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PROJECT REPORT
Larsen & Toubro Engineering Limited, Faridabad
SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE
AWARD OF THE DEGREE OF
BACHELOR OF TECHNOLOGY
(Electronics and Instrumentation)
SUBMITTED BY
Ujjwal Singh
11BEI0101
UNDER THE GUIDANCE OF
Mr. Anshul Kaushik
Manager of Control System
L&T Engineering
SCHOOL OF ELECTRICAL ENGINEERINGVIT University
VELLORE – 632014, Tamil Nadu, India
(JULY 2014)
A
FOUR WEEKS
SUMMER TRAINING PROJECT REPORT
ON
OVERVIEW OF INSTRUMENTATION IN PIPING INDUSTRY
(WITH EMPHASIS ON FIELD INSTRUMENTATION)
AT
LARSEN AND TOUBRO ENGINEERING LIMITED, FARIDABAD
DECLARATION
I hereby declare that the project is an authentic record of my own work carried out at Larsen
& Toubro Engineering Limited, Faridabad as requirements of Industrial Training semester
for the award of degree of B.Tech (Electronics and Instrumentation), VIT University,
Vellore(Tamil Nadu) under the guidance of Mr. Anshul Kaushik and Mr. Varneek Mathur.
Ujjwal Singh
Date: 9th July 2014
Certified that the above statement made by the student is correct to the best of our knowledge
and belief.
SANJAY TIWARI
HOD-CONTROL SYSTEMS
L&T-ENGINEERING
Acknowledgement
I would like to extend my gratitude towards Larsen & Toubro Limited for providing me with
an excellent opportunity to undergo summer training from this prestigious engineering
company of our country. I am grateful to the company for providing me access to the in-house
resources towards the completion of this report.
I would like to express my deepest thank to Mr. Sanjay Tiwari, Head of Department –
Control Systems, for providing me the very first introduction on the practical side of the
subject, thereby opening an interesting training opportunity of four weeks besides extending
me valuable guidance from time to time.
A special thanks to my training in-charge and mentor Mr. Anshul Kaushik and Mr. Varneek
Mathur– Control Systems Department. It was only with their active support, inspiration and
efforts to explain concepts clearly, that this training program became very interesting and
fruitful for me. Despite of their busy work schedule with the ongoing projects, they took out
time to help me collect plenty of study material from the in-house resources as well as made
himself available to clear all the doubts and problems.
My experience of the four weeks at L&T was very rewarding. The work environment within
the office was excellent. It has been a memorable first brush with the industry and that too with
an engineering company which lives by the motto: “It’s all about Imagineering”.
Table of Contents
ABSTRACT
COMPANY PROFILE
1 INTRODUCTION TO INSTRUMENTATION
1.1 WHAT IS INSTRUMENTATION
1.2 WHY INSTRUMENTATION?
1.3 SCOPE OF INSTRUMENTATION
1.4 PURPOSE OF INSTRUMENTATION:
1.5 CONTROL LOOPS
2 LEVEL MEASUREMENT
2.1 LEVEL GAUGES
2.2 FLOAT
2.3 DISPLACER LEVEL INSTRUMENTS
2.4 ULTRASONIC LEVEL MEASUREMENT
2.5 RADAR LEVEL MEASUREMENT
2.5.1 Guided Wave Radar Level Transmitter
2.6 CAPACITANCE TYPE
2.7 LEVEL INSTRUMENT SELECTION TABLE
3 TEMPERATURE MEASUREMENT
3.1 RESISTANCE TEMPERATURE DETECTOR (RTD)
3.2 THERMOCOUPLES
3.3 THERMISTOR
3.4 THERMOWELL
3.5 SELECTION OF TEMPERATURE INSTRUMENTS.
4 PRESSURE MEASUREMENT
4.1 TYPES OF PRESSURE:-
4.2 CLASSIFICATION OF PRESSURE MEASURING INSTRUMENTS:
4.3 SELECTION OF PRESSURE INSTRUMENT
4.4 DIFFERENT TYPES OF PRESSURE INSTRUMENTS:
4.4.1 Elastic Elements
4.4.2 Pressure Transmitter
5 FLOW MEASUREMENT
5.1 TYPES OF FLOW:
5.2 REYNOLDS NUMBER
5.3 PRESSURE BASED FLOW METERS
5.4 SELECTION OF FLOW INSTRUMENTS
5.5 METHODS OF FLOW MEASUREMENT
5.5.1 Inferential flow measurements
6 VALVE
6.1 CLASSIFICATION:-
6.2 BASIC COMPONENTS (PARTS)
6.3 CONTROL VALVE
6.3.1 Gate valve
6.3.2 Globe valve
6.3.3 Butterfly valve
6.3.4 Ball valve
6.3.5 Check valve
6.4 CAVITATIONS & FLASHING IN CONTROL VALVES
6.5 ACTUATOR
6.6.1 Pneumatic
6.6.2 Electric
6.6.3 Intelligent Actuators.
7 HAZARDOUS AREA CLASSIFICATION
7.1 STANDARDS USED FOR HAZARDOUS AREA
7.2 AREA CLASSIFICATION ACCORDING TO THE IEC
7.2.1 Zone Definition
7.2.2 IEC Marking
7.3 CLASSIFICATION ON THE BASIS OF NEC
7.3.1 Class Classification:
7.3.2 Division Classification:
7.4 TEMPERATURE CLASSIFICATION
7.4.1 Safe Equipment Operating Temperature
8 GENERAL TERMINOLOGY USED IN A PROJECT
8.1 P&ID DIAGRAMS
8.1.1 Studying P&ID
8.1.2 P&ID sheet
8.2 DIFFERENT TYPES OF FUNCTIONAL SYMBOLS
8.3 FIELD INSTRUMENT MAIN SYMBOLS
8.4 INSTRUMENT INDEX
8.4.1 Purpose
8.4.2 Contents
8.4.3 P&ID Sample
8.4.4 Sample Instrument Index:
8.5 DATA SHEET \ INSTRUMENT SPECIFICATION SHEET
8.5.1 Purpose
8.5.2 Inputs Documents
8.5.3 Activities
8.5.4 Contents
8.5.5 Sample Data Sheet
8.6 INSTRUMENTATION INSTALLATION & HOOK-UP DRAWINGS
8.6.1 Purpose
8.6.2 Input Documents
8.6.3 Activities
8.6.4 Contents
8.6.5 Sample Hook-Up Diagram
ABSTRACT
This project report consists of brief Overview of Instrumentation in Piping Industries with
emphasis on Field Instrumentation like temperature measurement, pressure measurement,
flow measurement and level measurement. We can say this report dealing with the various
types of temperature measuring instruments, pressure measuring instruments, flow measuring
instruments and level measuring instruments used in process industries. This report is also
consist types of valves used in process industries.
This report includes study of piping and instrumentation diagrams (P&ID). P&IDs having
legend sheets and these Legend sheets are required to study P&ID, which helps to identify all
the symbols in P&ID.
This report also contain instrument index of those P&IDs which were created by me during
training period. Instrument index contain information about instrument’s location, type, signal,
service etc. This report also contain instruments data sheets for field Instruments like pressure
gauges, pressure transmitters, temperature gauges , temperature elements, temperature
transmitters which were also created by me during training period.
C OMPANY PROFILE
Overview
L&T is India’s largest engineering and construction conglomerate with additional interests in
electrical, electronics and IT. Today it is one of India’s biggest and best known industrial
organizations with a reputation for technological excellence, high quality of products and
services, and strong customer orientation. Seven decades of a strong, customer-focused
approach and the continuous quest for world-class quality have enabled it to attain and sustain
leadership in all its major lines of business. L&T enjoys a premier brand image in India and its
international presence is on the rise, with a global spread of over 30 offices and joint ventures
with world leaders. It continues to grow its overseas manufacturing footprint, with facilities in
China and the Gulf region. The company's businesses are supported by a wide marketing and
distribution network, and have established a reputation for strong customer support.
