Petroleum Refining Design and Applications Handbook. A. Kayode Coker

and 14.17a–c, which enhance the detail in many of these standards. Various types of processing suggest unique, yet understandable symbols, which do not fit the generalized forms.

      Many symbols are pictorial which is helpful in representing process as well as control and mechanical operations. In general, experience indicates that the better the representation including relative location of connections, key controls and even utility connections, and service systems, the more useful will be the flowsheets for detailed project engineering and plant design.

      To aid in readability by plant management as well as engineering and operating personnel, it is important that a set of symbols be developed as somewhat standard for a particular plant or company. Of course, these can be improved and modified with time and as needed, but with the basic forms and letters established, the sheets can be quite valuable. Many companies consider their flowsheets quite confidential since they contain the majority of key processing information, even if in summary form.

Figure 14.16 (a) Process variables; (b) Pumps and solids [9]. (c) Storage and equipment; (d) Flow and instruments [9]. (e) Filters, evaporators, and driers [9].

14.10 Line Symbols and Designations

      The two types of lines on a flowsheet are (1) those representing outlines and details of equipment, instruments, and so on, and (2) those representing pipe carrying process or utility liquids, solids, or vapors and electrical or instrument connections. The latter must be distinguished among themselves as suggested by Figure 14.17d.

      In order to represent the basic type of solution flowing in a line, designations or codes to assign to the lines can be developed for each process. Some typical codes are:

RW	- River Water
TW	- Treated Water
SW	- Sea Water
BW	- Brackish Water
CW	- Chilled Water
S	- Low Pressure Steam
S150	- 150 psi Steam
S400	- 400 psi Steam
V	- Vent or Vacuum
C	- Condensate (pressure may be indicated)
D	- Drain to sewer or pit
EX	- Exhaust
M	- Methane
A-	- Air (or PA for Plant Air)
F	- Freon
G	- Glycol
SA	- Sulfuric Acid
B	- Brine
Cl	- Chlorine
P	- Process mixture (use for in-process lines not definitely designated by other symbols)

Figure 14.17 (a) Special types of descriptive flowsheet symbols [9]. (b) Commonly used instruments flowsheets [9]. (c) Flow diagram symbols. Valves, fittings, and miscellaneous piping [9]. (d) Line symbols (By permission from ISA Std. S51—1973 and 1984).

      Sometimes it is convenient to prefix these symbols by L to indicate that the designation is for a line and not a vessel or instrument.

14.11 Materials of Construction for Lines

      The process designer must also consider the corrosive nature of the fluids involved when selecting construction of materials for the various process and utility service lines. Some designers attach these materials designations to the line designation on the flowsheets, while others identify them on the Line Summary Table (Figure 14.20d). Some typical pipe materials designations are:

CS40	- Carbon steel, Sch. 40
CS80	- Carbon steel, Sch. 80
SS316/10	- Stainless steel 316m Sch. 10
GL/BE	- Glass bevel ends
N40	- Nickel, Sch. 40
TL/CS	- Teflon-lined carbon steel
PVC/CS Polyvinyl chloride	- lined CS
PP	- Solid polypropylene (designated weight sch)

14.12 Test Pressure for Lines

      The process designer also needs to designate the hydraulic test pressures for each line. This testing is performed after construction is essentially complete and often is conducted by testing sections of pipe systems, blanking off parts of the pipe or equipment, if necessary. Extreme care must be taken to avoid over pressuring any portion of pipe not suitable for a specific pressure, as well as extending test pressure through equipment not designed for that level. Vacuum systems must always be designed for “full vacuum,” regardless of the actual internal process absolute vacuum expected. This absolute zero designed basis will prevent the collapse of