Section
8 Specific requirements for welded aluminium
8.1 Scope
8.1.1 This Section
specifies requirements for the fabrication and welding of aluminium
alloys, and is in addition to those detailed in this Chapter.
8.1.2 Fabrication
and welding of these materials is to be in designated areas which
are separated from those used for other materials, such as carbon
steels, stainless steels and copper alloys. Where work is performed
in the same workshop as other materials, adequate barriers or screening
are to be provided to prevent cross-contamination of different material
types.
8.1.3 All tools
and equipment used are to be suitable for use on aluminium alloy materials.
The use of tools made of carbon steel materials is to be avoided where
possible.
8.2 Forming and bending
8.2.1 Aluminium
alloys are to be subject to cold forming and cold bending only.
8.3 Fabrication and welding
8.3.1 Welding
may be performed using gas tungsten arc welding (GTAW) or metal inert
gas welding (GMAW), MIG/MAG welding (GMAW), or variants thereof. The
use of other welding processes such as friction stir welding (FSW)
will be subject to special consideration and will require submission
of the process details, consumables and the weld properties achieved.
8.3.2 A comparison
of the mechanical properties for selected welded and unwelded alloys
is given in Table 13.8.1 Minimum mechanical properties for
aluminium alloys.
Table 13.8.1 Minimum mechanical properties for
aluminium alloys
| Alloy
|
Condition
|
0,2% proof stress, N/mm2
|
Ultimate tensile strength, N/mm2
|
| Unwelded
|
Welded
(see Note 4)
|
Unwelded
|
Welded
(see Note 4)
|
| 5083
|
O/H111
|
125
|
125
|
275
|
275
|
| 5083
|
H112
|
125
|
125
|
275
|
275
|
| 5083
|
H116/H321
|
215
|
125
|
305
|
275
|
| 5383
|
O/H111
|
145
|
145
|
290
|
290
|
| 5383
|
H116/H321
|
220
|
145
|
305
|
290
|
| 5086
|
O/H111
|
100
|
95
|
240
|
240
|
| 5086
|
H112
|
125
(see Note 2)
|
95
|
250
(see Note 2)
|
240
|
| 5086
|
H116/H321
|
195
|
95
|
275
|
240
|
| 5059
|
O/H111
|
160
|
160
|
330
|
330
|
| 5059
|
H116/H321
|
260
|
160
|
360
|
300
|
| 5456
|
O
|
125
|
125
|
285
|
285
|
| 5456
|
H116
|
200
(see Note 5)
|
125
|
290
(see Note 5)
|
285
|
| 5456
|
H321
|
215
(see Note 5)
|
125
|
305
(see Note 5)
|
285
|
| 5754
|
O/H111
|
80
|
80
|
190
|
190
|
| 6005A
|
T5/T6
|
Extruded: Open Profile
|
215
|
100
|
260
|
160
|
| (see Note 1)
|
|
Extruded: Closed Profile
|
215
|
100
|
250
|
160
|
| 6061
|
T5/T6
|
Rolled
|
240
|
125
|
290
|
160
|
| (see Note 1)
|
|
Extruded: Open Profile
|
240
|
125
|
260
|
160
|
|
|
|
Extruded: Closed Profile
|
205
|
125
|
245
|
160
|
| 6082
|
T5/T6
|
Rolled
|
240
|
125
|
280
|
190
|
|
|
|
Extruded:
Open Profile
|
260
|
125
|
310
|
190
|
|
|
|
Extruded:
Closed Profile
|
240
|
125
|
290
|
190
|
Note
1. These alloys are not normally
acceptable for application in direct contact with sea-water.
Note
3. The mechanical properties to be used
to determine scantlings in other types and grades of aluminium alloy
manufactured to National or proprietary Standards and specifications
are to be individually agreed with LR, see also
Ch 8, 1.1 Scope 1.1.5.
Note
4. Where detail structural analysis is
carried out, ’unwelded’ stress values may be used away from heat
affected zones and weld lines, see also
Pt 3, Ch 2, 1.3 Aluminium 1.3.3 of the Rules for Ships.
Note
5. For thickness less than 12,5 mm, the
minimum unwelded 0,2% proof stress is to be taken as 230
N/mm2 and the minimum tensile strength is to be taken as
315 N/mm2.
|
8.3.3 Misalignment
may be corrected by the application of steady even force (e.g. using
hydraulic or screw-type clamps). Hammering or heating is not permitted.
8.3.4 Correction
of distortion by the application of heat is not permitted.
