Module 1

Safety in the design of Chemical Process Plants

Safety checks in design• Safety of equipments depends on several features of both the process and the equipment.• It can be evaluated from quantitative accident and failure data and from best engineering practice and

recommendations.• Some of the safety elements that can be considered are: 1. Process materials properties 2. Process conditions (pressure, temperature, composition) 3. Inventory 4. Emergency and waste releases 5. Process control philosophy• Certain types of processes, process conditions, or fluids handled introduce factors which• affect the safety of the plant. These factors must be taken into consideration in the• design. They include:• 1. High-severity operating conditions, e.g., extremes of temperature or pressure.• 2. Batch or cyclic processes or processes undergoing frequent startup and• shutdown, where the opportunities for operating error are greater than normal.• 3. Processes subject to frequent upsets by integration with other plants or where• dangerous conditions may arise from utility failures.• 4. Unstable processes, in which decompositions, temperature runaways, or other• unstable reactions are possible

• 5. Fluid solids processes, in which stable and safe operations depend on the effectiveness of fluidization of solids to prevent reverse flow, e.g., catalytic cracking.

• 6. Fluid properties and characteristics such as flammability, vapor pressure, auto refrigeration, corrosion, erosion, toxicity, and chemical reactivity, including the variations in these properties which may occur at abnormal operating conditions.

• 7. Start up or shut down is an infrequent activity. Therefore, startup and emergency/normal shutdown procedures must be as simple and logical as possible. This must be incorporated into design considerations.

• 8. High noise evolution may pose communications problems and impair operator performance by creating additional stress.

Design Principles• The design of a new chemical process or the expansion or revision of

existing process require the use of engineering principles and theories combined with a practical realization of the limits imposed by environmental, safety and health concerns.

• Chemical process plant design includes all engineering aspects involved in the development of a new, modified or expanded commercial process in a chemical plant.

• This development involves (1) Process Development (2) making economic evaluation of new process (3) designing individual pieces of equipments (4) developing a plant layout for coordination of the overall operation

Design Principles

• The development of the overall design project involves many different design considerations.

• Some of the factors that requires particular attention in the development of a process or complete plant are those associated with various aspects of environmental protection, as well as the safety and health needs of plant personnel and the public.

• Other factors that affect the profitability of a process design include plant location, plant lay out, plant operation and control, utility requirements, structural design ,storage and buildings, material handling and patent considerations.

Process design developmentThe development of a process design involves many different steps. • The first step is the inception of the basic idea regarding the market

requirement of a particular product, followed by initiation of a preliminary research or investigation program. Here, a general survey of the possibilities for a successful process is made by considering the physical and chemical operations involved as well as the economic aspects.

• Next comes the process research phase , including preliminary market surveys, laboratory scale experiments, and production of research samples of the final product.

• Recognize environmental, safety and health concerns at this stage.• When the potentialities of the process are fairly well established to meet

the economic goals of the company, the project is ready for the development phase. At this point a pilot plant or a commercial development plant may be constructed.

Process design development• Design data and other process information are obtained during the

development phase. This information is used as the basis for carrying out the next phase of the design project. A complete market analysis is made, and samples of the final product are sent to prospective customers to determine if the product is satisfactory and if there is reasonable sales potential. Capital cost estimates for the proposed process are made. Probable returns on the required investment are determined, and a complete cost- and –profit analysis of the process is developed.

• Review the process again for environmental, safety and health effects• Before the final process design phase starts , company management

normally becomes involved to decide whether significant capital funds will be committed to the project.

• When the management has made a firm decision to proceed and provide sufficient funds to the project, the final process design phase is ready to begin.

Process design development• All the design details are worked out in the process design phase including controls,

services, piping layouts, firm price quotations, specifications and designs for individual pieces of equipments, and all the other design information necessary for the construction of the final plant.

• A complete construction design is then made with elevation drawings, plant layout arrangements, and other information required for the actual construction of the plant.

• The final stage consists of procurement of the equipments, construction of the plant, start up of the plant, overall improvement in the operation, and development of standard operating procedures (SOP) to provide the best possible results.

• The development of a design project proceeds in a logical , organized sequence requiring more and more time, effort and expenditure as one phase leads to the next.

