M ATERIALS AND W ELDING
4 F ABRICATION .1 General
4.1.1 Workmanship
4.1.1.1 All workmanship is to be of commercial marine quality and acceptable to the Surveyor. Welding is to be in accordance with the requirements of Sub-Section 5.
Any defect is to be rectified to the satisfaction of the Surveyor before the material is covered with paint, cement or any other composition.
4.1.2 Fabrication standard
4.1.2.1 Structural fabrication is to be carried out, in accordance with ‘IACS Recommendation 47, Shipbuilding and Repair Quality Standard for New Construction’ or a recognised fabrication standard which has been accepted by the Classification Society prior to the commencement of fabrication/construction.
4.1.2.2 The fabrication standard to be used during fabrication/construction is to be made available to the attending representative of the Classification Society, prior to the commencement of the fabrication/construction.
4.1.2.3 The fabrication standard is to include information, to establish the range and the tolerance limits, for the items specified as follows:
(a) Cutting edge
• the slope of the cut edge and the roughness of the cut edges (b) Flanged longitudinals and brackets and built-up sections
• the breadth of flange and depth of web, angle between flange and web, and straightness in plane of flange or at the top of face plate
(c) Pillars
• the straightness between decks, and cylindrical structure diameter (d) Brackets and small stiffeners
• the distortion at the free edge line of tripping brackets and small stiffeners (e) Sub-assembly stiffeners
• details of snipe end of secondary face plates and stiffeners (f) Plate assembly
• for flat and curved blocks the dimensions (length and breadth), distortion and squareness, and the deviation of interior members from the plate
(g) Cubic assembly
• in addition to the criteria for plate assembly, twisting deviation between upper and lower plates, for flat and curved cubic blocks
(h) Special assembly
• the distance between upper and lower gudgeons, distance between aft edge of propeller boss and aft peak bulkhead, twist of stern frame assembly, deviation of rudder from shaft centreline, twist of rudder plate, and flatness, breadth and length of top plate of main engine bed. Where boring out of the propeller boss and stern frame, skeg or solepiece is carried out at a late stage of
construction, it is to be carried out after completing the major part of the welding of the aft part of the ship. Where block boring is used, the shaft
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alignment is to be carried out using a method and sequence submitted to and recognized by the Classification Society. The fit-up and alignment of the rudder, pintles and axles, are to be carried out after completing the major part of the welding of the aft part of the ship. The contacts between the conical surfaces of pintles, rudder stocks and rudder axles are to be checked before the final mounting.
RCN 1 to July 2010 version (effective from 1 July 2012) (i) Butt joints in plating
• alignment of butt joint in plating (j) Cruciform joints
• alignment measured on the median line and measured on the heel line of cruciform joints
(k) Alignment of interior members
• alignments of flange of T longitudinals, alignment of panel stiffeners, gaps in T joints and lap joints, and distance between scallop and cut outs for
continuous stiffeners in assembly and in erection joints (l) Keel and bottom sighting
• deflections for whole length of the ship, and for the distance between two adjacent bulkheads, cocking-up of fore body and of aft body, and rise of floor amidships
(m) Dimensions
• dimensions of length between perpendiculars, moulded breadth and depth at midship, and length between aft edge of propeller boss and main engine (n) Fairness of plating between frames
• deflections between frames of shell, tank top, bulkhead, upper deck, superstructure deck, deck house deck and wall plating
(o) Fairness of plating in way of frames
• deflections of shell, tank top, bulkhead, strength deck plating and other structures measured in way of frames
4.2 Cold Forming
4.2.1 Special structural members
4.2.1.1 For highly stressed components of the hull girder where notch toughness is of particular concern (e.g. items required to be Class III in Table 6.1.3, such as radius gunwales and bilge strakes) the inside bending radius, in cold formed plating, is not to be less than 10 times the gross plate thickness for carbon-manganese steels (hull structural steels, see 1.1). The allowable inside bending radius may be reduced below 10 times the gross plate thickness, providing the additional requirements stated in 4.2.3 are complied with.
4.2.2 Other members
4.2.2.1 For main structural members, e.g. corrugated bulkheads and hopper knuckles, the inside bending radius, in cold formed plating, is not to be less than 4.5 times the gross plate thickness for carbon-manganese steels (hull structural steels, see 1.1).