History
Larsen & Toubro was founded in Bombay in 1938 by 2 Danish engineers Henning Holck-
Larsen and Soren Kristian Toubro. Both of them were strongly committed towards developing
India’s engineering capabilities to meet the demands of industry. Beginning with the import of
machinery from Europe, L&T rapidly took on engineering and construction assignments of
increasing sophistication. Today, the company sets global engineering benchmarks in terms of
scale and complexity.
Henning Holck-Larsen and Soren Kristian Toubro, school-mates in Denmark, would not have
dreamt, as they were learning about India in history classes that they would, one day, create
history in that land. In 1938, the two friends decided to forgo the comforts of working in
Europe, and started their own operation in India. All they had was a dream and the courage to
dare. Their first office in Mumbai (Bombay) was so small that only one of the partners could
use the office at a time. In the early years, they represented Danish manufacturers of dairy
equipment for a modest retainer. But with the start of the Second World War in 1939, imports
were restricted, compelling them to start a small work-shop to undertake jobs and provide
service facilities.
Germany's invasion of Denmark in 1940 stopped supplies of Danish products. This crisis
forced the partners to stand on their own feet and innovate. They started manufacturing dairy
equipment indigenously. These products proved to be a success, and L&T came to be
recognized as a reliable fabricator with high standards. The war-time need to repair and refit
ships offered L&T an opportunity, and led to the formation of a new company, Hilda Ltd., to
handle these operations. L&T also started two repair and fabrication shops - the Company had
begun to expand. Again, the sudden internment of German engineers (because of the War) who
were to put up a soda ash plant for the Tata’s, gave L&T a chance to enter the field of
installation - an area where their capability became well respected.
The Journey
In 1944, ECC was incorporated. Around then, L&T decided to build a portfolio of foreign
collaborations. By 1945, the Company represented British manufacturers of equipment used to
manufacture products such as hydrogenated oils, biscuits, soaps and glass.
In 1945, L&T signed an agreement with Caterpillar Tractor Company, USA, for marketing
earthmoving equipment. At the end of the war, large numbers of war-surplus Caterpillar
equipment were available at attractive prices, but the finances required were beyond the
capacity of the partners. This prompted them to raise additional equity capital, and on 7th
February 1946, Larsen & Toubro Private Limited was born.
Independence and the subsequent demand for technology and expertise offered L&T the
opportunity to consolidate and expand. Offices were set up in Kolkata (Calcutta), Chennai
(Madras) and New Delhi. In 1948, fifty-five acres of undeveloped marsh and jungle was
acquired in Powai. Today, Powai stands as a tribute to the vision of the men who transformed
this uninhabitable swamp into a manufacturing landmark.
In December 1950, L&T became a Public Company with a paid-up capital of Rs.2 million. The
sales turnover in that year was Rs.10.9 million. Prestigious orders executed by the Company
during this period included the Amul Dairy at Anand and Blast Furnaces at Rourkela Steel
Plant. With the successful completion of these jobs, L&T emerged as the largest erection
contractor in the country.
In 1956, a major part of the company's Bombay office moved to ICI House in Ballard Estate. A
decade later this imposing grey-stone building was purchased by L&T, and renamed as L&T
House - it’s Corporate Office.
The sixties saw a significant change at L&T - S. K. Toubro retired from active management in
1962. It was also a decade of rapid growth for the company, and witnessed the formation of
many new ventures: UTMAL (set up in 1960), Audco India Limited (1961), Eutectic Welding
Alloys (1962) and TENGL (1963).
Products & Services
Power
Heavy Engineering
Construction
Refineries
Ship Building
Switchgear
Electrical and Electronics
Information Technology
Machinery and Industrial products
The evolution of L&T into the country's largest engineering and construction organization is
among the most remarkable success stories in Indian industry. Today, L&T is one of India's
biggest and best known industrial organizations with a reputation for technological excellence,
high quality of products and services, and strong customer orientation. It is also taking steps to
grow its international presence.
1 INTRODUCTION TO INSTRUMENTATION
Instrumentation is the art of measuring the value of some plant parameter, pressure, flow, level
or temperature, miscellaneous measurements (Fire and Gas) etc and supplying a signal that is
proportional to the measured parameter. It is the study of different instrument which are used
to measure various parameters involved in process flow.
1.1 What is InstrumentationIt is the study of different instrument which are used to measure various parameters involved in
process flow.
1.2 Why instrumentation? Ease of Operation
Product Quality
Direct Material Saving
Cost Accounting
Plant Safety
Co-ordination
Process Simulators
1.3 Scope of Instrumentation Field Instrumentation related to Pressure, Flow, Temperature, Level Instrumentation,
Analytical Instruments, and Final Control Elements etc.
Control Room Instrumentation: Typical Control Loop and Control Systems.
1.4 Purpose of Instrumentation:
The purpose of instrumentation is to provide a system such that all the required information /
data / signal in the desired form and place are available and they work for safe monitoring,
controlling and operation of the process and associated systems and to make the required
information available at local control centres and Remote Telemetry Unit (RTU) interface in
required form.
Field Instruments:
All field instruments connected with well monitoring and control, and all facilities that are not
to be operated from a central control room, shall be pneumatic except those that are connected
to RTU, which shall be electronic, SMART type. The type of outpuet for smart transmitter
shall be in HART Protocol. All instruments connected to control room and remote unit control
panels of related systems shall be electronic, SMART type. For remote control application,
remote telemetry, tale-control and data gathering, electronic instruments shall be used. All
final actuation control device, controlled from remote / Central Control Room (CCR) shall in
general be pneumatically actuated. Instrument ranges shall be selected such that the normal
operating point is between 35% and 75% of the instrument total range.
Control Room Instrumentation:
All signals to and from the Central Control Room shall be electric / electronic. The standard
signal shall be analogue 4-20mA using 2-wire system, standard thermocouple, RTD output,
and / or suitable pulse signal. Instruments located on control panels and central control room
(CCR) shall be microprocessor based. On platforms with processing facilities, a Distributed
Control System (DCS) shall be provided for monitoring and controlling the process, and for
generating alarms in case of process upsets.
Safety Instrumentation System:
The new platforms shall be provided with the following safety systems:
a) Emergency shutdown (ESD) System: The ESD system shall initiate process shutdown in
case of abnormal condition of the specified process parameter.
b) The F&G system: The F&G system shall initiate emergency shutdown (ESD) upon
detection of appropriate level of hydrocarbon and/or H2S and fire shutdown (FSD) upon
accumulation or fire
c) Manual ESD & FSD Stations: The ESD & FSD stations shall be provided at all strategic
locations on the platform for manual initiation of ESD and FSD.
All shutdown and alarm switches shall be “Fail Safe” and the targeted abnormal conditions
shall cause a loss of actuating signal to the final control element. Parameters used for
shutdown shall be sensed by independent / individual sensors at independent tapping points.
Such sensors and tapping points shall not be shared by any other loop.
1.5 Control Loops
Control Loops are two types:
Open loops :-Open loop consists of measuring devices/initiating devices monitor for
analog /digital signals for monitoring purpose. Open loops are further divided into two types;
Analog for Indication- flow, pressure, temp, level, etc & Digital for alarm (high, low, high-
high, low-low), flow, pressure, temp & level Status- valve open / close, machine running /
stopped.
Figure 1 Open Loop
Closed loops : -Closed loop consists of measuring device, controller, and final
control element. Measuring device measures the process parameter (such as pressure, flow etc)
and sends signal to controller. Controller compares the measured value (pv) with set point (sp)
and sends output signal to final control element depending upon error (sp-pv). Final control
element (such as control valve) takes action to correct the process. Closed control loops are
further divided into two types
1. On / off control- Open/close of control valve & damper valve, Start/stop of
machine
2. Regulatory control-Regulation of pressure, temperature, flow, level, etc
Controller shall be pid type depending upon service.
Proportional (p) Corrective action is proportional to error (sv-pv)
Integral (i) Corrective action is based on integrated error.
Corrects the offset
Derivative (d) Corrective action is taken before the error is detected
Used for slow loops such as temperature
Figure 2 Closed Control Loop
Modes of controller
Auto mode
(i) Process parameter is adjusted automatically depending upon set point & measured
value.
