Section 4 Joints and connections

4.1.1 Requirements are given in this Chapter for welding connection details, aluminium/steel transition joints, aluminium/wood connection, riveting of light structure and chemical bonding.

4.1.2 Welded joints are to be detailed such that crevices or inaccessible pockets capable of retaining dirt or moisture are avoided. Where cavities are unavoidable, they are to be sealed by welding or protective compounds or made accessible for inspection and maintenance.

4.2.1 Weld symbols, where used, are to conform to a recognised National or International Standard. Details of such Standards are to be indicated on the welding schedule, which is to be submitted for appraisal.

4.3.1 A welding schedule containing not less than the following information is to be submitted:

1. Weld throat thickness or leg lengths.

2. Grades, tempers, and thicknesses of materials to be welded.

3. Locations, types of joints and angles of abutting members.

4. Reference to welding procedures to be used.

5. Sequence of welding of assemblies and joining up of assemblies.

4.4.1 All structural butt joints are to be made by means of full penetration welds and, in general, the edges of plates to be joined by welding are to be bevelled on one or both sides of the plates. Full details of the proposed joint preparation are to be submitted for approval, see also Pt 7, Ch 2, 4.19 Joint preparation.

4.4.2 Where butt welds form a T-junction, the leg of the T is, where practicable, to be completed first including any back run. During the welding operation special attention is to be given to the completion of the weld at the junction, which is to be chipped back to remove crater cracks, etc. before the table is welded.

4.4.3 For guidance purposes, a number of typical joint preparations for TIG and MIG welding are shown in Table 2.4.1 Typical joint preparations for TIG welding of aluminium alloys and Table 2.4.2 Typical joint preparations for semi-automatic MIG welding respectively.

Table 2.4.1 Typical joint preparations for TIG welding of aluminium alloys

Thickness (mm)	Joint design	Welding position/comments
2,5 – 3,0		Flat Horizontal Vertical Overhead
3,0 – 10,0		Flat and Vertical V = 60o Horizontal and Overhead V = 90o – 110o
Symbols and definitions
g w = weld gap, in mm V w = weld preparation angle, in degrees

Table 2.4.2 Typical joint preparations for semi-automatic MIG welding

Thickness (mm)	Joint design	Welding position/comments
5,0 – 6,5		Flat
7,0 – 15,0		Flat Horizontal Vertical Overhead One sided welding with temporary backing
12,0 – 25,0		All positions
Symbols and definitions
t p = plate thickness, in mm g w = weld gap, in mm

4.5.1 The throat thickness of fillet welds is to be not less than:

For weld fillet dimensions, see Figure 2.4.1 Weld dimensions and types.
Weld factors are contained in Table 2.4.3 Weld factors.

Figure 2.4.1 Weld dimensions and types

4.5.2 The length, in mm, of any weld fillet in any intermittent welding arrangement is to be at least 10t_p or 40 mm, whichever is the greater but need not exceed 75mm.

4.5.3 For ease of welding, it is recommended that the ratio of the web height to the flange breadth be greater than or equal to 1,5, see Figure 2.4.2 Web height/flange breadth ratio.

Figure 2.4.2 Web height/flange breadth ratio

4.5.4 The leg length of the weld is to be not less than times the specified throat thickness.

4.5.5 The plate thickness t _p to be used in Pt 7, Ch 2, 4.5 Fillet welds 4.5.1 is generally to be that of the thinner of the two parts being joined. Where the difference in thickness is considerable, the size of fillet will be specially considered.

4.6.1 The throat thickness limits given in Table 2.4.4 Throat thickness limits are to be complied with.

4.6.2 Where the throat thickness calculated in Pt 7, Ch 2, 4.5 Fillet welds 4.5.1 is less than the overriding minimum value, as required by Table 2.4.4 Throat thickness limits, the limiting value is to be taken as the greater of the two. The upper limit for the throat thickness is, in general, to be as required by Table 2.4.4 Throat thickness limits. Throat thicknesses above this limit will be specially considered.

4.7.1 Temporary backing bars for single sided welding may be austenitic stainless steel, glass tape, ceramic, or anodized aluminium of the same material as the base metal. Backing bars are not to be made of copper to avoid weld contamination and corrosion problems.

4.7.2 Temporary backing bars are to be suitably grooved in way of the weld to ensure full penetration.

4.8.1 Where double continuous fillet welding is proposed the throat thickness is to be in accordance with Pt 7, Ch 2, 4.5 Fillet welds 4.5.1 taking equal to 1.

4.8.2 The impact area referred to in Pt 7, Ch 2, 4.8 Double continuous fillet welding 4.8.5 and Pt 7, Ch 2, 4.9 Intermittent fillet welding (staggered/chain) 4.9.1 is defined as the area of the hull that, in normal design operation of the craft, will be subject to loads of sufficient magnitude and velocity for slamming to occur on a regular basis. Areas where conditions for slamming occur incidentally are not considered as impact areas.