The allowable inside bending radius may be reduced below 4.5 times the gross plate thickness, providing the additional requirements stated in 4.2.3 are complied with.
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4.2.3 Additional requirements
4.2.3.1 When steel is formed below 650°C with a radius of less than 10 or 4.5 times the gross plate thickness for special and other members, respectively, supporting data is to be provided. As a minimum, the following additional requirements are to be complied with:
(a) the steel is to be of grade D/DH or higher
(b) the material is impact tested in the strain-aged condition and satisfies the requirements stated herein. The deformation is to be equal to the maximum deformation to be applied during production, calculated by the formula
) 2
/( bdg grs
grs r t
t + , where tgrs is the gross thickness of the plate material and rbdg is the bending radius. One sample is to be plastically strained at the calculated deformation or 5%, whichever is greater and then artificially aged at 250°C for one hour then subject to Charpy V-notch testing. The average impact energy after strain ageing is to meet the impact requirements specified for the grade of steel used.
(c) 100% visual inspection of the deformed area is to be carried out. In addition, random checks by magnetic particle testing are to be carried out.
The bending radius is in no case to be less than twice the gross plate thickness.
4.3 Hot Forming
4.3.1 Temperature requirements
4.3.1.1 Steel is not to be formed between the upper and lower critical temperatures. If the forming temperature exceeds 650°C for as-rolled, controlled rolled, thermo-mechanical controlled rolled or normalised steels, or is not at least 28°C lower than the tempering temperature for quenched and tempered steels, mechanical tests are to be made to assure that these temperatures have not adversely affected both the tensile and impact properties of the steel. Where curve forming or fairing, by line or spot heating, is carried out in accordance with 4.3.2.1 these mechanical tests are not required.
4.3.1.2 Confirmation is required to demonstrate the mechanical properties after further heating meet the requirements specified by a procedure test using representative material, when considering further heating other than in 4.3.1.1 of thermo-mechanically controlled steels (TMCP plates) for forming and stress relieving.
4.3.2 Line or spot heating
4.3.2.1 Curve forming or fairing, by linear or spot heating, is to be carried out using approved procedures in order to ensure that the properties of the material are not adversely affected. Heating temperature, on the surface, is to be controlled so as not to exceed the maximum allowable limit applicable to the plate grade.
4.4 Welding 4.4.1 General
4.4.1.1 All welding is to be carried out by approved welders, in accordance with approved welding procedures, using approved welding consumables and is to comply with the Rules for Materials of the individual Classification Society.
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4.4.2 Welding sequence
4.4.2.1 Consideration is to be given to the assembly sequence and the effect on the overall shrinkage of plate panels, assemblies, etc., resulting from the welding processes employed. Welding is to proceed systematically, with each welded joint being completed in the correct sequence, without undue interruption.
4.4.2.2 Where practicable, welding is to commence at the centre of a joint and proceed outwards, or at the centre of an assembly and progress outwards towards the perimeter so that each part has freedom to move in one or more directions.
4.4.2.3 Generally, the welding of stiffener members, including transverses, frames, girders, etc., to welded plate panels by automatic processes is to be carried out in such a way as to minimize angular distortion of the stiffener.
4.4.3 Arrangements at junctions of welds
4.4.3.1 Welds are to be made flush in way of the faying surface where stiffening members, attached by continuous fillet welds, cross the completely finished butt or seam welds. Similarly, butt welds in webs of stiffening members are to be completed and made flush with the stiffening member before the fillet weld is made. The ends of the flush portion are to run out smoothly without notches or sudden changes of section. Where these conditions cannot be complied with, a scallop is to be arranged in the web of the stiffening member. Scallops are to be of a size, and in a position, that a satisfactory return weld can be made.
4.4.4 Leak stoppers
4.4.4.1 Where structural members pass through the boundary of a tank, leakage into the adjacent space could be hazardous or undesirable, and full penetration welding is to be adopted for the members for at least 150mm on each side of the boundary.
Alternatively, a small scallop of suitable shape may be cut in the member close to the boundary outside of the compartment, and carefully welded all around.
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