Section
9 Bars for welded chain cables
9.1 Scope
9.1.1 Provision
is made in this Section for rolled steel bars intended for the manufacture
of three Grades (U1, U2 and U3) of stud link chain cable for the anchoring
and mooring of ships and five Grades (R3, R3S, R4, R4S and R5) of
offshore mooring cable.
9.1.2 For the ship
grades, U1, U2 and U3, approval will permit the supply of bars of
the appropriate grades and size to any chain cable manufacturer.
9.1.3 For the offshore grades, R3, R3S, R4, R4S and R5, approval is confined to
bar to be supplied to a nominated chain manufacturer and will be given only after
successful testing of a completed chain. Separate approvals are required if bar is to be
supplied to more than one cable manufacturer. Approval of a higher grade does not cover
approval of a lower grade, as all grades must be individually approved. If it is
demonstrated to the satisfaction of LR that the higher and lower grades are produced to
the same manufacturing procedure using the same chemistry and heat treatment,
consideration will be given to qualification of a lower grade by a higher grade. The
parameters applied during qualification are not to be modified during production.
9.1.4 For all grades,
approval is normally given for diameters of bars no greater than those
of the bars used in procedure tests.
9.2 Manufacture
9.2.1 All grades of bar material are to be made from killed steel, and, all
grades of bar material except for Grade U1 chain cables are to be fine grained. For
Grades R3, R3S, R4, R4S and R5 the austenite grain size is to be 6 or finer, in
accordance with ASTM E112 or equivalent grain size index in accordance to ISO 643.
Measurements for circular sections are to be taken at one-third of the radius.
9.2.2 The bars
are to be made to a specification approved by LR which should include
the manufacturing procedure, deoxidation practice, heat treatment
and mechanical properties.
9.2.3 The rolling
reduction ratio of bars for Grades R3, R3S, R4, R4S and R5 must be
at least 5:1.
9.3 Chemical composition
9.3.2 For Grades
R3, R3S, R4, R4S and R5 the chemical composition is to comply with
an approved specification, see
Ch 3, 9.2 Manufacture 9.2.2.
9.3.3 For Grades
R4, R4S and R5 chain cable the steel should contain a minimum of 0,2
per cent molybdenum. The reported composition is to include the contents
of antimony, arsenic, tin, copper, nitrogen, aluminium and titanium.
9.3.4 For Grades
R4S and R5 the steel used must be vacuum degassed.
9.4 Heat treatment
9.4.1 Unless stipulated
otherwise, the bars are to be supplied in the as-rolled condition,
but the supplier is to be advised by the chain manufacturer of the
heat treatment to be used for the completed chain in order that the
mechanical test specimens may be tested in the condition of heat treatment
used for the chain.
9.4.2 For Grades
U1 and U2, the samples selected from each batch may be tested either
in the as-rolled condition, or after heat treatment where the chain
is to be used in the heat treated condition, in full cross-section
and in a manner simulating the heat treatment applied to the finished
cable.
9.4.3 For Grades
U3, R3, R3S, R4, R4S and R5 the sample is to be tested after heat
treatment as detailed in Ch 3, 9.4 Heat treatment 9.4.2.
Table 3.9.1 Chemical composition of killed
steel bars
Grade
|
Chemical composition %
|
C
max.
|
Si
|
Mn
|
P
max.
|
S
max.
|
Al
|
Nb
max.
|
V
max.
|
N
max.
|
Cr
max.
|
Cu
max.
|
Ni
max.
|
Mo
max.
|
U1
|
0,20
|
0,15–0,35
|
0,40
min.
|
0,04
|
0,04
|
—
|
—
|
—
|
—
|
—
|
—
|
—
|
—
|
U2
|
0,24
|
0,15–0,55
|
1,60
max.
|
0,035
|
0,035
|
0,02
min. see Note 1
|
—
|
—
|
—
|
—
|
—
|
—
|
—
|
U3
|
0,33
|
0,15–0,55
|
1,90
max
|
0,035
|
0,035
|
0,065
max. see Note 2
|
0,05
see Note 2
|
0,10
see Note 2
|
0,015
|
0,25
|
0,35
|
0,40
|
0,08
|
Note
1. Aluminium may be partly replaced by
other grain refining elements.