• It is extremely important, therefore , to stop and analyze the situation carefully before proceeding with each subsequent phase.

Types of process design• Depending upon the accuracy and details required process designs are

generally classified in the following manner: 1. Order-of-magnitude designs 2. Study or factored designs 3. Preliminary designs 4. Detailed-estimate designs 5. Final process designs• The first two types are quick estimating procedures that are used to

determine the level of investment required for a proposed design project.• Preliminary designs are ordinarily used as basis for determining whether

further work should be done on a proposed process. The design is based on approximate process methods, and approximate cost estimates are prepared. Few details are included and the time spent on calculations is kept to a minimum.

Types of process design• If the results of primary design show that further work is justified ,a

detailed- estimate design may be developed. In this type of design, the cost- and- profit potential of an established project is determined by detailed analyses and calculations. However exact specifications are not given for the equipment; piping and layout work is minimized.

• When the detailed-estimate design indicates that the proposed project should be a commercial success ,the final step before developing a construction plans for the plant is the preparation of a final process design.

• Complete specifications are presented for all the components of the plant, and accurate costs based on quoted prices are obtained.

• The final process design includes detailed printouts and sufficient information to permit immediate development of the final plans used during the construction phase of the project.

Feasibility analysis• A feasibility study is designed to provide an overview of the primary issues related to

a business idea. The purpose is to identify any “make or break” issues that would prevent your business from being successful in the marketplace. In other words, a feasibility study determines whether the business idea makes sense.

• A thorough feasibility analysis provides a lot of information necessary for the business plan. For example, a good market analysis is necessary in order to determine the project’s feasibility. This information provides the basis for the market section of the business plan.

• Because putting together a business plan is a significant investment of time and money, you want to make sure that there are no major roadblocks facing your business idea before you make that investment. Identifying such roadblocks is the purpose of a feasibility study.

• A feasibility study looks at three major areas: a. Market issues b.Organizational/technical issues c. Financial issues

Feasibility analysis• As noted above, the feasibility study is organized into three major sections

(market analysis, organizational/technical analysis, and financial analysis). • The market analysis should be conducted first because it is critical to the

success of the business. If you cannot substantiate through research that adequate demand for your product or service exists, or if you cannot obtain sufficient quantity to meet expected demand, then your project is not feasible. You should not continue to the next step in the feasibility study.

• Once market issues have been addressed, it is time to take a look at key organizational and technology issues that are relevant to your project.

• Once your analyses of marketing, organizational and technology issues have been completed, the third and final step of a feasibility analysis is to take a look at key financial issues.Your feasibility study should give you a clear idea whether the proposed project is a sound business idea.

Preliminary design• The first step in preparing the preliminary design is to establish the bases for

the design.• In addition to the known specification for the product and availability of raw

materials ,the design can be controlled by such items as the expected annual operating factor(fraction of the year that the plant will be in operation), temperature of the cooling water, available steam pressure, fuel used, value of by-products, etc.

• The next step consists of preparing a simplified process flow diagram showing the processes that are involved and deciding upon the unit operations that are required.

• A preliminary material balance at this point may very quickly eliminate some of the alternative cases.

• Flow rates and steam conditions for the remaining cases are now evaluated by complete material balances, energy balances and a knowledge of raw material and product specifications, yields, reaction rates, and time cycles.

Preliminary design• The temperature , pressure, and composition of every process stream

are determined.• Unit process operations are used in the design of the specific pieces

of equipment.• Equipment specifications are in the form of tables and included with

final design report.• As soon as the equipment needs have been firmed up, the utilities

and labor requirements can be determined and tabulated.• Estimates of the capital investment and the total product cost

complete the preliminary calculations.• Economic evaluation plays an important role in any process design.• Evaluation of costs of in the primary design phases greatly assist the

engineer in further eliminating many of the alternative cases.

Process flow diagrams• Flow diagrams are used to show the sequence of equipments and unit operations

involved in the overall process, principally to simplify visualization of the manufacturing procedures and indicate the quantities of materials and energy that are transferred.

• These diagrams were generally identified as qualitative, quantitative, or combined-detail.

