Fig.6.5.1 : Typical manually welded butt joints
Fig.6.6.1 : Intermittent fillet welds 6.6 'T' connections
6.6.1 The throat thickness (See Fig.6.6.1) of the fillet welds is given by:
throat thickness = tp . weld factor. d/s where,
tp = thickness [mm], of the thinner of the two parts being connected.
d = distance [mm], between the successive weld fillets.
s = length [mm], of the correctly proportioned weld fillets, clear of end craters
s is not to be less than 75 [mm].
The weld factors for various connections are generally to be as given in Table 6.6.1.
Where an approved automatic deep penetration procedure is used, the weld factors may be reduced by 15 per cent.
Table 6.6.1 : Weld factors for fillet welds Structural items Weld
factors
Permitted type of weld
Remarks Double
Cont.
Intermi -ttent Bottom Structure
Center girder To keel plate or bar keel
0.3 *
Double continuous welding is required in
bottom impact area.
See 6.6.5(g)
To face plate 0.15 *
To inner bottom 0.25 *
Side girder To bottom shell 0.15 *
To face plate 0.13 *
To floors 0.20 *
To inner bottom 0.15 *
Floors To keel plate 0.15 *
To shell plating 0.15 *
To centre girder 0.35 *
To longitudinal bulkheads
0.35 *
To inner bottom 0.15 *
To face plate 0.15 *
Stern-tube covering 0.15 * Bottom and inner
bottom longitudinals, frames
To shell plating 0.13 *
Inner bottom To side shell 0.4 *
Stiffeners To floors and girders 0.13 *
Structure in Machinery Space
Floors and girders To shell and inner bottom
0.3 *
See Note 1
To face plate 0.2 *
Transverse and longitudinal frames
To shell plating 0.15 *
Floors To centre girder in way of engine, thrust blocks and boiler seatings
- In single bottom 0.50 * - In double bottom 0.30 * Main engine
foundation
To top plate 0.5 *
Girders To hull structure 0.4 *
Floors To engine girder 0.4 *
Brackets etc. To engine girders 0.3 *
Side Structure
Transverse frames To side shell
- In tanks 0.13 *
- Elsewhere 0.11 *
Side longitudinals To shell plating 0.13 *
Web frames and side stringers
To shell plating - Within 0.2 x
span from ends
0.35 *
- Elsewhere 0.20 *
To face plate and tripping bracket
0.15 *
Web frames To side stringers 0.3 *
Table 6.6.1 : Weld factors for fillet welds (Continued….)
Structural items Weld factors
Permitted type of weld
Remarks Double
Cont.
Intermi -ttent Deck Structure
Strength deck To shell F.P.
See Note 2 Generally Other decks To shell and
bulkheads
0.3 *
Deck beams To deck plating
- In tanks 0.13 *
- elsewhere 0.11 *
Deck longitudinals To decks 0.13 *
Deck girders To deck plating - Within 0.2 x
span from ends
0.35 *
- Elsewhere 0.20 *
- To face plating and tripping brackets
0.15 *
Cantilever webs To shell, decks, face plates and
longitudinal girders at ends
0.35 *
Pillars To deck, inner
bottom and pillar brackets
0.40 *
Bulkheads and Partitions
Boundaries of Watertight, oiltight and wash bulkheads and shaft tunnels
0.4 *
Stiffeners On tank and wash bulkheads
0.13 *
On pillar bulkheads 0.13 *
On ordinary bulkheads
0.11 *
Vertical and
horizontal girders in tanks and wash bulkheads
To bulkhead plating - Within 0.2 x
span from ends
0.40 *
- Elsewhere 0.30 *
- To faceplate 0.30 *
- To tripping brackets
0.15 *
Vertical and horizontal girders elsewhere
To bulkhead plating - Within 0.2 x
span from ends
0.35 *
- Elsewhere 0.20 *
To faceplate and tripping brackets
0.15 *
Table 6.6.1 : Weld factors for fillet welds (Continued….) Superstructures and Deckhouses
External bulkheads To deck
See Note 3 - On 1st and 2nd
tiers
0.40 *
- Elsewhere 0.25 *
Internal bulkheads Boundaries 0.13 *
stiffeners To external bulkheads
0.10 *
Rudders and Nozzles Rudders
See Note 4 Main piece members To coupling flange F.P. *
To each other 0.44 *
Rudder plating To rudder webs, elsewhere
0.20 *
Nozzles Generally as for rudders
Miscellaneous Fittings and Equipment Framing ring for
manhole type covers
To deck and bulkhead
0.4 *
Continuous fillet weld of minimum 4 [mm]
throat thickness Framing around ports
and W.T./oiltight doors
To plating 0.4 *
Sea-chest boundary welds
Exposed to sea 0.5 *
- Elsewhere 0.4 *
Ventilators air pipes etc.
To deck 0.4 *
Bulwark stays To deck 0.4 *
To bulwark plating 0.2 *
Bilge keel To ground bars 0.2 * *
Bilge keel ground bar To side shell
0.35 *
Fabricated anchors F.P.
Masts derrick posts, crane pedestals, deck machinery and mooring equipment seating to deck etc.
To be considered in each individual case
Intermittent welding means chain intermittent, staggered intermittent or scalloped welding with rounded ends.
For permitted use see 6.6.6.
F.P. means full penetration weld
Note 1 : Preferably to be deep penetration or full penetration weld depending on the thickness of the engine girders.
