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PIPING AND INSTRUMENTATION
2
P s D safe working pressure, lb/in (or N/mm ),
2
2
s D safe working stress, lb/in (or N/mm ). 2 217
Schedule 40 pipe is commonly used for general purposes.
Full details of the preferred dimensions for pipes can be found in the appropriate
Handbook and Standards. The main United Kingdom code for pipes and piping systems
is the British Standard is BS 1600.
The UK pipe schedule numbers are the same as the American (US). A summary of the
US standards is given in Perry et al. (1997).
Example 5.5
Estimate the safe working pressure for a 4 in. (100 mm) dia., schedule 40 pipe, carbon
Ž
steel, butt welded, working temperature 100 C. The safe working stress for butt welded
Ž
2
2
steel pipe up to 120 C is 6000 lb/in (41.4 N/mm ).
Solution
40 ð 6000
schedule no. ð s 2 2
P s D D D 240 lb/in D 1656 kN/m
1000 1000
5.5.2. Pipe supports
Over long runs, between buildings and equipment, pipes are usually carried on pipe racks.
These carry the main process and service pipes, and are laid out to allow easy access to
the equipment.
Various designs of pipe hangers and supports are used to support individual pipes.
Details of typical supports can be found in the books by Perry et al. (1997) and Holmes
(1973). Pipe supports frequently incorporate provision for thermal expansion.
5.5.3. Pipe fittings
Pipe runs are normally made up from lengths of pipe, incorporating standard fittings for
joints, bends and tees. Joints are usually welded but small sizes may be screwed. Flanged
joints are used where this is a more convenient method of assembly, or if the joint will
have to be frequently broken for maintenance. Flanged joints are normally used for the
final connection to the process equipment, valves and ancillary equipment.
Details of the standard pipe fittings, welded, screwed and flanged, can be found in
manufacturer’s catalogues and in the appropriate national standards. The standards for
metal pipes and fittings are discussed by Masek (1968).
5.5.4. Pipe stressing
Piping systems must be designed so as not to impose unacceptable stresses on the
equipment to which they are connected.