Section 2 Cylindrical shells and drums subject to internal pressure
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Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Inland Waterways Ships, July 2022 - Part 5 Main and Auxiliary Machinery - Chapter 9 Pressure Vessels other than Boilers - Section 2 Cylindrical shells and drums subject to internal pressure

Section 2 Cylindrical shells and drums subject to internal pressure

Parent topic: Chapter 9 Pressure Vessels other than Boilers

2.1 Minimum thickness

2.1.1 The minimum thickness, t, of a cylindrical shell is to be determined by the following formula:

t =
where

t, p, Ri and σ are as defined in Pt 5, Ch 9, 1.2 Definition of symbols

J = the joint factor of the longitudinal joints (expressed as a fraction), see Pt 5, Ch 9, 1.9 Joint factors. In the case of seamless shells clear of openings J = 1,0.

2.1.2 The formula in Pt 5, Ch 9, 2.1 Minimum thickness 2.1.1 is applicable only where the resulting thickness does not exceed half the internal radius, i.e. where t is not greater than 0,5 Ri.

2.1.3 Irrespective of the thickness determined by the formula in Pt 5, Ch 9, 2.1 Minimum thickness 2.1.1, t is to be not less than 3 + mm, where Di is as defined in Pt 5, Ch 9, 1.2 Definition of symbols.

2.1.4 The minimum thickness permitted for vessels manufactured in corrosion resistant steels will be the subject of special consideration.

2.2 Unreinforced openings

2.2.1 The maximum diameter, d, of any unreinforced isolated opening is to be determined by the following formula:

d = 8,08 [D o t (1 – K)]1/3 mm

The value of K to be used is calculated from the following formula:

K = but is not to be taken as greater than 0,99
= where

p, D o and σ are as defined in Pt 5, Ch 9, 1.2 Definition of symbols

t = actual thickness of shell, in mm.

2.2.2 For elliptical or oval holes, d for the purposes of Pt 5, Ch 9, 2.2 Unreinforced openings 2.2.1, refers to the major axis when this lies longitudinally or to the mean of the major and minor axes when the minor axis lies longitudinally.

2.2.3 No unreinforced opening is to exceed 200 mm in diameter.

2.2.4 Holes may be considered isolated if the centre distance between two holes on the longitudinal axis of a cylindrical shell is not less than:

d + 1,1 with a minimum 5d

where
d = diameter of openings in shell (mean diameter if dissimilarly sized holes involved)
D = mean diameter of shell
t = actual thickness of shell

Where the centre distance is less than so derived, the holes are to be fully compensated.

2.3 Reinforced openings

2.3.1 Openings larger than those permitted byPt 5, Ch 9, 2.2 Unreinforced openings are to be compensated in accordance with Figure 9.2.1 Compensation for welded standpipes or branches in cylindrical shells (a) or (b). The following symbols are used in Figure 9.2.1 Compensation for welded standpipes or branches in cylindrical shells (a) and (b):

d o = diameter of hole in shell, in mm
t a = actual thickness of shell plate without corrosion allowance, in mm
t b = actual thickness of standpipe without minus tolerances and corrosion allowance, in mm
t d = thickness calculated in accordance with Pt 5, Ch 9, 5.1 Minimum thickness 5.1.1 without corrosion allowance, in mm
t r = thickness of added reinforcement, in mm
t s = calculated thickness of a shell without joint or opening or corrosion allowance, in mm
C = in mm
D = and is not to exceed 0,5d o, in mm
D i = internal diameter of cylindrical shell, in mm
L = width of added reinforcement not exceeding D, in mm
σ = shell plate allowable stress, in N/mm2
σp = standpipe allowable stress, in N/mm2
σr = added reinforcement allowable stress, in N/mm2
σw = weld metal allowable stress, in N/mm2

Note σp, σr and σw are not to be taken as greater than σ.

Figure 9.2.1 Compensation for welded standpipes or branches in cylindrical shells

2.3.2 For elliptical or oval holes, the dimension on the meridian of the shell is to be used for d o in Pt 5, Ch 9, 2.3 Reinforced openings 2.3.1.

2.3.3 The welds attaching standpipes and reinforcing plates to the shell are to be of sufficient size to transmit the full strength of the reinforcing areas and all other loadings to which they may be subjected.

2.3.4 Compensation is to be distributed equally on either side of the centreline of the opening.

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