Note 2 : Generally full penetration, but alternative proposals may be considered depending on tp. Note 3 : For end connections see 4.5.
Note 4 : See Chapter 8.
6.6.2 The throat thickness is not to be less than 3.0 [mm] for tp upto 8.0 [mm] and 0.21 tp or 3.25 [mm], whichever is greater, for tp over 8 [mm]. The throat thickness is also generally not to be greater than 0.44 tp for double continuous welds and the greater of 0.44 tp or 4.5 [mm] for intermittent welds.
6.6.3 The leg length is not to be less than √2 times the specified throat thickness
6.6.4 Where the connection is highly stressed, deep penetration or full penetration welding may be required. Where full penetration welding is required, the abutting plate may require to be beveled.
(See Fig. 6.6.4).
G ≤2 αο = 50o – 70o
βο = 70o – 90o Small angle fillet
θο = 30ο − 45ο
Single bevel tee with permanent backing
Single bevel tee
θο = 50o
R ≤ 3 mm R = 3 mm
G = 2.5 - 4 mm θο≥ 35o
r
r = 12 - 15 mm Single 'J' tee
θ = 50
R≤3 mm G ≤3 mm Double bevel tee symmetrical
t >19 mm
R≤3 mm G≤3 mm Double bevel tee assymetrical
G = 2.5 - 4 mm θ ≥35o
r
r = 12 - 15 mm
(Not normally for strength members)
t
t
G ≤ 3 mm
t
50o
G ≤ 6 mm
t>19 mm
Double J bevel symmetrical
R ≤3 mm
50o
Fig. 6.6.4 : Typical edge preparations for manually welded ‘T’ or cross joints
6.6.5 Continuous welding is to be adopted in the following locations and may be used elsewhere if desired.
a) Boundaries of weathertight decks and erections, including hatch coamings, companionways and other openings.
b) Boundaries of tanks and watertight compartments.
c) All structures in the afterpeak and the afterpeak bulkhead stiffeners.
d) All welding inside tanks intended for chemicals or edible liquids if any.
e) All lap welds in tanks.
f) Bottom framing structure in machinery spaces.
g) Where loading is mainly of dynamic nature e.g. bottom plating subjected to slamming and forebody side or bow impact area.
h) Under side of cross deck structure in case of multi-hull Ship.
i) Primary and secondary members to plating in way of end connection and end brackets to plating in the case of lap connection.
j) Where the thickness of the abutting member (i.e. stiffener web) is greater than 15 [mm] and also exceeds the thickness of the table member (e.g. plating).
k) Other connections as given in Table 6.6.1.
6.6.6 Where intermittent welding is used, the welding is to be made continuous around the ends of brackets, lugs, scallops and at other orthogonal connections with other members. Where intermittent welding is permitted as per Table 6.6.1, only scalloped welding is to be used in tanks for water ballast, cargo oil or freshwater.
Chain or staggered intermittent welding may be used in dry spaces or tanks arranged for fuel oil only.
6.6.7 Where structural members pass through the boundary of a tank, and leakage into the adjacent space could be hazardous or undesirable, full penetration welding is to be adopted for the members for at least 150 [mm] on each side of the boundary. Alternatively, a small scallop of suitable shape may be cut in the member close to the boundary outside the compartment, and carefully welded all round.
6.7 Lap connections
6.7.1 Overlaps are not to be used to connect plates which may be subjected to high tensile or compressive loading. However, where they are adopted, the width of overlap is to be adequate to ensure a good weld, the surfaces are to be in close contact and the joints should be closed all round by continuous fillet weld.
6.8 Slot weld
6.8.1 For the connection of plating to internal webs, where access for welding is not practicable, the closing plating is to be attached by continuous full penetration or slot welds to flat bars fitted to the webs. Slots are to be well rounded at ends, to have a minimum length of 75 [mm] and in general, a minimum width of twice the plating thickness. The distance between the slots is not to exceed 150 [mm]. Complete filling of the slots is normally not permitted.
6.9 End connection
6.9.1 In way of the end connections of girders double continuous welding is to be used all around.
The weld area is not to be less than the cross-sectional area of the member, and the throat thickness not less than that given by Table 6.6.1 for girder ends.
6.9.2 Where stiffeners have bracketed end connections, bracket arms are to be welded all around and the throat thickness is not to be less than 0.35 times the thickness of bracket.
6.9.3 Where stiffeners are continuous at girder, they are to be connected to the webs, either directly and/or by means of lugs. The weld area is to be such that the shear stress does not exceed 80/k [N/mm2]. Where the shear forces are high, a double sided connection to the web and/or a web stiffener welded on top of the continuous stiffener may be required.
6.10 Butt straps for aluminium alloy
6.10.1 In general the scantlings of welded structures are to be determined using the mechanical properties of aluminium alloy in the welded condition. However, where stiffeners are butt welded, consideration would be given to the use of suitable butt straps on the flanges which sufficiently reinforce the area of the weld to allow the scantlings to be determined using unwelded mechanical properties. The butt weld is to be completed and made flush with the flange of the stiffening member before the butt strap is fitted and the butt strap weld is to be continuous. The scantlings, arrangements and locations of all joints and butt straps are to be submitted for approval in such cases. Mechanical tests may also be required to be carried out to demonstrate the effectiveness of such arrangements.