target="_blank" rel="nofollow" href="#ulink_5d338473-d061-5b5d-ba20-861b95f7bee2">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 pipe and equipment should internal conditions vary. Some line design systems include the test pressure in the line code, but this often becomes too unwieldy for drafting purposes.
The usual complete line designation contains the following: (1) line size (nominal); (2) material code; (3) sequence number; and (4) materials of construction (see and Figures 14.18 and 14.20a–d).
| Examples: | 2″-CL6-CS40 |
| 3″-CL6a-CS40 | |
| 4″-RW1-CS40 | |
| 16″-S150-CS40 | |
| 3″-P-TL/CS |
Some engineers rearrange the sequence of the code although the information remains essentially the same. The line number sequence is conveniently arranged to start with one (1) or 100 for each of the fluid designations (CL, P, etc.). Since the sequence numbers are for coordination purposes and will appear on piping drawings, Line Schedule (Figure 14.20a through d), the number has no significance in itself. It is convenient to start numbering with the first process flow sheet and carry on sequentially to each succeeding sheet. Sometimes, however, this is not possible when several detailers are preparing different sheets, so each sheet can be given arbitrary beginning numbers such as 100, 300, 1000, etc. Although the sequential number may be changed as the line connects from equipment to equipment, it is often convenient to use the system concept and apply alphabetical suffixes to the sequence number as shown in Figures 14.18 and 14.19. This contributes materially to the readability of the flowsheets. Each line on the flowsheet must represent an actual section or run of piping in the final plant and