(ii) Set point to controller is either internal or external
(iii) External set point to controller is provided in case of cascade control, ratio
control & computer control (SCADA/advance process control).
Manual mode-
Process parameter is adjusted manually without any set point & any measured value.
Modes of operation of machinery
Local- Operation is from field through local control station, local control panel or
field mounted push-button assemblies
Remote- Operation is from central/remote location away from field such as control
room. In remote mode, operations can be further done in two modes-Auto & Manual
2 LEVEL MEASUREMENT
Many industrial processes require the accurate measurement of fluid or solid (powder, granule
etc.) height within a vessel. A wide variety of technologies exists to measure the level of
substances in a vessel, each exploiting a different principle of physics.
2.1 Level G auges The level gauge is to liquid level measurement as manometers are to pressure measurement: a
very simple and effective technology for direct visual indication of process level. In its
simplest form, a level gauge is nothing more than a clear tube through which process liquid
may be seen. The following photograph shows a simple example of a sight glass.
A functional diagram of a sight glass shows how it visually represents the level of liquid inside
a vessel such as a storage tank
Figure 3 Level Gauge mounted on Stand pipe
2.2 Float A device that rides on the surface of the fluid or solid within the storage vessel. The float itself
must be of substantially lesser density than the substance of interest and it must not corrode or
otherwise react with the substance.
Figure 4 Liquid level measurements using flexible floating tape by person
The Primary device is a float that by reason of its buoyancy will follow the changing level of
the liquid, and a mechanism that will transfer the float action to a pointer. The float is usually
attached to a cable, which around a pulley or drum to which the indicating pointer is attached.
The movement of the float is thus transferred to the pointer, which indicates the liquid level on
an appropriate scale.
2.3 Displacer level instruments Displacer level instruments exploit Archimedes’ Principle to detect liquid level by
continuously measuring the weight of a rod immersed in the process liquid. According to
Archimedes’ Principle, buoyant force is always equal to the weight of the fluid volume
displaced. As liquid level increases, the displacer rod experiences a greater buoyant force,
making it appear lighter to the sensing instrument, which interprets the loss of weight as an
increase in level and transmits a proportional output signal.
A drain valve allows the cage to be emptied of process liquid for instrument service and zero
calibration.
2.4 Ultrasonic Level Measurement
Principle of Operation:-
Both ultrasonic and sonic level instruments operate on principle of using sound waves to
determine fluid level. The frequency range for ultrasonic methods is 20–200 kHz, and the
sonic types use a frequency of 10 kHz.
Theory:-
A top-of-tank mounted transducer directs waves downward onto the surface of the material
whose level is to be measured. Echoes of these waves return to the transducer, which performs
calculations to convert the distance of wave travel into a measure of level in the tank. A
piezoelectric crystal inside the transducer converts electrical pulses into sound energy that
travels in the form of a wave at the established frequency and at a constant speed in a given
medium. This time will be proportional to the distance from the transducer to the surface and
can be used to determine the level of fluid in the tank.
Figure 5 Top mounted Ultrasonic level transducer
Advantages
Non-contact type of Level measurement
Quick and easy to calibrate
Disadvantage
Cannot be used for foam.
Will not work in vacuum.
Various factors like instrument accuracy vapour concentration, pressure temperature,
relative humidity, and pressure of other gases/vapors may affect the performance.
2.5 Radar Level Measurement RADAR stands for Radio Detecting and Ranging. Radar measurement technology measures
the time of flight from the transmitted signal to the return signal. From this time, distance and
level measurements are determined. Radar technology does not require a carrier medium and
travels at the speed of light (3x108m/s). Most industrial radar devices operate from 6 to 26
GHz. Principle of operation:-
A sensor oscillator sends down a linear frequency sweep, at a fixed bandwidth and sweep time.
The reflected radar signal is delayed in proportion to the distance to the level surface. Its
frequency is different from that of the transmitted signal and the two signals blend into a new
frequency proportional to distance.
Principle of Pulse Time of Flight:-
D=Ct/2
Where d - Distance to be measured (Level)
C - Velocity of light
t - Time flight
An advantage of this technique is that the level measurement signals are FM rather than AM.
Antennas for the Noninvasive methods come in two designs:
Figure 6 Radar type level Instruments
The Parabolic dish antenna tends to direct the signals over a wider area, while The Horn tends
to confine the signals in a narrower downward path. The choice of one or the other, and its
diameter, depends on application factors such as tank obstructions that may serve as reflectors,
the presence of foam, and turbulence of the measured fluid.
Advantages
Non-contact level measurement up to 40 meters (80 meters in special cases)
High accuracy +/- 3mm
2 wire loop powered 24VDC, 4-20mA output.
Application
Suitable for Aggressive liquids, hydrocarbons, toxic liquids and slurries. Granulated
material and most solids.
Not suited for solids except metals or large, rock like objects.
Non-contact measurement of liquid in larger tank.
2.5.1 Guided Wave Radar Level Transmitter
Guided-Wave Radar (GWR) is an invasive method that uses a rod or cable to guide the micro
wave as it passes down from the sensor into the material being measured and all the way to the
bottom of the vessel. The basis for GWR is time-domain Reflectometry (TDR). A generator
develops more than 200,000 pulses of electromagnetic energy that travel down the waveguide
and back.
Figure 7 Guided Wave Radar Level Transmitter
Applications
Transit time of pulses down and back is used as a measure of level.
Used for multi-applications like clean, viscous, slurry and interface services
Can be used in strong turbulence, agitated tank. Measurement is immune to change in
specific gravity of process fluid.
2.6 Capacitance Type
Principle of Operation:-
This technology uses the electrical characteristics of a capacitor for Level Measurement. As the
Level of conductive process material changes is proportional to the change in capacitance
occurs.
Theory:-
The basic principle behind capacitive level instruments is the capacitance equation:
C =ЄA/d
Where,
C = Capacitance
Є = Permittivity of dielectric (insulating) material between plates
A = Overlapping area of plates
d = Distance separating plates
A is constant (the interior surface area of the vessel is fixed, as is the area of the rod once
installed), only changes in or d can affect the probe’s capacitance. Capacitive level probes
come in two basic varieties: one for conductive liquids and one for nonconductive liquids
Figure 8 Capacitance level measurement conductive liquid
Consequently, capacitive level probes designed for conductive liquids are coated with plastic
or some other dielectric substance, so the metal probe forms one plate of the capacitor and the
conductive liquid forms the other. In this style of capacitive level probe, the variables are
permittivity (Є) and distance (d), since a rising liquid level displaces low-permittivity gas and
essentially acts to bring the vessel wall electrically closer to the probe.
If the liquid is non-conductive, it may be used as the dielectric itself, with the metal wall of the
storage vessel forming the second capacitor plate:
Figure 9 Capacitive level measurement of dielectric fluid
Permittivity of the process substance is a critical variable in the non-conductive style of
capacitance level probe.
Advantages
If the Probe mounted vertically then the system can be used for both continuous level
measurement and simultaneous multipoint level control.
If the Probe mounted horizontally then point level measurement can be possible but
number probes need to be installed.
This measurement is unaffected by changes in the temperature or exact composition of
the process material.
Limitation
Calibration is time consuming
Conductive residue coating will effect performance
Application
This method is suited for detecting the level of liquids, slurries, granular or interfaces
contained in a vessel.
2.7 Level Instrument Selection Table
S. no. ApplicationType of instrument most
commonly usedRemarks
1. Local Indication
a Clean services in vessels /columns
Reflex Gauge glass
b Interface Level/ Acid/ Caustic/ Dirty liquids
Transparent Gauge Glass, Capacitance type
Illuminator required in case of transparent gauge glass
c Liquid that may boil Large Chamber Gauges
dService where glass is likely to fail / Client preference
Magnetic typeNot used where forces will affect the magnetic field
e
Large tanks and underground tanks. Where other gauges cannot be used
Float and chord
2. Control Room Indication
a Clean ServiceDP Transmitter,
Guided Wave Radar
b Viscous ServiceDP Transmitter with purge or Remote seal Guided wave Radar
Check the suitability of fill liquid with reference to temperature while using Remote seal
c Slurry Service DP Transmitter with purge or
Remote seal
Guided wave Radar
d Interface ServiceDisplacer
Guided Wave Radar
e Corrosive Services Non Contact Type
3 TEMPERATURE MEASUREMENT
Basic thermodynamics concepts
Increased temperature and increased molecular activity go together. Higher temperature can
cause:
Metals to expand,
Liquids to expand
Solids to melt, and
Electrical properties (resistance) to change.
