P & ID. How To Read P&ID Drawing Easily. Piping & Instrumentation Diagram Explained.

P& ID Means Piping and Instrumentation Diagram.

A Piping and Instrumentation Diagram Is a Detailed Diagram Which Shows the Piping and Process Equipment along with the Instrumentation and Control Devices.

A Standard Set of Symbols Is Used to Prepare P and ID and these Symbols Are Based on International Society of Automation.

Importance Of P & ID.

P And ID Is Used for Identification of Components in a Process Plant.

It Shows,

1.How Instruments are Connected

2.Where they Are Located and also shows

3.Functions of Instruments Within the Process.

It is Used for,

1.Plant Construction,

2.Process Monitoring and also for

3.Troubleshooting in the Plant.

This Below Picture Shows a Part of a Process Plant

The P& ID of Such a Plant Will Be Like This.

Important Things to Note on a P&ID.

1. Thick Continuous Lines On a P&ID Drawing Represents Pipes Pipes in a Process Plant

2. When Two Lines Crossover or Make a Corner Without any Break in Drawn Lines on a P&ID, it Means that those two Pipes Are actually Connected in the Plant.

3. If the Drawn Lines in a P&ID Cross Over Each Other, But Show a Break or Gap at the Cross Over, It Means that Pipes are Not Connected in the Plant.

4. P & ID Shows the Direction of a Fluid Stream Flowing Within a Pipe. The Direction of Flow is Drawn as Solid arrowhead on the Line Representing the Pipe.

5. Revision Clouds and Revision Triangles:
There are two Common Methods of Indicating Revision Changes made in a Drawing.

A. The First is Cloud Method Where Each Change Made in the Drawing is Enclosed by a Hand Drawn Cloud Shape.

B. The Second Method Involves Placing a Triangle with the Revision Number Inside it Next to the Portion Where Revision Changes are Made

6. Process Flow Tag:
Many Drawings are Needed to Represent an Entire Plant. So, a Method for Showing Where a Pipe Goes Next Appears in Every Drawing that is the Process Flow Tag

This Symbol in the above pic Shows from Where the Pipeline is Coming and the Previous P&Id Drawing Number.

The Second Symbol in the above pic Shows to Where the Pipe Is Going and the Next P&Id Drawing Number.

7. Tie In or Termination Point

New Work in a Plant that Joins to the Existing Plant is Represented with the Termination Point.

8. Piping Hazard Level Rating
This Symbol Shows the Hazard Ratings According to the Product in the Pipe.

This Figure Shows the Main Hazard Level Ratings.

Hazard Level B Indicates the Pipe Which Carries Medium Level Hazard Product.
Hazard Level C Indicates the Pipe Which Carries Lower-Level Hazard Product and
Hazard Level E Indicates the Pipe Which Carries Negligible Hazard Level Product.

Instrument Symbols Associated with a P&ID.

A Circle with No Line in It Represents an Instrument that is Physically Located Somewhere in the Field.

This Figure Shows Some Field Mounted Instruments and how a Field Mounted Instrument is Represented in a P and ID

Circle With Single Horizontal Line This Represents Instruments That Are Mounted on The Control Panel.

Fig below shows how the Control Panel Mounted Instrument represented in a P&ID.

Circle With Double Horizontal Line This Represents Instruments That Are Mounted on The Sub Panels or Remote Locations.

Fig below shows how Instruments That Are Mounted on The Sub Panels or Remote Locations are represent in P and ID.

A Circle With a Single Dashed Horizontal Line represents the Instruments that Are Mounted inside or Back Side of the Control Panel which are generally Inaccessible.

Fig below shows how Instruments that Are Mounted inside or Back Side of the Control Panel are represent in P and ID.

The Above mentioned Symbols are the Symbols Associated with instruments.

If These Symbols are Enclosed Within a Square,
It means that they are a Part of DCS Control Process.

If the Shape of the Symbols are Diamond Enclosed Within a Square it means that they are a Part of PLC Control Process.

When You Spot One of These Symbols on a P &ID you will be able to Understand three things from It.

1. What is that Device

2. Where is it Located

3. Why is it There.

The What and Where Questions Can Be answered by the looking at the Symbol Shapes, and

The Why Part Can Be answered by the looking at the Text Placed Inside the Symbol. This Text Is Known as Instrument Tag Number.

