element ic11: pressure system hazards and...

© RRC Training Unit IC – Element IC11 | 11-1

Element IC11: Pressure System Hazards and Controls

• For pressure systems, reference to pressure relates to pressures above atmospheric pressure and a pressure vessel may be regarded as one at a pressure greater than 0.5 bar above atmospheric.

• The hazards of steam relate to its temperature, pressure and ability to condense and create an unwanted vacuum.

• If water comes into contact with a source of heat such as molten metal, a steam explosion can occur (one example being the Corus Blast Furnace in 2001).

• Liquid petroleum gas (LPG) is a colourless liquid which readily evaporates into a gas and, when mixed with air, can burn or explode when it meets a source of ignition. It is heavier than air, can collect in drains, will float on water and can cause cold burns to the skin.

• A steam generator or boiler is a device used to create steam by applying heat energy to water. The boiler incorporates a firebox or furnace in order to burn the fuel and generate heat, which is transferred to water to make steam for heating.

• Gases occupy a greater volume than liquids, so bulk storage of gases is more economical if the gas is liquefied.

• The refrigeration cycle extracts heat from a source at a lower temperature and discharges it to a heat sink at a higher temperature. It uses a circulating liquid refrigerant as the medium, which absorbs and removes heat from the space to be cooled and subsequently discharges the heat elsewhere.

Principles of Pressure Systems

Key Information

PressureIn general, reference to pressure relates to pressure above atmospheric pressure. The term ‘bar’ (equivalent to 1 atmosphere) is the one most often used and understood in industry; below is a list of equivalent values:

1 bar = 14.5038 psi (pounds per square inch)

29.530 in of Hg (inches of mercury)

33.4553 ft of H20 (feet of water)

0.986923 atmospheres

105 N/m2 (Newtons per square metre)

105 Pa (Pascals)

1.020 kgf/cm2 (kilogram force per square centimetre)

10197.2 kgf/m2 (kilogram force per square metre)

Pressure is one of the parameters that determines how much stored energy there is in a vessel and, consequently, the potential for harm if this pressure is released explosively.

The amount of stored energy in a vessel is generally considered to be directly related to the volume of the vessel and the pressure of the contents. The measure of the stored energy is expressed by multiplying the pressure by the internal volume (P x V), i.e. the pressure-volume product. If the values used are bar for pressure and litres for volume, the measure (or product) is given in bar.litres.

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Bar.litre

The bar.litre is the product of the pressure (bar) and the volume (litres) of a pressure system and is a measure of its stored energy (or in simple terms, capacity for danger).

The main safety concern with pressure systems is the danger to people from the unintentional release of stored energy in a pressurised system. A pressure vessel is generally regarded as a vessel at a pressure greater than 0.5 bar above atmospheric (the significance of steam systems will be considered later).

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Unit IC – Element IC11 | 11-2 © RRC Training


Consequently, the term positive pressure can be taken to mean above atmospheric pressure. A vessel at positive pressure will contain stored energy.

Similarly, a vessel at negative pressure will be at a pressure below atmospheric pressure. Negative pressure caused by condensation of steam, for example, can produce a vacuum great enough to collapse a vessel.

Hazards of SteamSteam is the transparent gas generated when water is heated above its boiling point. Consequently, steam is a good reservoir for heat energy and heat transfer, which is one of its industrial uses. However, if steam comes into contact with persons there is a serious risk of scalding.

Steam generated from a volume of water occupies over 1000 times this volume and this expansion process drives pistons or turbines in a steam engine. However, the pressure generated from this expansion has also been the cause of many boiler explosions in the past and consequently steam boilers require a range of protective devices to prevent overpressurisation.

Condensation of steam causes a reduction in volume and can produce a vacuum great enough to collapse a vessel.

Mechanism of a Steam ExplosionIf water comes into contact with a source of heat, such as molten metal, violent boiling of water into steam can occur. The water changes from a liquid to a gas with extreme speed, increasing dramatically in volume.

This can also occur if water is heated under pressure to above its boiling point. This process is called superheating, where the water does not boil until some disturbance allows steam bubbles to generate in the superheated liquid and expand explosively, flashing to steam.

A steam explosion sprays steam and boiling-hot water in all directions (if not confined by the walls of the container), creating a danger of scalding and burning.

A natural example of a steam explosion is when hot lava meets sea water, but an industrial example is the dangerous steam explosion that occurs when liquid water encounters hot, molten metal. As the water explodes into steam, it splashes the burning hot liquid metal along with it, causing an extreme risk of severe burns to anyone located nearby and creating a fire hazard.

Corus Blast Furnace, 2001Water in a furnace coming into sudden contact with hot material was the cause of the explosion at the Corus Blast Furnace (Port Talbot, South Wales, UK) in 2001. The immediate cause of the explosion was water and hot molten materials mixing within the lower part of the furnace vessel. The water had entered the furnace from

its cooling system following a chain of events initiated by the failure of safety-critical water cooling systems. At the time of the explosion, attempts were continuing to rectify the abnormal operating conditions that this had created and to recover the furnace. As water turned into steam it expanded rapidly, creating pressure, which blew a confined vessel apart. The entire furnace, which with its contents weighed approximately 5000 tonnes, lifted bodily at the lap joint, rising some 0.75m from its supporting structures, leading to the explosive release of hot materials and gases into the cast house. Three employees died and a further twelve employees and contractors sustained severe injuries. Many more suffered minor injuries and shock.

