API instrumentation unit 1

The higher the level of liquid in a tank, the greater the pressure at the bottom of the tank, A change in pressure at the bottom of the tank may also be used to indicate a change in liqu

INSTRUMENTATION FOR OPERATORS

Unit 1 Measuring Instruments

Section 1

Pressure Instruments

Instrumentation for Operators has been designed to give you, the operator, a feeling of how instrumentation plays its role in the efficient operation of a refinery The program is developed

in three units Unit One will familiarize you with many of the more common measuring instruments—how they work, when they are used and how they are protected from damage Unit Two will show you how the instruments are used in the control of a process, Finally, Unit Three integrates the ma- terial taught in Units One and Two and familiarizes you with controllers and modes of control

UNIT ONE

In Section 1 you will learn about pressure as an operating variable and how instruments are used to measure pressure Instruments covered include the barometer, manometer, bour- don tube, diaphragm and bellows gage

Tn Section 2 you will learn about temperature as an operating variable and temperature-measuring instruments You will learn the principles of the expandable-element thermometer, bimetallic thermometer and electrical thermometer

INSTRUCTIONS

This is a programed learning course

Programed learning gives information in a series of steps

called frames Each frame gives some information and asks

you to make use of it

Here is how it works First, cover the response column at the

right with a mask

Read this frame and use the information it gives to fill in the

Move the mask down to uncover the word at the right of the

frame If you have filled the blank with that word or a word

that means the same, you are ready to go ahead to the next

frame

The drawing of a micrometer provides information that will

help you fill in the next blanks

CAP

FRAME

Seven major parts are shown in the drawing, but only

object to be measured

small

anvil; spindle

The next frame calls fora choice Circle or underline the ap-

propriate word

Of the two parts that contact the object, only the (anvil/

spindle) moves

A program is a series of frames that work like the ones you

have just done:

Read the frame

Use the information to fill in the blanks or make a choice

Move the mask down and check the response column

Go on to the next frame,

Remember to cover the response column with a mask before

you begin each page

spindle

AN INTRODUCTION TO INSTRUMENTATION

FOR OPERATORS

1 Petroleum products like gasoline and lubricants are

made from crude oil

To be turned into fuels, lubricants, petrochemicals and

other praducts, the crude oil is , refined, or processed

2 Crude oil is processed in various pieces of equipment;

the equipment used depends on the products being

made,

PRODUCT

PRODUCT

— KEROSINE PRODUCT

—GAS OIL PRODUCT

— REDUCED CRUDE PRODUCT

For example, this fractionating unit takes crude oil

3 Crude oil is a mixture of many hydrocarbons, ranging

from asphalt, which boils at a high temperature, to

gasoline, which boils ata _. _ temperature low

=4, Many hydrocarbon products, for example kerosine,

have boiling ranges between those of asphalt and gaso-

line,

Kerosine has a ([] higher/[] lower) boiling range higher

than gasoline

Mixture ([] A/[] B) boils at the lower temperature

To separate gasoline out of a gasoline-kerosine mix-

ture by boiling, the mixture must be heated to the

right temperature

If the temperature is too (1) high/[] low) the gasoline

will not boil and vaporize

If the temperature is too the kerosine

will boil and vaporize with the gasoline

If the process is to be continuous, more gasoline-kero-

sine mixture must enter the process as

is separated out

To make sure that there is enough _— to

continue the process, the flow rate of feed into the unit

must be carefully controlled

If the mixture is being vaporized in a closed unit, the

can’t escape as the mixture is boiled

Pressure then ({{] increases/L decreases) in the closed

unit

When pressure increases, the boiling temperature in-

creases,

To boil gasoline at this increased pressure, the tempera-

ture must ((] increase/[ decrease),

Which of the following affect the separation of petro-

leum products:

temperature (E1 res/L] no)

feed rate (DC yes/Ƒ] no)

