|
Steel couplings or sockets may be used on pipes within
the limits below::-
TABLE
| Nominal
bore |
Maximum
Permissible Pressure |
Maximum permissible temperature |
| lbs./sq.
inch |
kg/cm2 |
oC |
oF |
Upto and
including 25 mm (1 in.)
Over 25mm (1”)upto and including 38 mm (1 ½”) |
175
150 |
12.25
10.5 |
260
260 |
500
500 |
Over 38
mm (1 ½”) upto and including
75mm (3”) |
125
100 |
8.75
7 |
260
260 |
500
500 |
| Over 76mm
(3”) upto and including 102mm (4”) |
120 |
8.5 |
177 |
350 |
| Over 102mm
(4”) upto and including 127 mm (5in.) |
100 |
7 |
171 |
340 |
Screwed joints are permitted at temperatures exceeding
260oC and size or pressure limits in excess
of those given the table provided that the following
conditions are satisfied, namely:-
(1)
All threads are tapered unless pressure tightness
depends on a seal weld or a seating surface other than
the threads and experience or test demonstrates the
suitability of the joint.
(2)
Pressure or temperature rating in appropriate
component standard like BS, ASME, DIN etc. or as
calculated under relevant regulation of these
regulations are not exceeded.
3)
Minimum specified tensile strength of screwed
pipes is greater than 330 N/mm2.
(4)
The minimum thickness of screwed pipes is not to
be less than that given in Table No.1.
(5)
The design temperature does not exceed 495oC.
(6)
The pressure limits given in Table No.2 are not
exceeded.
Screwed
joints are permitted for temperatures in excess of 495oC
and pressure in excess of those given in Table No.2 for
instrument insertion and tapping and for plug for access
opening for radiographic inspection provided following
conditions are satisfied:
(a)
They do not exceed 50mm nominal bore size or one
quarter of nominal pipe size, which ever is the smaller.
(b)
The minimum thread engagement is not less than
–
6 for up
to and including 20mm nominal bore;
7 for
over 20 mm up to and including 40mm nominal bore;
8 for 40
mm up to and including 50mm nominal bore.
(c) The connection is seal welded.
(d) The
design of instrument insertion withstands the fluid
characteristics, fluid flow and any vibrations.
Screwed
joints are permitted for pressure in excess of those
given in Table No.2 up to 345 bar for dead end
instrument lines at the outlet end and downstream of
shut off valves and instruments, control apparatus or
discharge of a sample cooler provided that the nominal
bore size of the pipe does not exceed 12mm.
Table
No.1
|
MINIMUM
THICKNESS OF SCREWED PIPES
|
|
Nominal
Pipe
size
|
Minimum
thickness
|
|
17.5 bar or
less for steam
7 bar and less
for water
over 105oC
|
Over 17.5 bar
for steam
Over 7 bar for
water over 105oC
|
|
mm
8
10
15
20
25
32
40
50
65
80
|
mm
2.24
2.31
2.77
2.87
3.38
3.56
3.68
3.91
5.16
5.49
|
Mm
3.02
3.20
3.75
3.91
4.55
4.85
5.08
5.54
7.01
7.62
|
Table
No. 2
|
MAXIMUM
PRESSURE FOR SCREWED PIPES
|
|
Nominal
pipe size
|
Maximum
pressure
|
|
mm
Over
50 up to and including 80
Over
25 up to and including 50
Over
20 up to and including 25
Up to and including 20
|
Bar
27.5
41.5
83
103.5."
|
|
