Section 8 Building tolerances and associated repairs
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Special Service Craft, July 2022 - Part 3 General Requirements and Constructional Arrangements - Chapter 1 General Regulations - Section 8 Building tolerances and associated repairs

Section 8 Building tolerances and associated repairs

Parent topic: Chapter 1 General Regulations

8.1 Tolerances - General

8.1.1 Tolerances to be used regarding the acceptability of defects affecting raw materials are to be in accordance with Pt 3, Ch 1, 8.2 Raw material surface tolerances.

8.1.2 Tolerances to be used for constructional misalignment for all materials are to be discussed between Owners/Builders and the Surveyor and acceptable Standards agreed subject to the requirements of this Chapter or National Authority requirements where applicable. The permitted degree of inaccuracy/misalignment will vary according to whether the defect is:

  1. In primary structure.

  2. In secondary structure.

  3. Aesthetically pleasing.

8.1.3 The requirements in respect of constructional mis-alignment of steel/aluminium craft are to be found in Pt 3, Ch 1, 8.6 Structural misalignment and fit (steel and aluminium). The requirements for construction using composite materials are contained in Pt 8, Ch 2 Construction Procedures.

8.2 Raw material surface tolerances

8.2.1 The surface cleanliness of steel/aluminium alloy materials in preparation for painting is to be in accordance with National or paint Manufacturer's Standards.

8.2.2 Where approved corrosion control coatings are to be used the quality of the surface treatment is to be in accordance with the grade specified in the approval documents.

8.3 Surface defects

8.3.1 The limits of depth and extent of surface defects on plate, cast or forged materials in relation to the material plate thickness are shown in Table 1.8.1 Limits of surface defects.

8.3.2 Defects are to be made good by grinding only subject to the plate thickness not being reduced by more than seven per cent of the nominal thickness or 3 mm whichever is the lower, and the area involved not exceeding two per cent of the surface area.

8.3.3 When the limits in Pt 3, Ch 1, 8.3 Surface defects 8.3.1 are exceeded, plates may be made good by weld repair in accordance with the requirements specified in Ch 13 Requirements for Welded Construction of the Rules for Manufacturing, Testing and Certification of Materials (hereinafter referred to as the Rules for Materials.

8.3.4 Where the depth of the deepest imperfection exceeds 20 per cent of the nominal thickness, or the defective area exceeds two per cent of the total surface area, such areas are to be cropped and replaced. See Pt 3, Ch 1, 8.5 Part replacement of plates.

8.3.5 Complete removal of the defects is to be verified by suitable non-destructive examination techniques and after welding the repair is to be proved free from further defects. The complete removal of defects is to be verified by nondestructive examination in accordance with the requirements specified in Ch 13 Requirements for Welded Construction of the Rules for Materials.

8.3.6 Care is to be taken in the repair of defects in higher tensile steel, and aluminium alloy materials. Low hydrogen electrodes with similar properties to the higher tensile steel are to be used with preheating as necessary. Aluminium alloys are to be heat treated after repair, see Pt 7, Ch 2, 3 Procedures for welded construction.

Table 1.8.1 Limits of surface defects

Normal thickness of material (mm) Maximum permissible depth of defect (mm)
Area affected - Unlimited Area affected ≤ 5% of Surface
< 8 0,2 0,4
8 to 25 0,3 0,5
25 to 40 0,4 0,6
≥ 40 0,5 0,8

Note 1. Defects are to be measured after shot blasting or plate cleaning.

Note 2. The depth of the deepest imperfection is to be considered.

Note 3. Defects not exceeding the limits shown need not be repaired.

Note 4. Where the depth of the defects reduces the material thickness to below the rolling/forging/casting tolerance (stated in the Rules for the Manufacture, Testing and Certification of Materials, July 2022) the values of column 2 and 3 will be accepted provided the areas involved do not exceed 15% and 2% respectively, of the plate/forging/casting surface.

Note 5. Defects exceeding the above limits are to be repaired.

Note 6. Crack-like defects are always to be repaired irrespective of their depth.

8.4 Plate laminations

8.4.1 Plates in which laminations are suspected or detected are to be ultrasonically tested to determine the full extent of such laminations.

8.4.2 Where laminations are confined to the plate edge, are less than 300 mm long and whose penetration is not more than half the plate thickness, then the defect may be chipped or ground out and rebuilt with weld material.

8.4.3 Where laminations are isolated, located near to the plate surface, and where the total area of the defect does not exceed two per cent of the surface area of the plate, the defect may be repaired as in Pt 3, Ch 1, 8.4 Plate laminations 8.4.2.

8.4.4 Defective plate, with defects in excess of those stated in Pt 3, Ch 1, 8.4 Plate laminations 8.4.2 and Pt 3, Ch 1, 8.4 Plate laminations 8.4.3, is to be cropped back and replaced, see Pt 3, Ch 1, 8.5 Part replacement of plates.

8.4.5 Complete removal of the defect is to be verified by non-destructive examination, and after welding, the repair is to be proved free from further defects.

8.5 Part replacement of plates

8.5.1 When defects exceed the limits laid down in Pt 3, Ch 1, 8.3 Surface defects 8.3.4 and Pt 3, Ch 1, 8.4 Plate laminations 8.4.4 above, the portion of the plate affected is to be cropped and replaced, see Table 1.8.2 Part replacement of plates.

8.6 Structural misalignment and fit (steel and aluminium)

8.6.1 For the requirements for the alignment and structural continuity of joints, see Pt 6, Ch 2 Construction Procedures and Pt 7, Ch 2 Construction Procedures.

