Section
6 Carbon and low alloy steel piping and components
6.1 Wrought steel pipes and bends
6.1.1 The
maximum permissible design stress, σ, is to be taken as the lowest
of the following values:
where
|
E
t
|
= |
specified minimum lower yield or 0,2 per cent proof stress at
the design temperature. In the case of stainless steel, the 1,0 per
cent proof stress at design temperature is to be used |
|
R
20
|
= |
specified minimum tensile strength at ambient temperature |
|
S
R
|
= |
average stress to produce rupture in 100 000 hours at the design
temperature |
Values of the maximum permissible design stress, σ, obtained
from the properties of the steels specified in Ch 6 Steel Pipes and Tubes of the Rules for Materials are shown in Table 1.6.1 Carbon and carbon-manganese steel
pipes and Table 1.6.2 Alloy steel pipes. For intermediate values of
specified minimum strengths and temperatures, values of the permissible
design stress may be obtained by interpolation.
6.1.2 Where
it is proposed to use, for high temperature service, alloy steels
other than those detailed in Table 1.6.2 Alloy steel pipes particulars of the tube sizes, design conditions and
appropriate national or proprietary material specifications are to
be submitted for consideration.
Table 1.6.1 Carbon and carbon-manganese steel
pipes
Specified minimum tensile strength,
N/mm2
|
Maximum permissible stress, N/mm2
|
| Maximum design temperature, °C
|
| 50
|
100
|
150
|
200
|
250
|
300
|
350
|
400
|
410
|
420
|
430
|
440
|
450
|
| 320
|
107
|
105
|
99
|
92
|
78
|
62
|
57
|
55
|
55
|
54
|
54
|
54
|
49
|
| 360
|
120
|
117
|
110
|
103
|
91
|
76
|
69
|
68
|
68
|
68
|
64
|
56
|
49
|
| 410
|
136
|
131
|
124
|
117
|
106
|
93
|
86
|
84
|
79
|
71
|
64
|
56
|
49
|
| 460
|
151
|
146
|
139
|
132
|
122
|
111
|
101
|
99
|
98
|
85
|
73
|
62
|
53
|
| 490
|
160
|
156
|
148
|
141
|
131
|
121
|
111
|
109
|
98
|
85
|
73
|
62
|
53
|
6.1.3 The
minimum thickness, t, of straight steel pipes is to be
determined by the following formula:
where p, D, e and a are as defined in Vol 2, Pt 7, Ch 1, 3.2 Design symbols 3.2.1
For pipes passing through tanks, an additional corrosion
allowance is to be added to take account of external corrosion; the
addition will depend on the external medium and the value is to be
in accordance with Table 1.6.4 Minimum thickness for steel
pipes.
Where the pipes are efficiently protected, the corrosion allowance
may be reduced by not more than 50 per cent.
Table 1.6.2 Alloy steel pipes
Type
of
steel
|
Specified minimum tensile strength, N/mm2
|
Maximum permissible stress, N/mm2
|
| Maximum design temperature, °C
|
| 50
|
100
|
200
|
300
|
350
|
400
|
440
|
450
|
460
|
470
|
| 1
Cr1/2 Mo
|
440
|
159
|
150
|
137
|
114
|
106
|
102
|
101
|
101
|
100
|
99
|
2
1/4 Cr 1 Mo
annealed
|
410
|
76
|
67
|
57
|
50
|
47
|
45
|
44
|
43
|
43
|
42
|
21/4 Cr 1 Mo
normalised and
tempered
(Note 1)
|
490
|
167
|
163
|
153
|
144
|
140
|
136
|
130
|
128
|
127
|
116
|
21/4 Cr 1 Mo
normalised and
tempered
(Note 2)
|
490
|
167
|
163
|
153
|
144
|
140
|
136
|
130
|
122
|
114
|
105
|
| 1/2 Cr 11/2 Mo
1/4 V
|
460
|
166
|
162
|
147
|
120
|
115
|
111
|
106
|
105
|
103
|
102
|
|
|
|
Maximum design temperature, °C
|
|
|
|
480
|
490
|
500
|
510
|
520
|
530
|
540
|
550
|
560
|
570
|
| 1 Cr 1/2 Mo
|
440
|
98
|
97
|
91
|
76
|
62
|
51
|
42
|
34
|
27
|
22
|
2
1/4Cr 1 M
o annealed
|
410
|
42
|
42
|
41
|
41
|
41
|
40
|
40
|
40
|
37
|
32
|
2
1/4 Cr 1 Mo
normalised and tempered
(Note 1)
|
490
|
106
|
96
|
86
|
76
|
67
|
58
|
49
|
43
|
37
|
32
|
2
1/4 Cr 1 Mo
normalised and tempered
(Note 2)
|
490
|
96
|
88
|
79
|
72
|