Pressure, temperature, and feed rate are three key

variables in any fractionating process

A condition which is changeable is called a

variable

15 Liquid level also affects a proeess

The liquid level in these two situations ((] affects/

16 Iäquid level ([] is/[] is not) a variablein refinery is

Running over a tank is hazardous, wastes gasoline,

18 The liqud_————— in a tank or other process level, or height vessel must be controlled

18 Process variables are related to each other

Heating water in a boiler causes its temperature to

rise The pressure inside the boiler also increases

20 Temperature and changes in a system pressure are directly related to each other,

21 When gas or liquid is heated in a closed space, its pres-

Liquid flows from ([] A te B/[] B to A) Ato B

24, Pressure is related to flow rate

The larger the pressure difference, the ([] higher/

ˆ

2B Liquid exerts pressure on the bottom of its container

Pressure near the bottom of an open container đepends

on the height of the in the container liquid, or level

26 A measurement of pressure at the bottom of the con-

tainer can be used to đetermine liquid —_———— level, or height

27 Liquid level can be determined by measuring the

at the bottom of the tank, pressure

28 The amount of pressure exerted by a liquid and gas

in a closed tank depends on which of these three

variables?

flow of liquid into the closed tank (F]ys/T]1 no) yes

29 When gas or liquid fiows in a pipe, its pressure de-

creases as it flows

A pressure change can be used to indicate the

of gas or liquid flowing amount, or direction

The higher the level of liquid in a tank, the greater

the pressure at the bottom of the tank,

A change in pressure at the bottom of the tank may also

be used to indicate a change in liquid

Liquid level and flow rate measurements can be in-

dicated by measuring changes in a

system,

One process variable ([] is/[] is not) related to the

other process variables

Refinery equipment is complex and expensive

Without help, a man can’t keep track of all the tem-

peratures, pressures, levels, and flow rates, and at the

same time keep these variables from —

too much,

Instruments such as flow meters, pressure gages, and

thermometers are more_———— — than man

senses alone

Some instruments show the operator the state of the

process at the moment he looks at it

1200° Fo

He can look at the dial and at the clock and see that

at 1 p.m the temperature of the process is _° F

But, at 2 p.m the same instrument can’t tell him what

the temperature was at 1 p.m,

The instrument measures and indicates; it ((] records/

(9 does not record)

A pen and graph paper can be added to the same in-

38

39

40

Let’s say that pressure is so crucial that a unit can

go off specifications if pressure increases even a small

amount

The pressure in this unit needs to be ([] automatically/

DD operator) controlled

After all, you can’t watch the pressure gage every

second of every hour

Vital processes are normally controlled (J automatic-

ally/(] manually)

The diagram below represents a fractionating unit

Each box indicates a pressure, temperature, or flow

rate which must be maintained at the exact value

shown in the box It is 2 a.m., rainy, and cold You

have a headache and your replacement is 20 minutes

GIN: EN

The molecules in a gas or a liquid move rapidly in

(E] one direetion/[| all direetions)

.2 This tank is filled with molecules of butane gas

These molecules strike each other and the — > _

of the tank,

3 When molecules hit something, they exert a force

The faster the molecules move, the more Shae

4, As more molecules strike an object, they exert a

(L1 greater/[] smaller) amount of force

5 The heavier the molecules, the ({ greater/[] smaller)

10

the amount of force they exert

The amount of force which molecules exert depends on:

the of the molecules,

the_— _— _ of moleeules striking the object,

and

the ———— _ of the molecules

Pressure is force on a specific area

”

nh SS _ v7 '

This block acts on an area of — square

inch

Pressure ean be described as the amount of

exerted on one square inch

Measuring the force of molecules striking a square

inch is one way of measuring

The amount of pressure which molecules exert depends

11 Pressure is usually measured in pounds on one square

inch,

Pounds per square inch (abbreviated psi) is the

_ of the molecules exerted on one square

inch,

12, This block is lying on a table

The molecules are exerting force on an

of one square inch of the table

18 Now stack another block on top of the original block

The pressure at the bottom ([J increases/(] decreases)

14, The taller the block, the ((] greater/(] smaller) the

amount of pressure it exerts

15 Thus, a taller block exerts (() more/{] less) pressure

than a shorter block of the same material

16 If the block is made out of lighter material, it exerts

——_/_ foree on one square inch than the

17, Which of these containers exerts more pressure?

