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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 on the piping drawings.

Figure 14.18 Examples of line numbering.

Figure 14.19 Use of alphabetic suffixes with line symbols.

Figure 14.20a Line schedule.

Figure 14.20b Pipe line list.

Figure 14.20c Line schedule sheet.

Figure 14.20d Line summary table.

Suggested guides for line identification for any one principal fluid composition:

1 1. Main headers should keep one sequence number (Figure 14.18).

2 2. New sequence numbers should be assigned:(a) Upon entering and leaving an item of equipment.(b) To take-off or branch lines from main headers.(c) To structural material composition of line changes.

3 3. Alphabetical suffixes should be used in the following situations as long as clarity of requirements is clear, otherwise add new sequence numbers.(a) For secondary branches from headers or header branches.(b) For by-pass lines around equipment, control valves, etc. Keep same sequence number as the inlet or upstream line (Figure 14.18).(c) For identical multiple systems, piping corresponding identical service items, and lines.

In order to coordinate the process flowsheet requirements with the mechanical piping specifications, Line Schedules are prepared as shown in Figures 14.20a through d. The complete pipe system specifications are summarized by codes on these schedules.

Equipment code designations can be developed to suit the particular process, or as is customary a master coding can be established and followed for all projects. A suggested designation list (not all inclusive for all processes) for the usual process plant equipment is given in Table 14.4 and process functions in Table 14.5. The various items are usually numbered by type and in process flow order as set forth on the flowsheets. For example:

Table 14.4 A system of equipment designations.

AD	- Air Drier
AF	- Air Filter
Ag	- Agitator
B	- Blower
BR	- Barometric Refrigeration Unit
C	- Compressor
CP	- Car Puller
CT	- Cooling Tower
CV	- Conveyor
D	- Drum or tank
DS	- Desuperheater
E	- Heat Exchanger, condenser, reboiler, etc.
Ej	- Jet Ejector
Ex	- Expansion Joint
F	- Fan
FA	- Flame Arrestor
Fi	- Filter (line type, tank, centrifugal)
GT	- Gas Turbine
MB	- Motor for Blower
MC	- Motor for Compressor
MF	- Motor for Fan
MP	- Motor for Pump
P	- Pump
PH	- Process Heater or Furnace
R	- Reactor
S	- Separator
St	- Strainer
ST	- Steam Turbine
Str	- Steam trap
SV	- Safety Valve
Tr	- Trap
V	- Valve
VRV	- Vacuum Relief Valve

Item Code	Represents
C-1a	Three compressors of identical size operating in the same process service, connected in parallel.
C-1b
C-1c
C-2	Single compressor in different service (by fluid or compression ratio) from C-1’s above. S-1 First separator in a process
S-2	Second separator in a process
S-3a	Two identical separators connected in parallel, in the same process service.
S-3b

Some equipment code systems number all items on first process flowsheet with 100 series, as C-101, C-102, P-106 to represent compressors number 101 and 102 in different services and pump 106 as the sixth pump on the sheet. The second sheet uses the 200 series, etc. This has some engineering convenience but is not always clear from the process view.

To keep process continuity clear, it is usually best to number all like items sequentially throughout the process, with no concern for which flowsheet they appear on. Also, another popular numbering arrangement is to identify a system such as reaction, drying, separation, purification, incineration, vent, and cooling tower waters and number all like process items within that system for example:

Table 14.5 Typical identification for flowsheet process functions.