3.1 Resistance Temperature Detector (RTD)
Principle:
RTDs are sensors used to measure temperature by correlating the resistance of the RTD
element with temperature. It is made of conductor i.e. its resistance increases as we increase
the temperature of the device or it is a Positive Temperature Co-efficient device.
Common Resistance Material for RTDs
Platinum (most popular and accurate)
Nickel
Copper
Tungsten (rare)
Figure 10 RTD
A probe consists of an RTD element mounted inside a metal tube, also known as a sheath. The
sheath protects the element from the environment. RTD head shall be weatherproof IP-65
minimum and suitable for area classification.
Lead wire compensation
RTDs are resistive devices, so lead wire resistance directly affects its accuracy. This error can
be quite large, depending on the lead wire resistance (measured in ohms / foot).so we use lead
wire compensation it order to reduce the effective resistance of the lead.
3.2 Thermocouples
Principle
The principle of operation of thermocouple is based on the Seeback effect. If two conductors
of different materials are joined together and their junction is placed at different (say t1 and t2),
an EMF is created between the open ends which are dependent upon the temperature of the
junction.
They are positive temperature coefficient devices i.e. their effective Resistance increases with
the increase in Temperature. The junction is placed in the process, the other end is in iced
water at 0C.This is called the reference junction. A thermocouple construction consists of two
conductors, welded together at the measuring point and insulated from each other long the
length.
Figure 11 Thermocouples
Laws of thermocouple:-
a) Law of Intermediate temperature:-
Sum of the EMF`s generated by two thermocouple, one with its junction at 0`C and some
reference temperature, the other with its junction at same reference temperature and the
measured temperature is equivalent to that produced by single thermocouple with its junction
at 0`C and the measured temperature.
b) Law of Intermediate Metals:-
The third metal introduced into the circuit will have no effect on EMF produced so long as the
junctions of the third metal with other two are at the same temperature
Advantage
Self-powered, simple, rugged
Wide Temperature Range
Wide variety of physical forms
Disadvantage
Non linear
Least stable
Thermocouple types:-
TYPE
WIRE
COMPOSITION
mV
per F
RANGE
(`C)
SCALE
LINEARITY
ATMOSPHERE
ENVIRONMENT
RECOMMENDED
B Pt 70 – Rh 30 (+)
Pt 94 - Rh 6 (-)
0.0003 -
0.006
0 -
1800
Good at high
temp poor
below 1000 `F
Inert or slow
oxidizing
E Chromel (+)
constantan (-)
0.015 –
0.042
-184 -
900
good oxidizing
J Iron (+)
constantan (-)
0.014 –
0.035
0 - 800 good Reducing
K Chromel (+)
alumel (-)
0.009 -
0.024
-184 -
1200
good Oxidizing
R Pt 87 – Rh 13 (+)
platinum (-)
0.003 -
0.008
0 -
1600
Good at high
temp poor
below 1000 `F
Oxidizing
S Pt 90 – Rh 10 (+)
platinum (-)
0.003 -
0.007
0 -
1700
Good at high
temp poor
below 1000 `F
Oxidizing
T Copper (+)
constantan (-)
0.008 -
0.035
-184 -
350
Good but
crowded at
low end
Oxidizing or
reducing
Y Iron (+)
constantan (-)
0.022 -
0.033
-120 -
750
good Reducing
3.3 Thermistor They are very small, solid, semi-conductor made of metal oxides.The electrical resistance
decrease with an increase in temperature. For temperature measurements ,they are used in
bridge circuits, like the resistance thermometer.
Advantages
Fast
Fragile
Disadvantages
Non-linear
Limited temperature
Figure 12 Thermistor
3.4 Thermowell Thermowell is just for protecting the thermal element from any mechanical damage and
corrosion. It is used with every temperature element .Its temperature range is from cryogenic
upto1950`C. Thermowell permits temperature elements to be removed for calibration,
replacement or repair or the use of portable sensor. It is fixed into pipe or vessel secured by
threads, flanges or welds allowing the temperature element to be inserted without stress.
Standard Thermowell material is 316SS.
Figure 13 Thermowell
3.5 Selection of temperature instruments .
Sr.
NoApplication
Type of instrument
generally used
Normal
Temperature
Range (deg C)
Remarks
1 Local Indication a) Bi-metallic
b) Filled system
Liquid (other than
mercury)
Gas
0 to 400
-185 to 315
-273 to 760
2 Control room Indication
a) Various equipment like
fractionating towers,
process & utilities lines,
storage tanks etc.
b) Reactors
c) Furnace tube skin, fire
box
d) Bearings
e) Thermister
Thermocouple Type
E
K
S
T
Resistance temperature
Detector (RTD)
Thermocouple
Skin type thermocouple
(K Type)/RTD
- 40 to 900
- 40 to1200
0 to1600
- 40 to 350
-200 to 800
-50 to 150
Design is
project
specific
4 PRESSURE MEASUREMENT
Pressure is defined as Force Applied per Unit Area. Mathematically, pressure is expressed as;
P = F/A Where P – Pressure, F – Force, A – Area
4.1 Types of Pressure :-1. Gauge Pressure - Pressure above atmospheric pressure. Hence, the Zero of the Gauge
Pressure scale depends on the Atmospheric Pressure at that location.
2. Absolute Pressure – Pressure above the absolute Zero.
3. Atmospheric Pressure or Barometric Pressure
4. Vacuum - Pressure less than atmospheric Pressure.
5. Differential Pressure
Units of pressure:-
Pascal (N/m2), bar, kgf/cm2, psi (lb.f/in2), Torr (mm Hg) and mm H20)
4.2 Classification of pressure measuring instruments :-
1) Liquid Column Elements
U – tube manometer
Well manometer
Inclined manometer
Liquid barometer
2) Elastic Elements
Bourdon tubes
Diaphragm
Metallic capsule
Bellow
3) Pressure Transmitter
Piezoelectric transmitter
Capacitance transmitter
Strain gauges transmitter
Potentiometric transmitter
Magnetic (inductive transmitter) & magnetic (Reluctive transmitter)
4) High Vacuum Measurement
Thermal conductivity gauge
Pirani gauge
Ionization ( hot cathode )
Ionization ( cold cathode )
5) High Pressure Sensors (greater than 1400 bars)
Optical - 4338 bars
Dead weight piston gauge typical 5 psig to 100000 psig (ie. 6896 bars)
4.3 Selection of pressure instrument
Sr.
No
Application Type of instrument most
commonly used
Typical accuracy
minimum or better
Remarks
1 Local indication Pressure gauge
a Clean services,
gases, liquids, steam
Bourdon + 1 % FS Syphon, pulsation
dampener, liquid
filling as
recommended in
respective section
b Viscous / corrosive Diaphragm seal + 1 % FS
c Low Pressure Diaphragm + 1 % FS
d Differential Pressure Diaphragm / capsule + 1 % FS
2 Control room indication
a Clean service Normal Pressure transmitter + 0.25 % FS
b Viscous / corrosive Diaphragm seal Pressure
transmitter
+ 0.25 % FS Check the
suitability of fill
liquid with
reference to
temperature while
using remote seal
c Absolute Pressure
(where variation in
atmospheric pressure
shall have an effect
on measurement)
Absolute pressure
transmitter
+ 0.25 % FS
d Differential pressure
that is across filter
across packing in
packed columns
Differential pressure
transmitter
+ 0.25 % FS To be suitably
compensated for
condensing vapors
when tapping are at
different levels
4.4 Different types of pressure Instruments:
4.4.1 Elastic Elements
4.4.1.1 Bourdon pressure sensor Bourdon tube type pressure elements are used to detect higher pressure, because their spring
gradient is insufficient for detecting lower pressure or vacuums. Bourdon tubes are
manufactured in C, helical and spiral form. When these elements are pressurized, there cross
section tend to become more circular, which tend to straighten their shape. Helical and spiral
elements are used when it is desired to reduce the stress in tube and to increase tip movement.
