unit 2 engineering drawings

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UNITS IN THIS COURSE

UNIT 1 INDUSTRIAL DRAWINGS.

UNIT 2 ENGINEERING DRAWINGS.

UNIT 3 ORTHOGRAPHIC DRAWINGS.

UNIT 4 ISOMETRIC DRAWINGS.

UNIT 5 P & ID SYMBOLS.

UNIT 6 DIMENSIONS AND SCALES.

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TABLE OF CONTENTS

Para Page

2.0 COURSE OBJECTIVES 2

2.1 ENGINEERING DRAWINGS 4

2.2 BLOCK DIAGRAMS 4

2.3 PLOT PLANS 5

2.4 PROCESS EQUIPMENT DRAWINGS 6

2.4.1 Piping Diagrams 7

2.4.2 Fluid Power Diagrams 8

2.4.3 Electrical Diagrams 10

2.5 PROCESS FLOW DIAGRAMS 12

2.6 PIPING AND INSTRUMENT DIAGRAMS 14

2.7 ASSEMBLY DRAWINGS 16

2.8 SPECIAL DRAWINGS 18

2.8.1 Exploded Views 19

2.8.2 Cutaways 20

2.8.3 Sectional Views 21

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2.0 COURSE OBJECTIVES

This course explains the reasons why industrial drawings are needed, and thedifferent types of industrial drawings which are used. Other units in this course givemore detailed information so that, on completion of the course, the student will beable to:

Identify and explain the basic information given on industrial drawings,

blueprints and engineering drawings.

Recognise an orthographic drawing and be able to draw an object in

orthographic views.

Recognise an isometric drawing and be able to draw an object in isometric

view.

Identify and explain the reasons for exploded and assembly drawings.

Recognise and explain the symbols used on piping and instrumentationdiagrams.

Take dimensions off a drawing and understand the use of scale drawings.

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2.1 ENGINEERING DRAWINGS

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There are a great many different types of engineering drawings. Each type has aspecific purpose. Many of the different types of drawings are useful to operators.The different types of engineering drawings which will be shown in this unit are;

Block Diagrams

Plot Plans

Process Equipment Drawings

Process Flow Diagrams

Piping and Instrument Diagrams

Assembly Drawings

Special Drawings.

Two specific types of engineering drawings, called orthographic drawings andisometric drawings, are described in Units 3 and 4 of this course.

Note that engineering drawings may also be called 'diagrams' or 'plans'.

2.2 BLOCK DIAGRAMS

Block diagrams are the first drawings you do when you plan a system. They mustbe completed before anything else can be decided about the system. All otherdrawings are based on the block diagrams.

In block diagrams the components of the system and other important informationare shown by a block (or rectangle) with writing in it. The blocks can show manydifferent things, depending on the type of system they represent. Figure 4-9 showsa simple block diagram of an oil process. Block diagrams can give the followinginformation;

The total amount of space needed for a system.

The main components of a system.

o The main direction of flow in a process.

The relative positions of the, parts in a system.

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Figure 2-1 Simple Block Diagram

The block diagram can be used to see which part of the plant you are interested in.Then the key words in the block diagram can be used to get other drawings withthat word in their titles.

2.3 PLOT PLANS

Plot plans show a top view of existing equipment, main pipelines, control buildingsand traffic ways. An example of a plot plan is shown in Figure 2-2. Plot plans areused when new buildings must be built or large equipment has to be installed. Their

purpose is to help in planning where to put the new buildings or equipment.

Plot plans are used to;

Decide where new buildings or new equipment can go in an existing plant

making the most economical use of existing utility supplies, piping andequipment.

Show the best place for a new building or new equipment with respect to

controls, traffic and transportation.

Provide information about the distance between equipment and buildings.

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Figure 2-2 Example of a Plot Plan

2.4 PROCESS EQUIPMENT DRAWINGS

Process equipment drawings (or diagrams) are drawings that provide informationabout the equipment used in a process plant. From these drawings an operator canlearn where components are and how they are connected to each other. They alsoshow the size of piping, the parts in hydraulic and pneumatic systems and the partsof electrical circuits.