• A qualitative flow diagram indicated the flow of materials, unit operations involved, necessary equipments, and special information on operating temperatures and pressures.

• A quantitative flow diagram showed the quantities of materials required for the process operation.

• Preliminary flow diagrams were made during the early of the design project, but as the design moved towards completion, detailed information on flow quantities and equipment specification became available and combined-detail flow diagrams were prepared.

• This type diagram showed the qualitative flow pattern and served as a base reference for providing equipment specifications, quantitative data, and sample calculations.

Process flow diagrams• A more complete modeling of the chemical process being designed is now

possible, with the aid of computer software, once the overall flow sheet and required equipments have been established.

• This is accomplished with process flow diagrams (PFDs).• These are approximate models to the actual chemical process that include -all major processing operation units -all necessary auxiliary equipments such as pumps and compressors and - all material and energy streams.• PFDs present a more complete picture of the process design requirements and

allows for improved accuracy in design when compared with the flow sheets developed in the past.

• Present PFDs can also assist in other aspect of design, including equipment sizing, piping net work design, and control schemes for the process.

Piping and Instrumentation Diagram

• An important level in process design is the generation of piping and instrumentation diagram(P&IDs)

• P&IDs provide an additional level of detail for the overall design process that is essential for simulation and later construction and operation of the process.

• The PFD is the principal source of information for developing the P&ID.• P&IDs contain schematics for all piping , associated fixtures such as valves, various

components of instrumentation such as pneumatic air lines, and control mechanisms such as control valves.

• P&IDs shows symbolically all instruments and instrument loops with conventions to indicate whether they are located in the control room or on the plant

• Such diagrams allow the design engineer to simulate various operating conditions and to investigate the effect that these changes will have on the operability and economics of the process.

• The diagrams are therefore required for reference while operating a process to serve as guide for operators.

• This has led to legal requirement for maintaining the currency of P&IDs and make them available to facilitate operational safety in chemical plants.

Batch versus continuous operation• In general, continuous processing is the preferred mode of operation used in the

production of commodity chemicals, petroleum products, plastics, paper, solvents, etc; because of reduced labor costs, improved process control, and more uniform product quality.

• Batch and semi continuous processes are processes are often utilized when production rates are small such as in the manufacture of specialty chemicals ,pharmaceuticals, and electronic materials or the product demand is intermittent.

• This is particularly true when the product is interspersed with demand for one or other products that can be manufactured using essentially the same processing equipments.

• The choice between continuous or batch processing is commonly made very early in the process synthesis step.

• Normally, continuous processing is assumed unless a qualitative analysis indicates that batch or semi continuous processing provides a better mode of operation .

• Besides the design engineer may opt for batch or semi continuous operation when the process involves hazardous or toxic chemicals or the safety of the process is a major concern.

Equipment scale-up in design• The goal of the chemical engineer in process or plant design is to develop and present

a complete chemical process that can operate on an effective industrial basis.• To achieve this goal, the chemical engineer must able to combine many separate units

into one smoothly operating plant. • If the process plant is to be successful, each piece of equipment must be capable of

performing its necessary function. The design of equipment, therefore is an essential part of process design.

• When accurate data are not available in the literature in the literature or when the past experience does not give an adequate design basis, pilot plant tests may be necessary to design effective plant equipment.

• The result of these test may be scaled up to the plant capacity.• The design engineer should be acquainted with the limitations of scale up methods and

should know how to select the essential design variables. • Pilot plant data are almost required for the design of process equipments like Reactors,

Crystallizers, Filters, Centrifuges etc. unless specific information is already available for the type of materials and conditions involved.

• Heat exchangers, Distillation columns, Pumps and many other type of conventional equipments can usually be designed adequately without using pilot plant data.

Equipment Specifications• A generalization for equipment design is that standard equipment should be selected whenever possible,

because if the equipment is standard the manufacturer may have the desired size in stock.• The manufacturer can usually quote a lower price and give better guarantee for standard equipment than

for special equipment.• Before the manufacturer is contacted, the engineer should evaluate the design needs and prepare a

preliminary specification sheet for the equipment.• This preliminary specification sheet can be used by the engineer as a basis for the preparation of the final

specification.• Preliminary specification for equipment should show the following:• 1. Identification• 2. Function• 3. Operation• 4. Materials handled• 5. Basic design data• 6. Essential controls• 7. Insulation requirements• 8. Allowable tolerances• 9. Special information and details pertinent to the particular equipment, such as material of construction,

installation, necessary delivery date, supports etc.

