M7-Drawings and Diagrams

Abu Dhabi Gas Liquefaction Company Ltd

Basic Maintenance Technician Course

Module 7

Drawings and Diagrams

ADGAS Personnel & Training Division

Personnel & Training Division Basic Maintenance Technician

Drawings and Diagrams/Rev. 1.0 of 61

Contents Page No. Abbreviations and Terminology ................................................ 4 1 Introduction ………………………………………………………….. 5 2 Engineering Drawings…………………………………………....... 7 3 Electrical Circuit Diagrams………………………………………... 11 4 Process Diagrams………………………………………..............… 15 4.1 Process Flow Diagrams (PFDs)…………………………... 18 4.2 Piping and Instrumentation Diagrams (P&IDs)………… 20 5 Title Blocks…………………………...........……………..............… 26 6 Pictorial Drawings………………………………………..............… 28 6.1 Oblique Drawings…………............................................... 29 6.2 Isometric Drawings…………............................................ 31 6.3 Freehand Sketching…………........................................... 33 6.4 Exploded Drawings…………............................................ 36 7 Orthographic Drawings………………………………………......... 37 7.1 Layout of Views………….................................................. 39 7.2 Types of Line…………...................................................... 45 7.3 Dimensions…………......................................................... 46 7.4 Sections…………............................................................... 48 7.5 Drawing Springs and Screws…………............................ 54 8 Piping Layout Drawings…………………………………............... 56 9 Summary………………………………….......................……......... 59

10 Glossary……………........................…………………………......... 60 Exercises 1 – 8............................................................................. 61



Pre-Requisite Completion of A.T.I. Maintenance Programme and ADGAS Induction Course

Course Objectives

The Basic Maintenance Technician Course is the first phase of the development programme intended specifically for the maintenance developee.

On completion of the Course the developee will have acquired an awareness of the equipment, terminology, and safety requirements related to the ADGAS LNG plant and Maintenance Training Workshops.

Module Objectives

On completion of this module, the developee will have an appreciation of the types of drawings and diagrams encountered by the Maintenance Technician.

He will be able to correctly :

• identify and state the purposes of engineering drawings, piping layouts, electrical circuit diagrams, PFDs and P&IDs

• identify information given in title blocks

• produce simple oblique and isometric freehand sketches

• identify and state the purposes of detail and assembly drawings

• identify types of lines used on orthographic drawings

• interpret information from simple orthographic drawings including sections and threaded components

• produce simple, dimensioned freehand orthographic sketches

Methodology The above will be achieved through the following:

• pre-test

• classroom instruction

• audio visual support

• tasks & exercises

• post-test



Abbreviations and Terminology

ANSI American National Standards Institute

BSI British Standards Institute

ISO International Standards Organisation

LNG Liquefied natural gas

P&ID Piping and instrumentation diagram

PFD Process flow diagram

R Radius

φ Diameter

Assembly A group of components fitted together

Component A part of a machine, electric circuit, etc.

Diagonal A sloping line, e.g. a line joining opposite corners of a square

Fittings (pipe) Items used to join sections of pipe, e.g. elbows, tees,

Flange Circular item for joining pipes or fitting pipes to equipment

Impurities Anything in a substance that stops it from being pure

Isometric A type of pictorial drawing

Legend A list giving the meanings of symbols used in a drawing

Liquefaction The process of turning something into liquid form

Oblique A type of pictorial drawing

Offset Not in line

Orthographic A type of drawing showing an object viewed from different directions, usually at 90o to each other, e.g. front, top, side

Projection A type of engineering drawing, e.g. isometric projection, orthographic projection.

Also the way that orthographic views are constructed by drawing horizontal and vertical lines between views.

Schematic A simplified diagram using symbols, particularly of an electric circuit

Signal A message, usually electrical, that causes something to happen



1 Introduction

Drawings and diagrams are one of the most important ways in

which engineers and technicians communicate.

They use international symbols instead of words wherever possible and are drawn

using rules, just like a language. If you understand the symbols and know the rules,

you can read most drawings and diagrams, whatever language you speak.

You can find all the rules and symbols that are needed to make and read drawings and

diagrams in International, National and Company Standards, e.g.:

• ISO (International Standards Organisation)

• ANSI (American National Standards Institute)

• BSI (British Standards Institute)

There is an important difference between a drawing and a diagram:

• A drawing shows the shape and size of an object or group of objects. Some

symbols may be used but, with practice, you can recognise the appearance of

an object from its drawing.

• A diagram, sometimes called a schematic, shows the flow of something and

what it flows through. This ‘something’ may be water, gas, electricity, or

anything else that can flow. It flows through pipes or wires and through

equipment such as pumps, instruments, resistors, etc. A diagram uses many

more symbols to represent objects than a drawing. It need not

show correct shape, size, distances or locations but does show

the correct order of equipment in the flow, i.e. what comes first, second, etc.

To represent is to stand in the place of something.

You communicate with someone when you give or receive information.



You will find that in practice, the word ‘drawing’ is often used to describe both

drawings and diagrams.

In this module you will look at the types of drawings and diagrams that you will see

while working as a technician for ADGAS. You will need to work with some more

than others, depending on whether you are a mechanical, electrical or instrumentation

technician. But, all maintenance technicians should be able to recognise all of these

types of drawings and diagrams. You should also know what type of information they

show and why they are needed.

