Section 2 Welding
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, July 2022 - Part 4 Steel Unit Structures - Chapter 8 Welding and Structural Details - Section 2 Welding

Section 2 Welding

Parent topic: Chapter 8 Welding and Structural Details

2.1 General

2.1.1 Requirements for welding are given in Ch 12 Welding Qualifications and Ch 13 Requirements for Welded Construction of the Rules for the Manufacture, Testing and Certification of Materials (hereinafter referred to as the Rules for Materials) and general requirements for hull construction are also given in Pt 3, Ch 10, 2 Welding of the Rules for Ships.

2.1.2 Additional requirements with respect to unit types as indicated in this Section should also be complied with, as applicable.

2.2 Impact test requirements

2.2.1 Charpy V-notch impact tests are to be carried out in the weld metal, fusion line and heat affected zone in accordance with Pt 4, Ch 8, 2.2 Impact test requirements 2.2.2 to Pt 4, Ch 8, 2.2 Impact test requirements 2.2.4.

2.2.2 For special structure, the impact test temperature and minimum absorbed energy for the weld and heat affected zone are to be the same as that specified for the base materials being welded.

2.2.3 For primary and secondary structure, the impact test temperature and the minimum absorbed energy for the weld metal and heat affected zone are to be in accordance with the requirements of the material grade being welded, as specified in Ch 12, 2.12 Mechanical test acceptance criteria for steels 2.12.4 in Ch 12 Welding Qualifications of the Rules for Materials.

2.2.4 Fabrications whose thickness exceeds 65 mm are, in general, to be subjected to a post weld heat treatment. Impact tests are required to be made on specimens heat treated in the same manner as the actual construction. The absorbed energy is to be in accordance with Pt 4, Ch 8, 2.2 Impact test requirements 2.2.2 and Pt 4, Ch 8, 2.2 Impact test requirements 2.2.3; however, the test temperatures may be 10°C higher.

2.3 Workmanship and inspection

2.3.1 Checkpoints examined at the construction stage are generally to be selected from those welds intended to be examined as part of the agreed quality control programme to be applied by the Builder. The locations and numbers of checkpoints are to be agreed between the Builder and the Surveyor. Special attention is to be paid to the welded connections of primary bracings and their end connections and other structure defined as special in Pt 4, Ch 2, 2 Structural categories.

2.3.2 Additional locations for NDE for ship units and other surface type units are shown in Table 8.2.1 Additional non-destructive examination of welds on surface type units (as applicable).

2.3.3 Typical locations for NDE and the recommended number of checkpoints to be taken in column-stabilised and self-elevating units are shown in Table 8.2.2 Non-destructive examination of welds on column-stabilised and self-elevating units. For other unit types, the extent of NDE will be specially considered in each case. Critical locations as identified by LR’s ShipRight Fatigue Design Assessment and other relevant fatigue calculations are also to be considered, where applicable. A document detailing the proposed items to be examined is to be submitted by the Builder for approval.

2.3.4 For the hull structure of units designed to operate in low air/sea temperatures, the recommended extent of non-destructive examination will be specially considered.

2.3.5 All NDE is to be performed in accordance with the requirements specified in Ch 13, 2 Specific requirements for ship hull structure and machinery of the Rules for the Manufacture, Testing and Certification of Materials, July 2022, and the general NDE requirements as per Ch 1, 5.1 General NDE requirements of the Rules for the Manufacture, Testing and Certification of Materials, July 2022.

2.3.6 In general, fabrication tolerances are to comply with Pt 4, Ch 8, 6 Fabrication tolerances. It is important to ensure that compatibility exists between design calculations and construction standards, particularly in fatigue sensitive areas.

Table 8.2.1 Additional non-destructive examination of welds on surface type units (as applicable)