8.4 Non-destructive examination
Table 13.8.2 Acceptance criteria for surface
imperfections of aluminium
| Surface
discontinuity
|
Classification
according to
ISO 6520-1
|
Acceptance
criteria
|
| Crack
|
100
|
Not permitted
|
| Lack of fusion
|
401
|
Not permitted
|
| Incomplete root penetration in butt
joints welded from one side
|
4021
|
Not permitted
|
| Surface pore
|
2017
|
d ≤ 0,3s or 0,3a or 1,5 mm (whichever is the lesser)
|
| Linear porosity (see Note 1)
|
2014
|
Not permitted
|
| Uniformly distributed porosity
(see Note 2)
|
2018
|
≤ 1% of area
|
| Clustered porosity
|
2013
|
Not permitted
|
| Continuous undercut
|
5011
|
h ≤ 0,1t or 0,5 mm (whichever is the lesser)
|
| Intermittent undercut
|
5012
|
h ≤ 0,1t or 1,0 mm (whichever is the lesser)
|
| Excess weld metal (see Note 3)
|
502
|
h ≤ 1,5 mm + 0,15b or 8 mm (whichever is the lesser)
|
| Excess penetration
|
504
|
h ≤ 4 mm
|
| Root concavity (see Note 3)
|
515
|
h ≤ 0,1t or 1 mm (whichever is the lesser)
|
| Linear misalignment (see Notes
4 and 5)
|
507
|
h ≤ 0,1t or 1,0 mm (whichever is the lesser)
|
| Angular misalignment
|
508
|
(see Note 6)
|
| Symbols
|
|
a
|
= |
nominal throat thickness of a fillet weld |
|
b
|
= |
width of weld reinforcement |
|
d
|
= |
diameter of a gas pore |
|
h
|
= |
height or width of an imperfection |
|
s
|
= |
nominal butt weld thickness |
|
t
|
= |
wall or plate thickness (nominal size) |
|
Note
1. For these acceptance criteria, linear
porosity is to be considered as three aligned gas pores in a length of
25 mm.
Note
2. To be in accordance with ISO
10042.
Note
3. A smooth transition is required.
Note
4. Linear misalignment is to be a maximum
of 0,5 mm in highly stressed areas. For other areas, the linear
misalignment is to be a maximum of 1,0 mm locally, where the sum of
the length of imperfection is not more than 10% of the weld
length.
Note
5. The limits for linear misalignment
relate to deviations from the correct position. Unless otherwise
specified, the correct position is that when the centrelines
coincide.
Note
6. Angular misalignment shall be mutually
agreed between the designer and the fabricator.
|
Table 13.8.3 Radiographic acceptance criteria
for internal imperfections of aluminium
| Internal discontinuity
|
Classification according to ISO
6520-1
|
Acceptance criteria (see Notes
1 & 2)
|
| Crack
|
100
|
Not permitted
|
| Lack of fusion
|
401
|
Not permitted
|
| Incomplete penetration
|
402
|
Not
permitted
|
| Gas pores
|
2011
|
d ≤ 0,3s or 0,3
a or 5 mm max (whichever is the lesser)
|
| Linear porosity
|
2014
|
Assess as lack of fusion
|
| Uniformly distributed porosity
(see Note 3)
|
2012
|
0,5 < t < 3 mm ≤ 2% of
area L = 100 mm
|
|
|
|
3 < t < 12 mm ≤ 4% of
area L = 100 mm
|
|
|
|
12 < t < 30 mm ≤ 6% of
area L = 100 mm
|
|
|
|
t > 30 mm ≤ 8% of area
L = 100 mm
|
| Clustered (localised) porosity
(see Note 3)
|
2013
|
dA ≤ 20 mm or
dA max ≤ wp (whichever is the
lesser)
|
| Elongated cavity and wormholes
(see Note 3)
|
2015
2016
|
l ≤ 0,3 s or 4 mm max
(whichever is the lesser)
|
| Oxide inclusion
|
303
|
l ≤ 0,5 s or 5 mm max
(whichever is the lesser)
|
| Tungsten inclusion
|
3041
|
l ≤ 0,3 s or 4 mm max
(whichever is the lesser)
|
| Copper inclusion
|
3042
|
Not permitted
|
| Symbols
|
| d
= diameter of a gas pore
s = nominal butt weld thickness
t =
material thickness
wp = width of
weld
d A = diameter of area
surrounding gas pores
l = length of
imperfection in longitudinal direction of weld
L = any 100 mm testing length, in (millimetres)
|
|
Note 1. Any two
adjacent imperfections separated by a distance smaller than the major
dimension of the smaller imperfection shall be considered as a single
imperfection.
Note 2. Indications
shall not be divided into different ranges L.
Note 3. Further
guidance regarding determination of porosity areas and summation of
acceptable areas may be referenced within the informative annexes of ISO
10675-2.
|
Table 13.8.4 Applicable methods for the testing of aluminium weld joints
| Materials and weld
joints
|
Parent material
thickness
|
Applicable volumetric NDE test methods (see Notes 1 & 2)
|
| Aluminium butt welds with full
penetration
|
Thickness < 6 mm
|
RT, RT-D
|
| Thickness ≥ 6 mm
|
RT, RT-D, PAUT, TOFD
|
| Aluminium tee joints and corner joints with full
penetration
|
Thickness ≥ 6 mm
|
RT, RT-D, PAUT (see Note 3)
|
| Aluminium cruciform joints with full
penetration
|
Thickness ≥ 6 mm
|
PAUT
|
|
Note 2. Ultrasonic testing may be specially considered upon
agreement with LR.
Note 3. RT and RT-D may be applied; however, it is noted that for
these configurations, there may be limitations.
|
8.4.2 Alternative
NDE acceptance criteria will be subject to special consideration provided
that they are equivalent to these requirements.
|
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