The drawings described in this module are:

• engineering drawings (including piping layout drawings)

• electrical circuit diagrams

• process flow diagrams (PFDs)

• piping and instrumentation diagrams (P&IDs)

It is unlikely that any of you will have to produce these drawings but you will all need

to read drawings and make sketches at some time.

All technicians should be able to read engineering drawings as these are used to

describe the equipment you work with: pumps and compressors, electric motors and

switchgear, process instruments, etc.



2 Engineering Drawings

There are many types of engineering drawing and you will look at these in more detail

later in this module. Engineering drawings show the shape and size of an object and

can give enough information to make the object. They may also show how a group of

objects fit together to form an assembly. This information is important if you are

going to take something apart for maintenance and even more important if you want

to re-assemble it correctly afterwards.

The two main types of engineering drawings are:

• pictorial drawings

• orthographic drawings

You will easily recognise an object from a pictorial drawing. They show a single

view that is something like a photograph. Figure 2.1 shows a photograph of an object

and a pictorial drawing of the same object.

Pictorial drawings give a good general idea of what an object looks like but some

parts will always be hidden. If you want to make the object, or if you want someone

else to make it for you, these drawings do not show enough information unless the

object is very simple.

Figure 2.1: Pictorial Drawing and Photograph of a Casting



Orthographic drawings show the object looked at from different directions: the front,

top, side, etc. Each of these drawings is called a view and they are drawn on the same

sheet. Three views are enough for many simple objects but more can be added if

needed.

Figure 2.2 shows an orthographic drawing of something you will recognise.

Figure 2.2: Orthographic Drawing of Aircraft



Figure 2.3 shows an orthographic drawing of the object in Figure 2.1.

See how the three views are located in the orthographic drawing in Figure 2.3.

• The front is chosen to show the general shape most clearly. The front view is

what you see if you look from directly in front of the object.

• The top view, or plan, is what you see if you look directly down from above

the object. See how it is drawn exactly above the front view.

• The side view is shown on the right of the front view. That means it is what

you see if you look from that side (the right side).

This layout of the three views is called ‘third-angle orthographic projection’. This is

the layout you will find on most orthographic drawings.

Figure 2.3: Third-angle Orthographic Projection of Figure 2.1

CASTING

Top view

Side viewFront view



Orthographic drawings can show all the details and all the dimensions needed to make

the object. But, you need to look carefully at all the views and to use your

imagination to picture the final shape of the object from the drawing (Fig. 2.4).

Figure 2.4: Imagining an Object from an Orthographic Drawing

CASTING



3 Electrical Circuit Diagrams

Electrical circuit diagrams show the connections and components in an electric

circuit. Electrical technicians use circuit diagrams to build circuits, search for faults

when troubleshooting and to identify isolation points to make electrical equipment

safe for maintenance or removal.

Unlike drawings, circuit diagrams do not show you what the finished circuit looks

like. They show you the path of the electricity as it flows through components and

equipment and the order in which it flows through them.

They use lines to represent wires and symbols to represent equipment and

components.

Wires are drawn as single straight lines on the diagram.

If two wires cross but are not joined, so electricity can not flow from one to the other,

they may be drawn in two ways, as shown in Figure 3.1.

OR

If two wires are joined so that electricity can flow from one to the other, they are

drawn as in Figure 3.2.

OR

Figure 3.1: Crossing Wires

Figure 3.2: Joined Wires



Some common electrical symbols for equipment and components are shown in Table

3.1.

Symbol Component

Battery

Alternating current supply

Switch

Light bulb

Indicator lamp

or

Resistor (fixed value)

or

Resistor (variable) Capacitor

Earth

Motor

Transformer

Fuse

Circuit breaker

Transistors

The best way to read any diagram that shows the flow of something around a circuit is

to start at the point where the flow starts. For a circuit diagram, flow starts at a power

supply.

Table 3.1: Circuit Diagram Symbols



Figure 3.3(a) shows a drawing of a simple electric circuit with a battery of cells

supplying a lamp through a switch. Figure 3.3(b) shows a diagram of the same

circuit.

Can you identify:

• the battery

• the switch

• the lamp

in the circuit diagram?

(a) Drawing of Lighting Circuit (b) Lighting Circuit Diagram

Figure 3.3: Simple Lighting Circuit



Figure 3.4 shows a circuit for an amplifier

Can you identify:

• resistors?

• capacitors?

• transformer?

• transistors?

• where wires cross without connecting?

• where wires are joined?

Figure 3.4: Amplifier Circuit



4 Process Diagrams

The LNG liquefaction process on Das Island takes a mixture of gases coming from

the gas fields or from ADMA-OPCO, removes the impurities,

separates the gases and turns them into liquids for export.

The main product from the process is liquefied natural gas (LNG).

There are two types of diagrams that describe the gas liquefaction process on the

plant:

• process flow diagrams (PFDs)

• piping and instrumentation diagrams (P&IDs)

Both of these types of diagram show the flow of fluid through pipes

and equipment as the gas is processed.

The purpose of a PFD is to describe the changes that are made to the fluid and the

main items of equipment that make those changes.

The purpose of a P&ID is to describe the way the process is controlled.

Both types of diagram use similar lines and symbols.

A fluid is something that flows, like a gas or a liquid.