19 The pressure a substance exerts depends on:

20 Since the molecules of gases and liquids move in all

directions, they exert force in all directions

Pressure is exerted in (L] one đirection/E] all điree-

13

31 The atmosphere is a “blanket” of gases which sur-

rounds the earth This height of atmosphere exerts

14.7 pounds of pressure on each square inch of earth

uw ATMOSPHERE

Atmospheric pressure is _ pounds per square

inch (psi) at sea level

22, If the atmosphere were deeper, atmospheric pressure

would be ([] more than/[] less than) 14.7 psi

23 Look at the drawing

ATMOSPHERIC PRESSURE

At the top of the mountain, the height of the atmos-

phere is ({) more/f less) than its height at sea level

24 Thus, the pressure that the air exerts depends on the

of the air

25 At the top of the mountain, atmospheric pressure is

(CJ more/ less) than 14.7 psi

Since liquids cannot be squeezed, this pressure makes

some of the tank liquid . _into the tube

connected to the tank

The higher the pressure, the ([E] higher/[] lower) the

level of liquid in the tube

If the piston is pulled back up, the liquid (7 stays in

the tube/{J runs back into the tank),

Iis. ———_— that supports the liquid in the tube

82 Atmospheric pressure can also support liquid in a tube

ATMOSPHERIC

If there is no pressure at the top of the tube (vacuum),

the pressure of the ———— — pushes liquid up

into the tube

33 If the tube were open at the top, atmospheric pressure

would push down there too

The liquid ([] would/[] would not) move up in the

tube

34 The liquid moves only if there is a difference in

85 The liquid moves from a (Ƒ] high/[] low)-pressure

area to a (] high/L] low)-pressure area

HOW PRESSURE IS MEASURED

liquid metal) ; the tube is turned over into the dish

Some of the mercury runs out of the tube and into

There ((] is/{ is no) pressure in this space is no

Since there is no pressure in this space, no downward

pressure is exerted on the mercury in the ([j tube/

Since the mercury can’t be squeezel,_———————-

pressure forces some of the mercury to rise up into

the tube

Repeated testing has shown that 14.7 psi of pressure

supports a column of mercury 30 inches high

If the atmospheric pressure decreases, the column of

mercury is ([] more/[ less) than 30 inches

This is the barometric pressure that a weatherman

talks about

When he says that the barometer is rising he means

that atmospheric pressure is ([7] increasing/D decreas-

Tt takes (7a lot of /[) relatively little) pressure to hold

the mercury up in the tube

14.7 psi can support more ([] water/[] mercury)

To measure atmospheric pressure, you need more

(J water/C] mercury)

By using mercury instead of water, a barometer tube

can be made much ([] shorter/] taller)

A barometer indicates pressure as the

The Manometer

48 Let’s take a barometer, cut off the end, and bend it

into a U-shaped tube (manometer)

50 The Hquid ([] moves/[] will not move)

ð1 The liquid level is ([] the same/[] đifferenf) on each

side

52, One end of this manometer is hooked into a gas line

20 psi mm 14.7 PSI

‘The amount of pressure pushing down at Á is (] more/

(0 less) than the amount of pressure pushing down

When the liquid level increases or decreases, it indi-

cates that pressure is changing

The manometer measures the between

two pressures,

When the level is higher in side B, you know that pres-

sure is greater in ([] side A/L] side B)

When the level is the same on both sides, there is no

pressure

This manometer is measuring the difference between

the pressure in a process line and the pressure of the

atmosphere

The pressure at B is about psi,

Pressure is greater at (J A/( B)

Suppose the pressure in the process line decreases to

60 This manometer is measuring the pressure difference

between two tanks,

Pressure is greater in ({) tank A/Z tank B), tank B

61 You don’t know the pressure in either tank

Can the manometer tell what the pressure is in either

62 It can only tell you ———— —ỉn pressure differences

63, As pressure on one side of the manometer increases,

the mereury rises on the other side

40 PSI

14.7 PSI 20 PSI

As the amount of pressure difference increases, the

difference in level between the two sides === increases

64,

65

66

67

The manometer must be WE g enough to pre-

vent mercury from spilling out of the top

To measure large pressure differences, you need

Since manometer tubes are made from glass, the addi-

tional length needed makes them more

Manometers are impractical when they must be moved

around, treated roughly, or used in high-pressure ser-

When more air is pushed in than the walls of the bal-

Joon can support, the balloon

The most common kinds of pressure instruments work

on this expansion principle

Expandable-element gages have a part which moves

72 The bourdon tube is probably the most common of the

expandable-element gages

| VALVE

ÚQ

t

The gage consists of a hollow, curved

made from flexible metal

78 One end of the tube is connected through a yalve to

the source of —_ :

