mechanics-of-solids-and-fracture

mechanics-of-solids-and-fracture                                      mechanics-of-solids-and-fracture

mechanics-of-solids-and-fracture

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corrosion types summary photo

corrosion types summary photo                                          corrosion types summary photo

corrosion types summary photo

Protection of metallic materials against corrosion BS EN 12502

Protection of metallic materials 

against corrosion

BS EN 12502-1:2004

This document gives guidance for the assessment of the corrosion likelihood of metallic materials in water
distribution and storage systems, as a result of corrosion on the water-side.
NOTE This document lists the different types of corrosion and describes in general terms the factors influencing
corrosion likelihood.
Water distribution and storage systems considered in this document are used for waters intended for human
consumption according to EC directive 98/83/EEC and for waters of similar chemical composition.
This document does not cover systems that convey the following types of water.
 sea water;
 brackish water;
 geothermal water;
 sewage water;
 swimming pool water;
 open cooling tower water;
 recirculating heating and cooling water;
 demineralized water.

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Corrosion Types

Corrosion Types                            Corrosion Types                                     Corrosion Types

Corrosion Types

CORROSION CASE STUDY ,PRINCIPLES AND TYPES

CORROSION CASE STUDY ,PRINCIPLES AND TYPES 

INTRODUCTION
Corrosion removal deals with the taking away of mass from the surface of materials by their environment and other forms of environmental attack that weaken or otherwise degrade material properties.

Principles of Corrosion

Corrosion of metals and alloys is an electro chemical process. The scientific basis of corrosion in aqueous systems is well understood. In these electrochemical corrosion processes, the following steps take place:
· A difference exists between the oxidation reduction potential for two materials or sites that are connected electrically. The material with the most negative oxidation reduction potential is the anode and the material with the most positive oxidation reduction potential is the cathode.
· The anode loses positively charged ions and electrons flow away from the anode. This process is referred to as oxidation. The anode is the portion of the metal surface that is corroded.
The general form of the anodic reaction is:

M → Mⁿ⁺ + ne⁻

Where M is the substance being oxidized, and n is the number of electrons (e⁻) given up by M. Iron, zinc, nickel, tin, and copper typically release two electrons.
· The electrons from the anode flow through a conductor to the cathode and react with positive ions in the electrolyte at the cathode.
· The electrons react with positive ions in the electrolyte at the cathode. This process is referred to as reduction. The cathode does not have to be another component, but can be hydrogen ions, dissolved oxygen or metal ions.
There are several cathodic reactions that may occur:
Mⁿ⁺ + ne⁻ → M (Metal deposition)
O2 + 4H⁺ + 4e⁻→ 2H2O (Oxygen reduction in an acidic solution)
O2 + 2H2O + 4e⁻ → 4OH⁻ ( Oxygen reduction in a neutral or alkaline solution)
Mⁿ⁺ + e⁻ → M(ⁿ¹)⁺ (Metal ion reduction)
2H⁺ + 2e⁻ → H2 (Hydrogen ion reduction, causing hydrogen gas evolution)
2H2O + 2e⁻ → 2OH⁻+ H2 (Reduction of water)

Corrosion is classified as general or localized. For general corrosion of a metal surface, the whole surface consists of continually shifting anodic and cathodic sites, so that any point on the surface is alternately anodic and cathodic during the time corrosion is taking place. For localized corrosion, the anodic and cathodic sites are permanently separated from each other.

The slowing down or retardation of the corrosion process
is called polarization. There are three types of polarization that can retard corrosion:
activation polarization, resistance polarization and concentration polarization.
· Activation polarization occurs when activation energy is required to enable the corrosion reaction to occur.
· Resistance polarization occurs when the electrolyte resistance is sufficiently high that the current resulting from corrosion polarizes the anodes and the cathodes.
· Concentration polarization occurs when the reaction is controlled by the diffusion of a reactant (such as Fe²⁺, H⁺ or oxygen) through the electrolyte to the metal surface.
types of corrosion
The major types of corrosion that may occur at a nuclear power station include:
· General or Uniform Corrosion

· Localized Corrosion
· Galvanic Corrosion
· Intergranular Corrosion
· Dealloying Corrosion
· Cracking Phenomena

General or Uniform Corrosion
General or uniform corrosion is a corrosion that occurs without significant localized degradation. Although rapid general corrosion can occur if improper materials are selected, this type of degradation is normally the least dangerous type due its predictability. The susceptibility of a given metal or alloy to general corrosion in a given environment can be classified in one of three ways:
· General corrosion occurs and corrosion product dissolves.
· General corrosion occurs, but a passive protective coating develops and significantly reduces the corrosion rate.
· The metal or alloy does not corrode in the given environment.