Equipment Specifications• Final specification can be prepared by the engineer; however care should be

exercised to avoid unnecessary restrictions.• The engineer should allow potential manufacturer to make suggestions before

preparing detailed specifications.IN this way the final design can include small changes that reduce the first cost with no decrease in the effectiveness of the equipment.

• For example, the tubes in standard heat exchangers are usually2.44, 3.66, 4.88, 6.10 m in length. And these lengths are usually kept in stock by manufacturers.

• If a design specification called for tubes 4.57 m in length, the manufacturer would probably use 4.88 m tubes.

• Thus an increase from 4.57 to 4.88 m for the specified tube length could cause a reduction in the total cost for the unit, because the labor charge for cutting the standard length tube would be eliminated.

• In addition, if the replacement of the tube become necessary after the heat exchanger had been in use, the replacement costs with the 4.88 m tubes would be less than with the 4.57 m tubes

Safety in designing• Recommended safety factors for equipment design are given in literature.• These factors represent the amount of overdesign that would be used to account

for not only the changes in the operating performance with time , but also the uncertainties in the design process.

• The indiscriminate application of safety factors can be very detrimental to a design.• Each piece of equipment should be designed to carry out its necessary function.• Then if uncertainties are involved , a reasonable safety factor can be applied.• The role of the particular piece of equipment in the overall operation must be

considered along the consequences of under design.• Fouling, which may occur during operations should never be overlooked when a

design factor is determined.• Potential increase in capacity requirements are sometimes used as an excuse for

applying large safety factors. • This practice , however can result in so much over design that the process or

equipment never has an opportunity to prove its economic value.

Inherent safety• In the chemical and process indusrties , a process has inherent safety if it

has a low level of danger even if things go wrong. • Inherent safety contrasts with other processes where a high degree of

hazard is controlled by protective systems. • As perfect safety cannot be achieved, common practice is to talk

about inherently safer design.• “An inherently safer design is one that avoids hazards instead of

controlling them, particularly by reducing the amount of hazardous materials and the number of hazardous operations in the plant.”

• The concept of reducing rather than controlling hazards stems from British chemist Trevor Kletz in a 1978 article entitled “What You Don’t Have, Can’t Leak” on lessons from the Flixborough disaster on 1 June 1974, and the name ‘inherent safety’ from a book which was an expanded version of the article

Inherent safety

• The four main methods for achieving inherently safer design are

• Minimize: Reducing the amount of hazardous material present at any one time, e.g. by using smaller batches.

• Substitute: Replacing one material with another of less hazard, e.g. cleaning with water and detergent rather than a flammable solvent

• Moderate:Reducing the strength of an effect, e.g. having a cold liquid instead of a gas at high pressure, or using material in a dilute rather than concentrated form

• Simplify: Eliminating problems by design rather than adding additional equipment or features to deal with them. Only fitting options and using complex procedures if they are really necessary

• The Dow Fire and Explosion Index is essentially a measure of inherent danger and is the most widely used quantification of inherent safety

Inherent safety• An inherently safe plant relies on chemistry and physics to prevent accidents rather

than on control systems, interlocks, redundancy, and special operating procedures to prevent accidents.

• Inherently safer plants are tolerant of errors and are often the most cost effective.• A process that does not require complex safety interlocks and elaborate procedures is

simpler, easier to operate, and more reliable.• Smaller equipment, operated at less severe temperatures and pressures, has lower

capital and operating costs.• Simpler plants are friendlier than complex plants because they provide fewer

opportunities for error and because they contain less equipment that can cause problems.

• Often, the reason for complexity in a plant is the need to add equipment and automation to control the hazards. Simplification reduces the opportunities for errors and misoperation. For example, (1) piping systems can be designed to minimize leaks or failures, (2) transfer systems can be designed to minimize the potential for leaks, (3) process steps and units can be separated to prevent the domino effect, (4) fail-safe valves can be added, (5) equipment and controls can be placed in a logical order, and (6) the status of the process can be made visible and clear at all times.