4.8.3 In the impact area, for welding arrangements where t_p ≤ 8mm and the requirements of Pt 7, Ch 2, 4.5 Fillet welds (considering ) and Pt 7, Ch 2, 4.6 Throat thickness limits are complied with, it is permitted to reduce the length of the weld to not less than 80 per cent of the total length of a theoretical double continuous weld joining the elements in the arrangement. Welding is to be by an intermittent staggered arrangement, see Figure 2.4.3 Overlapping intermittent staggered welding. This requirement does not supersede others relating to end connections.

Figure 2.4.3 Overlapping intermittent staggered welding

4.8.4 The slamming zone area referred to in Pt 7, Ch 2, 4.8 Double continuous fillet welding 4.8.2 is defined as the region where the operational non-displacement mode pressures exceed the operational displacement mode pressures.

4.8.5 Double continuous fillet welding is to be adopted in the following locations and may be used elsewhere if desired:

1. Boundaries of weathertight decks and erections, including hatch coamings, companionways and other openings.

2. Boundaries of tanks, watertight compartments and gastight compartments or in spaces or locations where condensation, spray or leakage water can accumulate.

3. Main engine seatings.

4. Bottom framing structure in way of machinery and jet room spaces of high speed craft as appropriate.

5. The side and bottom shell structure in the impact area of high speed craft (see Pt 7, Ch 2, 4.8 Double continuous fillet welding 4.8.3).

6. The underside of the cross-deck structure in the impact area of high speed multi-hull craft.

7. Structure in way of ride control systems, stabilisers, foils, lifting devices, thrusters, bilge keels, foundations and other areas subject to high stresses.

8. The shell structure in the vicinity of the propeller blades.

9. Stiffening members to plating in way of end connections, scallops and of end brackets to plating in the case of lap connections.

10. Primary and secondary members to plating in way of end connections, and end brackets to plating in the case of lap connections.

11. Face flats to webs of built-up/fabricated stiffening members in way of knees/end brackets and for a distance beyond such knees/end brackets of not less than the web depth of stiffener in way.

12. Locations where double continuous welding is required to qualify assumptions used in structural calculations, e.g. weld of girder flange in way of large cutout in the web.

4.8.6 In all locations where double continuous fillet welds are required, the fillet welds shall be continued around the ends of stiffeners or cut-outs to seal all edges.

4.8.7 Where intermittent welding is permitted, the length of double continuous fillet welding required in way of primary and secondary member end connections to plating is as shown in Pt 7, Ch 2, 4.8 Double continuous fillet welding 4.8.8 and is not to be less than the greater of the following:

• the web depth of the smaller stiffening member extending either side of a stiffener crossing (weld length is required on both sides of the crossing members);
• twice the height of the stiffening member extending from either end of the stiffener if the stiffener is sniped;
• the height of the stiffening member plus the leg length of the attached bracket if the stiffener is bracketed; or
• 0,1 x stiffener span.

4.8.8 Proposals to reduce the double continuous weld lengths for secondary members may be specially considered provided that supporting documentation is submitted which considers effects such as strength, stiffness and dynamic loading frequency and other fatigue aspects.

Figure 2.4.4 Extent of double continuous welding at end connections of primary and secondary members

4.9.1 Staggered or chain intermittent welding may be used, outside of the impact area in the side and bottom shell or the underside of the crossdeck structure of high speed craft. Supporting evidence is to be provided and agreed by LR demonstrating that no intermittent welding is applied in the impact areas of high speed craft, see Lloyd’s Register Guidance Note – Extent of double continuous welding for special service craft. Consideration should be given to the relevant service area notation, service type notation and craft type notation.

4.10.1 Depending on the structural design of the joint and design loads on the primary member, full penetration welding of flanges and web plates may be required to attain full section properties in the end connections of primary members. See also Pt 6, Ch 3, 1.22 Primary member end connections. Otherwise weld factors for the connections of primary structure are given in Table 2.4.3 Weld factors.

4.10.2 The weld connection to shell, deck or bulkhead is to take account of the material lost in the notch where longitudinals or stiffeners pass through the member. Where the width of notch exceeds 15 per cent of the stiffener spacing, the weld factor is to be multiplied by:

4.10.3 Where direct calculation procedures have been adopted, the weld factors for the 0,1 x overall length at the ends of the members will be considered in relation to the calculated loads.

4.11.1 Welding of end connections of primary members is to be such that the area of welding is not less than the cross-sectional area of the member, and the weld factor is to be not less than 0,34 in tanks or 0,27 elsewhere.