To get all this information we must study the three main types of process equipmentdrawings:

Piping Diagrams which deal with valves, connections and the size of piping.

Fluid Power Diagrams which show how hydraulic and pneumatic systems are

arranged and what they do.

Electrical Diagrams which show the arrangement of electrical circuits in a

system.

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2.4.1 Piping Diagrams

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Piping is found in every area of a process plant. Therefore, piping diagrams are veryuseful for operators.

Piping diagrams show how the flow of fluid is controlled in different parts of theplant, and how pipelines and pipe sections are connected together.

There are two kinds of piping diagrams;

single line piping diagrams which use one line to show the pipes,

double line piping diagrams which use two lines to show the pipes.

Figure 2-3 shows a simple piping diagram as both single line and double line. Theinformation given by the two diagrams is the same.

he single line piping diagram is much simpler and cheaper to produce so it is used

much more often. However, pipe sizes of 38 mm (1.5 in) diameter and smaller arealways drawn in single line because a double line diagram for that size of pipe isimpossible to draw.

Figure 2-3 Simple Piping Diagrams of the Same System

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2.4.2 Fluid Power Diagrams

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Fluid power diagrams represent and describe fluid power systems. A fluid powersystem is a piping circuit which carries fluid under controlled pressure to provide asource of power. The fluid can be either gas or liquid. Air is the most commonlyused gas and a special type of oil (hydraulic oil) is the most commonly used liquid.

There are three types offluid power diagrams;

1. Cutaway Diagrams, which are double line drawings of a fluid power system.(These diagrams should not be confused with the cutaways as described in'Special Drawings, paragraph 2.8.)

Pictorial Diagrams, which are single line drawings which use pictures to

represent the components.

Schematic Diagrams, which use symbols and single lines to represent the parts

of the system.

Schematic diagrams are the most common type offluid power diagrams. Figure 2-4gives examples of the three types offluid power diagrams.

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Figure 2-4 Three Types of Fluid Power Diagram

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2.4.3 Electrical Diagrams

There are electrical circuits in almost every part of a process plant. The drawingswhich show the electrical circuits are called electrical diagrams. There are two majortypes of electrical drawings, examples of which are shown in Figure 2-5;

1. Wiring Diagrams show where the components are in the circuit. Because ofthis, wiring diagrams are very useful for maintenance or repair work.

1. Schematic Diagrams use single lines and symbols to show the componentsand their connections. These drawings are used to show the flow of currentthrough the circuit. A schematic diagram helps you to see how an electricalsystem works.

The positions of contacts, circuit breakers, etc. shown on electrical schematicdiagrams are almost always shown with the circuit de-energised. If the circuit isshown energised it will be clearly stated on the drawing.

Both wiring diagrams and schematic diagrams show the components of an electricalcircuit. The most common components are listed below.

1. Switches. These start, stop, or change the flow of electricity in a circuit.

1. Power sources. These can be transmission lines from the power company,generators, or batteries.

1. Loads. These are the components which actually use the electricity supplied bythe circuit; for example, motors and heaters. There are many different kinds ofloads.

1. Coils, Inductors and Transformers. These are components used to makechanges in electrical power using electromagnetism.

1. Fuses, Circuit Breakers and Ground Connections (earth connections).These are devices used to protect electrical systems.

1. Resistors. These are used to control the voltage or the current in an electricalcircuit.

1. Contacts. These are used to join two or more components in an electricalcircuit.

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Figure 2-5 Examples of Electrical Drawings

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2.5 PROCESS FLOW DIAGRAMS

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Process Flow Diagrams (often called PFD) show the operator how process fluidsflow through different areas of the plant. They provide important information about;

The normal operating conditions. They show thing like temperature, level,

pressure and flow in each part of the plant and at each stage in the

process.

The main instruments used in each part of the plant, and where they are

located.

The type of equipment and piping used in each step of the process.

The utilities used in the different stages of operation in the plant.