They have fast speed of response ( usually 0.1 sec full scale ) and good sensitivity ( 0.01 %
of maximum pressure when unrestrained ). Their limitation includes nonlinearity which can
be compensated.
C – Bourdon pressure sensor: - It is used in direct indicating gauges, the process pressure is
connected to fixed socket end of the tube, while the tip end is sealed, because of the difference
between inside and outside radii, the bourdon tube presents different areas to pressure, which
causes the tube to tend to straighten when pressure is applied.
The pressure applied to the bourdon tube tends to straighten it and move its tip to the left the
flexure transmits the resulting force to the lower end of the force bar.
Bourdon pressure element Force balance C bourdonFigure 14 B&C – Bourdon pressure sensor
The pressure applied to the bourdon tube tends to straighten it and move its tip to the left the
flexure transmits the resulting force to the lower end of the force bar. Due to force balance
nature of the unit, the force bar is constantly balanced, therefore the sensing bourdon does not
move as long as the pressure sensed is within the range of instrument .If range is exceeded then
lower end of force bar move to the left, where it is supported by limit stop.
Spiral bourdon pressure sensor
The free end motion of C – bourdon tube is insufficient to operate some of the motion balance
devices such as the transmitters. When pressure is applied this flat spiral tends to uncoil and
produces a greater movement of the free end requiring no mechanical amplification. This
increases the sensitivity and accuracy of the instrument because no lost motion or friction is
introduced through links or levers.
Figure 15 Motion balance pressure transmitter with spiral element
In the above diagram the air supply passes through a restriction before being applied to the top
of the relay diaphragm and the nozzle. An increase in process pressure tends to straighten out
the spiral, which causes the flapper to move closer to the nozzle, this increases the nozzle back
pressure sensed by the relay diaphragm, which will move down, opening up air supply to the
output. The increased output pressure is felt by the feedback bellows and restores the flapper to
its throttling position. For each value of process pressure there is a corresponding definite
flapper position and output pressure.
Helical bourdon pressure sensor
This sensor produces even greater motion of the free end than spiral element, eliminating the
need for mechanical specification, it is suitable for pressure measurement on a continuously
fluctuating services. Other advantages include the high over range protection ; for example
a 0 to 1000 PSIG element may be safely exposed to 10,000 PSIG pressure.
4.4.1.2 Diaphragm or capsule type sensorPressure detection is based on deflection of the diaphragm. Diaphragm has nonlinear behavior
which can be corrected by using microprocessor. Microprocessor does not eliminate
nonlinearity of diaphragms, but it does memorize the amount of nonlinearity and electronically
corrects for it. The diaphragm is a flexible disc, either flat or with concentric corrugations,
which is made from sheet metal of precise dimensions.
Figure 16 Diaphragms and capsule
The capsule consists of two diaphragms welded together at their peripherals. Two basic types
of capsules are illustrated: the convex and the nested. Evacuated capsules are used for absolute
pressure detection and single diaphragms are used for highly sensitive measurement.
The design of sensor is based on pressure reference used (full vacuum or atmospheric) and
whether it is force or motion balance. When atmospheric reference is used, the reading is
called gauge pressure, and the reference is full vacuum, the measurement is called absolute
pressure. When differential pressure is measured there is no reference as the two measurements
are only subtracted. Motion balance units are capable of driving local, direct reading indicators,
but are subjected to hysteresis, friction and dead band errors. Force balance designs are
transmitting devices with high accuracy but without direct indication capability.
Diaphragm seals:-
Diaphragm seals can be installed on almost any pressure measuring instrument.
Use of diaphragm seal does not require an additional sealing element due to the all
metallic construction, and thus require less maintenance.
Two or more measuring devices can be installed on one sanitary diaphragm seal to
provide for example local and remote readings.
Use of metallic diaphragm seals on a non ceramic measuring cell does not hinder the
built – in overpressure safety of the instrument.
Bellows type pressure sensor
Bellows are formed from seamless tubes made from brass, beryllium copper, stainless steel etc.
The main advantages of bellows (relative to diaphragm capsule) are their ability to provide
longer strokes and to handle higher forces. Their sensitivity increases with their diameter.
Their limitation includes their sensitivity to ambient temperature effects, drift, friction and
elastic hysteresis. In most cases the elastic action of bellows is insufficient for accurate
measurement and spring needs to be added to precisely characterize the relationship between
force and movement.
4.4.2 Pressure Transmitter
4.4.2.1 Strain gauge transmitter Resistance Type devices used in pressure transducers are:
1. Strain Gauges
2. Moving Contacts
Strain Gauge is simply a fine wire in the form of a grid. When the grid is distorted,
the resistance of the wire changes.
R = K * L / A
Where, K = a constant for the particular kind of wire
L = length of wire
A = cross sectional area.
As the Strain gauge is distorted by the elastic deformation element, its length is increased and
its cross-sectional area is reduced. Both of these changes increase the resistance. Because little
distortion is required to change the resistance of a strain gauge through its total range, this type
of transducer can be used to detect very small movements and, therefore, very small pressure
changes.
Figure 17 Strain gauge transmitter
4.4.2.2 Capacitance Transmitter Capacitance Type Pressure Transducers consist of two conductive plates and a dielectric. As
the pressure increases, the plate moves, changing the capacitance
Advantage:
Good accuracy
Range ability
Linearity
Speed of response
Disadvantage
Temperature sensitivity
Short lead from sensors
High output impedance
Sensitivity to stray capacitance
4.4.2.3 Piezoelectric transmitter Piezoelectric manometers work on the principle of piezoelectric effect, i.e. The appearance of
electric charges on the surface of some materials .When they are subjected to a compression in
a specified direction. The material most commonly used is quartz on account of its high
mechanical properties and the variance of its piezoelectric constant over a very wide
temperature range extending from 0 to 500 degree centigrade.
Figure 18 Piezoelectric transmitter
Advantage:-
Small size
Rugged construction
High speed of response
Self generated signal
Disadvantage:-
Limited to dynamic measurement
Sensitive to temperature variation
Require special cabling and output signal amplification.
5 FLOW MEASUREMENT
The determination of the quantity of a fluid, either a liquid, vapor, or gas, that passes through a
pipe, duct, or open channel is called flow measurement. Flow may be expressed as a rate
of volumetric flow (such as liters per second, gallons per minute, cubic meters per second,
cubic feet per minute), mass rate of flow (such as kilograms per second, pounds per hour), or
in terms of a total volume or mass flow (integrated rate of flow for a given period of time).
Q=VA
Q- Flow rate, V- Velocity, A- Area
5.1 Types of flow: There are three types of flow: 1. laminar (viscous) flow
2. Turbulent flow
3. Transitional flow
Laminar Flow:
Let a liquid flow slowly and steady over a fixed horizontal surface such that the layer of the
liquid will move parallel to it, with their velocity increasing uniformly from one layer to the
next. The velocity is maximum at the free surface of the liquid. Such a type of liquid flow in
which its layers glide over one another without mixing is called laminar flow.
Figure 19 Laminar Flow
Turbulent flow:
If the liquid is pushed in the tube at a rapid rate, the flow may become turbulent. In the case,
the velocity of different particles passes though the same point may be different and change
erratically with time. The motion of water in high fall is a fast flowing river is in general
turbulent.
Figure 20 Turbulent flow
Transitional flow:
Transitional flow is the flow between laminar and turbulent. Transitional flow exhibits the
characteristics of both laminar and turbulent patterns. In some cases transitional flow will
oscillate between laminar and turbulent flow.
Figure 21 Transitional flow
5.2 Reynolds number In flow metering, the nature of flow can be described by a number-the Reynolds Number,
which is the average velocity x density x internal diameter of pipe divided by viscosity. In
equation form, this is expressed as
ρ v D
R = ---------
µ
Where, v = velocity
D = inside diameter of pipe
ρ = fluid density
µ = viscosity
The Reynolds Number has no dimensions of its own. From the Reynolds Number, it can be
determined whether the flow is laminar or turbulent.
