Section 2 Cylindrical shells subject to internal pressure
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Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Special Service Craft, July 2022 - Part 15 Piping Systems and Pressure Plant - Chapter 4 Pressure Plant - Section 2 Cylindrical shells subject to internal pressure

Section 2 Cylindrical shells subject to internal pressure

Parent topic: Chapter 4 Pressure Plant

2.1 Minimum thickness

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

where

t, p, R i and σ are defined in Pt 15, Ch 4, 1.7 Definition of symbols.

J = the joint factor of the longitudinal joints (expressed as a fraction), see Pt 15, Ch 4, 1.9 Joint factors 1.9.1. In the case of seamless shells clear of openings, J = 1,0

2.1.2 The formula in Pt 15, Ch 4, 2.1 Minimum thickness 2.1.1 is applicable only where the resulting thickness does not exceed half the internal radius, i.e. where R o is not greater than 1,5R i.

2.1.3 For fusion welded pressure vessels, t, is to be not less than , where D i is as defined in Pt 15, Ch 4, 1.7 Definition of symbols.

2.1.4 The minimum thickness of vessels manufactured of steels with improved corrosion resistance properties will be the subject of special consideration.

2.2 Unreinforced openings

2.2.1 The maximum diameter, d, of any unreinforced isolated openings is to be determined by the following formula:
  • in mm
The value of K to be used is calculated from the following formula:
  • but is not to be taken as greater than 0,99
where
p, D o and σ = are as defined in Pt 15, Ch 4, 1.7 Definition of symbols
t = actual thickness of shell, in mm.

2.2.2 For elliptical or oval holes, d, for the purposes of Pt 15, Ch 4, 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:
  • with a minimum 5d
where
d = diameter of openings in shell (mean diameter if dissimilarly sized holes are 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 by Pt 15, Ch 4, 2.2 Unreinforced openings are to be compensated in accordance with Figure 4.2.1 Compensation for welded standpipes or branches in cylindrical shells. The following symbols are used in Fig. 4.2.1(a) and (b):

t s = calculated thickness of a shell without joint or opening or corrosion allowance, in mm
t d = thickness calculated in accordance with Pt 15, Ch 4, 3.1 Minimum thickness without corrosion allowance, 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 r = thickness of added reinforcement, in mm
D i = internal diameter of cylindrical shell, in mm
d o = diameter of hole in shell, in mm
L = width of added reinforcement not exceeding D, in mm
C = in mm
D = and is not to exceed 0,5d o, in mm
σ = shell plate allowable stress, N/mm2
σp = standpipe allowable stress, N/mm2
σr = added reinforcement allowable stress, N/mm2
σw = weld metal allowable stress, N/mm2

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

2.3.2 For eliptical or oval holes, the dimension on the meridian of the shell is to be used for d o in Pt 15, Ch 4, 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.

Figure 4.2.1 Compensation for welded standpipes or branches in cylindrical shells
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