Recommended extent of testing, see Note 1

General, see Notes 8 and 9

   
Structural item Local Checkpoints, see Note 1
Penetrations and attachments to hull, e.g. sea inlets, piping, anode supports Throughout 100%
Moonpool integration structure Throughout See Notes 2 and 4
Topside support structure connections to hull and hull structure in way Throughout 25%, see Notes 4 and 5
Flare stack, crane pedestals and boom rests, and integration structure of heavy-lift cranes with the hull. Throughout 100%, see Notes 4 and 5
Connections to deck Local 100%
Other structural items Throughout See Notes 3 and 4
Side shell butts, seams and intersection welds where vessel is strengthened for operations in ice Forward end See Note 6
Remainder See Note 7
Exposed shell butts, seams and intersection welds where vessel is designed for low temperature operations Throughout See Note 7
Local areas identified as fatigue sensitive, e.g.:    
• Identified bracket connections at intersections of side shell longitudinals and transverse frames and bulkheads Local See Note 3
• Key locations identified on moonpool integration structure Local 100%
• Topside support stool welds to upper deck and underdeck welds in way Local 100%
• Flare stack support welds to upper deck and underdeck welds in way Local 100%
Other items Local See Notes 3 and 4
NOTES
1. The diameter of each checkpoint is to be between 0,3 and 0,5 m, and volumetric and magnetic particle checks are to be carried out unless indicated otherwise.
2. 10% selection of butts and seams and 20% at intersections. Particular attention is to be given in way of stops and starts of automatic and semi-automatic welding during fabrication.
3. Random selection to the Surveyor’s satisfaction.
4. Particular attention is also given to ends of bracket connections where fitted.
5. Particular attention to be given in way of weld intersections and discontinuities at stop and start positions.
6. 10% of butts and seams and 30% at intersections. Particular attention to be taken in way of stops and starts of automatic and semiautomatic welding during fabrication.
7. 10% selection of butts and seams and 25% at intersections. Particular attention to be given in way of stops and starts of automatic and semi-automatic welding during fabrication.
8. Agreed locations are not to be indicated on blocks prior to the welding taking place, nor is any special treatment to be given at these locations.
9. Particular attention is to be given to repair rates. Additional welds are to be tested in the event that defects such as lack of fusion or incomplete penetration are repeatedly observed.

Table 8.2.2 Non-destructive examination of welds on column-stabilised and self-elevating units

Recommended extent of testing, see Note 9

General, see Note 1

   
Structural item Volumetric checkpoints Magnetic particle checkpoints
Bracing butt and seam welds 100% 100%
Bracing weld connections to:
  • columns
  • pontoons
  • upper hull
  • lower nodes
 100% 100%
Attachments to legs and bracings — 100%
Penetrations through legs and bracings 100% 100%
Bracing shell attachment of diaphragms, gussets, stiffeners 100% 100%
Column shell butts and seams See Note 4 20%
Column weld connections to:
  • pontoons
  • upper hull
  • in way of anchor fairleads and sheaves
 100% 100%
Internal column structure connections 5%, see Note 5 See Note 3
Pontoons, hull, shell and bulkhead butts/seams See Note 4 20%
Leg footings or mats See Note 4 20%
Internal pontoon structure 5%, see Note 5 See Note 3
Hull penetrations, sub-sea inlets, anode and attachments, piping connection supports, etc. 100% —
Bilge keel butts 100% 100%
Self-elevating unit leg connections
  • leg chords
  • leg trusses
  • leg attachments to footings or mats
  • butts and seams in chords and trusses
 100% 100%
Upper hull: Main bulkheads/deck girders See Notes 2 & 4 See Note 6
Strength decks and drill floor See Notes 2 & 4 See Note 7
In way of windlasses and mooring winches — 100%
Topside support structure connections to deck 25% 25%
Flare stack, crane pedestals and boom rests, integration structure of heavy-lift cranes with the hull, and gusset connections to deck 100% 100%
Drill floor, derrick substructure and moonpool structure See Notes 4 and 7 See Note 7
Helideck primary support, cantilevered life boat platform primary support 20% 20%
Helideck and lifeboat platform remainder See Note 8 —
Other items See Note 8 See Note 8
NOTES
1. Back-up structure of the items in question is also to be included, where applicable.
2. 100% in way of full penetration welding at end of diaphragm plates, gussets, stiffeners, etc.
3. 50% in way of fillet welds around stiffener ends, notches, cut-outs, drain hole openings, etc.
4. 10% selection of butts and seams and 20% at intersections. Particular attention to be taken in way of stops and starts of automatic and semi-automatic welding during fabrication.
5. 10% random selection of butt welds, of pontoon and column shell longitudinal stiffeners and transverse and longitudinal bulkheads stiffeners.
6. 10% random selection of fillet welds in way of stiffener ends, drain hole openings, cut-outs, notches, etc.
7. Girder and sub-structure butt welds 100% UT; principal connections to deck and main structure 100% UT and 100% MPI.
8. Random spot checks to the Surveyor’s satisfaction.
9. The diameter of each checkpoint is to be between 0,3 and 0,5 m.

2.4 Fillet welds

2.4.1 Additional weld factors for structure not specifically covered by the Rules for Ships are given in Table 8.2.3 Additional weld factors.

Table 8.2.3 Additional weld factors

Item Weld factor Remarks
(1) General application:    
(a) Shell boundaries of columns to lower and upper hulls full penetration except as required below
(b) Internal watertight or oiltight plate boundaries 0,34 generally, but alternative proposals will be considered in specific areas
(2) (a) Upper hull framing and hull framing on self-elevating units:    
(i) Webs of web frames and stringers:
  • to shell
  • to face plate