To export something is to sell it to another country.



Pipes and wires are drawn as straight lines.

Some of these lines are shown in Table 4.1.

Line Type of pipe or wire

Pipes carrying the main fluid being processed

Pipes carrying other process fluids, cooling water, refrigerant, etc.

L L L L Pipes carrying hydraulic fluid (water or oil) to operate valves etc.

// // // // Pipes carrying air to operate valves etc.

Wires carrying low-voltage electrical signals for controllers, switches, etc.

Two pipes that cross but are not joined, so that fluid can not flow from one to the

other, are drawn as shown in Figure 4.1.

Two pipes that are joined, so that fluid can flow from one to the other, are drawn as

shown in Figure 4.2.

Table 4.1: Lines on PFDs and P&IDs

Figure 4.1: Crossing Pipes

(a) Fluid from the vertical pipe joins the flow in the horizontal pipe

(a) Fluid from both horizontal pipes flows into the vertical pipe

Figure 4.2: Joined Pipes



Some examples of common symbols for process equipment are shown in Table 4.2.

Symbol Equipment

Vessel (typical)

Valve (typical)

Pump (centrifugal)

Heat Exchanger

Compressors (centrifugal)

or Turbine/turbo-expander

The meanings of the symbols used may be shown on the diagram sheet in a section

called the legend. This is normally on the right of the diagram sheet, in the area above

the title block (Section 5).

The size of the symbol does not tell you the size of the equipment. A small valve has

exactly the same size symbol as a big one.

The best way to read a flow diagram is to follow the flow, starting where the fluid

enters the diagram. You will normally see the fluid entering the process at the left of

the diagram and flowing from left to right. In the ADGAS process, where lighter

fluids (gases) are separated from heavier fluids (liquids), the lighter fluids flow

towards the top of the diagram and heavier fluids towards the bottom (Fig. 4.3)

Table 4.2: Equipment Symbols

General flow direction



Remember, diagrams show how the fluid flows through pipes and equipment but they

do not show you what the system looks like on the plant.

4.1 Process Flow Diagrams (PFDs)

PFDs are diagrams that describe a process. They show what is happening to the fluid

in the simplest way.

PFDs show:

• the path of the fluids as they go through a process or part of a process

• the main items of equipment in the process

• some important instruments and controls may be shown

• important temperatures and pressures in the process may be shown

Process flow diagrams are very useful for process operators, but everyone working for

ADGAS should know what the plant does and how it does it. All maintenance

technicians maintain the equipment that processes the gas. You should know what

job each item of equipment does in the process.

Figure 4.4 shows a PFD of the Train III production process on Das Island.

Figure 4.3: General Flow Directions

General product flow direction

Ligh

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Figure 4.4: Simplified PFD of Train III

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Can you identify:

• where the gas enters the process?

• different types of vessels and tanks—how many are there?

• pumps—how many are there?

• compressors—how many are there?

• heat exchangers—how many are there?

• where the main product (LNG) leaves the system?

• what other products does the process produce—where do they leave?

4.2 Piping and Instrumentation Diagrams (P&IDs)

P&IDs describe how the process equipment is controlled.

They show:

• pipes, hydraulic lines, instrument air lines, electric wires for instrument

signals

• equipment, valves, drain points

• instruments, where they are located and where their readings are displayed

• alarm, emergency shutdown and process control systems

P&IDs have many uses for the maintenance department as they identify equipment

and instruments and show where in the system you can find them. A P&ID does not

show you the exact place in the plant where these things are located but, if you follow

a pipeline from any point in the process, you will find everything in the same order as

it is shown on the diagram.

You should be able to locate the correct isolation valves and drain points on a P&ID

before working on any equipment in the plant.

Figure 4.5(a) is a drawing of the pipes and instrumentation on a small section of a

process.



Figure 4.5(b) shows the same information on a P&ID.

Look at this figure to see how the components shown on the drawing in Figure 4.5(a)

are represented on the P&ID in Figure 4.5(b).

(a) Drawing of Piping and Instrumentation

Figure 4.5: System Drawing and P&ID

(b) P&ID of the Same System



Three types of line are shown:

• main process line

• by-pass line around the pressure control valve

• control signal lines

Five valves are shown: they are different types (gate and globe valves) but the

symbols are similar.

They all use the same basic valve symbol with additions to show the

type of valve, e.g. for a ‘globe’ valve.

The pressure control valve, PCV 123, is operated by the control room pressure

recording controller, PIRC 123.

Instrument symbols are circles. They show where the instrument is located and

contain information to identify the instrument.

Instrument symbols are shown in Table 4.3.

Symbol Instrument Location

Mounted locally (fitted on or near the pipe or equipment where the reading is taken)

On a local panel (close to the pipe or equipment where the reading is taken)

Behind a local panel

On main control room panel

Behind main control room panel

Part of a computerised control system

Table 4.3: P&ID Instrument Symbols



Each item of equipment and instrument has its own identification made up of:

• letters at the beginning that identify the type of equipment or instrument, e.g.

pressure gauge, valve, etc.

• numbers that identify each item separately, as there are usually many similar

items in a process, e.g. there will be many pressure gauges with the same

identity letters but different numbers

• there may be more letters at the end that give other information

Some examples of typical identity letters are shown in Table 4.4.