Reynolds Number < 2000, the flow is laminar
2000<Reynolds Number <4000,the flow is transion
Reynolds Number > 4000, the flow is turbulent.
5.3 Pressure based flow meters
Bernoulli’s equation- is an expression of the Law of Energy Conservation for an in
viscid fluid stream. It states that the sum total energy at any point in a passive fluid stream
(i.e. no pumps or other energy- imparting machines in the flow path) must be constant.
Bernoulli’s Equation:- p/ρ + gh + 1/2 V2 = constant
5.4 Selection of flow instruments
Sr
No
.
Service
Type of
instrument
commonly
used
Typical
Accuracy
+
Range
ability
As per code /
Standard
a)
Clean liquids, steam and
gases, Reynolds no above
10,000
Concentric 3 to 4 % 1:3
ISO 5167 /
AGA / API
14.3 / ANSI
2530 / ASME
MFC 3M
b)
Two phase fluid with a large
quantity of undisolved gas or
gas with condensable
Eccentric 3 to 4 % 1:3
c) Slurries Segmental 3 to 4 % 1:3
d)Viscous services, Reynolds
number less than 10,000
Quadrant
Edge3 to 4 % 1:3 BS 1042
e)Very viscous service,
Reynolds number up to 250Conical 3 to 4 % 1:3
f)High viscous liquids, very
low Reynolds number Wedge Type 3 to 5 % 1:10
g) Dry or wet gas, condensate V -cone 3 to 4 % 1:3
h) For low process flow , line
size 1” to1.5”
Integral /
Honed
section
3 to 4 % 1:3
i)
Low pressure drop, large line
size, cooling water, air ducts,
compressor suction line
Averaging
Pitot Tube1 % 1:10 ISO 3966
j)
Fluid same as for orifice
plate. Better pressure
recovery, higher flow
capacity under same
condition compared to
orifice plate
Flow Nozzle 3 to 4 % 1:3
k) Clean liquids, steam and
gases and requirement is
Venturi
Tube / Flow 2 % 1:3 ISO 5167 /
AGA / API
lower permanent head loss
(Typically 10 to 14 % of the
dP depending on d/D and
straight run requirement are
usually shorter than orifice
and flow nozzle)
tube14.3 ASME
MFC 3M
Sr
NoService
Type of
instrument
commonly
used
Typical
Accuracy +
Range
ability
As per
Code /
Standard
a)Purge, small flows and local
indication / transmitter
Variable area
meter
(Rotameter)
1.6 % of
FS1:10
b)Light Product, custody
transferTurbine
0.10% of
FS1:7
API
MPMS,5.3
c)
Fluid viscosity greater than
10 CST, and volumetric flow
measurement with local
totalizer
Positive
Displacement /
Oval meter
0.05 to
0.15%1:10
API STD
1101 / ISO
2714
d) Liquid, Steam and Gas Vortex 1% FS
1:20
liquids
1:15
Gases
e)
Slurry , dirty, viscous waste
water and minimum
conductivity of 2 micromho /
cm
Magnetic 0.5% of FS 1 : 10
f) Mass flow measurementMass
coriolis
0.1% liquid
0.5% Gas1 : 10
5.5 Methods of flow measurement Many different methods are used to measure flow in a wide variety of industrial applications.
These can be divided into three broad categories as follows:
1. Inferential type flow meters 2. Quantity flow meters 3. Mass flow meters
5.5.1 Inferential flow measurements
In the inferential type of flow measuring methods, the flow rate is inferred from a characteristic
effect of a related phenomenon
The following are the inferential type of flow measuring methods
1. Variable head or differential flow meters
2. Variable area meters
3. Magnetic flow meters
4. Turbine meters
5. Target meter
6. Vortex flow meters,
7. Ultrasonic flow meters
5.5.1.1 Variable head or differential flow meters
Orifice plate
The simplest and the most common pipeline restriction used in DP method of flow
measurement is the Orifice Plate, which is a thin, circular metal plate with a hole in it. It is held
in the pipeline between two flanges called orifice flanges. It is the easiest to install and to
replace.
Concentric Orifice Plate: It is most widely used. It is usually made of stainless steel and its
thickness varies from 3.175 to 12.70mm (1/8 to 1 /2 inch.) depending on pipe line size and
flow velocity. It has a circular hole (orifice) in the middle, and is installed in the pipe line with
the hole concentric to the pipe.
Eccentric Orifice Plate: It is similar to the concentric plate except for the offset. It is useful
for measuring fluids containing solids, oils containing water and wet steam. The eccentric
orifice plate is used where liquid fluid contains a relatively high percentage of dissolved gases.
Segmental Orifice Plate: This orifice plate is used for the same type of services as the
eccentric orifice plate. It has a hole which is a segment of a circle.
Quadrant Edge Orifice Plate: This type of orifice plate is used for flows such as heavy
crudes, syrups and slurries, and viscous flows. It is constructed in such a way that the edge is
rounded to form a quarter-circle.
Figure 22 Orifice plate
Advantages
Low cost
Can be used in a wide range of pipe sizes (3.175 to 1828.8 mm.)
Can be used with differential pressure devices
Disadvantages
Cause relatively high permanent pressure loss,
Tend to clog, thus reducing use in slurry services
Have square root characteristics
Accuracy dependant on care during installation
Changing characteristics because of erosion, corrosion and scaling.
Venturi tubeThe venturi tube (see figure 4-5) consists of a section of pipe with a conical entrance (typically
20 degrees),a short straight throat, and a conical outlet (typically, a 5- to 6-degree recovery
cone). The velocity increases and the pressure drops at the throat. The dp is measured between
the input(upstream of the conical entrance) and the throat.
A Venturi tube is used where permanent pressure loss is of prime importance, and where
maximum accuracy is desired in the measurement of high viscous fluids. The pressure taps are
located one-quarter to one-half pipe diameter up-stream of the inlet cone and at the middle of
the throat section. The venturi tube can be used to handle a fluid which is handled by an orifice
plate and fluids that contain some solids, because these venturi tubes contain no sharp corners
and do not project into the fluid stream. It can be also used to handle slurries and dirty liquids.
Advantages
Causes low permanent pressure loss
Widely used for high flow rates
Available in very large pipe sizes
More accurate over wide flow ranges than orifice plates or nozzles
Can be used at low and high beta ratios
Disadvantages
High cost,
Generally not useful below 76.2 mm pipe size
More difficult to inspect due to its construction
Limitation of a lower Reynolds number of 150,000
5.5.1.2 Variable area flow meters (rotameters) A variable-area flow meter is one where the fluid must pass through a restriction whose area
increases with flow rate. This stands in contrast to flow meters such as orifice plates and
venturi tubes where the cross-sectional area of the flow element remains fixed. The simplest
example of a variable-area flow meter is the Rotameter, which uses a solid object (called a
plummet or float) as a flow indicator, suspended in the midst of a tapered tube. As fluid flows
upward through the tube, a pressure differential develops across the plummet. This pressure
differential, acting on the effective area of the plummet body, develops an upward force (F =
P/A). At some point, the flowing area reaches a point where the pressure-induced force on the
plummet body exactly matches the weight of the plummet.
This is the point in the tube where the plummet stops moving, indicating flow rate by it
position relative to a scale mounted (or etched) on the outside of the tube.
5.5.1.3 3 Magnetic flow meterMagnetic Flow meter is based upon Faraday's law of induction which states that the voltage
induced across any conductor as it moves at right angles thru a magnetic field is proportional
to the velocity of that conductor. A voltage, "Es", will be induced within this fluid which is
mutually perpendicular to the direction of the fluid velocity and the flux linkages of the
magnetic field; i.e., in the axial direction of the meter electrodes.
The electrode voltage is the summation of all incremental voltages developed within
Each fluid particle that passes under the influence of the magnetic field .