Note
2. To obtain fine grain steel, at least
one of these grain refining elements must be present in sufficient
amount.
|
9.5 Embrittlement tests
9.5.1 For Grades
R3, R3S, R4, R4S and R5 the bar manufacturer is to provide evidence
that the material is not susceptible to strain ageing or to temper
brittleness under the conditions of manufacture of the chain. The
results of the relevant tests are to be reported to LR at the approval
stage. Approval will be restricted to the specified steel composition
and if later this is altered then re-approval will be required. Temper
brittleness testing may be waived if the chain is to be quenched after
tempering.
9.5.2 Each heat
of steel bars of grades R3S, R4, R4S and R5 is to be tested for hydrogen
embrittlement (see
Ch 2, 5.3 Hydrogen embrittlement tests).
In the case of continuous casting, test samples representing both
the beginning and the end of the heat are to be taken. In the case
of ingot casting, test samples representing two different ingots are
to be taken.
9.5.3 Each sample
is to be heat treated in a manner simulating the heat treatment of
the finished chain. From each sample two specimens are to be prepared
from the mid-diameter of the bar and tested in accordance with Ch 2, 5.3 Hydrogen embrittlement tests.
9.5.4 The ratio Z
1/Z
2 is to be greater than
or equal to 0,85, where Z
1 is the reduction
in area without baking and Z
2 the reduction
in area after baking.
9.5.5 If the requirement
is not met, the material is to be subjected to a hydrogen degassing
treatment which is subject to approval by LR. Further tests are to
be performed after degassing.
9.6 Mechanical tests
9.6.1 Bars of the
same nominal diameter are to be presented for test in batches of 50
tonnes or fraction thereof from the same cast. A suitable length from
one bar in each batch is to be selected for test purposes. Test pieces
are to be taken from the positions as shown in Figure 3.9.1 Sampling of steel bars.
Figure 3.9.1 Sampling of steel bars
9.6.2 For all grades,
one tensile test is to be taken from each sample length selected.
Additionally, for Grades U3, R3, R3S, R4, R4S and R5 material, one
set of three Charpy V-notch impact test specimens is to be prepared.
Impact tests are also required for Grade U2 when the chain is to be
supplied in as-welded condition.
9.6.3 The results
of all tensile and, where applicable, impact tests are to be in accordance
with the appropriate requirements of Table 3.9.2 Mechanical properties.
Table 3.9.2 Mechanical properties
Grade
|
Yield stress
N/mm2 minimum
|
Tensile strength
N/mm2
|
Elongation on 5,65% minimum
|
Reduction of area %
minimum
|
Charpy V-notch impact tests
|
Test
temperature °C
|
Average energy J minimum
|
Average energy flash weld J minimum
|
U1
|
—
|
370–490
|
25
|
—
|
—
|
—
|
—
|
U2
|
295
|
490–690
|
22
|
—
|
0
(see Note 1)
|
27
|
—
|
U3
|
410
|
690
minimum
|
17
|
40
|
0
|
60
|
—
|
|
|
|
|
|
–20
(see Note 2)
|
35
|
—
|
|
|
|
|
|
|
|
|
R3
|
410
(see Note 3)
|
690
minimum (see Note 3)
|
17
|
50
|
0
|
60
|
50
|
|
|
|
|
|
–20
(see Note 2)
|
40
|
30
|
|
|
|
|
|
|
|
|
R3S
|
490
(see Note 3)
|
770
minimum (see Note 3)
|
15
|
50
|
0
|
65
|
53
|
|
|
|
|
|
–20)
(see Note 2)
|
45
|
33
|
|
|
|
|
|
|
|
|
R4
|
580
(see Note 3)
|
860
minimum (see Note 3)
|
12
|
50
|
–20
|
50
|
36
|
Grade
R4S (see Note 4)
|
700
(see Note 3)
|
960
minimum (see Note 3)
|
12
|
50
|
–20
|
56
|
40
|
Grade
R5 (see Note 4)
|
760
(see Note 3)
|
1000
minimum (see Note 3)
|
12
|
50
|
–20
|
58
|
42
|
Note
2. Testing may be carried out at either
0°C or –20°C, at the option of LR.