Identification letters Instrument

FCV Flow Control Valve

LCV Level Control Valve

PCV Pressure Control Valve

PT Pressure Transmitter

PI Pressure Indicator

PRC Pressure Recording Controller

PC Pressure Controller

TI Temperature Indicator

Table 4.4: Instrument Symbols



If you look at Figure 4.5 you will see that there are five instruments shown:

(Figure 4.5 is repeated below)

• PI 123—Pressure Indicator

• TI 123—Temperature Indicator

• PT 123—Pressure Transmitter

• PIRC 123 —control room Pressure (Indicating and) Recording Controller

• PCV 123—Pressure Control Valve

You can see where these instrument are located by their symbols:

• PI 123; TI 123; PT 123 and PCV 123 are mounted locally on the pipes

• PIRC 123 is panel-mounted in the main control room

• PCV 123 is a valve. Because it is automatically controlled from PIRC 123 it

is a part of the instrumentation system so it is identified in an instrument

circle

Notice that the P&ID is not exactly the same shape as the drawing in Figure 4.5(a).

Now try Exercise 1 & 2



Figure 4.6 shows a P&ID of the plant simulator located at the ADGAS Training

Workshop.

This system pumps water from one drum to another and back again. The water can be

heated in drum 01-X-D-02. Because the fluid can flow in both directions, this

diagram does not follow the general rule of flow from left to right.

Your instructor will take you to the simulator where you can follow the flow of the

fluid on the P&ID and in the plant. Identify all the items shown on the P&ID and find

them on the plant simulator.

Now try Exercise 3

Figure 4.6: P&ID of Plant Simulator

M

M

S

S

S

S

SCALE ISSUE DATE REMARKS DRN ENGCHK

HV10

NOTES:

1. LSL-01/02 STOPS 01-X-G-01/02 RESPECTIVELY

2. HIGH PRESSURE ON PT-01/02 OPENS XV1/2RESPECTIVELY

3. LSHH-02 CLOSES FV1 AND OPEN XV1 AT THE SAME TIME

4. LSL-02 SWITCHES THE HEATER OFF

5. LSHH-01 CLOSES FV2AND OPENS XV2

6. XVI/2 ARE RE-CYCLE VALVES

LEGEND:

S

GATE VALVE

CONTROL VALVE

SOLENOIDOPERATED VALVE

PRESSURE RELIEFVALVE

HEATER ELEMENT

M

ELECTRIC MOTOROPERATED PUMP

LOGIC CONTROLLER

LOCALLY MOUNTEDINSTRUMENT

FRONT PANELMOUNTEDINSTRUMENT (IN CONTROL ROOM)

ABU DHABI GAS LIQUEFACTION COMPANY LIMITED

P&ID PLANT 01 - TRAIN X (SIMULATOR)TITLEMOD. No.

TRAIN - X DRG. No. EX3.1 ISSUE 1

01-X-G-02

K8PIC02

PT02

K4

K1

K6

LSHH 02

LSH 02

TT01

LSL 02

TY01

TY01

01-X-D-02

01-X-D-01

01-X-E-01

FY02A

FC02

FT02

FC01

FY01A

FT01 K3

K7

K2

K5

PIC01

PT01

LSHH 01

LSH 01

LSL 01

LT01

HV11

HV12

HV1

HV2HV3FV1

HV4

XY1

XV1

01-X-G-O1

FY1

HV5

HV6

XV2XY2

HV7

HV8

HV9

FV2 FY2 FEED WATER

PSV1

1 12.05.03 PNS

P R O V I S I O N A L



A

B

C D F

E

H

G

5 Title Blocks

All drawings and diagrams have a title block in the bottom right corner of the drawing

sheet. This title block shows standard information for all types of drawings and

diagrams. Figure 5.1 shows the standard ADGAS title block.

The information located in the sections A to H shown in Figure 5.1 is described in

Table 5.1.

Section Information

A Company Name

B Title or brief description of the drawing or diagram

C Drawing number to identify this drawing sheet

D Gas production train number: 1, 2, 3,etc. Used for process diagrams.

E Used for drawings but not diagrams. Shows the size of the drawn object relative to the actual object

F, G and H Modifications and issues tell you about changes made to the drawing

Additional information is written here: • Legend • Parts or Items List • Notes


0 2003 ISSUED FOR APPROVAL/COMMENTS

MOD No. TITLE

ISSUE DATE REMARKS DRN CHK ENG

DO NOT SCALE THIS PRINT ALL DIMENSIONS ARE IN mm UNLESS OTHERWISE STATED

SCALE TRAIN DRG No. ISSUE

Figure 5.1: Standard ADGAS Title Block

Table 5.1: Standard ADGAS Title Block Information



The title block often continues upwards above section A. This part can contain extra

information and notes including:

• the legend—symbols used on a diagram and their meanings

• materials and items list—identification of components and materials on a

drawing



(a) Cutaway of Piston Engine (b) Heavy Vehicle Axle

6 Pictorial Drawings

Pictorial drawings show as much of an object as possible in a single view. There are

two main types of pictorial drawings:

• oblique

• isometric

The same object is drawn using both these projections in Figure 6.1. The difference

is explained in Sections 6.1 and 6.2.

These drawings give a general idea of the appearance of an object and you may see

them in manufacturers’ manuals to illustrate a piece of equipment (Figure 6.2).