A common form of general corrosion is the attack of oxygenated water on iron, which
produces rust. Rust is a combination of three compounds:
· Ferrous hydroxide (Fe(OH)2)
· Ferric hydroxide (Fe(OH)3)
· Magnetite (Fe3O4)
Acid and alkaline corrosion are other forms of general corrosion.

Localized Corrosion
Localized corrosion is a general term that describes corrosion mechanisms that preferentially attack specific areas of a SSC. In some instances, localized corrosion can appear as an area where the rate of attack of general corrosion is greater in a specific part of the SSC.

Many examples of localized corrosion arise from conditions that establish differences in the environments present at different regions on a metallic surface. The environmental differences develop anodes and cathodes, creating local corrosion cells.
Service water systems are susceptible to localized corrosion arising from oxygen concentration cells. The regions of higher oxygen concentration become cathodic, gaining electrons through the reaction:
O2 + 2H2O + 4e⁻ → 4OH⁻ 
The service water piping and components, normally carbon steel, act as the anodes in the oxygen depleted areas through the reaction:
Fe → Fe²⁺ + 2e⁻
The Fe²⁺and OH⁻ ions combine to form ferrous hydroxide (Fe(OH)2).

Pitting Corrosion
Pitting occurs when corrosion selectively removes small volumes of metal, creating cavities in the metallic body of a structure or component. Generalized pitting usually arises from defects or weak areas in the protective film or coating on a metallic surface. The rate of corrosion will depend
upon the specific electro chemical reaction, local environmental conditions and the number of pits. Pit growth rate will generally decrease as the number of pits increases.

Crevice Corrosion
Crevice corrosion occurs when a liquid filled crevice (or crack) undergoes corrosion. If the opening of the crevice is tight enough, the liquid in the crevice will be stagnant. Corrosion will deplete the oxygen in the crevice faster than it can be replaced through diffusion. The depletion of the oxygen in the crevice creates a concentration cell relative to the liquid outside of the crevice.
The crevice region becomes an anode and corrosion rates in the crevice accelerate. The accelerated corrosion can result in acidic conditions within the crevice, further increasing the corrosion rates. Places where crevice corrosion is commonly seen include flanges, bolt holes, heat exchanger tube sheets, threaded connections and unsealed joints

Tuberculation
Tubercles are lumps or mounds of corrosion products and deposits that form on carbon steel pipe exposed to oxygenated water. Tubercles cover regions of metal loss and create oxygen concentration cells. Besides contributing to pipe wall degradation, tubercles also reduce flow by clogging pipes.
Tubercle formation is started when carbon steel corrodes due to contact with oxygenated water. The corrosion products coalesce into a structure that reduces oxygen diffusion to the area underneath. The corrosion beneath the structure depletes the oxygen and an oxygen concentration cell is established, causing accelerated corrosion and tubercle growth. The tubercle’s growth is enhanced by deposits from the water flowing through the pipe. Tubercles are most commonly found in service water piping, but can also be found in heat exchangers, pumps and storage tanks.

Underdeposit Corrosion
Underdeposit corrosion is the result of the shielding of surfaces by deposits, creating the conditions necessary to establish concentration cells. Deposits containing corrosive substances will directly attack the surrounding metal. Substances that can lead to underdeposit corrosion include silt, sand and shells.

Microbiologically Influenced Corrosion (MIC)
MIC is of particular interest, as it gives the appearance that microorganisms are “eating” metal. In actuality, MIC arises from a variety of normal electrochemical reactions that are influenced by the presence of living microbial organisms on metallic structures or components.
MIC can attack both carbon and stainless steels. In carbon steel, MIC may result in random pitting, general corrosion and formation of tubercles or corrosion product deposits. MIC of stainless steels is characterized by pitting, most commonly at weldments. These pits often exhibit very small entrance and exit penetrations with very large subsurface cavities. Pits in stainless steels caused by MIC can also tunnel, where the corrosion changes direction. MIC can also attack commonly used copper
alloys (coppernickels, brasses, aluminum bronzes and admiralty brass) and high nickel alloys (Monels, Incoloys and Inconels).
Microbes can cause crevice corrosion due to the formation of corrosion cells beneath areas of microbial growth. Other microbes can produce substances (metabolites) that are corrosives, such as acids, ammonia or hydrogen sulfide. Some microbes can concentrate halides, causing severe localized corrosion. Other microbes can influence corrosion rates by attacking protective coatings.