AS	- Air Supply
BD	- Blowdown
BF	- Blind Flange
CBD	- Continuous Blowdown
CD	- Closed Drain
CH-O	- Chained Operated
CSO	- Car Seal Open
CSC	- Car Seal Closed
DC	- Drain Connection
EBD	- Emerg. Blowdown Valve
ESD	- Emerg. Shutdown
FC	- Fail Closed
FO	- Fail Open
HC	- Hose Connection
IBD	- Intermittent Blowdown
LO	- Lock Open
ML	- Manual Loading
NC	- Normally Closed
NO	- Normally Open
OD	- Open Drain
P	- Personnel Protection
QO	- Quick Opening
SC	- Sample Protection
SO	- Steam Out
TSO	- Tight Shut Off
VB	- Vacuum Breaker

Reactor System, R:	Reactor is RD-1
Reactor vent cooler is RE-1
Reactor vent condenser is RE-2
Reactor recycle pump is RP-1
Level control valve is RLC-1
Relief valve is RSV-1

Then, establish the same concept for all other unit or block processing systems. This is often helpful for large projects, such as refinery or grass roots chemical processes. Valve identification codes are usually used in preference to placing each valve specification on the flowsheet. This latter method is feasible for small systems, and is most workable when a given manufacturer (not necessarily the same manufacturer for all valves) can be selected and his valve catalog figure number used on the flowsheet. For large jobs, or where many projects are in progress at one time, it is common practice to establish valve specifications for the various process and utility services (see Figures 14.21 and 14.22) by manufacturers’ catalog figure numbers. These are coded as V-11, V-12, V-13, etc., and such code numbers are used on the flowsheets whenever these valves are required (also see Figures 14.8 and 14.9). By completely defining the valve specification in a separate specification book the various valves—gate, globe, butterfly, plug, flanged end, screwed end, welding end—can be identified for all persons involved on a project, including piping engineers and field erection contractors.

Figure 14.17c summarizes a system for representing components on the flowsheets. The instrument symbols of Table 14.6 and Figures 14.18a and b are representative of the types developed by the Instrument Society of America and some companies.

Figure 14.21 Typical valve codes and specifications. By permission, Borden Chemicals and Plastics Operating Ltd. Partnership.

Some other designation systems indicate the recording or indicating function in front of rather than behind the instrument function. For example:

RTC-1,	Recording Temperature Controller No. 1
VRTC-1,	Control Valve for Recording Temperature Controller No. 1
RFM-6,	Recording Flow Meter No. 6
ORFM-6,	Orifice flanges and plate for Recording Flow Meter No. 6
OTrRFC-1,	Orifice flanges and plate used with Transmitter for recording Flow Controller No. 1
TrRFC-1F,	Flow Transmitter for Recording Flow controller No. 1
IPC-8,	Indicating Pressure Controller No. 8
IFC-6,	Indicating Flow Controller No. 6
IFM-2,	Indicating Flow Meter No. 2
RLC-,	Recording Level Controller
RLM-,	Recording Level Meter
ILC-,	Indicating Level Controller
LC-,	Level Controller
PC-,	Pressure Controller

Control valves carry the same designation as the instrument to which they are connected. Thermocouples carry the same designation as the recorder or indicator to which they are connected. Sequential point numbers are indicated thus (see Table 14.6):

RTM-6-4,	Thermocouple connected to point No. 4
RTM instrument No. 6. Also see Figure 14.9.

Additional symbols include:

PG-6,	Pressure Gage No. 6 connected in the field on some item of equipment. If panel board mounted, it becomes-6B.
LTA-1,	Low Temperature Alarm No. 1
HTA-1,	High Temperature Alarm No. 1
LPA-2,	Low Pressure Alarm No. 2
HPA-2,	High Pressure Alarm No. 2
LLA-6,	Low Level Alarm No. 6
HLA-8,	High Level Alarm No. 8
PG-,	Push Button

Figure 14.22 Partial presentation of piping materials specifications for a specific process service. By permission, Borden Chemicals and Plastics, Operating Limited Partnership.

Process flowsheets do not normally show companion flanges for valves unless these serve as blinds or for orifice plates. This detail is sometimes shown on the piping flowsheet, but here again the use of detail, which does not contribute to the communication function of the sheets, is avoided. Such detail can be time consuming when considered over the entire set of sheets for a process. Figures 14.7 and 14.9 are typical of reasonably good presentation without unnecessary detail. Such specifications as heights of a seal leg, locked open valve, or other information not summarized elsewhere must be recorded on the flowsheets.