(a) Oblique Projection (b) Isometric Projection

Figure 6.1: Pictorial Drawings of a Turnkey

Figure 6.2: Isometric Technical Illustrations



Pictorial sketches of simple objects can be very useful in helping you to describe

something to someone. You can make quick, simple sketches using oblique drawings.

6.1 Oblique Drawings

An oblique drawing shows the true shape of the front face of the object. All vertical

edges are drawn as vertical lines but side edges are drawn at an angle, often 45o, to the

horizontal. This makes your drawing look like a solid object, even though you are

drawing it on a flat piece of paper.

To make the object look more realistic, you can draw the side edges that are going

away from you shorter than they really are. If you draw these about half their true

length the drawing looks better.

In Figure 6.3, which block looks like its edges are all the same length, (a) or (b)?

Now check them.

Block (b)’s edges are all the same length. Block (a)’s edges look all the same length,

but the side edges are half the length of the front and back edges.

If there are any circular parts or holes on the object, try to show them on the front

face. Any circles on the sides are not drawn as true circles.

(b)

Figure 6.3: Shortened Edges in Oblique Projection

(a)



The procedure for making an oblique drawing of the object in Figure 6.4 is described

below.

Draw the view you see if you are looking in the direction

of arrow A in Figure 6.4.

Draw the side edges that are going away from you all

at the same angle (B) to the horizontal. Angle B is

usually 45o.

Draw edges that are parallel to the front edges to

form a framework that contains the object.

Draw circular parts of the object.

Go over the outline of the object with a darker line.

You can then erase the lines you do not want.

Notice that the circles and half-circles on faces parallel

to the front are true shapes. Those drawn on the other faces are not,

they are distorted. If you sketch objects with circular parts you must

practice sketching true circles and distorted circles. There is some

help for this in Section 6.3.

Figure 6.4: Making an Oblique Drawing

A distorted shape has been changed from its original shape.



6.2 Isometric Drawings

Isometric drawings look even more realistic than oblique drawings, but they are a

little harder to draw. All vertical edges are drawn as vertical lines, but all horizontal

edges are drawn at 30o to the horizontal. These edges are drawn parallel to the

isometric axes shown in Figure 6.5.

The next step is to find the overall dimensions of the object you are drawing. Draw a

box that would just contain the object. Draw the edges of the box parallel to the

isometric axes. The size of the box you draw depends on the scale of your drawing.

For sketches, you can estimate lengths as long as they are in proportion, i.e. if one

edge is twice as long as another, draw it twice as long. The actual length is not so

important on a sketch.

Figure 6.6 shows an isometric drawing of an object. Its overall dimensions are

84mmx30mmx25mm.

Can you work that out from the

dimensions on the drawing?

Figure 6.5: Isometric Axes

Figure 6.6: Dimensioned Isometric

30o 30oHorizontal

Isometric axis Isometric axis

Isometric axis



This is how to make the drawing:

• Draw a box with its edges parallel to the

isometric axes. The length is about three

times the width and the height is a little less

than the width; this gives the correct

proportions.

• Next, draw the edges of the object. You can

imagine that the box you have drawn is a block

of material and you are cutting the object out of

that block.

• Now sketch in any curves or other details.

Notice that all the lines drawn so far are thin,

light lines. These are called construction lines.

Some are not wanted on the final drawing and, if

you draw them lightly, you can easily erase them

later.

• Now decide which lines make the outline of the

object. Go over these again, making them darker

and thicker. Then you can clean up your sketch

by erasing the construction lines you do not want.



6.3 Freehand Sketching

You do not have to be an artist to make good pictorial freehand sketches. Anybody

can do it if they take some care and follow the steps described.

Always start your drawing with light construction lines. You can make the final

outline darker when you are pleased with your drawing.

When you freehand sketch straight lines, start by marking

the start and end points of the line as shown in Figure

6.7. Then draw the line, always looking at the point

where the line will end.

For short lines, draw the line in one go, without taking

your pencil from the paper.

For long lines, draw the line using a number of short strokes of your pencil. This

helps to keep the line straight.

Remember, you can always turn the paper so that it is at a better angle for drawing the

line you want.

Curves are the most difficult part but there are some things you can do to help you to

sketch better curves.

Use your wrist as a turning point (Fig 6.8(a)), like the centre point of a compass.

Turn the paper as you draw the curve so that your wrist is in the most comfortable

position (Fig. 6.8(b))

Figure 6.7: Sketching a Straight Line

(a) (b) Figure 6.8: Drawing Curves

start end



Draw circles inside a square.

Draw lines joining the mid-points of the sides.

Draw the circle so that it just touches, but does not cross, the mid-

point of each side.

Go over the circle again to make it darker.

Then erase your construction lines.



If you need more points to draw your circle through, join opposite corners of the

square, these lines are the diagonals of the square. Now divide each line from the

centre to the corner roughly into three, as shown in Figure 6.9.

Draw the circle so that it just touches the marks farthest from the centre and is

perpendicular to the diagonals.

To draw the distorted circles on isometric and oblique drawings, draw them inside an

isometric or oblique square, as shown in Figure 6.10.

Figure 6.9: Extra Points for Sketching Circles

Figure 6.10: Sketching Oblique and Isometric Circles

Now try Exercise 4



6.4 Exploded Drawings

Manufacturers often use exploded drawings in their manuals to show the parts of an

assembly and how they fit together. Figure 6.11(a) and (b) shows exploded drawings

of two types of pump.