Note
3. The ratio of yield strength to tensile
strength should be 0,92 maximum unless specially approved.
Note
4. The aim maximum hardness for R4S is to
be HB330, and for R5 is to be HB340.
|
9.6.4 Failure to
meet the requirements will result in the rejection of a batch of material,
unless it is clearly attributed to improper simulated heat treatment.
This is to be confirmed to be to the satisfaction of LR, and further
heat treatment and testing will be required prior to acceptance.
9.7 Structure and hardenability tests
9.7.1 For Grades
R4S and R5, the following tests are to be carried out on each heat:
-
Assessment and quantification
of the level of non-metallic micro inclusion. These must be acceptable
for the final product.
-
Macro etching on a
representative sample, in accordance with ASTM E381 or equivalent.
This must be free from any injurious segregation or porosity.
-
Jominy hardenability
tests in accordance with ASTM A255 or equivalent.
9.8 Dimensional tolerances
9.8.1 The tolerances
on diameter and ovality of the bar are to be in accordance with Table 3.9.3 Dimensional tolerance of bar
stock.
Table 3.9.3 Dimensional tolerance of bar
stock
Nominal diameter mm
|
Tolerance on diameter mm
|
Tolerance on roundness (d
max– d
min) mm
|
≤20
|
–0/+1,0
|
0,60
|
>20 ≤25
|
–0/+1,0
|
0,60
|
>26 ≤35
|
–0/+1,2
|
0,80
|
>36 ≤50
|
–0/+1,6
|
1,10
|
>51 ≤80
|
–0/+2,0
|
1,50
|
>81 ≤100
|
–0/+2,6
|
1,95
|
>101 ≤120
|
–0/+3,0
|
2,25
|
>121 ≤160
|
–0/+4,0
|
3,00
|
>161 ≤210
|
–0/+5,0
|
4,00
|
9.9 Non-destructive examination
9.9.1 For the grades
U1, U2 and U3 all bars are to be free from internal and surface defects
that might impair proper workability, use and strength. Subject to
agreement by the Surveyor, surface defects may be removed by grinding
provided the acceptable tolerances are not exceeded.
9.9.2 For the R3,
R3S, R4, R4S and R5 grades all bars are to be inspected by a magnetic
particle or eddy current method and are also to be subjected to ultrasonic
examination.
9.9.4 All non-destructive
examination operators are to be qualified in the method of non-destructive
examination to a minimum of Level II in accordance with a recognised
standard.
9.9.5 The bars
are to be free from pipes, cracks, flakes, and injurious surface defects
such as seams, laps, and rolled in mill scale. Longitudinal discontinuities
may be removed by blending to a smooth contour provided that their
depth is not greater than 1 per cent of the bar diameter, and that
the required diameter tolerances are not compromised. The contour
radiuses are to be a minimum of four times the excavation depth.
9.9.6 The frequency
of non-destructive testing may be reduced at the discretion of LR,
provided statistical evidence is available that the required quality
is achieved consistently.
9.10 Identification
9.11 Certification of materials
9.11.1 Each consignment
of bars is to be accompanied by a certificate of a type and in accordance
with Ch 3, 1.13 Certification of materials but with the addition
of the grade of chain cable, the rolling reduction ratio, the results
of the hydrogen embrittlement, micro inclusion, macro etch and hardenability
tests, where required by each grade.
|