Flow 7 Diagrams

8/10/2019 Flow 7 Diagrams

1/12

Flow

Diagrams and

instrumentation

Flow diagrams describe in a schematic drawing format

the flow of fluids and gases through a unit or an entire

plant. By using symbols to represent various pieces of

equipment, the flow diagram provides the piping designer

with an overall view of the operation of a facility.

The flow diagram used in this chapter is representative

of the types used by many companies in the piping indus-

try. While actual symbols may vary slightly from one

company to the next, the "look and feel" of flow dia-

grams is the same throughout the piping industry.

Students must becom e fam iliar with the piping, equip-

ment, instrumentat ion symbols and abbreviat ions used on

flow diagrams, in order to be able to "read" and interpret

them.

One of the most difficult concepts for students to com-

prehend is the absence of scale in the preparation of flow

diagrams. The flow diagram should be laid out in a very

simplistic and logical order and be read from left to right.

It guides the drafter and designer in the same manner a

road map guides a traveler.

USES OF FLOW DIAGRAMS

The flow diagram is used by the piping group to

develop and lay out the plot plan. When developing the

plot plan, the arrangement of the equipment in the facility

TYPE OF FLOW DIAGRAMS

Process engineers are responsible for developing flow

diagrams. In many large engineering firms, an entire

department is dedicated to the development of flow dia-

grams. Today almost all flow diagrams are laid out with

CAD, using third-party piping packages such as Pro-

Flow or individually developed company packages.

Process Flow Diagram

The process flow diagram is the first flow diagram

developed by the flow diagram department. It includes

the following:

1. major eq uipment

2. main piping

3. direction of flow

4. operating pressure and temperature

5. major instrumentat ion

The process flow diagram will denote the following:

9 Cond itions to be used for the design of various

pieces of equipment (fract ionation columns, pumps,

heaters, etc.) required for facility operation.

9 Operating and design condit ions under which a par-


2/12

2

Pipe Draftingand Design

Figure 7-1 shows a sample process f low diagram.

Mechan ical Flow Diagram

From the process f low diagram, the mechanical group

develops the mechanical f low diagram. The mechanical f low

diagram provides much more detailed data than the process

flow diagram. Man y co mpanies refer to the mechanical f low

diagram as the "P & ID" (process and instrument diagram).

Often referred to as the bible of the design process, this

drawing provides the pipe drafter with the design criteria for

the unit. Mechanical flow diagrams include the following:

1. pipe l ine numbers and direction of f low

2. pipe specif ications and l ine sizes

3. all equipment

4. all valves

5. all instrumentation with controll ing devices

The mechanica l f low d iagram def ines the exact

sequence in which a l l equ ipmen t , va lves , ins t rumenta t ion ,

connect ions , e tc . , a re to be made on each p ipe th roughout

the facility.

Figure 7 -2 shows a sample o f the mechanica l f low

diagram.

The Uti l i ty Flow Diagram

The uti l i ty f low diagram shows the piping, valves, and

instrumentation for the basic plant uti l i t ies. Util i t ies are

services that are essential to the proper function of the

plant. These uti l i t ies correspond to some of the same uti l-

i t ies used in a typical house, such as water , gas, and sewer

drains.

Some of the common plant uti l i t ies are:

9 s team

9 fuel oil

9 instrument air

9 drainage systems

9 condensa te

9 utility air

9 coo l ing water

9 f lare syste m


3/12

F

w

D

a

a

m

a

n

u

m

a

o

1

.

0

.m

~

t

c

(

D

E

(

D

r

0

.

E

0c

t

a

,

L


4/12

114

Pipe Draftingand Design

The flow diagram is a dynamic docum ent. It may be revised

and updated during the project to reflect the client's changes o r

modifications imposed by governmental regulations.

Figure 7-3 shows a sample utility flow diagram.

