Page 217 - Chemical engineering design

CHAPTER 5

Piping and Instrumentation

5.1. INTRODUCTION

The process flow-sheet shows the arrangement of the major pieces of equipment and their
interconnection. It is a description of the nature of the process.
The Piping and Instrument diagram (P and I diagram or PID) shows the engineering
details of the equipment, instruments, piping, valves and fittings; and their arrangement.
It is often called the Engineering Flow-sheet or Engineering Line Diagram.
This chapter covers the preparation of the preliminary P and I diagrams at the process
design stage of the project.
The design of piping systems, and the specification of the process instrumentation and
control systems, is usually done by specialist design groups, and a detailed discussion
of piping design and control systems is beyond the scope of this book. Only general
guide rules are given. The piping handbook edited by Nayyar et al. (2000) is particularly
recommended for the guidance on the detailed design of piping systems and process
instrumentation and control. The references cited in the text and listed at the end of the
chapter should also be consulted.

5.2. THE P AND I DIAGRAM

The P and I diagram shows the arrangement of the process equipment, piping, pumps,
instruments, valves and other fittings. It should include:

1. All process equipment identified by an equipment number. The equipment should
be drawn roughly in proportion, and the location of nozzles shown.
2. All pipes, identified by a line number. The pipe size and material of construction
should be shown. The material may be included as part of the line identification
number.
3. All valves, control and block valves, with an identification number. The type and
size should be shown. The type may be shown by the symbol used for the valve or
included in the code used for the valve number.
4. Ancillary fittings that are part of the piping system, such as inline sight-glasses,
strainers and steam traps; with an identification number.
5. Pumps, identified by a suitable code number.
6. All control loops and instruments, with an identification number.

For simple processes, the utility (service) lines can be shown on the P and I diagram.
For complex processes, separate diagrams should be used to show the service lines, so

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