Galvanic Corrosion
Galvanic corrosion is one of the most familiar types of material degradation. Galvanic corrosion occurs when two materials with sufficient galvanic potential difference are immersed in an electrolyte and have a separate electrically conductive pathway. A sample of relative galvanic potential differences is given in Table 1 below. A metal that is lower on the chart (more active) will undergo galvanic corrosion in the presence of a metal higher on the chart (more noble)

table 1

One important aspect of galvanic corrosion is the area effect. If the surface area of the more noble metal is relatively large in comparison to the surface area of the more active metal, very rapid galvanic corrosion can occur due to the greater anodic current density. This is important when protective coatings are only used on the anodic surface to prevent galvanic corrosion.

Intergranular Corrosion
Intergranular corrosion takes place when the corrosion rate of the grain boundary areas of an alloy exceeds that of the grain interiors. For example, sensitized austenitic stainless steels are very susceptible to intergranular corrosion. Sensitization of austenitic stainless steels occurs when chromium carbides precipitate at the grain boundaries. This precipitation depletes the matrix of chromium adjacent to the grain boundaries, causing a wide difference in corrosion rates between the grain boundaries and the remainder of the matrix. Welding is one of the primary causes of sensitization of austenitic stainless steels. The welding process can bring the weld's heat affected zone (HAZ) into the temperature range for chromium carbide precipitation. Carbides will precipitate and a zone somewhat removed from the weld will become susceptible to intergranular corrosion. Some plant examples are the thermal sleeve and safe end of the reactor at Boiling Water Reactor nuclear plants.

Dealloying Corrosion
Dealloying corrosion occurs when one constituent of an alloy is preferentially removed, leaving a different structure. Dealloying has been observed in copperbased alloys and
cast iron. Terms to describe dealloying include dezincification (for brass), graphitic corrosion (for cast iron), selective leaching and parting.

Cracking Phenomena
Cracking phenomena, or environmental cracking, is the result of tensile stress and corrosion. The most common cracking phenomenon at nuclear power plants is fatigue type cracking and stress corrosion cracking (SCC), which occurs when three requirements are met:
· Susceptible material (normally ductile) involved.
· Sufficient tensile stress exists, either residual or applied. The amount of stress required is dependant upon the specific alloy, corrodent concentration and temperature.
· Initiating corrodent is present. Specific alloys are susceptible to SCC only if the correct initiating corrodent is present.

Stress corrosion cracking is a combined electrochemical and mechanical phenomenon. The tensile stress ruptures the existing oxide film, exposing the base metal to corrosive attack. The film-free base metal surface is anodic compared to the film covered surface and corrosion occurs, causing grooves to form. The tensile stresses concentrate at the tips of the grooves, causing further cracking and preventing the formation of a new protective oxide film.

BOILER TUBE FAILURES

BOILER TUBE FAILURES                                 BOILER TUBE FAILURES                                     BOILER TUBE FAILURES

BOILER TUBE FAILURES

INTRODUCTION
• Corrosion damage leads to untimely production upsets, costly equipment failures and lost
opportunities
• Failure analysis an effective tool in establishing true root cause of failure
• Root cause determination provides a path to effective corrective actions
• Common corrosion mechanisms and case histories presented

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CRC HANDBOOK OF ENGINEERING tables Richard c. dorf

CRCHANDBOOK

OF

ENGINEERINGtables

Richard c. dorf

The purpose of the CRC Handbook of Engineering Tables is to provide in a single volume a ready reference for the practicing engineer in industry, government, and academia. The tables and figures provided in this book include data and information from all fields of engineering in a comprehensive format. This information is organized into five sections: Electrical and Computer Engineering; Civil and Environmental
Engineering; Chemical Engineering, Chemistry and Material Science; Mechanical Engineering; and
General Engineering and Mathematics. The 450 tables and figures are compiled from 51 books and are inclusive of most ready available, important data widely used by the engineering practitioner.