0,16

0,13

  
(ii) Tank side brackets to shell and inner bottom 0,34  
(b) Primary hull framing and girders on lower hulls, columns and caissons of column-stabilised units   to be in accordance with the Rules for Ships
(3) Decks and supporting structure:    
Primary deck girders and connections between primary members on column-stabilised units.   generally to comply with the Rules for Ships, but full penetration welding may be required
(4) Self-elevating units:    
(a) Leg construction, general full penetration  
(b) Leg connections to footings or mats full penetration  
(c) Internal webs, girders and bulkheads in footings and mats 0,44 full penetration may be required
(d) Internal stiffeners in footings and mats 0,34  
(e) Jackhouses, general 0,44 full penetration may be required
(f) Bulkheads and primary structures in way of leg wells 0,44 full penetration may be required
(5) Main bracings and ‘K’ joints, etc.:    
(a) Ring frames, girders and stiffeners full penetration generally, but alternative proposals may be considered
(b) Shell boundaries and end connections including brackets, gussets and cruciform plates full penetration  
(6) Miscellaneous structures, fittings and equipment:    
(a) Rings and coamings for manhole type covers to shell on stability columns and lower hulls full penetration generally, but alternative proposals may be considered
(b) Rings for manhole type covers, to deck or bulk head 0,34  
(c) Frames of watertight and weathertight bulk head doors 0,34  
(d) Stiffening of doors 0,21  
(e) Ventilator, air pipes, etc. coamings to deck 0,34 Load line positions 1 and 2
(f) Ventilator, etc. fittings 0,21 elsewhere
(g) Scuppers and discharges, to deck 0,44  
(h) Masts, flare structures, derrick posts, crane pedestals, etc. to deck 0,44 full penetration welding may be required
(j) Deck machinery seats to deck 0,21 generally
(k) Mooring equipment seats and fairleads 0,44 full penetration welding may be required
(l) Bulwark stays to deck 0,21  
(m) Bulwark attachment to deck 0,34  
(n) Guard rails, stanchions, etc. to deck 0,34  
(o) Bilge keel ground bars to shell 0,34 continuous fillet weld, minimum throat thickness 4 mm
(p) Bilge keels to ground bars 0,21 light continuous or staggered intermittent fillet weld,minimum throat thickness 3 mm
(q) Fabricated anchors full penetration  
(r) Turret and swivel supports 0,44 full penetration welding may be required
(s) Process plant stools to deck 0,44 full penetration welding may be required
(t) supports for risers, umbilicals and caissons 0,44 full penetration welding may be required
2.4.2 Continuous welding is to be adopted in the following locations:
  1. All weldings inside tanks and peak compartments.
  2. Primary and secondary members to shell in lower hulls and stability columns.
  3. Primary and secondary members to main bracings, trusses or ‘K’ joints.

2.5 Welding of tubular members

2.5.1 Welding is to comply with agreed Internationally or Nationally accepted Codes such as AWS or API and all welding generally is to conform to the following:
  1. All steel is to be joined by complete penetration groove welds.
  2. Unless single sided welding has been agreed for the particular weld configuration, double sided welds are to be used, wherever practicable.
  3. In lattice type structures, a minimum weld attachment length at the cord of 1,5 times the brace wall thickness is required at all locations. This is based on fatigue considerations.
  4. Care is to be taken to ensure the weld surface profile is smooth and blends with the parent material.
  5. Backing strips are not to be used unless specially agreed with LR.
  6. Root gaps are to be generally in the range of 3 to 6 mm.
  7. Bevels are to be such that the included angle is in the range 45° to 60°. However, when the dihedral angle is less than 45°, the included angle may be reduced as indicated for locations 4 and 5, see Figure 8.2.2 Local dihedral angle for weld profile locations.
  8. Where saddle weld toe grinding has been agreed as a method of improving fatigue life, at the locations agreed, the grinding of the weld toe is to produce a smooth transition between the weld and the parent plate. The grinding should remove all defects, slag inclusions and any undercut. Overgrinding into the parent plate is not to exceed 2 mm or 0,05 times the plate thickness, whichever is less. The grinding tool should preferably have a spherical head (e.g. a tungsten carbide burr) and, in general, disc-grinders are to be avoided except for initial heavy grinding. Any marks made by rotation of the grinding tool are to be aligned with the direction of stress. The surface of the main body of the weld may be dressed to produce a better concave profile if the as-welded profile is poor, see Figure 8.2.1 Grinding of weld toe and Figure 8.2.8 Weld grinding. Care must be exercised in order that overgrinding does not excessively reduce the size of the attachment weld and in no case less than that required by the Rules.

2.5.2 Locations 1, 2, 3, 4 and 5 are related to the local dihedral angle (the angle between the brace wall and chord wall). Transition from one detail to another is to be by gradual uniform level preparation and surface profile, see Pt 4, Ch 8, 2.5 Welding of tubular members 2.5.2.

Figure 8.2.1 Grinding of weld toe

Figure 8.2.2 Local dihedral angle for weld profile locations

Figure 8.2.3 Welding at location 1

Figure 8.2.4 Welding at location 2

Figure 8.2.5 Welding at location 3

Figure 8.2.6 Welding at location 4

Figure 8.2.7 Welding at location 5

Figure 8.2.8 Weld grinding
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