FLOW DIAGRAM INSTRUMENTS

Instruments function by sensing changes in the vari-

ables they monitor. The four basic instrument groups are"

Flow (F)

Level (L)

Pressure (P)

Temperature (T)

The types of instruments used to sense, control and

monitor these variables are:

Controller (C)

Indicator (I)

Gauge (G)

Alarm (A)

Recorder (R)

By learning these nine terms, students will be able to

understand most of the instrument symbols found on a

mechanical flow diagram.

Figure 7-4 i l lustrates a combination of the symbols and

abbreviat ions used to represent an instrument 's function

on flow diagrams. The first letter in the symbol indicates

the instrument group, and the second and/or third letters

indicate the instrument type.

To indicate a change or to control the flow, level, pres-

sure, or temperature, an instrument must first sense a

change in the variable. Once a change has been detected,

the instrument then transmits this information via

mechanical , electronic, or pneumatic means to a control

panel where i t can be observed and recorded. At the sam e

time, the instrument may activate other devices to affect

and change process conditions in the facility. Some

instruments are read in the plant at the instrument's actual

location. Others are displayed on a control panel located

in an operator 's control room.

Instrument Types

Gauges. Gauges are instruments that measure the l iq-

uid level inside a vessel or the temperature and/or pres-

sure in the piping system. Level, temperature, or pressure

gauges are locally mounted to enable plant operators to

obtain a visual reading.

HOT OIL

TO & FROM

E-101

COOUNC 1

ATER

TO & FROM

E-102

,,

PSV-2

TO FLARE

FROM V-102

-r


5/12

Flow Diagramsand Instrumentation

11w

r )

L O C A LL Y M O U N T E D IN S T R U M E N T

BO A R D M O U N T E D IN S T R U M E N T

FLO W I N S T R U M E N T S

F ~ ) F L O W , ~ ~ ,

FL O W E L E ME NT

- )

F L O W N D IC A TO R

FR F L O W R EC O R D ER

FRq F L O W R E C O R D I N G C O N T R O L L E R

L E V E L I N S T R U M E N T S

@

_C

J

, G )

L E V E L A L A RM

L E V E L A L A R M H I G H

L E V E L A L A RM L O W

L E V E L C O N T R O L L ER

LEVEL GLASS

T E M P E R A T U R E

T ~ )

TI

T F

C

I N S T R U M E N T S

T E M P E R A TU R E A L A R M

TE MP E RA TURE I ND I CA TO R

T E M P E R A T U R E R E C O R D E R

T E M P E R A T U R E R E C O R D I N G

CO NTRO L L E R

T E M P E R A T U R E W E L L

P R E S S U R E

~C

@

(~)

Pl(

@

~V RELIEF VALVE

I N S T R U M E N T S

P R E S S U R E C O N T R O L L E R

P R E S S U R E I N D I C A T O R

P R E S S U R E R E C O R D E R

P R E S S U R E I N D I C A T I N G

CO NTRO L L E R

P R E S S U R E R E C O R D I N G

CO NTRO L L E R

P R E S S U R E S A F E T Y V A L V E


6/12


7/12

Contro l le rs . Devices used to main ta in a spec i f ied l iq -

uid level, temperature, pressure, or f low inside a vessel or

piping system. They activate the control valve that regu-

lates the level, temperature, pressure, and f low in and out

of the vessel .

Alarms. Signals v ia l igh ts o r horns tha t ind ica te the

liquid level, temperature, or pressure inside a vessel is too

high or too low or that there is no f low or reverse f low.

Ind ica tors . Devices used to ind ica te the l iqu id leve l ,

temperature, pressure or f low rate inside a piping system.

Recorders . Devices used to record the l iqu id leve l ,

temperature, pressure, and f low rate inside a vessel or

piping system throughout a certain shif t or period of t ime.

These same inst ruments may be found in combinat ion

such as Level Recording Controller . Here the instrument

not only records the l iquid level but also sends a signal to

a control valve to control the l iquid level inside the vessel .