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Sterilization - Steam sterilizers- Large sterilizers BS EN 285:2015

Sterilization — Steam

sterilizers — Large sterilizers

BS EN 285:2015

This European Standard specifies requirements and the relevant tests for large steam sterilizers
primarily used in health care for the sterilization of medical devices and their accessories contained in
one or more sterilization modules. The test loads described in this European Standard are selected to
represent the majority of loads (i.e. wrapped goods consisting of metal, rubber and porous materials)
for the evaluation of general purpose steam sterilizers for medical devices. However, specific loads (e.g.
heavy metal objects or long and/or narrow lumen) will require the use of other test loads.
This European Standard applies to steam sterilizers designed to accommodate at least one sterilization
module or having a chamber volume of at least 60 l.
Large steam sterilizers can also be used during the commercial production of medical devices.
This European Standard does not specify requirements for large steam sterilizers intended to use,
contain or be exposed to flammable substances or substances which could cause combustion. This
European Standard does not specify requirements for equipment intended to process biological waste
or human tissues.

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Explanation Properties and use of steam

Explanation Properties and use of steam 

introduction
In both the open and closed thermodynamic systems the transfer and conversion of energy needs a working substance. In power plant such as internal combustion engines and steam turbines its purpose is to receive heat energy from the fuel and then release it in the form of external work. Steam is an excellent working substance.

It can carry large amounts of heat energy. It is produced from water which is plentiful and it is environmentally friendly. In most of our larger power stations, the electrical generators are driven by steam turbines. Steam is also widely used as a heat source in industrial processes and in hospitals for central heating and the sterilization of equipment.

Phases of a substance
 the substance H2O can exist in three different states. It can exist as a solid in the form of ice, as a liquid which is water and as a gas, which is of course steam. These different states are known as phases. When a substance is of the same nature throughout its mass, it is said to be of a single phase. If two or more phases can exist together, the substance is then said to be two-phase mixture. In a single phase the substance is said to be homogenous and in a two phase mixture it is said to be heterogeneous.

FIG 1

Principle of Conservation of Energy
When two systems are at different temperatures, the transfer of energy from one system to the other is called heat transfer. For a block of hot metal cooling in air, heat is transferred from the hot metal to the cool air. The principle of conservation of energy may be stated as

energy cannot be created nor can it be destroyed

and since heat is a form of energy, this law applies to heat transfer problems. A more convenient way of expressing this law when referring to heat transfer problems is in figure 2:

FIG 2

Internal Energy
Fluids consist of a very large number of molecules moving in random directions within the fluid. When the fluid is heated, the speeds of the molecules are increased, increasing the kinetic energy of the molecules. There is also an increase in volume due to an increase in the average distance between
molecules, causing the potential energy of the fluid to increase. The internal energy, U, of a fluid is the sum of the internal kinetic and potential energies of the molecules of a fluid, measured in joules. It is not usual to state the internal energy of a fluid as a particular value in heat transfer problems, since it is normally only the change in internal energy that is required.
The amount of internal energy of a fluid depends on:
(a) the type of fluid; in gases the molecules are well separated and move with high velocities, thus a gaseous fluid has higher internal energy than the same mass of a liquid
(b) the mass of a fluid; the greater the mass, the greater the number of molecules and hence the greater the internal energy
(c) the temperature; the higher the temperature the greater the velocity of the molecules

FIG 3

Saturation temperature (ts⁰C)
When water receives heat energy, its temperature rises. This, you may recall, is known as sensible heat because its flow can be sensed by a temperature measuring device and that the specific heat capacity of water cw is 4187 J kg⁻¹ K⁻¹. Eventually a condition is reached where the water cannot absorb any more heat energy without undergoing a change of phase. It is then said to be saturated with sensible heat and is known as saturated water.

As heat is added to saturated water, it is turned into saturated steam. The amount of heat required to turn 1 kg of saturated water into saturated steam is called the specific latent heat of vaporisation, and is given the symbol, hfg. The total specific enthalpy of steam at saturation temperature, hg, is given by:

the specific sensible heat + the specific latent heat of vaporization

hg = hf +hfg

where
hg = specific enthalpy of dry saturated steam, i.e. dry steam at ts⁰C
hfg =specific enthalpy of vaporisation, i.e. the specific latent heat
hf =specific enthalpy of saturated water, i.e. water at ts⁰C
Dry saturated steam
This is another term which sounds rather strange. Dry saturated steam is steam which has just received all of its latent heat, hfg so that it is dry, but still at the saturation temperature, ts⁰C. The enthalpy per kilogram, hg and specific volume, vg of dry saturated steam at any given pressure is given in steam property tables.
 The units of specific volume are m³ kg⁻¹, i.e. cubic metres per kilogram.

