Industrial Automation - I&C Drawings and Documentation

I&C Drawings and Documentation

Introduction to Plant Design:

Plant design (process plant design, power plant design, etc.) refers to the automation technologies, work practices and business rules supporting the design and engineering of process and power plants. Such plants can be built for chemical, petroleum, utility, shipbuilding, and other facilities. Plant design is used to designate a general market area by the many vendors offering technologies to support plant design work.

Process diagrams

The ‘process’ is an idea or concept that is developed to a certain level in order to

determine the feasibility of the project. ‘Feasibility’ study is the name given to a

small design project that is conducted to determine the scope and cost of implementing the project from concept to operation. To keep things simple, for example, design an imaginary coffee bottling plant to produce bottled coffee for distribution. Start by creating a basic flow diagram that illustrates the objective for the proposed plant; this diagram is called a “Process Block Diagram”.

Process block diagram

The block diagram shown in Figure is where it all starts. It is here that the basic components are looked at and the basic requirements determined. This is a diagram of the concept, giving a very broad view of the process. The example below has all ingredients listed and shows that milk, sugar and black coffee make up different permutations of the final product. With this philosophy diagram complete, there is a need to determine the technical requirements. This is done by simultaneously developing two documents; the ‘Process Flow Diagram’ and the ‘Process Description Manual’.

                             Basic flow diagram of Coffee bottling plant

Process flow diagram or piping flow diagram (PFD)

The PFD is where we start to define the process by adding equipment and the piping that joins the various items of equipment together. The idea behind the PFD is to show the entire process (the big picture) on as few drawing sheets as possible, as this document is used to develop the process plant and therefore the process engineer wants to see as much of the process as possible. This document is used to determine details like the tank sizes and pipe sizes. Those familiar with mimic panels and SCADA flow screens will notice that these resemble the PFD more than the piping and instrumentation diagram (P&ID) with the addition of the instruments, but not the instrument function. Mass balance: In its most simple form, what goes in must come out. The totals at the end of the process must equal the totals fed into the system.

Process description

The process description details the function / purpose of each item of equipment in the plant. This description should contain the following information:

• Installation operation – The installation produces bottled coffee

• Operating principles – Each part of the process is described

• Water supply – Filtered water at ambient temperature is supplied to the water holding tank, the capacity of the tank should be sufficient for all recipes

• Coffee supply – Due to the viscosity of the coffee syrup, the syrup is fed from a pressurized vessel to the autoclave, this line should be cleaned frequently with warm water. There will be batches of caffeinated and decaffeinated coffee, the coffee tanks and pipelines must be thoroughly cleaned between batches

• Milk supply – There will be an option for low fat or full cream milk, the milk supply should be sufficient for three days operation and should be kept as close to freezing as possible to ensure longevity of the milk

• Sugar supply – Sugar will be supplied in a syrup form, we will offer the coffee with no sugar, 1 teaspoon (5 ml of syrup) or two teaspoons (10 ml of syrup). Syrup lines must be cleaned on a regular basis

• Circuit draining/make-up – How to start-up or shutdown the facility, cleaning and flushing

• Liquid characteristics – A detailed description on analysis of each liquid type in the system. Includes specific gravity, viscosity, temperature, pressure, composition etc.

• Specific operating conditions linked to the process – The installation operates 24 hours a day, 365 days a year. As the installation deals with foodstuff, all piping and vessels are to be manufactured from stainless steel

• Specific maintenance conditions linked to the process – Hygiene levels to be observed

• Specific safety conditions linked to the process – Hygiene, contamination of product

• Performance requirements – This section describes the amount

                               Process flow diagram

Piping and Instrumentation Diagram (P&ID)

The Piping & Instrumentation Diagram, which may also be referred to as the Process & Instrumentation Diagram, gives a graphical representation of the process including hardware (Piping, Equipment) and software (Control systems); this information is used for the design construction and operation of the facility. The PFD defines “The flow of the process” The PFD covers batching, quantities, output, and composition. The P&ID also provides important information needed by the constructor and manufacturer to develop the other construction input documents (the isometric drawings, or orthographic physical layout drawings, etc.). The P&ID provides direct input to the field for the physical design and installation of field-run piping. For clarity, it is usual to use the same general layout of flow paths on the P&ID as used in the flow diagram.