Engineered safety• In general, the safety of a process relies on multiple layers of

protection.• The first layer of protection is the process design features. • Safety measures are considered at the design stage of process

equipments and systems.• Subsequent layers include • control systems,• interlocks, • safety shutdown systems,• protective systems,• alarms, and • emergency response plans

Safety in Start-up• Many potential hazards can be realized during start-up of plant or process. • Specific operating procedures should be provided which take account of all eventualities. • For some specific plant items, start-up is known to present particular additional hazards;

some examples of these are:• Dryers – when starting up a drying system after maintenance or a plant shutdown, the

actual temperature the dryer might reach before the control system gets stabilized ,may result in an increased chance of a dust explosion or overheating of product causing fire;

• Furnaces – explosions may occur if ignition of fuel is delayed;• Vessels, Tanks, Reactors – ignition of flammable vapours introduced may occur for systems

relying on elimination of oxygen to prevent explosions, unless inert gas purging is carried out effectively;

• Reactors – start-up of batch reactors after agitator failure may cause an uncontrollable exothermic reaction.

• The start-up procedures should be ordered and phased so that interlinked plant operations can resume in a safe and controlled manner.

Safety Precautions for Shutdown Activities

• There are two kinds of chemical plant shut down, i.e. planned shutdown and emergency or unplanned shutdown.

• An example of planned shutdown is as preparation for Turn Around or yearly preventive maintenance programs.

• Emergency plant shutdown can be triggered by many factors, such like electric power failure, machinery failure, instrumentation trouble and many more.

• In both shutdown cases, there are safety precautions that need to be taken into account.

• Such safety precautions are required to prevent potential hazards that commonly appear during plant shut down.

• Various potential hazards such as over pressure, fire and explosion exist, which could present real danger to the plant and people inside it.

Safety Precautions for Shutdown Activities

• The safety precautions given below will not cover all the potential hazards because each plant has different potential hazards.

• However, they may represent the most common potential hazards during plant shutdown.

• Temporary electric connections are commonly used for driving portable pumps or exhaust blowers in shutdown time. Put extra care to avoid electric spark generation because many flammable materials exposures.

• Chemical splash and spill hazards will more likely occur during maintenance works.

• Release pressure that may be trapped between two closed valves or closed process equipment loops. If liquid trapped inside is decomposing and releasing gas, such as hydrogen peroxide, the condition will be worst.

• Replace flammable gas inside vessel or piping line to below its Lower Explosive Limit (LEL) with inert gas, for instance nitrogen if hot work is planned to be done surround that area.

Safety Precautions for Shutdown Activities

• Do not just rely on pressure gauge indication to make sure zero pressure. Open all available drain or vent valves to release the remaining pressure. Beware of pressure that trapped in a dead zone.

• Bring any high temperature process to ambient, except there is a strong requirement keeping that high temperature It is not only saving energy but also eliminate one hazard source..

• During plant shut down period, it is to perform many jobs in the same time. Be careful not to use same hoses or transferring pump to avoid unintended reaction. Consider material compatibility. Read MSDS to find out material compatibility.

• There will be much flammable combustible material spread around the plant site. Do not dispose used absorbent materials that still contain flammable liquid into trash bin.

• Utilization of temporary lines or hoses may increase in shutdown period. Dispose damaged hoses and only use good hoses with the right specifications.

• Several equipments or pipelines are designed to be used only in shutdown time. Be careful, because some part of the equipments or pipes may have been corroded and would not be able to hold certain pressure rating.

• During normal operation there may be a leak through steam valve. Insert a blind plate to stop process heating by steam, otherwise pressure inside will build up and may create over pressure or over heating condition.

Safety Precautions for Shutdown Activities

• Used drums are usually used during plant shutdown in order to recover lubrication oils, chemicals or catalysts. Use only used drums that are originally used for those chemicals or ones that have been washed and cleaned up.

• In yearly preventive maintenance period, there are not only permanent workers involved in plant shutdown activities but there will be contractor workers and temporary workers. Educate them adequately about all the potential hazards that may exist in the area where they work.