Perhaps you can see why they are called ‘exploded’ drawings. The parts that make up

the assembly are all separated but they are shown in their correct relative positions.

You can imagine that this is how something would look if it had been photographed

just as an explosion took place.

Exploded drawings are very useful for maintenance work as they show

the order of dismantling and re-assembling equipment.

(a) Vane Pump

Figure 6.11: Exploded Drawings

(b) Gear Pump

To dismantle something is to take it apart.



7 Orthographic Drawings

To show enough information for most engineering purposes, orthographic drawings

are needed.

There are two main types of orthographic drawing:

• detail drawings

• assembly drawings

Detail drawings show a single part with all the dimensions needed to make that part.

Any other information needed is also put on the detail drawing. Most items of

equipment are made of many parts. Each part has its own detail drawing.

Assembly drawings show a group of parts fixed together. They may show some

important dimensions that can not be shown on the detail drawings, like the overall

size of the assembly. Assembly drawings have an items list where all the parts and

their detail drawing numbers are identified. Any other information needed for the

assembly is shown on the assembly drawing.

Sometimes, when you dismantle a piece of equipment, you can remove a section that

is a number of parts fixed together. This is called a sub-assembly, as it is a part of the

main assembly. Sub-assemblies have their own sub-assembly drawings.

Every piece of equipment that you work on will have its own set of drawings that may

include all of these:

• assembly drawings of the whole item

• sub-assembly drawings of groups of parts that can be removed as one piece

• detail drawings of each separate part

Standard parts like nuts, bolts, washers, etc. are listed in the items list of the assembly

and sub-assembly drawings. They will not usually have their own detail drawings.



Figure 7.1 shows a typical assembly drawing with its sub-assembly and detail

drawings.

DRG No A/0001

ABU DHABI GAS LIQUEFACTION COMPANY TITLE

PULLEY

ALL DIMENSIONS IN mm

DRG No A/0001


TITLE PULLEY ASSEMBLY

DRG No A/0007


TITLE PULLEY SUB-ASSEMBLY

(c) Assembly Drawing

(b) Sub-assembly Drawing (a) Detail Drawing

Figure 7.1: Full Set of Orthographic Drawings



7.1 Layout of Views

You saw how three views of a third-angle orthographic drawing are arranged on the

paper in Section 2. Some objects need more views to show all their details, some

need fewer. Figure 7.2 shows an object and the six directions that you could view it

from to look at all its sides. The man is shown viewing it from the normal three sides

only.

To draw all these orthographic views, follow the rules you learnt in Section 2.

Choose the side that best shows the shape of the object and make that the front view.

This side is coloured red in Figure 7.2.

In third-angle projection:

• the view of the object you see when you look from above the front view, you

draw above the front view

• the view of the object that you see from the right of the front view, you draw

on the right of the front view

Figure 7.2: Six Possible Orthographic Viewing Directions



Figure 7.3 shows a third-angle projection drawing of the object shown in Figure 7.2

showing views from all six sides.

Remember that when you read a third-angle drawing:

• a view drawn above is what you see when you look from above

• a view drawn on the right is what you see when you look from the right

• a view drawn on the left is what you see when you look from the left

• etc.

For most objects, three views are enough:

• front view

• top view or plan

• one end view—viewed from the side where you can see the most detail

Notice again how the views are lined up exactly. This is done by ‘projecting’ lines

from one view to another as shown in Figure 7.4.

Figure 7.3: Six possible Orthographic Views

A

B

D D

E C

C E

F

F



Notice also in Figure 7.4 the symbol at the bottom.

You will find some orthographic drawings that have views arranged differently.

These are first-angle orthographic projections. Most drawings are now made in third-

angle projection, but you may see some first-angle drawings so it is best to know how

to recognise them.

Figure 7.5 shows the same object again, but this time drawn in first-angle projection.

Figure 7.5: Three-view First-angle Orthographic

Figure 7.4: Three-view Third-angle Orthographic



FrontLeft side

Notice that the views look the same, but are located in different places.

In first-angle drawings the views are positioned on the opposite side:

• a view drawn below is what you see when you look from above

• a view drawn on the right is what you see when you look from the left

• etc.

Notice the symbols at the bottom of Figures 7.4 and 7.5.

They are similar but not quite the same. These symbols tell

you if a drawing is in first or third-angle projection. Can

you see the difference?

The symbol represents a cone with its top cut off.

Look at it from the front and you see a triangle with its top cut off.

Look at it from the left side and you see two circles: one is the small end

and the other the big end.

In third angle, you would draw this end view, seen from the

left, on the left.

This symbol means that the drawing is in third-angle

projection.

In first angle you would draw this end view, seen from the

left, on the right.

This symbol means that the drawing is in first-angle

projection.



Always look for this symbol on an orthographic drawing, usually in the title block. If

it is not there you will have to use your knowledge to decide if the drawing you are

looking at is in first- or third-angle projection.

Figure 7.6 shows six examples of orthographic drawings labelled A to F. An

isometric of the object drawn is shown next to each one. An arrow points to the

‘front’ of each object.

Are these drawings in first or third-angle projection?