The P&ID ties together the system description, the flow diagram, the electrical control schematic, and the control logic diagram. It accomplishes this by showing all of the piping, equipment, principal instruments, instrument loops, and control interlocks. The P&ID contains a minimum of text in the form of notes (the system description minimizes the need for text on the P&ID). The typical plant operation’s environment uses the P&ID as the principal document to locate information about the facility, whether this is physical data about an object, or information, such as financial, regulatory compliance, safety, HAZOP information, etc. The P&ID defines “The control of the flow of the process” where the PFD is the main circuit; the P&ID is the control circuit. Once thoroughly conversant with the PFD & Process description, the engineers from the relevant disciplines (piping, electrical & control systems) attend a number of HAZOP sessions to develop the P&ID.

P&ID standards

Before development of the P&ID can begin, a thorough set of standards is required. These standards must define the format of each component of the P&ID.

The following should be shown on the P&ID:

• Mechanical Equipment

• Equipment Numbering

• Presentation on the P&ID

• Valves

• Hand valves

• Control valves

• Piping

• Pipe numbering

• Nozzles & Flanges

• Equipment & instrument numbering systems

                                                                    

Completed P&ID

Instrumentation documentation

Instrumentation documentation consists of drawings, diagrams and schedules. The documentation is used by various people for different purposes. Of all the disciplines in a project, instrumentation is the most interlinked and therefore the most difficult to control. The best way to understand the purpose and function of each document is to look at the complete project flow from design through to commissioning.

• Design

• Design criteria, standards, specifications, vendor lists

• Construction

• Quantity surveying, disputes, installation contractor, price per meter, per installation

• Operations

• Maintenance commissioning

Instrument list

This is a list of all the instruments on the plant, in the ‘List’ format. All the instruments of the same type (tag) are listed together; for example, all the pressure transmitters ‘PT’ are grouped together. 

1. Instrument index lists 

Associated documentation such as loop drawing number, datasheets, installation details and P&ID.

2. Loop List 

The same information as the instrument list but ordered by loop number instead of tag number. This sort of order will group all elements of the same loop number together. 

3. Function 

Gives a list of all the instrumentation on the plant and may include ‘virtual’ instruments such as controllers in a DCS or PLC.

4.Tag No 

The instrument tag number as defined by the specification. 

5.Description 

Description of the instrument as denoted by the tag number. 

6.Service Description 

A description of the process related parameter.

7.Functional Description 

The role of the device. 

8.Manufacturer 

Details of the manufacturer of the device. 

9.Model 

Details of the model type and number.

Instrument location plans

The instrument location drawing is used to indicate an approximate location of the instruments and junction boxes. This drawing is then used to determine the cable lengths from the instrument to the junction box or control room. This drawing is also used to give the installation contractor an idea as to where the instrument should be installed.

Cable racking layout

Use of the racking layout drawing has grown with the use of 3D CAD packages;

this drawing shows the physical layout and sizes of the rack as it moves through

the plant.

                                     

                                           Cable racking layout

Cable routing layout

Prior to the advent of 3D CAD packages, the routing layout used a single line to indicate the rack direction as well as routing and sizes and was known as a ‘Racking & Routing layout’.

                                         

                                         Cable routing layout

Block diagrams – signal, cable and power block diagrams

Cable block diagrams can be divided into two categories: Power and Signal block

diagrams. The block diagram is used to give an overall graphical representation of the cabling philosophy for the plant.

                                                                     

                                    Block diagram

Field connections / Wiring diagrams

1. Function

To instruct the wireman on how to wire the field cables at the junction box.

2. Used by 

The installation contractor. When the cable is installed on the cable rack, it is left lying loose at both the instrument and junction box ends. The installation contractor stands at the junction box and strips each cable and wires it into the box according to the drawing.

Power distribution diagram

1.Function 

There are various methods of supplying power to field instruments; the various formats of the power distribution diagrams show these different wiring systems.

2. Used 

by Various people depending on the wiring philosophy, such as the panel wireman, field wiring contractor.

Earthing diagram

1. Function Used to indicate how the earthing should be done. Although this is often undertaken by the electrical discipline, there are occasions when the instrument designer may or must generate his own scheme – Eg. for earthing of zener barriers in a hazardous area environment.

2. Used by

Earthing contractor for the installation of the earthing. This drawing should also be kept for future modifications and reference.

Loop diagrams

1. Function 

A diagram that comprehensively details the wiring of the loop, showing every connection from field to instrument or I/O point of a DCS/PLC.

2.Used by

Maintenance staff during the operation of the plant and by commissioning staff at start up.

Electrical documentation

The electrical schematics section covers the layout of electrical schematic diagrams, lists and various symbols used.