PIPING SYMBOLS

Figure 7 -5 shows some f low d iagram p ip ing symbols .

Notice all valves, no matter the pipe size and pound rat-

ing, are drawn the same size. Generally, nozzles and

reducers a re no t shown on the mechanica l f low d iagram.

The f low d iagram in Figure 7 -2 shows reducers in o rder

to aid the students in visualizing and understanding the

flow diagram and its relationship to the actual piping

ar rangement d rawing . Symbols used on f low d iagrams

represen t the ac tua l p iece o f equ ipment . Typica l ly these

Flow Diagramsand Instrumentation 117

symbols have some resemblance to the ac tua l p ieces o f

equipment in the f ield.

FLOW PLAN ARRANGEMENT

The f low plan should be arranged in a logical order of

f low. The main f low through the unit should be obvious

by even a brief examination of the f low plan. Use the

fo l lowing check l is t as an a id when develop ing a f low

diagram.

9 Avoid crossing l ines where possible.

9 Space equip ment on the sketch to avoid overcrowding.

9 Use no tes w i th symbols w here necessary fo r c la r ity .

9 Use arrows to show flow direction.

9 Show equipment numbers when i t i s necessary to

iden t i fy equ ipment .

9 Show control sy stem s on the sketch. The control

scheme is f requent ly the most impor tan t par t o f a

f low plan sketch.

9 Show important valves, or if ice f langes, and control

valves.

9 Show f low d i rec tions th rough exchangers wi th

a r r ows .

9 Do not run l ines diagonally across the drawing.

9 Lab el feed l ines e ntering the u nit from the f ield

where the l ine enters the unit . Label product l ines

leaving the unit by name.

9 Do not draw lines any closer together than necessary.


8/12

8 Pipe Drafting and Design

CHAPTER 7 REVIEW QUIZ

1. List f ive i tems shown on the process f low diagram.

2. List f ive i tems shown on the mechanical f low diagram.

3. List the four basic instrument groups.

4. List the f ive instrument functions.

5. What type of instrument is used to maintain a certain l iquid level?

6. Identify the following instrument abbreviations"

a . L G

b. FA

c. TI

d. PC

e. TRC

f. LC


9/12

EXERCISE NFORMATION

Use the instructions accom panying Figure 7-6 to create

the flow diagram symbols with AutoCAD as shown. Use

the BASE command to place the base point as indicated.

BLOCK each objec t us ing the exact symbol name pro-

vided. OOPS the symbol to redisplay. SAVE the drawing

a s F L O S Y M B L .

Flow Diagrams and Instrumentation 119

Exercises 1 2 and 3

Recreate the flow diagrams as shown. Using the

symbols in Figure 7-6 where applicable. Symbols repre-

senting other pieces of equipm ent can be developed on an

as-needed basis. Although equipment is not drawn to

scale, i t should be proport ional to the other symbols used

in the drawing.

F LO W S H E E T S Y M BO L S

TO D RAW FLOW SHEET SY MBOLS SET GRID TO .125 AND SNAP TO .0625

THE .125 GRI D SH OW N BEL OW HAS BEE N ENL ARGE D FOR BETTER VISUALIZATIION.

DRAW AND BLOCK EACH SYM BOL. BASE POINT ( } i ~ ) &

%

SYMBOL NAME L AME] HAVE BE EN INC LUD ED FOR PRO PER IDENTIFICATION.


10/12

1

P

i

p

D

r

a

n

a

D

e

g

C

7

D

W

I

N

E

S

I

J

m

0n

I

J


11/12

F

o

w

D

a

a

m

a

n

u

m

a

o

1

1

1

r

c

1

1

1

X

1

1

1


12/12

P

i

p

D

r

a

n

a

D

e

g

c

L

ur

o

t

r

L

U

XU

J

Date post:	02-Jun-2018
Category:	Documents
Upload:	ine-florez-palacioz
View:	230 times
Download:	0 times

Flow 7 Diagrams

Documents