Cover the orthographic views. See if you can imagine the three orthographic views

by looking at the isometric.

Now cover the isometric views. See if you can imagine what the object looks like in

the isometric view.

Do this for each of the objects in Figure 7.6.



Figure 7.6: Orthographic Drawings



7.2 Types of Line

Two things help to tell you what a line represents an orthographic drawing:

• whether the line is broken or unbroken

• the thickness of the line

The main lines used are shown in Table 7.1.

Line Description Use

Thick, unbroken line Outlines and edges that can be seen

Thin, unbroken Dimension, extension and leader

lines. Also cross hatching for sections

Thin, unbroken and not straight

Edges of parts that are cut away to see inside or behind

Thin, broken with equal length short dashes

Outlines and edges that are hidden

——— - ——— - ——— Thin, broken with long and short dashes

Centre lines. Also extreme positions of moveable parts

Thin, broken with long and short dashes—thick ends

Cutting planes for sections

Figure 7.7 shows examples of some of these lines on a single-view drawing.

Table 7.1: Line Types for Orthographic Drawings

Figure 7.7: Use of Line Types

Now try Exercise 5



7.3 Dimensions

Dimensions show the size of the object and the positions of holes, etc. Dimensions

are drawn outside the main outline of a drawing wherever possible.

Extension lines are drawn from the object outlines. Dimension lines, ending in

arrowheads, touch the extension lines. Figure 7.8 shows a simple outline with

extension lines and dimension lines.

Notice that:

• there are no dimension lines inside the outline

• dimension lines end in arrowheads that just touch extension lines

• there is a small gap between the outline and the extension lines

• extension lines end just past the dimension line arrowheads

• there is plenty of space between dimension lines and they are not too close to

the outline

• larger dimensions are put outside smaller ones so that extension lines or

dimension lines do not cross

• hole positions are dimensioned to centre lines

Figure 7.8: Dimensions

Diameter

Extension line

Dimension line Dimension lines

well spaced



Figure 7.8 shows one way of dimensioning a hole diameter. Other ways of

dimensioning circular parts are shown in Figure 7.9. Notice the symbol φ, which

stands for diameter, and R, which stands for radius.

Dimensions are written neatly, usually above the dimension lines, never below.

Always add dimensions so that they can be read from the bottom or from the right

side of the drawing as shown in Figure 7.10

Figure 7.9: Dimensioning Diameters and Radii

Figure 7.9: Dimensioning Diameters and Radii

Figure 7.10: Dimensions Read from Bottom or Right of Drawing



Notice how the very small distances (6 and 3) are dimensioned in Figure 7.10, with

arrowheads outside the extension lines.

Two ways of dimensioning outside diameters are shown in the figure.

Follow the same rules when you put dimensions on any sketches you make,

orthographic and pictorial.

7.4 Sections

One way to show details that you can not see from the outside of an object is by using

thin dashed lines to show outlines and edges that are hidden; these are called hidden

detail lines.

Another way to show parts that can not be seen from the outside is to use sections.

You saw a cutaway drawing of an engine in Figure 6.2. A cutaway drawing is a

section shown on a pictorial drawing. Figure 7.11 shows another cutaway section,

this time showing the inside of a hydraulic cylinder.

Figure 7.11: Cutaway Section in Isometric Drawing

Now try Exercise 6



Sections are mentioned in Table 7.1 and Figure 7.7 shows two sections. Sections

show what is hidden inside or behind something.

To understand sections, imagine that the object is cut through and the front is

removed. The part of the object left behind is the section. The imaginary surface that

you cut along is the cutting plane. Any metal that is cut through is

shaded with diagonal lines called cross-hatching.

Figure 7.12(a) shows an object actually being cut through to see the inside. The saw

cuts along the section plane. In Figure 7.12(b) the front is removed to show the

section that is left. See how any material that has been cut is cross-hatched. In

section drawings you just imagine that this cut has been made.

In Figure 7.13 you can see two orthographic views of the object shown in the last

figure.

In Figure 7.13(a), the hidden edges are shown using hidden detail lines.

In Figure 7.13(b), they are shown using a section view. Note how the cutting plane

and the direction you look in to see the section are shown.

Is first- or third-angle projection being used in Figure 7.13(b)?

(a) Making the Imaginary Cut (b) The Section

Figure 7.12: Imaginary Cut to make a Section View

A plane is a flat surface.



A Section A-A

A

Sometimes, to see more detail you need to make a ‘cut’ that is not straight. Figure

7.14 shows a section taken to see both the holes.

(a) Hidden Detail in Side View

(b) Sectioned Side View

Figure 7.13: Two Ways to ‘See’ Inside an Object



Notice that where the cutting plane is bent, or offset:

• there is a centre line on the section view where this happens

• cross hatching lines do not line up where they meet this centre line

Is first- or third-angle projection used in Figure 7.14?

Sometimes, when an object is symmetrical it is enough to section just

one side. It would waste time to draw both sides as they are the same.

Figure 7.15 shows a half-section of a symmetrical object.

Figure 7.14: Offset Cutting Plane

Figure 7.15: Half-section

A symmetrical object is exactly the same on both sides of a line called the line of symmetry

Bend in cutting plane



If it is enough to cut away a small area to show a detail, local or part-sections are

used. You saw a part-section in Figure 7.7. Figure 7.16 shows another example of a

part-section.