74 Can a bourdon tube gage measure pressure in a frac-

tỉonating tower? ([] yes/[] no}

75 When the valve between the process and the bourdon

tube is closed, pressure in the tube is low and the tube

remains curved,

But when the valve is opened, pressure increases and

the tube tends to ([] curve more/[] straighten out)

By connecting the tube to a pointer, through a gear

train, pressure is indicated on a dial

Increasing pressure in the equipment causes the

This movement raises the _———— — eonnected to

the gear mechanism,

The gear turns to the right

The pointer moves toward the -hand

The dial shows an increase in pressure as the pointer

moves from ([Ị left to right/[] right to left)

Because this kind of bourdon tube is shaped like the

letter C it is sometimes calleda —_ -tube

Spiral ond Helix Bourdon Tubes

81

82

Metals and metal alloys are usually hard and not very

flexible

This means that the amount of end movement which

a bourdon tube can produce is relatively ([] large/

O small)

Tf a pressure change is very , the tube

83 The bourdon tube can be made more sensitive to small

For increased sensitivity, the shape and the

of the tube are changed

Compare these spiral and C-type bourdon tubes

eee

With a longer tube, the amount of end movement pos-

The spiral and the helix are preferred to the C-tube

for ([] high/[] low)-pressure service,

length

increased, or greater

low

86

87

88

89,

Like the mercury manometer, the bourdon tube is af-

fected by atmospheric pressure

Atmospheric pressure acts on the (f outside/(] in-

side) of the tube

If atmospheric pressure is greater than process pres-

sure, the tube ((] moves/(] does not move) because the

pointer mechanism is resting against the zero limit

stop

Atmospheric pressure offers resistance to movement

as the tube tries to ([] curÌ/[] straighten out)

Actually, the bourdon tube measures the difference be-

tween process pressure and_. _ _ — — — pressure

Using the Bourdon Tube

90 The chart shows a few of the metals from which bour-

don tubes are made

Material Characteristic

brass weakened by corrosive material

melts and ruptures in fire stainless steel resistant to damage from corrosion

Pressure readings on a hot oil line are being made with

a bourdon tube, ‘The oil contains sulfur,

The best tube for this process is probably made from

91, Stainless steel is expensive

A bourdon tube is not usually made out of stainless

steel if a less sd metal will perform as

well

92 The bourdon tube measures the difference between

process pressure and atmospheric pressure

Can this bourdon tube be used to measure the pressure

difference between two processes? ([]† yes/[] no)

The Diaphragm Gage

93 The diaphragm, gage is also an expandable-element

gage

FLEXIBLE DIAPHRAGM

27

expensive

no

diaphragm

Since the diaphragm is made of rubber or some

other flexible material, changes in pressure cause it to

The diaphragm does not move when the two pressures

are ([] the same/[] different)

The diaphragm gage reads in ([] absolute pressure/

differential pressure)

Look at this operating diaphragm gage

(] a Pressure is greatest in process A

b Pressure is greatest in process B

Cc Pressure is the same in both processes,

Diaphragm movement is transmitted to a pointer by

means of a linkage connected to the center of the

The size and thickness of the diaphragm determine

its differential-pressure range

For example, a very thin diaphragm would not be

used for ([{] high/({] low)-pressure differences,

101 Diaphragms can be made from very flexible materials,

and can be made to produce movement even for a very

small pressure change

Greater movement for a smaller change pressure

can be achieved with a diaphragm gage than with a

bourdon tube,

102 The (( diaphragm/{[ bourdon tube) gage is preferred diaphragm for services where pressure differences are small

The Bellows Gage

103 The bellows gage works on similar principles to the

diaphragm gage

25 PSI 1° PSI

i

Process pressure enters the bellows and tends to

([] compress/[] expand) the segments of the bellows expand

104 As the pressure increases, the segments expand more

This expansion, transferred through the linkage and

the pointer, is indicated onth _ _ dial, or scale

105 ‘The bellows has a larger area for the pressure to act

on than the diaphragm does

5 PSI

The bellows can move _ for small pres-

sure changes than the diaphragm can,

106 The bellows is generally ((] more/[ less) sensitive

and ([] more/[] less) accurate than the diaphragm

107, This bellows gage measures:

PROCESS PRESSURE

108 Bellows can be used to measure a difference in pres-

sure between two processes

When there is no pressure._ — between

process A and process B, the pointer indieates “0,”

109 If pressure is greater at A, the pointer moves to the

(OQ right/C left)

110 When both pressures are the same, the pointer points

Process pressure A pushes on the _ _ of the

bellows and pressure B pushes on the

113 When pressure B is greater than pressure A, the bel-

113 Which of these gages measure the difference between

process pressure and atmospheric pressure?