Process flow diagrams provide information about what happens in each stage of aprocess. Because of this, they are useful when you need to change operatingconditions. They also help prevent accidents by showing critical flow control points.

Process flow diagrams must include information on;

Vessels,

Heat Exchangers,

Pumps and Compressors,

Heaters,

Instruments,

Valves,

Piping.

There are three main types of process flow diagram;

Process Flow Sheets,

Mechanical Flow Diagrams,

Utility Flow Diagrams.

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Mechanical flow diagrams and utility flow diagrams are more usually called 'Piping

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and Instrument Diagrams'; shortened to P & ID. These types of drawings aredescribed separately in Paragraph 2.7 in this Unit.

Process flow sheets show the main stages in a process. They show all majorequipment and piping. They also give temperatures, pressures and otheroperational information at critical points in the process. They show how materialmoves through a process.

Because they include only the main pieces of equipment, these drawings are easyto read and to understand.

You will learn the symbols for equipment later in this course.

Figure 2-6 shows an example of a process flow sheet for the depropanizing stage ofa refining process.

Figure 2-6 Example of a Process Flow Diagram

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2.6 PIPING AND INSTRUMENT DIAGRAMS

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Piping and Instrument Diagrams (P & ID) give more detail than process flow sheets.They give information on;

Sizes and types of piping used (manufacturers provide schedules of specificationsfor pipes).

Operating conditions at every step of the process.

All the equipment used, not just the main components.

All the instruments used.

Piping and instrument diagrams are also called mechanical flow diagrams and utilityflow diagrams. The difference between the two types of drawings is that mechanicalflow sheets show the main equipment of the process. Utility flow sheets show theutility services such as air, water, steam, drains, etc. which are supplied to theprocess.

Examples of piping and instrument diagrams are shown in Figures 2-7 and 2-8.Compare the detail on these to the process flow diagram shown in Figure 2-6.

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Figure 2-7 Example of a Piping and Instrument Diagram(Mechanical Flow Diagram)

Because of the detail shown on them, piping and instrument diagrams use a lot ofsymbols and abbreviations to save space on the drawing. There are a great manysymbols and abbreviations which you will learn with practice. Every set of drawingshas a list of the symbols and abbreviations used. You should always get a copy ofthis list to help you understand the drawings. It will also help you learn the symbols.

Because there are so many symbols on a P & ID, many of the symbols are almostthe same. Make sure you read the symbols correctly and understand what theymean.

You will learn the symbols for instruments later in this course.

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Figure 2-8 Example of a Piping and Instrument Diagram (Utility Flow Diagram)

2.7 ASSEMBLY DRAWINGS

Assembly drawings show how the different parts of a piece of equipment are puttogether (assembled) to make a complete unit. They show where each part goes inrelation to other parts.

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Figure 2-9 Two Types of Assembly Drawing

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2.8 SPECIAL DRAWINGS

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The following types of drawings can be classified as 'special' drawings;

Exploded views,

Cutaways,

Sectional views.

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2.8.1 Exploded Views

Figure 2-10 shows an exploded view. As the name suggests, the parts of acomponent are 'exploded' (separated) to show how they fit together. There areguidelines in the drawing to make sure that all the parts are shown in their correctpositions.

Figure 2-10 An Exploded View

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2.8.2 Cutaways

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Figure 2-11 shows an example of a cutaway drawing. The drawing is produced ineither isometric view or perspective view. Usually one quarter of the outer casing ofthe equipment is removed to show what is inside. The amount of casing removed onthe drawing can vary.

Figure 2-11 Cutaway Drawing

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2.8.3 Sectional Views

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Figure 2-12 shows an example of a sectional view of a valve. The separate partswhich make up the valve are shown with different hatch markings. A sectional viewcan be used as an assembly drawing.

Sometimes only half of the piece of equipment is shown in sectional view. The otherhalf is an external view. The centre line of the equipment is used to divide thedrawing into these two halves.

Figure 2-12 Sectional View

unit 2 engineering drawings

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