• Chemical splash and spill hazards will more likely occur during maintenance works• Flammable gas concentration may zero in tank or column, but beware of nitrogen

hazard, since nitrogen could make oxygen concentration less than safe concentration

• Maintain nitrogen blanket for tank containing flammable liquid during plant shut down. Flammable vapor is still released.

• When pressure indication just relies on pressure gauge consider error indication. Seek another one for comparison.

Safety checks in the design of equipments• Hazard and Operability Analysis (HAZOP)• Hazard and Operability Analysis (HAZOP) is one of the most used safety analysis methods in the process industry. It is one of the simplest approaches to hazard identification.• HAZOP involves a vessel to vessel and a pipe to pipe review of a plant.• HAZOP is based on guide words such as no, more, less, reverse, other than, which should be asked for every pipe and vessel. HAZOP can be used in different stages of process design but in restricted mode.• A HAZOP is used to question every part of the process to discover what deviations

from the intention of the design can occur and what their causes and consequences maybe.

• This is done systematically by applying suitable guide words.• This is a systematic detailed review technique for both batch and continuous plants

which can be applied to new or existing processes to identify hazards.• A HAZOP study requires considerable knowledge of the process, its instrumentation,

and its operation.

Safety checks in the design of equipments

• Material Hazard• Information about the chemicals used in a process, as well as chemical intermediates, must be comprehensive enough for an accurate assessment of fire and explosion characteristics, reactivity hazards, safety and health hazards to workers, and corrosion• and erosion effects on process equipment and monitoring tools. • The information of material can be summarized in document of Materials Safety Data Sheet (MSDS).• The MSDS contains the information needed to begin analyzing materials and process hazards, to understand the hazards to which the workforce is exposed, and to respond to a release of the material or other major incident where emergency response personnel may be exposed to the material.• The process design engineer should always collect the MSDS of every component used in the process, including solvents, acids, bases, adsorbents, etc., at as early a stage in the design as possible.• The information in the MSDS can be used to improve the inherent safety of the process, for example, by

eliminating incompatible mixtures or substituting less hazardous chemicals as feeds, intermediates, or solvents.

• The MSDS information can also be used to ensure that the design meets regulatory requirements on vapor recovery and other emissions.

Safety checks in the design of equipments

• Fire Protection• Fire protection systems are expected to meet a combination of purposes.• Designing a fire protection system requires knowing the purposes it must serve.• To prevent the fire accidents, the equipment design should be planned very well. • Performance-based design centered around the following major steps is considered: 1. Defining the Project Scope 2. Identifying the Fire Safety Goals 3. Defining Stakeholder and Design Objectives 4. Developing Performance Criteria 5. Developing Design Fire Scenarios 6. Developing Trial Designs 7. Evaluating Trial Designs 8. Selecting the Final Design

Non destructive testing• Nondestructive testing - NDT - use test methods to examine an object,

material or system without impairing its future usefulness. Non-destructive testing is often required to verify the quality of a product or a system. Commonly used techniques are

• AET - Acoustic Emission Testing• ART - Acoustic Resonance Testing• ET - Electromagnetic Testing• IRT - Infrared Testing• LT - Leak Testing• PT - Dye Penetrant Testing• RT - Radiographic Testing• UT - Ultrasonic Testing• VT - Visual Testing (VI - Visual Inspection)

Non destructive testing• AET - Acoustic Emission Testing• Acoustic Emission Testing takes advantage of the sharp sound that PCCP emits when it

breaks or slips to identify areas of active distress within a construction. AET can be used to verify the structural integrity of pressure vessels, spheres, high temperature reactors and piping, coke drums, above ground storage tanks, cryogenic storage tanks and more. The inspection is executed externally and shut-down of the process may often not be necessary.

• ART - Acoustic Resonance Testing• After an impact a specimen will vibrate in certain characteristic modes and frequencies

that can be measured by a microphone or laser vibrometer. Acoustic sonic and ultrasonic resonance analysis is a non-destructive testing technique that allows testing of a wide range of test objects. Typical detecting faults are cracks, cavities, detached layers, material inconsistencies, hardness deviation in materials.