E = BDV
C
Where:
E = induced electrode voltage B = magnetic field strength (magnetic flux density)
D = pipe diameter C = dimensionless constant
Advantages
No moving components
Totally obstruction less & hence no pressure loss
Measurements unaffected by viscosity, density, temperature and pressure
Linear analog output
Disadvantages
Relatively expensive
Works only with fluids which are adequate electrical conductors
Must be full at all times
5.5.1.4 Turbine flow meter Turbine Flow meter is an electromechanical, volumetric flow measurement instrument. The
flow causes the bladed rotor to turn at an angular velocity directly proportional to the velocity
of the liquid measured. Because the cross sectional area of the meter is fixed, the angular
velocity of the rotor is directly proportional to volume flow rate. As the blades on the rotor
pass beneath a magnetic pickup coil, an AC signal is generated. Each AC pulse is equivalent to
a discrete volume of fluid. Since AC frequency is directly proportional to the angular velocity
of the rotor, the frequency is directly proportional to flowrate.
Advantage of turbine flow meter
Provides excellent repeatability and rangeability.
Fairly low pressure drop.
Can be compensated for viscosity variations.
Disadvantage of turbine flow meter
High cost
Limited use for slurry applications.
Problems caused by non-lubricating fluids.
6 VALVE A device for closing or allowing or modifying the passage or controlling the flow of a media
through a pipe.
6.1 Classification :-
CLASSIFICATION OF VALVES VAVVAVALVES
6.2 Basic Components (Parts)
BASED ON FUNCTION
ON-OFF
VALVES
REGULATING
VALVES
NON RETURN
VALVES
CONTROL
VALVES
GATE VALVES
BALL VALVE
GLOBE
VALVES
PLUG VALVE
GLOBE VALVES
NEEDLE VALVES
BUTTERFLY
VALVES
CHECK
VALVES
SPLIT DISC
VALVES
SWING
CHECK
VALVES
LIFT CHEK VALVES
PISTION CHEK
VALVES
BALL
VALVES
GATE
VALVES
DIAPHRAGM
VALVES
BUTTERFL
Y VALVES
Figure 23 Valve
1. Body
The Body & Bonnet houses the stem / trim.
# Selection of the material to fabricate the interior of the wall body is important if the valve is
used for the process of chemical.
# Some Valves may be obtained with the entire interior of the body lined with corrosion
resistant material.
2. Bonnet
The Bonnet is a part which is attached with the body of the valve.
# The Bonnet is classified on the type of attachment as Bolted, Bellow, Sealed, Screwed-on,
Welded, Union, Pressure Sealed etc.,
3. Stem
The Stem moves the disc.
4. Screwed stem - two categories
(a) Rising stemHand wheel can either rise with the stem, or stem can rise through the stationary hand wheel.
(b) Non-rising stem# The Hand Wheel and the stem are in the same position weather the valve is opened or closed.
# In this case, the screw is inside the Bonnet and in contact with the fluid
5. Disc, seat & port
# The part directly affecting the flow is termed as Disc regardless of its shape.
# The Non-moving part the body bears is termed as seat.
1 Plug Stem2 Packing Flange 3 Packing Flange Nut4 Packing Flange5 Packing Follower6 Packing7 Lantern Ring (Optional)8 Valve Bonnet9 Body Stud10 Body Stud Nut11 Body Gasket12 Guide Bushing13 Cage (2)14 Seat Ring15 Seat Ring Gasket16 Plug17 Plug Pin18 Valve Body19 Drive Nut
# The port is the maximum internal opening for flow.
6. Seals / gaskets
# Gasket is used in between a bolted bonnet and valve body.
# Metal Bellows where high vacuum or corrosive, flammable fluids are to be handled.
# Flanged Valves use gasket to seal against the line flanges.
6.3 Control valve
6.3.1 Gate valve
Gate valve is used for isolation. On –off applications, works well with flow from either
direction. Blocked in volume when valve is closed. Gate valve are used when a straight line
flow of fluid and minimum restriction is desired. Gate valve are so named because they either
stop or allow flow through the valve. The gate is usually wedge shaped when the valve is wide
open the gate is fully drawn up to into the valve leaving an opening for flow through the valve
the same size as the pipe in which the valve is installed.
Advantage
Can be used when the fluid contains suspended solids (in paper industry)
Gives good shut off, used as on-off valves.
Normally not used as control valve
6.3.2 Globe valve
The globe valve is used for regulation. Works best with flow from one direction. Suitable for
the use in wide range of conditions, available in size up to about NPS14. No blocked in volume
when valve is closed.
Advantages
Low likelihood of cavitation and noise
Wide range of special designs for corrosive, abrasive. High temperature and high
pressure applications
Linear relationship between control signal and valve stem movement
Small dead band/hysteresis
Disadvantages Higher cost
Lower capacity
Higher gland leakages
6.3.3 Butterfly valve
The butterfly valve have a body like a butterfly disk , a stem, packing a notched positioning
plate and a handle.
Advantages
Lower cost (compared with globe)
Higher flow capacity ( 2 -3 times of globe)
Reduced erosion
Low stem leakage
Disadvantages
High pressure recovery leads to low vena contracta pressure, increases the chances of
cavitations.
Due to high capacity, it has the tendency of small valve in large pipe, leads to higher
pressure drop.
Actuator needs to be oversized because of high break torque requirement.
High leakages.
Cannot be used without positioners.
Figure 24 Butterfly valve
6.3.4 Ball valve
There is a ball is used to just to stop and start the flow of fluid ball perform
the same function as the disk in globe valve. When the valve hand is
operated to open the valve, the ball rotate to a point where the hole through
the ball is in line with the valve body inlet and outlet. When the valve is
shut which requires only a 90 degree rotation of the hand well for most
valves, the ball is rotated so the hole is perpendicular to the flow opening
of the valve body and flow is stopped. Advantages
Lower cost (compared with globe)
Higher flow capacity ( 2 -3 times of globe)
Better shut-off
Can provide near =% characteristic
Disadvantages
High pressure recovery leads to low vena contracta pressure,
increases the of cavitations
Due to high capacity, it has the tendency of small valve in large
pipe, leads to higher pressure drop
Actuator needs to be oversized because of high break torque
requirement.
Cannot be used without positioners control applications.
Figure 25 Ball valve
6.3.5 Check valve
Check valve works only with flow from one direction Suitable for use in wide range of
conditions and available in any sizes. No blocks in volume when the valve is closed. Almost
always prone to leaks through seat.
6.4 Cavitation & Flashing in Control valves
• Cavitations - Two stage process,
• Formation of bubbles
• Collapse of bubbles
• Cavitations occur when the pressure inside the valve (Pmin) goes < vapour pressure of
fluid (PV) at that temp & recovers above the vapour pressure of fluid at outlet of valve.
• Flashing -Flashing occurs when valve outlet pressure is low enough that vapour
bubbles no longer collapse.
Effects of cavitations
• Increased noise
• Vibration in piping system
• Damage to valves
• Reduced capacity of valve
Remedy
• Selection of hard trim material to increase life
• By reducing the pressure in stages
6.5 Actuator Part of valve responds to applied signal and causes motion of valve resulting in modification of
flow.
Type of actuators:6.5.1 Pneumatic
Diaphragm/Spring
High thrust at low air pressures
Fail safe position with springs
Large size and weight
6.5.2 Electric
Electromechanical actuators
Utilizes a reversible motor
Can be used for both linear and rotary valves.
Torque switches are provided for safeguarding motor in case of is failure and during
valve choking.
Electro-hydraulic actuators
Advantages:
Higher actuator stiffness
Excellent throttling ability
Disadvantages:
Complexity and maintenance difficulty
Fail-safe action only with accessories
6.5.3 Intelligent Actuators.
Additional information is available for operator which can useful for optimization and
diagnostics
Can protect electric motors from burning (during reverse phasing or valve jammed)
Self-calibrating
7 HAZARDOUS AREA CLASSIFICATION
When electrical equipment is used in, around, or near an atmosphere that has flammable gases
or vapors, flammable liquids, combustible dusts, ignitable fibers or flying, there is always a
possibility or risk that a fire or explosion might occur is often called a hazardous (or classified)
location/area. Currently there are two systems used to classify these hazardous areas; the
Class/Division system and the Zone system. The Class/Division system is used predominately
in the United States and Canada, whereas the rest of the world generally uses the Zone system.