4.11.2 The welding of secondary member end connections is to be not less than as required by Table 2.4.5 Secondary member end connections welds. Where two requirements are given the greater is to be complied with.

4.11.3 The area of weld, A _w, is to be applied to each arm of the bracket or lapped connection.

4.11.4 Where a longitudinal strength member is cut at a primary support and the continuity of strength is provided by brackets, the area of weld is to be not less than the cross-sectional area of the member.

4.12.1 The weld connection of strength deck plating to sheerstrake is to be by double continuous fillet welding with a weld factor of 0,44. The welding procedure, including joint preparation, is to be specified and the procedure qualified and approved for individual Builders.

Table 2.4.5 Secondary member end connections welds

Connection	Weld area, A w in cm2	Weld factor
(1) Stiffener welded direct to plating	0,25A s or 6,5 cm2 whichever is the greater	0,34
(2) Bracketless connection of stiffeners or stiffener lapped to bracket or bracket lapped to stiffener:
(a) in dry space		0,27
(b) in tank		0,34
(c) main frame to tank side bracket in 0,15 L R forward	as (a) or (b)	0,34
(3) Bracket welded to face of stiffener and bracket connection to plating	-	0,34
(4) Stiffener to plating for 0,1 x span at ends, or in way of the end bracket if that be greater	-	0,34
Symbols
A s = cross section area of the stiffener, in cm2 A w = the area of the weld, in cm2, and is calculated as total length of weld, in cm, x throat thickness, in cm Z = the section modulus, in cm3, of the stiffener on which the scantlings of the end bracket are based
Note For maximum and minimum weld fillet sizes, see Table 2.4.4 Throat thickness limits.

4.13.1 Air and drain holes are to be kept clear of the toes of brackets, etc. Openings are to be well rounded with smooth edges, see also LR's Guidance Notes for Structural Details.

4.14.1 Notches and scallops are to be kept clear of the toes of brackets, etc. Openings are to be well rounded with smooth edges. Details of scallops are shown in Figure 13.2.1 Weld dimensions and types in Chapter 13 of the Rules for Materials.

4.14.2 Scallops are to be of such a size, and in such a position that a satisfactory weld can be made around the ends of openings.

4.15.1 Watertight collars are to be fitted, where stiffeners are continuous through watertight or oiltight boundaries, see also LR's Guidance Notes for Structural Details.

4.16.1 The area of the weld connecting secondary stiffeners to primary structure in the bottoms of the hulls and cross-deck structure in areas subjected to impact pressures is to be not less than the shear area from the Rules. This area is to be obtained by fitting two lugs or by other equivalent arrangements. Some typical lug connections are shown in Figure 2.4.5 Typical lug connections and Figure 3.1.7 Cut-outs and connections in Chapter 3.

Figure 2.4.5 Typical lug connections

4.16.2 Lugs or tripping brackets are to be fitted where shell longitudinals are continuous through web frames in way of highly stressed areas of the side shell (e.g. in way of fenders, etc).

4.16.3 Lugs or tripping brackets are also to be fitted where continuous secondary stiffeners are greater than half the depth of the primary stiffeners.

4.17.1 Where thick insert plates are butt welded to thin plates, the edge of the thick plate may require to be tapered. The slope of the taper is generally not to exceed one in three.

4.17.2 The corners of insert plates are to be suitably radiused.

4.18.1 Doubler plates are to be avoided in areas where corrosion may be a problem and access for inspection and maintenance is limited.

4.18.2 Where doubler plates are fitted, they are to have well radiused corners and the perimeter is to be continuously welded. Large doubler plates are also to be suitably slot welded, the details of which are to be submitted for consideration.

4.19.1 Typical butt joints are shown in Table 2.4.1 Typical joint preparations for TIG welding of aluminium alloys and Table 2.4.2 Typical joint preparations for semi-automatic MIG welding, see also LR's Guidance Notes for Structural Details.

4.20.1 The minimum requirements for construction tolerances are to be in accordance with Pt 3, Ch 1, 8 Building tolerances and associated repairs.

4.21.1 Where it is proposed to adopt riveted construction, full details of the rivets or similar fastenings, including mechanical test results, are to be indicated on the construction plans submitted for approval or a separate riveting schedule is to be submitted.

4.21.2 Samples may be required of typical riveted joints made by the Builder under representative construction conditions and tested to destruction in the presence of the Surveyor in shear, tension, compression or peel at LR's discretion.

4.21.3 Where riveting strength data sheets have been issued by a recognised Authority, the values quoted in these sheets will normally be accepted for design purposes.

4.21.4 Where two dissimilar metals are to be joined by riveting, precautions are to be taken to eliminate electrolytic corrosion to LR's satisfaction, and where practicable, the arrangements should be such as to enable the joint to be kept under observation at each survey without undue removal of lining and other items.

