 5.3.7 Zones for ultrasonic testing on
shafts and Figure 5.3.8 Zones for ultrasonic testing on
machinery components. Areas of other components not shown in these
drawings are to be agreed with the Surveyor.
Figure 5.3.7 Zones for ultrasonic testing on
shafts
Figure 5.3.8 Zones for ultrasonic testing on
machinery components
3.5.6 Ultrasonic acceptance criteria are shown in Table 5.3.3 Acceptance criteria for ultrasonic
testing of shafts and machinery components DGS Method Normal probes and Ch 5, 3.5 Non-Destructive Examination 3.5.6. Other acceptance criteria may be applied, providing they meet these
minimum criteria, and are acceptable to the Surveyor.
Table 5.3.3 Acceptance criteria for ultrasonic
testing of shafts and machinery components DGS Method Normal probes
| Type of
forging
|
Zone
|
Allowable disc
shape according to DGS (see Notes 1 & 2)
|
Allowable length of
indication
|
Allowable distance
between two indications (see Note 3)
|
| Propeller shaft
Intermediate shaft
Thrust shaft
Rudder
stock
|
II
|
outer: d ≤ 2
mm
inner: d ≤ 4 mm
|
≤ 10 mm
≤ 15
mm
|
≥ 20 mm
≥ 20
mm
|
| III
|
outer: d ≤ 3
mm
inner: d ≤ 6 mm
|
≤ 10 mm
≤ 15 mm
|
≥ 20 mm
≥ 20 mm
|
| Connecting rod
Piston rod
Crosshead
|
II
|
d ≤ 2
mm
|
≤ 10 mm
|
≥ 20 mm
|
| III
|
d ≤ 4
mm
|
≤ 10 mm
|
≥ 20 mm
|
|
Note
1. DGS: Distance Gain Size.
Note
2. Outer part means the part beyond one-third of the shaft radius
from the centre; inner part means the remaining core area.
Note
3. In case of accumulations of two or more isolated indications
which are subjected to registration, the minimum distance between two
neighbouring indications should be at least the length of the larger
indication. This applies to the distance in axial directions as well as
to the distance in depth. Isolated indications with shorter distances
between them are to be determined as one single indication.
|
Table 5.3.4 Acceptance criteria for ultrasonic testing of shafts and machinery components
DAC Method Normal probes
| Type of
forging
|
Zone
|
DAC reference
level, based on 3 mm FBH (see Notes 1 & 2)
|
Allowable length of
indication
|
Allowable distance
between two indications (see Note 3)
|
|
Propeller shaft
Intermediate shaft
|
II
|
Outer: DAC minus 7
dB
Inner: DAC + 5 dB
|
≤ 10 mm
≤
15 mm
|
≥ 20 mm
|
| III
|
Outer: + 0 DAC
Inner: DAC + 12 dB
|
≤ 10 mm
≤
15 mm
|
≥ 20 mm
|
| Thrust
shaft
Rudder stock
|
II
|
Outer: DAC minus 7
dB
Inner: DAC + 5 dB
|
≤ 10 mm
≤ 15
mm
|
≥ 20 mm
|
| III
|
Outer: + 0
DAC
Inner: DAC + 12 dB
|
≤ 10 mm
≤ 15
mm
|
≥ 20 mm
|
| Connecting rod
Piston rod
Crosshead
|
II
|
DAC minus 7
dB
|
≤ 10 mm
|
≥ 20 mm
|
| III
|
DAC + 5 dB
|
≤ 10 mm
|
≥ 20 mm
|
|
Note
1. The requirement of a 3 mm FBH is to standardise the DAC
reference blocks for clarity and consistency. The dB value for the
FBH/DAC setting is equivalent to the disc-shaped reflector stated above,
corresponding to the applicable zone.
Note
2. Other size FBHs may be used for the DAC Method (and the dB
value adjusted accordingly to provide equivalence with the stated
FBH/disc-shaped reflector). Where other size FBHs are used, the
ultrasonic procedure is to state the equivalence using an appropriate
calculation formula.
Note 3. In case of accumulations of two or more isolated indications
which are subject to registration, the minimum distance between two
neighbouring indications must be at least the length of the larger
indication. This applies to the distance in axial directions as well as
to the distance in depth. Isolated indications with shorter distances
between them are to be determined as one single indication.
|
|