7.1 Standards used for Hazardous areaWorld standards for the classification of hazardous areas are moving toward harmonization.
a) International electro-technical Commission (IEC) - European Standard
b) National Electric Code (NEC) - U.S. Standard
c) Canadian Electric Code (CEC) - Canadian Standard
7.2 Area Classification according to the IECThe IEC classification system used throughout much of the world. It recognizes three levels of
probability that a flammable concentration of material might be present. These levels of
probability are known as Zone 0, Zone 1, and Zone 2.
7.2.1 Zone Definition
The hazardous location areas are defined by taking into account the different dangers presented
by potentially explosive atmospheres.
Zone 0 - In which ignitable concentrations of flammable gases or vapors are:
Present continuously
Present for long periods of time
Zone 1 - In which ignitable concentrations of flammable gases or vapors are:
Likely to exist under normal operating conditions
May exist frequently because of repair, maintenance operations, or leakage
Zone 2 - In which ignitable concentrations of flammable gases or vapors are:
Not likely to occur in normal operation
Occur for only a short period of time
Become hazardous only in case of an accident or some unusual operating condition.
7.2.2 IEC Marking
7.3 Classification on the basis of NEC
7.3.1 Class Classification:
Classes define the type of hazard in terms of whether it is a gas or vapors, a combustible or
conductive dust or an ignitable fiber or flying. Class I - A location in which a flammable gas or vapor is or may be present in
sufficient quantity to cause an explosive atmosphere
Class II - A location in which a conductive or combustible dust is or may be present
in sufficient quantity to cause a fire or an explosive hazard.
Class III - A location in which easily ignitable fibers or flying are present in
sufficient quantity to present a serious risk of.
7.3.2 Division Classification:
Divisions define the probability of the presence of the hazard being present during normal or
abnormal conditions.
Division 1 - The defined hazard is present during normal operational conditions.
Division 2 - The defined hazard is present only during abnormal conditions such as
equipment failure.
7.4 Temperature Classification A mixture of hazardous gases and air may be ignited by coming into contact with a hot surface.
The conditions under which a hot surface will ignite a gas depends on surface area,
temperature, and the concentration of the gas. The same can be said about combustible
dusts. The T code of a product denotes the maximum surface temperature that a given product
will not exceed under a specified ambient temperature. For example, a product with a T code
of T3 means that its maximum surface temperature will not exceed 200 deg C provided it is
operated in a ambient temperature defined by the manufacturer.
7.4.1 Safe Equipment Operating Temperature
8 General terminology used in a Project
Equipment location drawings- Show the exact floor plan for location of equipment in
relation to the plant’s physical boundaries.
PFD and P&ID- Process Flow Diagrams (PFD) and Process and Instrument Diagrams
(P&ID) are used to outline or explain the complex flows, equipment, instrumentation,
electronics, elevations, and foundations that exist in a process unit. A PFD is a simple
flow diagram that describes the primary flow path through a unit. A P&ID is a complex
representation of the various units found in a plant. Standardized symbols and diagrams
have been developed for most pieces of industrial equipment, process flows, and
instrumentation.
Elevation drawings- A graphical representation that shows the location of process
equipment in relation to existing structures and ground level. In a multistory structure,
the elevation drawing provides the technician with information about equipment
location. This information is important for making rounds, checking equipment,
developing checklists, catching samples, and performing startups and shutdowns.
Electrical drawings- Symbols and diagrams that depict an electrical process.
Legends- A document used to define symbols, abbreviations, prefixes, and specialized
equipment (ISA S5.1)
Loop Diagram- A loop diagram traces all instrument connections between the field
instrument and the control room panel. This includes wiring connections at field
junction boxes, and control room panels and front connections.
8.1 P&ID Diagrams
A P&ID in simplest terms is defined as - P&ID is a schematic diagram that shows piping,
equipment and instrumentation connections with in various process units in any plant. A few
examples of this are oil refineries, petrochemical and chemical plants, natural gas processing
plants, power plants, treatment plants and pharmaceutical plants. A P&ID is key document that
supplies vital engineering information on process and instrumentation requirement to design
engineers for carrying out detailed engineering activities of the plant. P&ID is a dynamic
document during project execution as it undergoes several cycles of reviews and revisions
during course of detail design activity.
An instrumentation engineer can get the following information:-
How many instruments and type are there in the project?
What kinds of pipes are needed and what is their specification? It is required to prepare
accurate Hook-up drawing s with respect to piping class and process service.
Idea of the process in consideration
Type of system (DCS, Local PLC, ESD PLC etc.) which is associated with a particular
instrument
8.1.1 Studying P&ID
In a particular P&ID diagram we need the following basic things before we start evaluating the
P&ID sheet
Legend sheet for the particular P&ID sheet
Basic idea of the process under consideration (PFD)
Instrument specification sheet for instrument type, connection type/ size etc.
Where possible the diagram should be arranged so that the process material flows from
left to right, with upstream units on the left and downstream units on the right.
8.1.2 P&ID sheet
Final P&ID sheet contain layout of the plant in a schematic form for the understanding of the
engineers. It show specification, position, fitting & use instruments.
8.1.2.1 Line
8.1.2.2 Valves
Figure 26 Valves
8.2 Different types of Functional Symbols
Figure 27 Functional Symbols
8.3 Field Instrument Main Symbols
Figure 28 Field Instrument Main Symbols
8.4 Instrument Index Generally Instrument Index is prepared in EXCEL (.xls format). An instrument index contains
all the parameters and data related to an instrument in a given P&ID sheet. It is mandatory to
cover every instrument in a given P&ID sheet. Once we make an instrument index data base
for a project then, it becomes very easy to keep a track on all the instrument logistics. With the
help of an instrument index we can order instrument and spare parts very easily. Instrument
Index contains some mandatory fields and some optional/ additional fields as per client
requirements. Basic Instrument Index is prepared at very early stage of a project and gets
modified at later stages.
8.4.1 Purpose
To reflect instrument tag numbers, make, model numbers and relevant drawings numbers. It
acts as a database of all the instruments and it is the reference document to prepare many other
documents such as I/O list, Hook-up etc.
8.4.2 Contents
Tag number
Service
Item description
Location
P & ID number
Instrument Range
Vendor / Model number
M.R/ R.F.Q number
Installation drawing number
Loop schematic number
Instrument layout number, etc.
8.4.3 P&ID Sample:
8.4.4 Sample Instrument Index :
8.5 Data Sheet \ Instrument Specification Sheet
8.5.1 Purpose
To reflect the design requirement of instrument and are enclosed as a part of RFQ(request for
quotation) to enables obtain bids from the instrument vendors.
8.5.2 Inputs Documents
P & IDs
Bid Package documents – design Criteria and Instrument Data Sheets
Process Instrument Data Sheets
Piping & Material Specifications
8.5.3 Activities
Carry out Preliminary Sizing Calculations if applicable.
Preparation of Instrument Data Sheet
Attach relevant standard specifications with instrument data sheets.
8.5.4 Contents
Genera data
Process and Instrumentation data
Materials specification
Purchase and notes.
8.5.5 S ample Data Sheet
(a)
b) Data sheet for Level Indicating Trasmitter
Figure 29 Data sheet_02-2
c) Data sheet for Differential Pressure Indicator
Figure 30 Data sheet_03
8.6 Instrumentation Installation & hook-up drawings
8.6.1 Purpose
To enable the installation of instruments and listing of Instrumentation fittings used.
8.6.2 Input Documents
Instrument data sheet
P&ID
Instrument Index
Piping Material specifications
8.6.3 Activities
Preparation of installation of instruments and hook up drawings.
8.6.4 Contents
Piping specification references.
Tag number references.
Bill of material including item numbers, item description, quantity and material.
Any special notes.
Reference documents.
8.6.5 Sample Hook-Up Diagram
Figure 31 Hook-Up Diagram
Figure 32 Hook-Up Diagram
END…
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