Enthalpy
If saturated water continues to receive heat energy, a change of phase starts to take place. The water begins to evaporate and the temperature stays constant at the boiling point, or saturation temperature, ts⁰C whilst the change is taking place
The amount of heat energy required to change 1 kg of saturated water completely into steam is of course its specific latent heat of vaporisation. It is also called the specific enthalpy of vaporisation which is given the symbol hfg
The value of the specific enthalpy of vaporisation depends on the pressure at which the steam is being generated. At a normal pressure of 101.325 kPa or 1.01325 bar where the saturation temperature is 100 ⁰C its value is 2256.7 kJ kg⁻¹.
The sum of the internal energy and the pressure energy of a fluid is called the enthalpy of the fluid, denoted by the symbol H and measured in joules. The product of pressure p and volume V gives the pressure energy, or work done pressure energy = pV joules

FIG 4

Thus, enthalpy= internal energy + pressure energy (or work done)

 H = U + pV

specific enthalpy   hfg =enthalpy /mass = H /m

Figure 4  shows how the enthalpy of water and steam at a given pressure increases with temperature. The following subscripts indicate the condition of the working substance:
hw = specific enthalpy of water below its saturation temperature
hf  = specific enthalpy of saturated water, i.e. water at ts⁰C
hfg = specific enthalpy of vaporisation, i.e. the specific latent heat
hg = specific enthalpy of dry saturated steam, i.e. dry steam at ts⁰C
hsup = specific enthalpy of superheated steam 

As the pressure and saturation temperature increase, the specific enthalpy of vaporisation hfg becomes less, falling to zero at the critical pressure and temperature. Its value at any pressure may be obtained from the column headed hfg in steam property tables.
Sensible Heat
The specific enthalpy of water, hf, at temperature 𝛳°C is the quantity of heat needed to raise 1 kg of water from 0°C to𝛳°C, and is called the sensible heat of the water. Its value is given by:

specific heat capacity of water (c) × temperature change(𝛳)

hf = c 𝛳

Wet steam and its dryness fraction (x)
As the steam bubbles rise out of the water in a boiler, they carry with them small droplets of water. This is known as wet steam. Wet steam has not received all of the latent heat required to change it completely to dry steam. The amount of latent heat which it has received is given by its dryness fraction, x. 
For example, if wet steam has a dryness fraction of x = 0.9, this means that it has received 90% of its latent heat and that one tenth of its mass will be made up of water droplets.

Superheated steam
If dry saturated steam continues to receive heat energy, its temperature will start to rise again. It is then known as superheated steam, which is of course a vapour until its temperature exceeds 374.15 8C, the critical temperature. Thereafter it becomes supercritical steam, as we have described. The number of degrees by which the temperature
of superheated steam exceeds its saturation temperature, ts⁰C, is known as its degrees of superheat. The enthalpy per kilogram, hsup and specific volume, vsup of superheated steamat given temperatures and pressure are given in steam property tables.
The temperature v. enthalpy diagram, Figure 5, shows how the various values of specific enthalpy values of saturated water, hf , dry saturated steam, hg, and vaporisation hfg, vary with saturation temperature and pressure.

FIG 5

SUMMARY 
- A vapour is a substance in its gaseous phase below its critical temperature
- The boiling point of a liquid is also called its saturation temperature.
- The dryness fraction of wet steam is the fraction of the latent heat of vaporisation that it has received.
- Degrees of superheat is the number of degrees above saturation temperature.

Thermal resistance and thermal transmittance — Calculation method (ISO 6946:2007)

Thermal

resistance and thermal

transmittance —

Calculation method

(ISO 6946:2007)

This International Standard provides the method of calculation of the thermal resistance and thermal
transmittance of building components and building elements, excluding doors, windows and other glazed units,
curtain walling, components which involve heat transfer to the ground, and components through which air is
designed to permeate.
The calculation method is based on the appropriate design thermal conductivities or design thermal
resistances of the materials and products for the application concerned.
The method applies to components and elements consisting of thermally homogeneous layers (which can
include air layers).
This International Standard also provides an approximate method that can be used for elements containing
inhomogeneous layers, including the effect of metal fasteners, by means of a correction term given in
Annex D. Other cases where insulation is bridged by metal are outside the scope of this International
Standard.

