LR V.7 Cargo tank boundaries

LR V.7.1.1 The requirements of this Section are related to the application of mild steel, solid stainless steel or stainless clad steel. Thicknesses derived for clad steel include the cladding. The thickness of the cladding itself is to be at least 1,5 mm at the tank sides and top, and 2,0 mm at the tank bottom.

LR V.7.1.2 In no case may tanks integral with the hull structure be used for a pressure/vacuum relief valve setting exceeding 0,7 bar gauge. The negative setting is assumed not to exceed 0,07 bar gauge.

LR V.7.1.3 Scantlings are to be suitable for the relative densities of the cargoes intended to be carried.

LR V.7.1.4 Where it is proposed to carry cargoes requiring temperature control for reasons of safe carriage, the temperature control arrangements are to be appropriate to the intended service and the characteristics of the cargo. Details are to be submitted.

LR V.7.1.5 Tank boundary scantlings are to be not less than the minimum standard required for oil tankers, i.e. as required by Pt 4, Ch 9 Double Hull Oil Tankers*, without correction for relative density.

LR V.7.1.6 The ends of corrugated bulkheads are to be suitably supported, where necessary by fitting additional stiffening.

LR V.7.2.1 The symbols used in this Section are defined as follows:

f

=

1.1 - but need not exceed 1,0

• h ₁, h ₂, h ₃ are vertical distances, in metres, from a point one-third of the height of the plate above its lowest edge to:
• for h ₁ the highest point of the tank, excluding the hatchway
• for h ₂ the top of the overflow
• for h ₃ the level of test head defined in Pt 3, Ch 1, 8 Inspection and workmanship*
• h ₄, h ₅, h ₆ are vertical distances, in metres, from the mid-point of the stiffener length, l _e, to:
• for h ₄ the highest point of the tank, excluding the hatchway
• for h ₅ the top of the overflow
• for h ₆ the level of test head defined in Pt 3, Ch 1, 8 Inspection and workmanship*

K c	=	plate thickness factor, in mm, see LR V.7.4 Plating
l	=	overall length of stiffener between the support points, in metres
l e	=	effective length of stiffener, in metres, as defined in Table 1.9.1 Watertight and deep tank bulkhead scantlings of Pt 4, Ch 1*
p	=	pitch of symmetrical corrugations, in mm
s	=	stiffener spacing for plane and double plate bulkheads, in mm
	=	breadth of flange or web, whichever is the greater, for corrugated bulkheads, in mm
αp	=	α1, α2, α3, whichever is the greatest, where
α1	=
α2	=
α3	=
αs	=	α4, α5, α6, whichever is the greatest, where
α4	=
α5	=
α6	=
γ	=	1,4 for rolled or built sections and double plate bulkheads
	=	1,6 for flat bars
	=	1,1 for symmetrical corrugations
ω1, ω2	=	end constraint factors, values given in Table 1.9.3 Bulkhead end constraint factors of Pt 4, Ch 1*.

LR V.7.2.2 Other symbols are defined in LR V.1.2 General definitions and symbols.

LR V.7.3.1 Where stainless steel is used, the minimum thickness in cargo tanks required by Pt 4, Ch 9, 10.2 Compartment minimum thickness* may be reduced by ( 2,5-K _c) mm, or is to be increased if K _c is greater than 2,5 mm. The final overall thickness of material is to be not less than 6,5 mm for tops and sides, and 7 mm for the bottoms, of tanks. See also LR V.7.1 General for minimum thickness of cladding.

LR V.7.4.1 The thickness of plating forming boundaries of cargo tanks is to be not less than given below, but may be required to be increased locally on account of high shear forces, in accordance with Pt 3, Ch 4, 6 Hull shear strength*:

LR V.7.4.2 For mild steel construction, the value of the plate thickness factor, K _c, is 2,5 mm. For stainless steel, K _c depends upon the type of material and its position, as represented by the designation of the adjacent space. See Table 1 Values of plate thickness factor, K _c for solid and clad stainless steel .

LR V.7.5.1 The section modulus of rolled or fabricated stiffeners and double plate bulkhead supports is to be not less than:

LR V.7.5.2 The inertia of rolled or fabricated stiffeners is to be not less than:

LR V.7.5.3 For symmetrical corrugations, the section modulus is to be not less than:

LR V.7.5.4 The remaining requirements of Pt 4, Ch 9, 6 Inner hull, inner bottom and longitudinal oiltight bulkheads* or Pt 4, Ch 9, 7 Transverse oiltight bulkheads* as applicable in respect of the proportions of stiffening members and corrugations are also to be fulfilled.

LR V.7.5.5 Where stainless steel is employed, the plating thickness calculated for corrugated bulkheads in accordance with LR V.7.5 Stiffeners and corrugations may be reduced by (2,5-K _c) mm.

LR V.7.5.6 The section modulus of mild steel stiffeners attached to solid or clad stainless steel plating is to be based on the actual plating thickness.

LR V.7.5.7 Where solid stainless steel stiffeners are to be fitted, the thickness may be as required for mild steel, reduced by 0,5 mm.

LR V.7.5.8 Where σ₁ or σ₂ is less than 235 N/mm² (24 kgf/mm²), scantlings are to be increased by substituting the corresponding value of k ₁ or k ₂ for k in tank boundary formulae for stiffener modulus and plating thickness. The value of k ₁ or k ₂ is not, however, to be used to reduce Rule inertia or plate thickness requirements as given, for example, in LR V.7.5 Stiffeners and corrugations and item 1(b) in Table 9.7.1 Transverse oiltight bulkhead scantlings of Pt 4, Ch 9* respectively.

LR V.7.6.1 Weld factors as given in Pt 3, Ch 10*, Table 10.2.1 Weld factors item (7) for Chemical Tankers are to be applied in conjunction with item (6) for Tankers of this Table.