G (L] yes/] no) yes

32

114 Which of these gages can measure the difference be-

tween two process pressures?

115 Which one of these bourdon tubes shown below is more

sensitive to small pressure changes?

Operating Problems with Pressure Gages

Assume that permanent damage may be caused by pres-

sure greater than 150% of the range of the gage

Doubling the pressure the gage was made for ([J could/

( could not) permanently damage the gage

For example, the operating range of this gage is from

1 to 10 psi, 150% of the range is 15 psi

DANGER ZONE

The gage may be damaged if it is used at pressures

If a bourdon tube is used at a pressure above that for

which it was designed, it may rupture and become a

safety hazard

lt is important to know the — limit of

the tube

You must also know the pressure range of the

you are measuring,

Bourdon tubes are usually housed in a metal case

The caso — — the tube from đirt and the

weather

Tf a tube is over-pressured and ruptures, the process

fluid is released into the case

Pressure in the case ([] increases/() decreases)

This pressure build-up may cause the case to

‘The case may be fitted with a blow-out disc to protect

against over-pressuring This dise ig mounted in the

back of the gage to prevent glass from blowing into

the operator's face

BLOW.OUT DISC

When pressure increases in the casing, the flexible

: is forced out of the housing,

By releasing the excess pressure to the atmosphere,

the disc prevents a 2

A bourdon tube may be connected in a process which

contains material which could damage the gage

If a bourdon tube is directly connected to a steam line

without proteetion, hot —— — — passes directly

into the tuhe

The temperature of the gage increases

Excessively high temperatures —_ — —— metal

parts,

High temperatures also cause metal parts of the gage

to ([] expand/L] contract) and to change the tube

characteristics

If this happens, the gage is no longer

Gages sometimes break because they expand or move

too far

The gage may be equipped with safety devices to pro-

tect the gage from — too much

131

132

133

134

Over-range protection usually consists of a mechanical

stop which . the moving part from mov-

ing too far

All these pressure gages have over-range protection

The over-range stop prevents the ele-

ment from moving too far

Under extremes of pressure (200% or more), -

stop devices can’t protect the gage

Gages must be properly connected to the process

lf the conneetion is too loose,a_——— may

develop at the point where the gage is coupled to the

When liquid or gas leaks from the system, pressure

readings are inaccurate; thus all connections to the

gage must be

Teflon tape on the pipe threads can generally be used

to _ leaks

Do not loosen or tighten a gage by grasping the gage

by hand because the tube may be twisted out of shape

Always use an adjustable wrench on the flats

The reading taken from a twisted gageis_ _— _„

To measure pressure, the valves located between the

gage and the equipment must be open

D4

If the valve is closed, no. mmMWU from the line

is transmitted to the gage *

It may be necessary to close a valve when cleaning or

repairing a line If you must take a gage out, close

the block valve under it, and slowly unscrew the gage

Be sure the pressure bleeds to zero before taking the

gage completely out

To put the gage in service again, be sure to

the valve slowly

Lines to the gage must not be blocked

Plugged lines cause readings

Pulsation in pressure (rapid swings back and forth)

causes excess movement of gage parts

Too much movement causes moving parts to

A dampening device smooths out pulsations or rapid

148 Excessive vibration has the same effect as pulsation

Vibration can also cause you to make an inaccurate

reading because a vibrating needle is difficult to

read

144, Vibration, like pulsation, can be corrected with a

145 A gage may be coupled to the process pressure remotely

The vibration of the equipment has the least effect on

146, To prevent the effects of vibration, a gage may be

mounted - —— — — from the equipment, remotely, or away

How are Gages Sealed?

147 Some process materials damage the metals used in

pressure gages,

gage, or bourdon tube, ‹ pressure element

38 [Now tum the pe

In such cases, the process fluid must not be allowed

to contact the