64
|
56
|
49
|
43
|
37
|
32
|
| 1/2 Cr 1/2 Mo
1/4 V
|
460
|
101
|
99
|
97
|
94
|
82
|
72
|
62
|
53
|
45
|
37
|
Note
1. Maximum permissible stress values
applicable when the tempering temperature does not exceed 750°C
Note
2. Maximum permissible stress values
applicable when the tempering temperature exceeds 750°C
|
Table 1.6.3 Values of c for steel pipes
| Piping service
|
c
mm
|
| Superheated steam systems
|
0,3
|
| Saturated steam systems
|
0,8
|
| Steam coil systems in cargo tanks
|
2,0
|
| Feed water for boilers in open circuit
systems
|
1,5
|
| Feed water for boilers in closed circuit
systems
|
0,5
|
| Blow down (for boilers) systems
|
1,5
|
| Compressed air systems
|
1,0
|
| Hydraulic oil systems
|
0,3
|
| Lubricating oil systems
|
0,3
|
| Fuel oil systems
|
1,0
|
| Cargo oil systems
|
2,0
|
| Refrigerating plants
|
0,3
|
| Fresh water systems
|
0,8
|
| Sea-water systems in general
|
3,0
|
Table 1.6.4 Minimum thickness for steel
pipes
External
diameter
D
in mm
|
Pipes
in general
in mm
|
Venting,
overflow and sound-
ing pipes
for
structural tanks
in mm
|
Bilge,
ballast and
general sea-water
pipes in
mm
|
Bilge,
air, overflow and sounding pipes through
ballast and fuel
tanks, ballast lines through fuel
tanks and fuel lines
through ballast tanks in mm
|
| 10,2–12
|
1,6
|
–
|
–
|
–
|
| 13,5–19
|
1,8
|
–
|
–
|
–
|
| 20
|
2,0
|
–
|
–
|
–
|
| 21,3–25
|
2,0
|
–
|
3,2
|
–
|
| 26,9–33,7
|
2,0
|
–
|
3,2
|
–
|
|
|
|
|
|
|
| 38–44,5
|
2,0
|
4,5
|
3,6
|
6,3
|
| 48,3
|
2,3
|
4,5
|
3,6
|
6,3
|
| 51–63,5
|
2,3
|
4,5
|
4,0
|
6,3
|
| 70
|
2,6
|
4,5
|
4,0
|
6,3
|
| 76,1–82,5
|
2,6
|
4,5
|
4,5
|
6,3
|
|
|
|
|
|
|
| 88,9–108
|
2,9
|
4,5
|
4,5
|
7,1
|
| 114,3–127
|
3,2
|
4,5
|
4,5
|
8,0
|
| 133–139,7
|
3,6
|
4,5
|
4,5
|
8,0
|
| 152,4–168,3
|
4,0
|
4,5
|
4,5
|
8,8
|
| 177,8
|
4,5
|
5,0
|
5,0
|
8,8
|
|
|
|
|
|
|
| 193,7
|
4,5
|
5,4
|
5,4
|
8,8
|
| 219,1
|
4,5
|
5,9
|
5,9
|
8,8
|
| 244,5–273
|
5,0
|
6,3
|
6,3
|
8,8
|
| 298,5–368
|
5,6
|
6,3
|
6,3
|
8,8
|
| 406,4–457,2
|
6,3
|
6,3
|
6,3
|
8,8
|
Note The pipe diameters and wall thickness given in the table
are based on common international standards. Diameter and thickness
according to other National or International Standards will be
considered.
|
6.1.4 The
minimum thickness, t
b, of a straight steel
pipe to be used for a pipe bend is to be determined by the following
formula, except where it can be demonstrated that the use of a thickness
less than t
b would not reduce the thickness
below t at any point after bending:
where p, D, R, e and a are as defined in Vol 2, Pt 7, Ch 1, 3.2 Design symbols 3.2.1
σ and c are as defined in Vol 2, Pt 7, Ch 1, 6.1 Wrought steel pipes and bends 6.1.3. In general, R is
to be not less than 3D.
6.1.5 Where
the minimum thickness calculated by Vol 2, Pt 7, Ch 1, 6.1 Wrought steel pipes and bends 6.1.3 or Vol 2, Pt 7, Ch 1, 6.1 Wrought steel pipes and bends 6.1.4 is less than
that shown in Table 1.6.4 Minimum thickness for steel
pipes,
the minimum nominal thickness for the appropriate standard pipe size
shown in the Table is to be used. No allowance is required for negative
tolerance, corrosion or reduction in thickness due to bending on this
nominal thickness. For larger diameters, the minimum thickness will
be considered. For threaded pipes, where permitted, the minimum thickness
is to be measured at the bottom of the thread.
6.1.6 For
air, bilge, ballast, fuel, overflow, sounding and venting pipes as
listed in Table 1.6.4 Minimum thickness for steel
pipes, where
the pipes are efficiently protected against corrosion, the thickness
may be reduced by not more than 1 mm.
|