• ET - Electromagnetic Testing• Electromagnetic testing is the process of inducing electric currents and/or magnetic

fields inside a test object and observing the response. A defect in the test object may be detected where electromagnetic interference creates a measurable response.

Non destructive testing• IRT - Infrared Testing• Infrared testing is a technique that uses thermography, an infrared imaging and

measurement camera, to see and measure infrared energy emitted from an object. Can be used to heat development, lack of insulation, thin walls in constructions and more.

• LT - Leak Testing• Techniques used to detect and locate leaks in pressure containment parts,

pressure vessels, and structures. Leaks can be detected by using liquid and gas penetrant techniques, electronic listening devices, pressure gauge measurements or soap-bubble tests.

• PT - Dye Penetrant Testing• The dye penetrant testing can be used to locate discontinuities on material

surfaces. A highly penetrating dye on the surface will enter discontinuities after a sufficient penetration time, and after removing the excess dye with a developing agent, the defects on the surface will be visible.

Non destructive testing• RT - Radiographic Testing• Radiographic testing can be used to detect internal defects in castings,

welds or forgings by exposure the construction to x-ray or gamma ray radiation. Defects are detected by differences in radiation absorption in the material as seen on a shadow graph displayed on photographic film or a fluorescent screen.

• UT - Ultrasonic Testing• Ultrasonic testing uses high frequency sound energy to conduct

examinations and make measurements. Ultrasonic inspection can be used for flaw detection/evaluation, dimensional measurements, material characterization, and more.

• VT - Visual Testing (VI - Visual Inspection)• Visual testing or inspection offers a wide range of options to secure proper

system or product quality.

Emergency safety devices• PRESSURE RELIEF SYSTEMS• Emergency pressure relief systems are intended to provide the last line of protection and

thus must be designed for high reliability, even though they will have to function infrequently.

• The most common method of overpressure protection is through the use of safety relief valves and/or rupture disks which discharge into a containment vessel, a disposal system, or directly to the atmosphere

• EMERGENCY RELIEF DEVICE EFFLUENT COLLECTION AND HANDLING• The three most commonly used types of equipment for handling emergency relief device

effluents are blow down drums (also called knockout drums or catch tanks), cyclone vapor-liquid separators, and quench tanks (also called passive scrubbers).

• FLAME ARRESTERS• Flame arresters are passive devices designed to prevent propagation of gas flames through

pipelines. • Typical applications are to prevent flames entering a system from outside (such as via a tank vent) or propagating within a system (such as from one tank to another)

Scrubber systems• Scrubber systems are a diverse group of air pollution control devices that

can be used to remove some particulates and/or gases from industrial exhaust streams.

• Traditionally, the term "scrubber" has referred to pollution control devices that use liquid to wash unwanted pollutants from a gas stream.

• Recently, the term is also used to describe systems that inject a dry reagent or slurry into a dirty exhaust stream to "wash out" acid gases.

• Scrubbers are one of the primary devices that control gaseous emissions, especially acid gases.

• Scrubbers can also be used for heat recovery from hot gases by flue gas condensation.

• There are several methods to remove toxic or corrosive compounds from exhaust gas and neutralize it.

Scrubber systems• Wet scrubbing• The exhaust gases of combustion may contain substances considered harmful to the

environment, and the scrubber may remove or neutralize those. A wet scrubber is used to clean air, fuel, gas or other gases of various pollutants and dust particles. Wet scrubbing works via the contact of target compounds or particulate matter with the scrubbing solution. Solutions may simply be water (for dust) or solutions of reagents that specifically target certain compounds.

• Process exhaust gas can also contain water soluble toxic and/or corrosive gases like hydrochloric acid (HCl) or ammonia (NH3). These can be removed very well by a wet scrubber.

• Removal efficiency of pollutants is improved by increasing residence time in the scrubber or by the increase of surface area of the scrubber solution by the use of a spray nozzle or packed tower .

• Wet scrubbers can also be used for heat recovery from hot gases by flue gas condensation.• In this mode, termed a condensing scrubber, water from the scrubber drain is circulated

through a cooler to the nozzles at the top of the scrubber. The hot gas enters the scrubber at the bottom.

• If the gas temperature is above the water dew point, it is initially cooled by evaporation of water drops. Further cooling cause water vapor to condense, adding to the amount of circulating water.