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Type of pumps Telugu TechGuru

Type of pumps Telugu TechGuru

HVAC Pumps HANDBOOK by JAMES B RISHEL

HVAC Pumps HANDBOOK by JAMES B RISHEL

The emergence of digital electronics has had a tremendous impact on industrial societies throughout the world. In the heating, ventilating, and air-conditioning (HVAC) industry, the development of digital electronics has brought an end to the use of many mechanical devices; typical of
this is the diminished use of mechanical controls for HVAC air and water systems. Today’s digital control systems, with built-in intelligence, more accurately evaluate water and system conditions and adjust pump operation to meet the desired water flow and pressure conditions.
Drafting boards and drafting machines have all but disappeared from the design rooms of heating, ventilating, and air-conditioning engineers and have been replaced by computer-aided drafting (CAD) systems. Tedious manual calculations are being done more quickly and accurately by computer programs developed for specific design applications. All this has left more time for creative engineering on the part of designers to the benefit of the client.

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Reciprocating positive displacement pumps and centrifugal pumps — Test methods BS ISO 12809:2011

Reciprocating positive

displacement pumps and

centrifugal pumps — Test

methods

BS ISO 12809:2011

This International Standard specifies test methods and the environmental conditions for evaluating the performance of positive displacement pumps and centrifugal pumps designed for crop protection equipment.
It is not applicable to pesticide metering pumps for injection systems.

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Pumps Basic Types & Operation

In process operations, liquids and their movement and transfer from place to place, plays a large part in the process. Liquid can only flow under its own power from one elevation to a lower elevation or, from a high pressure system to a lower pressure system. The flow of liquid is also affected by friction, pipe size, liquid viscosity and the bends and fittings in the piping. To overcome flow problems, and to move liquids from place to place, against a higher pressure or to a higher elevation, energy must be added to the liquid. To add the required energy to liquids, we use ' PUMPS '. A pump therefore is defined as ' A machine used to add energy to a liquid '. Pumps come in many types and sizes. The type depends on the function the pump is to perform and the size (and speed) depends on the amount of liquid to be moved in a given time.

types of valves photo

types of valves photo                                 types of valves photo                          types of valves photo 

types of valves photo 

Valve Types, Valve Connections, Operation, Materials | Piping Official

Pipeline transportation systems — Pipeline valves BS EN 13942

Pipeline

transportation systems

— Pipeline valves

BS EN 13942

This International Standard specifies requirements and provides recommendations for the design, manufacturing, testing and documentation of ball, check, gate and plug valves for application in pipeline
systems meeting the requirements of ISO 13623 for the petroleum and natural gas industries. This International Standard is not applicable to subsea pipeline valves, as they are covered by a separate
International Standard (ISO 14723).
This International Standard is not applicable to valves for pressure ratings exceeding PN 420 (Class 2 500).
On-land supply systems used by the gas supply industry are excluded from the scope of this standard.

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Pressure Relief Valve Engineering Handbook

Pressure Relief Valve

Engineering Handbook

The Crosby

The Crosby® Pressure Relief Valve Engineering Handbook contains important technical information relating to pressure relief valves.
The primary purpose of a pressure relief valve is protection of life and property by venting fluid from an over pressurized vessel. Information contained in this handbook applies to the overpressure protection of pressure vessels, lines and systems.
Reference is made to the ASME Boiler and Pressure Vessel Code, Section VIII, Pressure Vessels. The
information in this handbook is NOT to be used for the application of overpressure protection to power boilers and nuclear power plant components which are addressed in the ASME Boiler and Pressure Vessel Code, Section I, Power Boilers, and Section III, Nuclear Power Plant Components, respectively.

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AN INTRODUCTION TO VALVE TYPES AND APPLICATIONS

AN INTRODUCTION TO VALVE TYPES AND APPLICATIONS

Valve functions can be defined as ON/OFF service, throttling service (flow control), prevention of reverse flow (or back flow), pressure control, regulation and pressure relief. Valves can be classified as either linear (gate valve) or rotary (ball valve) based on the action of the closure member. They are also classified by the shape of their closure member such as gate, globe, butterfly, ball, plug, diaphragm, pinch, and check.
Their primary function, however, is to control the flow of liquids and gases, including plain water, corrosive fluids, steam, toxic gases, or any number of fluids with widely varying characteristics. Valves must also be able to withstand the pressure and temperature variations of the systems in which they are used. Some valves on combined water service mains, and those handling flammable material, may be required to be fire safe or approved for fire protection use.

VALVE COMPONENTS
The following are the primary components of a valve.