To show the shape of some items, it is enough to turn or revolve the section through

90o. If the section is drawn on the same view, it is called a revolved section (Fig.

7.17(a)). If it is drawn somewhere else, it is called a removed section (Fig. 7.17(b)).

Figure 7.16: Part-section

(b) Removed Section (a) Revolved Section

Figure 7.17: Revolved and Removed Sections



Two things are not cross-hatched, even when they are cut by a section plane. These

are:

• shafts, and anything similar to a shaft including nuts and bolts—when cut

along their length

• thin strengthening parts called webs and ribs—when cut along their length

Figure 7.18 shows examples of parts that are not cut through in a section view.

Is first- or third-angle projection used in Figure 7.18?

Section A-A

Figure 7.18: Items Not Sectioned

Now try Exercise 7

Nut

Bolt

Shaft

Web



7.5 Drawing Springs and Screws

Some items that are often used in equipment are drawn in a special way to save time.

Screw threads and springs are examples of these. The ways in which they are drawn

are shown in Table 7.2.

Item Simplified drawing Description

Compression spring

Tension spring

External thread

Internal thread

Thread assembly

Threads may be:

• external—cut on the outside of a round shaft, e.g. a bolt

• internal—cut on the inside of a hole, e.g. a nut

Notice that:

• when you look at the end of an external thread, you see the outside diameter

of the shaft. This is drawn as a thick, unbroken circle. The thread is cut into

this material and is drawn as a thin broken circle on the inside.

• when you look on the end of an internal thread, the hole you see is the inside

diameter of the thread. This is drawn as a thick, unbroken circle. The thread

is cut into the material and is drawn as a thin broken circle on the outside.

Table 7.2: Spring and Thread Drawings



Look back at Figure 7.14. Notice how the left hand hole is drawn. What can you say

about this hole?

Now try Exercise 8



8 Piping Layout Drawings

These drawings show the actual path, or shape, of a piping layout, the lengths of pipe

runs and distances between valves and fittings. They may also show pipe sizes.

Simple piping layouts can be double-line drawings. These show pipes and fittings

more realistically but take longer to produce so are only used where appearance is

important and layouts are simple. Figure 8.1 shows a simple double-line piping

layout drawing.

For most piping layouts, single-line drawings are used. These show pipes as a single

thick line, drawn where the centre of the pipe would run. Symbols are used to

represent valves and fittings. Symbols for valves are the same as or similar to those

used on PFDs and P&IDs. Figure 8.2 shows a single line drawing of the pipe layout

shown in Figure 8.1.

Figure 8.1: Double-line Piping Layout Drawing

Figure 8.2: Single-line Piping Drawing



Figure 8.3: Isometric Showing Piping in More than One Plane

Figures 8.1 and 8.2 show simple layouts that are in a single plane, i.e. they can be laid

flat on a surface.

If the layout is in more than one plane, isometric or

orthographic projections are needed to describe it.

Figure 8.3 shows a section of piping that is in more than

one plane. You could not describe this with the simple

piping layout drawings shown in Figures 8.1 and 8.2.

Figure 8.4 shows a single-line isometric piping layout drawing.

Figure 8.4: Isometric Piping Layout



Notice the way that two crossing pipes are shown on this drawing. The pipe that is

shown ‘broken’ passes behind another pipe.

Also notice how equipment that is connected to the pipeline is shown using long and

short dashes, like a centre line.

Figure 8.5 shows a third-angle orthographic drawing of the same pipe layout.

Notice how flanges on pipes that are coming towards you or going away from you are

shown as circles. You can see the open end of the pipe on flange C in the side view;

the open end of a flange is shown as two circles to represent the flange and the pipe.

You are looking at the back of flange A in the side view; the back of a flange is shown

as a single circle.

Figure 8.5: Orthographic Piping Layout



Figure 8.6 shows a manually operated gate valve with flanges on either side, like the

valves shown in Figure 8.5.

9 Summary

You have now seen some of the most important types of drawings and diagrams used

by ADGAS. You should be able to recognise them when you see them and be able to

identify the type of drawing or diagram by looking at the lines and symbols used.

You should also be able to read simple orthographic drawings and make your own

dimensioned sketches of simple objects.

Figure 8.6: Flange-mounted Valve

Flanges

Valve

Now try Exercise 9



10 Glossary

Here are some words used in this module that might be new to you. You will find

these words in coloured italics in the notes. There is a short definition in a box near

the word in the notes.

Word First Used on

Page:

Part of Speech Meaning Example of Use

Dismantle 36 verb To take to pieces The equipment had to be dismantled before the fault could be found.

Distorted 30 adjective Pull or twist out of shape

He was not going fast, but the front of his car was completely distorted when he hit the car in front.

Fluid 15 noun A substance that can flow, e.g. gas or liquid

Hydraulic fluid is usually a thin oil.

Plane 49 noun A flat surface that might be real or imaginary

The U.A.E. forms a flat plane with mountains along its eastern edge.

Represent 5 verb To stand in place of something.

The ADGAS logo represents a burning gas flame.

Symmetrical 51 adjective Having two identical halves, as if reflected in a mirror

He folded his ‘gil’ neatly, so that it was exactly symmetrical on his head.



Exercises

M7-Drawings and Diagrams

Documents

Transcript of M7-Drawings and Diagrams