Wet ventury scrubber

Scrubber systems• Dry scrubbing• A dry or semi-dry scrubbing system, unlike the wet scrubber, does not saturate the

flue gas stream that is being treated with moisture. In some cases no moisture is added, while in others only the amount of moisture that can be evaporated in the flue gas without condensing is added.

• Therefore, dry scrubbers generally do not have a waste water handling/disposal requirements. Dry scrubbing systems are used to remove acid gases (such as SO2 and H Cl) primarily from combustion sources.

• There are a number of dry type scrubbing system designs. However, all consist of two main sections or devices: a device to introduce the acid gas sorbent material into the gas stream and a particulate matter control device to remove reaction products, excess sorbent material as well as any particulate matter already in the flue gas.

• Dry scrubbing systems are often used for the removal of odorous and corrosive gases from waste water treatment operations. The medium used is typically an activated alumina compound impregnated with materials to handle specific gases such as hydrogen sulfide.

Flare stack system

A gas flare, alternatively known as a flare stack, is a gas combustion device used in industrial plants such as petroleum refineries, chemical plants, natural gas processing plants as well as at oil or gas production sites having oil wells, gas wells, offshore oil and gas rigs and landfills.

Schematic flow diagram of an overall vertical, elevated flare stack system in an industrial plant is shown.

Flare stack system

Flare stack system• A knockout drum to remove any oil and/or water from the relieved gases.• A water seal drum to prevent any flashback of the flame from the top of the flare

stack.• An alternative gas recovery system for use during partial plant startups and/or

shutdowns as well as other times when required. The recovered gas is routed into the fuel gas system of the overall industrial plant.

• A steam injection system to provide an external momentum force used for efficient mixing of air with the relieved gas, which promotes smokeless burning.

• A pilot flame (with its ignition system) that burns all the time so that it is available to ignite relieved gases when needed.

• The flare stack, including a flashback prevention section at the upper part of the stack.

• There is also a safe method to divert the flare gas which is insertion of Liquid U seal with Liquid Hold up vessel. The Liquid U seal is designed to take pressure up to permitted back pressure of the system.

• This helps to divert the flare gas to recovery system.• In case of plant upset, pressure rises and liquid in the U seal will move into Liquid

Hold up vessel. On normalization, the Liquid U seal will start diverting the gas again

Pressure testing• Pressure Testing is a non-destructive test performed to ensure the integrity of the

pressure shell on new pressure equipment, or on previously installed pressure and piping equipment that has undergone an alteration or repair to its boundary(s).

• Pressure testing is required by most piping codes to verify that a new, modified, or repaired piping system is capable of safely withstanding its rated pressure and is leak tight. Compliance to piping codes may be mandated by regulatory and enforcement agencies, insurance carriers, or the terms of the contract for the construction of the system.

• Pressure testing, whether or not legally required, serves the useful purpose of protecting workers and the public.

• Pressure testing may also be used to establish a pressure rating for a component or special system for which it is not possible to establish a safe rating by calculation.

• There are a great many codes and standards relating to piping systems. Two codes of major importance for pressure and leak testing are the ASME B31 Pressure Piping Code and the ASME Boiler and Pressure Vessel Code

Leak Testing Methods• There are many different methods for pressure and leak testing in the field. Seven of these

are:• Hydrostatic testing, which uses water or another liquid under pressure• Pneumatic or gaseous-fluid testing, which uses air or another gas under pressure• A combination of pneumatic and hydrostatic testing, where low pressure air is first used to

detect leaks• Initial service testing, which involves a leakage inspection when the system is first put into

operation• Vacuum testing, which uses negative pressure to check for the existence of a leak• Static head testing, which is normally done for drain piping with water left in a standpipe for a

set period of time• Test Pressures• The selected test method and fluid test medium, together with the applicable code, will also

establish the rules to be followed in calculating the required test pressure. In most cases a pressure greater than the design pressure rating is applied for a short duration, say at least 10 minutes. The magnitude of this initial test pressure is often at least 1.5 times the design pressure rating for a hydrostatic test.

• However, it may be different, depending upon which code is applicable and whether the test is hydrostatic or pneumatic.