FIG 1

1. A valve body is the housing for all the internal working components of a valve and it contains the method of joining the valve to the piping system.
2. The closure element, known as the disk or plug, is a valve component that, when moved, opens or closes to allow the passage of fluid through the valve. The mating surface of the disk bears against the seat.
3. The actuator is a movable component that, when operated, causes the closure element to open or close.
4. The stem is a movable component that connects the actuator to the closure element. The bonnet is a valve component that provides a leak proof closure for the body through which the stem passes and is sealed.
6. The seat is a component that provides a surface capable of sealing against the flow of fluids in a valve when contacted by a mating surface on the disk. The seat is attached to the valve body.
7. The stuffing box is the interior area of the valve between the stem and the bonnet that contains the packing.
8. Packing is the material that seals the stem from leaking to the outside of the valve. The packing is contained by the packing nut on the bonnet.
9. The backseat is a seat in the bonnet used in the fully open position to seal the valve stem against leakage into the packing. A bushing on the stem provides the mating surface. Backseating is useful if the packing begins to leak and it provides a means to prevent the stem from being ejected from the valve. Back seating is not provided on all valves.
10. The stroke of a closure member is the distance the member must travel from the fully opened to the fully closed position.

VALVE TYPES

1- GATE VALVES
Gate valves, illustrated in Fig. 2, use a wedge-shaped disk or gate as the closure member operating perpendicular to the flow; it is raised to open and lowered to close the valve. As the disk closes, it fits tightly against the seat surfaces in the valve body. A gate valve is used fully opened or closed only. It should not be used for throttling service (partly open), as the gate will vibrate and quickly become
damaged and subject to wire drawing caused by the velocity of the liquid flowing past the disk.

FIG 2

Disk Design. There are three types of disk constructions: solid wedge, split wedge, and flexible wedge (illustrated in Fig. 3).

FIG 3

Solid Wedge. Solid wedge disks are most prevalent because of their simple and usually less expensive design.
Split Wedge. Split wedge disks, also called double disks, have somewhat better sealing characteristics than solid disks because the two disk halves are forced outward against the body seats by a spreader after the disk has been fully lowered into its seating position. When the valve is opened, pressure on the disk is relieved before it is raised, eliminating the friction and scoring of body seats and disk.
Flexible Wedge. Flexible wedge disks are solid only at the center and are flexible at the outer edge and seating surface. This design enables the disk face to overcome the tendency to stick in high-temperature service where wide swings in temperature occur. This type of disk is generally found only in steel valves.

2- GLOBE VALVES
Globe valves are so named due to the globular shape of the valve body. Globe valves are used where throttling and/or frequent operation is desired. Each uses the same method of closure-a round disk or tapered plug-type disk that seats against a round opening (port). This design deliberately restricts flow, so globes should not be used where full, unobstructed flow is required. 
There are three basic types of globe valve: the standard globe valve (Fig. 4), the angle globe valve (Fig. 5), and the needle valve (Fig.6).

FIG 4

FIG 5

FIG 6

Angle valves are identical to standard globe valves in seat design and operation. The basic difference is that the body of the angle valve acts as a 90 ⁰ elbow, eliminating the need for a fitting at that point in the system. Angle valves also have less resistance to flow than the combination of globe valves and the fittings they replace. Needle valves are generally small in size and are intended to provide
precise flow control. Many turns of the handle are required to adjust flow in order to achieve precise control.

3- PLUG VALVES
A plug valve, shown in Fig. 7, is a quarter-turn valve that uses a tapered cylindrical plug that fits a body seat of corresponding shape. When the port in the plug is aligned with the body opening, flow is permitted in a way similar to a ball valve.A one-quarter (90⁰) turn operates the valve from opened to closed and vice versa.
Plug valves fall into two basic categories, lubricated and nonlubricated

FIG 7

4- BALL VALVES
A ball valve utilizes a ball with a hole drilled through it as the opening/ closing device. It is a quarter-turn valve. The ball seals by fitting tightly against resilient
seat rings on either side. Flow is straight through, and pressure loss depends on the size of the opening in the ball (port).
Ball valves are available in one-, two-, or three-piece body types (Fig. 8).