8.6.2  Table 1.8.3 Structural misalignment and fit (steel and aluminium), Table 1.8.4 Structural misalignment and fit (steel and aluminium) and Table 1.8.5 Structural misalignment and fit (steel and aluminium) define the minimum limits of accuracy required to be achieved in the various welded joint designs. When these values are not achieved, the defects are to be discussed and agreed by the Builder and the Surveyor before remedial action is taken.

8.6.3 Welding defects are generally to be dealt with in accordance with Ch 13 Requirements for Welded Construction of the Rules for Materials. Limits for weld undercut and remedial action to be taken depend on plate thickness and are to be discussed and agreed by the Builder and the Surveyor prior to commencement of repairs.

8.7 Post welding plate deformation

8.7.1 Post welding plate deformation for steel and aluminium alloy construction is to be limited, see Table 1.8.6 Plate deformation limits and Figure 1.8.1 Measurement of plate deformation.

8.7.2 Deformation outside the limits of Figure 1.8.1 Measurement of plate deformation is to be faired by local heating or the plating renewed.

8.7.3 Local heating of steel is not to exceed 900oC (red heat) when flame straightening is employed.

8.7.4 Local heating of aluminium alloys is not to be carried out. All repairs are to be by renewal of plating.

Table 1.8.2 Part replacement of plates

A x B Parts to be replaced Shell, strength deck, tank top, top and bottom strakes of longitudinal bulkheads Elsewhere
End and corner of plate 1000 x 1000 1000 x 300
Side of plate 1000 x 300 1000 x 300
Insert 1000 x 300 1000 x 300
Line of plate replacement to be not less than 100 from extreme edge of defect.
All dimensions are in mm.

Note 1. All dimensions are minimum.

Note 2. Rolling direction of replaced plate to be the same as that of the parent plate.

Note 3. Minimum distance from outermost defect to line of weld – 100 mm.

Note 4. Dimensions in millimetres:

x = 50
d = 1,5 x plate thickness with minimum 6 and maximum 20
r = 75 minimum

Table 1.8.3 Structural misalignment and fit (steel and aluminium)

Joint Location Acceptable dimensions (mm) Remedial action
Fabricated frames a ≤ ± 0,03 x a > ± 0,03 x Reject
Beams, girders and longitudinals      
Butt welded face flats primary structure a ≤ 0,03W(max 6 mm) a > 0,03W Reject
Secondary structure a ≤ 0,04W (max 8 mm) a > 0,04W Reject
Obtuse angle fillet weld a ≤ t 1/2 a > t 1/2 Reject
All areas d ≤ 0,1t 1 (max 0,8 mm) d > 0,1t 1 Repair by welding or grinding depends on thickness ‘t 1’ in accordance with 8.3
All areas d ≤ 0,1t
(max 0,8 mm) 		d > 0,1t As above

Table 1.8.4 Structural misalignment and fit (steel and aluminium)

Joint Location Permitted misalignment Remedial action
All areas (Continuous fillet weld) a (mm) a (mm) Increase weld leg length by ‘a’
  0,25t 1 to 0,5t 1 (t 1 max = 5 mm)
< 0,25t 1 (a max = 1 mm) 0,5t 1 to t 1 (t 1 max = 15 mm) Vee material to +/–45o. Fit backing strip and weld. Remove backing strip and complete weld.
a > t 1 Realign and replace
All areas (intermittent weld) < 0,25t 1 0,25 to 0,5t 1 (t 1 max = 3 mm) Increase weld lengths by 50%
0,25t 1 to 0,5t 1 (t 1 max = 5 mm) Continuous weld
a > t 1 As for continuous weld above
Strength members a ≤ t 2/3 t 2/3 ≤ a ≤ t 1/2 Increase weld leg length of welds by 10%
Others a ≤ t 2/2 a > t 2/2 Realign
Higher tensile steel joint in designated critical areas a ≤ t 3/3 a > t 3/3 Realign
Strength members a ≤ 0,15t 1(max 3,0 mm) a > 0,15t 1 Realign
Others a ≤ 0,2t 1 (max 3,0 mm) a > 0,2t 1 Realign
All areas a in accordance with weld procedure a ≤ t 1 Build one side of butt until a in accordance with weld procedure.
a >t 1 (max 10 mm) Cut back 150 mm and fit insert plate

Table 1.8.5 Structural misalignment and fit (steel and aluminium)

Joint Location Acceptable dimensions (mm) Remedial action
All 1 ≥ 40 mm – Adjust to suit
All 2 ≥ 20 mm – Adjust to suit
All 1 > 50 mm 1 < 30 mm Treat as an insert
All 2 ≥ 20 mm 2 < 15 mm Adjust to suit
All a ≤ 1,0 a < 5 Increase weld leg length by actual ‘a’
All a ≤ 1,0 a ≤ 5 Adjust to suit
Strength members a ≤ 0,15t 1 (max 3,0 mm) a > 0,15t 1 Reject
Other a ≤ 0,2t 1 (max 3,0 mm) a > 0,2t 1 Reject
All For angle or tee longitudinal a ≤ 0,2t 1 a > 0,2t 1 Reject
For offset bulb longitudinal a ≤ 0,2t 2 a > 0,2t 2 Reject

Table 1.8.6 Plate deformation limits

Position s/t δp/s
in 0,6L amidship ≤ 80 1/100
  > 80 1/75
Remainder all 1/50
where
s = stiffener spacing, in mm
t = plating thickness, in mm
δp = panel deflection, in mm

Figure 1.8.1 Measurement of plate deformation
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