Instrument Tag Number in a P&ID

Instrument Tag Number as an Alphanumeric Code that Provides Specific Information about an Instrument or its Function.

Instrument Tag Number Has Two Lines in It.

1.Upper Line, it is a Short Form for Functionality that Instrument Provides.

2. Lower Line, it is a Loop Number that Corresponds to the Equipment in the Plant.

Since Most Plants Have Many Instruments of Same Type a Unique Number Is applied, So that Each One Can Be Individually Identified. This Number is Known as Loop Number.

In the Instrument Tag shown in the above fig, the
First Letter in The Upper Line Indicates the Type of Process Variable That Instrument Is Used For.

The Succeeding Letters Are Used to Represent the Function of Instruments. The Lower Line Represents the Loop Number.

Locally Indicating Device Symbols in a P&ID

Local Indicator Shows the Measured Value in The Equipment and The Process Lines.
This Figure Shows How Primary Indicating Devices Are Shown in a P&ID.

Transmitting Device Symbols in a P&ID

The Transmitter Send the Measured Value to the Control Cabinets, allowing Us to Control and Monitor the Process.
This Figure Shows How Common Transmitters Are Represented in a P&ID.

Valve Symbols

Valves Are Used to Control the Direction, Flowrate and Pressure of Fluids.
Below fig shows a Symbolic Representation of Different Types of Valves in a P& ID.

It Should Be Noted that Globe and Gate Valves Will Be Often Represented by the Same Valve Symbol.
In Such Cases Information Concerning the Valve Type May Be Conveyed by the Component Identification Number or By the Legend Section of the Drawing.

Valve Actuators:

Some Valves Are Provided with Actuators to allow Remote Operation and To Increase Mechanical advantage.
The Combination of a Valve and Actuator Is Commonly Called a Control Valve.
Control Valves Are Symbolized by Combining the Appropriate Valve Symbols and Actuator Symbols.

This Figure Shows the P&Id Symbols for The Common Valve Actuators. Although Each Actuator Is Shown attached to a Gate Valve, an Actuator Can Be Attached to Any Type of Valve Body.

If No Actuator Is Shown on a Valve Symbol, It May Be Assumed That the Valve Is Equipped with a Hand Wheel for Manual Operation.

Control Valve Designations:

A Control Valve May Serve any Number of Functions Within a Fluid System.
To Differentiate Between Valve Uses, a Balloon Labelling System Is Used to Identify the Function of a Control Valve as Shown in The Figure.

Common Convention is that the First Letter Used in the Valve Designator Indicates the Parameter to Be Controlled by the Valve.

The Second Letter is Usually a ” C “and Identifies the Valve as a Controller and The Third Letter is a ” V ” to Indicate that the Piece of Equipment Is a Valve.

Line Symbols

The Piping of a System May Contain More Than a Single Medium.
These Are the Symbols Used for Indicating the Medium Carried by the Piping and For Differentiating Between Piping, Instrumentation Signal and Electrical Wires.

The Most Common Line Type Is Solid Line Which Is Used to Represent Main Piping.

Instrument Line or Impulse Piping Is Shown by A Thin Line.
A Line with Short Dashes Represent Electrical Signals.
A Line with Long Dashes Means the Pipe Is Existing in the Plant.
A Line with Short Double Slanting Lines Represents Pneumatic Signal,  Which Is the Instrument to Control Valve or Devices.

Line Number

Every Pipe on a P and ID Requires a Unique Number, So that it Can Be Uniquely Identified During Design or Referenced in Operating Procedures.

Line Number Is a Unique Number Assigned to Every Line.
Line Number Has Basically 5 Parts
First Part Is Line Size. It Represents the Size of The Pipe
Second Part Is Conveyed Fluid. This Is a Service Code for Material that Normally Flows in the Line.
The Third Part Is Pipe Area Code. It Is a Unique Number Based on The Pipe Location in a Plant.
Fourth Part Is Pipe Material Classification
And the Fifth One Is Insulation Code and Thickness

Now Let’s See an Example of Line Number

In This Line Number,
3 Represents Line Size.
KE Represents Conveyed Fluid.
1006 Represents Area Code.
CD 121 Represents Piping Material Classification.
and The Last Part Represent Insulation Type and Size.

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