4.21.5 Where a sealing compound is used to obtain an airtight or watertight joint, details are to be submitted of its proposed use and of any tests made or experience gained in its use for similar applications.

4.21.6 Aluminium alloy rivets in accordance with Ch 8, 2 Aluminium alloy rivets of the Rules for Materials are to be used where practicable. However, in the case of composite structures, including steel and GRP, consideration will be given to the use of steel rivets. In such cases, the mating surfaces are to be coated with a sealing paint.

4.21.7 Sealing paints or compounds are not to be used with hot driven rivets.

4.22.1 Where chemical bonding of aluminium alloy of any load-bearing structure is proposed, details of the materials and the processes to be used are to be submitted for approval. These details are to include test results of samples manufactured under LR survey under workshop conditions to verify the strength, ageing effects and moisture resistance.

4.22.2 The adhesive manufacturer's recommendations in respect of the specified jointing system, comprising preparation of the surfaces to be adhered, the adhesive, bonding and curing processes, are to be strictly followed as variation of any step can severely affect the performance of the joint.

4.22.3 Meticulous preparation is essential where the joint is to be made by chemical bonding. The method of producing bonded joints is to be documented so that the process is repeatable after the procedure has been properly established.

4.22.4 Bonded joints are suitable for carrying shear loads, but are not in general to be used in tension or where the load causes peeling or other forces tending to open the joint. Loads are to be carried over as large an area as possible.

4.22.5 Bonded joints are to be suitably supported after assembly for the period necessary to allow the optimum bond strength of the adhesive to be to be developed. Entrained air pockets are to be avoided.

4.22.6 The use of adhesives for main structural joints is not to be contemplated unless considerable testing has established its validity, including environmental testing and fatigue testing where considered necessary by LR.

4.23.1 Particular care is to be taken to avoid triaxial stresses which may result from poor joint design. Detailed joint design is of particular importance in aluminium structures more so than many other materials. Some recommendations in this respect are contained in LR's Guidance Notes for Structural Details.

4.24.1 In general, the scantling derivation of welded structures are to be determined using the mechanical properties of the aluminium alloy in the welded condition in accordance with Pt 7, Ch 2, 2.4 Mechanical properties for design. However, where stiffeners are butt welded, special consideration will 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 the unwelded mechanical properties. The butt weld is to be completed and generally made flush with the flange of the stiffening member before the butt strap is fitted and the butt strap weld is to be continuous. Where this jointing method is proposed, the scantlings, arrangements and locations of all joints and butt straps are to be submitted. Additionally, LR may require mechanical tests to be carried out to demonstrate the effectiveness of such arrangements.

4.25.1 Joints between adjacent extruded aluminium alloy planking, and the attachment of the planking to the supporting structure is in general to be by means of continuous welding.

4.25.2 The planking is generally not to be included in the determination of the section properties for both section modulus and inertia. However, special consideration will be given to the inclusion of such materials on the basis of the efficiency of the connection to the supporting structure.

4.26.1 Provision is made in this Section for explosion bonded composite aluminium/steel transition joints used for connecting aluminium structures to steel plating. Such joints are to be used in accordance with the manufacturer's requirements, see also Ch 8, 4 Aluminium/steel transition jointsof the Rules for Materials.

4.26.2 Transition joints are to be manufactured by an approved producer in accordance with an approved specification which is to include the maximum temperature allowable at the interface during welding.

4.26.3 The aluminium material is to comply with the requirements of Pt 7, Ch 2, 2 Materials and the steel is to be of an appropriate grade complying with the requirements of Ch 3, 2 Normal strength steels for ship and other structural applicationsof the Rules for Materials.

4.26.4 Alternative materials which comply with International, National or proprietary specifications may be accepted provided that they give equivalence to the requirements of Pt 7, Ch 2, 4.26 Aluminium/steel transition joints 4.26.3 or are approved for a specific application.

4.26.5 Intermediate layers between the aluminium and steel may be used, in which case the material of any such layer is to be specified by the manufacturer and is to be recorded in the approval certificate. Any such intermediate layer is then to be used in all production transition joints.

4.26.6 Bimetallic joints where exposed to seawater or used internally within wet spaces are to be suitably protected to prevent galvanic corrosion.

4.27.1 To minimise corrosion of aluminium when in contact with wood in a damp or marine environment the timber is to be primed and painted in accordance with good practice. Alternatively the surface of the aluminium in contact with the timber is to be coated with a substantial thickness of a suitable sealant.

4.27.2 Timbers such as western red cedar, oak and chestnut are not, unless well seasoned, to be directly in contact with aluminium.

4.27.3 Timber preservatives of the following types should be avoided: copper napthanate, copper-chrome-arsenate, borax-boric acid.