FIG 8

5- BUTTERFLY VALVES
A butterfly valve has a wafer-shaped body with a thin rotating disk as the closing device. Like the ball valve, the butterfly operates with a one-quarter turn from fully opened to fully closed. The disk is always in the flow path, but since it is relatively thin, it offers little restriction to the flow. When the valve is closed, the disk edge fits tightly against a ring-shaped liner (seat).
These valves generally have one-piece bodies that fit sandwich-style between two pipe flanges.
The two most common body types are wafer body and lug body, illustrated in Fig. 9

FIG 9

6- DIAPHRAGM VALVES
A diaphragm valve uses a rubber, plastic or elastomer diaphragm to seal the stem. The diaphragm not only seals the stem but forms the closure element. There are two styles of diaphragm valves, one having a body with a weir and the other having a straight-through body.Fig 10
Since the diaphragm is not metallic and forms the closure, the valve is severely limited in pressure and temperature. A wide variety of diaphragm materials are available for use with different fluids.

FIG 10

7- PINCH VALVES
A pinch valve (Fig. 11) uses a round elastomeric sleeve connected to the valve body from inlet to outlet that completely isolates the liquid passing through the valve from all internal valve components. Closure is made by a movable closure element outside the sleeve that pinches the sleeve between the element and the valve body. This type of valve is used for slurry and other liquids with highly corrosive properties.

FIG 11

8- CHECK VALVES
Check valves (Fig.12) automatically check or prevent the reversal of flow. Basic types are the swing check, lift check, ball check, and wafer check designs. Another designation used for sanitary waste systems is a backwater valve. The swing check has a hinged disk, sometimes called a flapper, that swings on a hinge pin. When flow reverses, the pressure pushes the disk against a seat. The flapper may have a composition disk, rubber or Teflon, rather than metal when tight closure is required.
Swing checks offer little resistance to flow.

FIG 12

The lift check has a guided disk that is raised from the seat by upward flow pressure. Reversal of flow pushes the disks down against the seat, stopping back flow. Lift checks have considerable resistance to flow, similar to that of a globe valve. They are well suited for high-pressure service.
Another common check is a wafer design which fits between flanges in the same fashion as a butterfly valve. Wafer checks come in two types: a dual flapper that is hinged on a center post and a single flapper that is similar to the standard swing check. They are generally used in larger size piping (4 in and larger) because they are much lighter and less expensive than traditional flanged end swing check valves.
A demand check value is of two-piece construction, with one piece having a spring-loaded closure similar to the air values found on automobile tires. The second piece, when inserted into the first, opens the valve, allowing free passage of air. The demand check valve is used for connecting gauges, allowing removal without permitting air to escape from the pipe.

9- MISCELLANEOUS VALVE TYPES
Various other types of valves are often used in utility systems. They can be either independently installed to operate as self-contained units or controlled electronically from a panel, system signal, or other remote source.
Pump Control Valve
This type of valve is used on pumped systems to control or eliminate surges caused by pump start and stop. It operates by using a spring-loaded closure member that opens or closes slowly to restrict the initial flow of water when a pump starts and stops.
Flow Control Valve
This valve operates by using a calibrated orifice or venturi tube to control the flow of liquid to a predetermined set point regardless of fluctuating line pressure.
Pressure Control Valve
Similar to the flow control valve, this valve limits the pressure of a flowing liquid to a predetermined set point regardless of fluctuating flow rate.
Level Control Valve
This valve accurately controls the level of liquid in a tank or vessel. An altitude valve uses a controlling device to maintain the level, and a float valve uses a movable float on an arm (similar to that in a water closet) to stop the flow at a predetermined level.

FIG 13

10- Conduit Valve
A conduit valve (Fig. 14) is used where an unobstructed opening through the valve is required, such as when pigs are used to clean the pipeline.

FIG 14

11- pressure relief valve

A pressure relief valve is a safety device designed to protect a pressurized vessel or system during an over pressure event. An over pressure event refers to any condition which would cause pressure in a vessel or system to increase beyond the specified design pressure or maximum allowable working pressure

FIG 15

VALVE ACTUATORS
There are three operating methods for valve actuators: multiturn (used for gate, globe, and diaphragm valves), quarter-turn (used for plug, ball, and butterfly valves), and linear (used for gate, diaphragm, and globe valves). The valves can either operate manually or be power actuated. There is no generally recognized code or standard for valve operators outside of those concerned with specific, high-risk industries, for example, nuclear work.
Manual Operation
Manually operated valves are usually used when the valve is easily accessible
Power Actuators
Power actuators are used where valves are remotely located, frequent operation is required, or automatic operation is necessary due to system considerations
Actuators are classified by their source of power: electric, pneumatic, or hydraulic.