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  Reg. 367

Steel Screwed and Socketed Joints and Mountings of Steel

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."

 
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