Corus Blast Furnace – View of Cast House Floor Shortly After Explosion Source: The explosion of No. 5 Blast Furnace, Corus UK Ltd, Port Talbot, HSE, 2008 (http://www.hse.gov.uk/pubns/web34.pdf)

Properties of Liquid Petroleum GasLiquid petroleum gas (LPG) is a mixture of hydrocarbon gases (propane or butane) used as a fuel. It is a colourless liquid which readily evaporates into a gas. It has no smell, although it will normally have an odour added to help detect leaks.

When mixed with air, the gas can burn or explode when it meets a source of ignition. It is heavier than air, so it tends to sink towards the ground. LPG can flow for long distances along the ground and can collect in drains, gullies and cellars. It is less dense than water, so liquid releases will float on water.

The liquid can cause cold burns to the skin and the gas is slightly anaesthetic and suffocating in high concentrations.

Storage of LPGLPG is stored in pressurised tanks to keep it liquefied. The tanks can be installed above or below ground. They are strong and not easily damaged, but liquid or gas leaks can occur from valves and pipe connections.

LPG can be stored in spherical tanks or cylindrical ‘torpedo’ shaped tanks, as shown in the following figures.

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Spherical tanks are very strong structures. The even distribution of stresses on the sphere’s surfaces, both internally and externally, generally means that there are no weak points and they have a smaller surface area per unit volume and therefore less pressurisation due to external heat.

Spherical Tanks

Cylindrical tanks take up less space, are more convenient to make inlet/outlet connections to and are easier to fabricate.

Horizontal Cylindrical Tanks

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Operation of a Basic Steam Heating SystemA steam generator or boiler is a device used to create steam by applying heat energy to water. The boiler incorporates a firebox or furnace in order to burn the fuel. This generates heat, which is transferred to water to make steam for heating or power generation via a turbine and alternator. There are two basic ways to generate steam:

• Fire-Tube Boiler

In a fire-tube boiler, the hot flue gases from the burner pass through tubes that are surrounded by the fluid to be heated. The body of the boiler is the pressure vessel and contains the fluid. In most cases this fluid is water that will be circulated for heating purposes or converted to steam for process use.

These boilers are relatively inexpensive, easy to clean, compact and good for space heating and industrial process applications. However, they are not suitable for high pressure applications and are of limited use for high capacity steam generation.

The entire tank is under pressure, so if the tank bursts it creates a major explosion.

Fire-Tube Boiler

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• Water-Tube Boiler

In a water-tube boiler, the water runs through a rack of tubes that are positioned in the hot gases from the fire. Once the water reaches boiling point, bubbles of steam are produced, which rise to the water surface and burst. The steam is released into the space above, ready to enter the steam system. The industrial water-tube boiler typically produces steam or hot water primarily for industrial process applications, and is used less frequently for heating applications.

Water-tube boilers are available in sizes that are far greater than the fire-tube design and are able to handle higher pressures and high temperatures. However, the initial capital cost is higher, cleaning is more difficult and physical size may be an issue.

Water-Tube Boiler

The quality of feedwater supplied into the boiler is important. It must be at the correct temperature to avoid thermal shock to the boiler and of the correct quality to avoid damage to the boiler. Ordinary untreated water is not entirely suitable for boilers and can quickly cause them to foam and scale up. The water must therefore be treated with chemicals to reduce the impurities it contains.

Chemical dosing of the boiler feedwater will lead to the presence of suspended solids in the boiler. These will inevitably collect in the bottom of the boiler in the form of sludge, and are removed by a process known as blowdown.

If the water level inside the boiler were not carefully controlled, the consequences could be catastrophic. If the water level drops too low and the boiler tubes are exposed, the boiler tubes could overheat and fail, causing an explosion. If the water level becomes too high, water could enter the steam system and upset the process. For this reason, automatic level controls are used.

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Liquefaction of Gases for Bulk Storage Under Pressure/Refrigeration

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Critical Temperature

Gases can be converted to liquids by compressing the gas at a suitable temperature. Gases become more difficult to liquefy as the temperature increases because the kinetic energies of the particles that make up the gas also increase. The critical temperature of a substance is the temperature above which the vapour of the substance cannot be liquefied, no matter how much pressure is applied.

For example, ammonia, a common refrigerant gas, can be liquefied by pressure providing the temperature does not exceed its critical temperature of 1320°C - it can easily be liquefied by pressure at room temperature (20°C).

In comparison, oxygen has a critical temperature of -119°C and therefore can’t be liquefied by pressure unless it is cooled to below this temperature. Hence liquid oxygen is a cryogenic (extremely cold) liquid.

Gases occupy a greater volume than liquids so bulk storage of gases is more economical if the gas is liquefied. At temperatures below its critical temperature, a gas is also called a vapour, and can be liquefied by compression alone, without cooling.

Consequently, fuel gases such as LPG are compressed to a liquid and supplied in pressurised steel cylinders. LPG will evaporate at normal temperatures and pressures and if it is drawn of from its container at a high rate vaporisation of the gas will cause the bottle to cool.

Operation of a Closed-Circuit Refrigeration CycleThe refrigeration cycle extracts heat from a source at a lower temperature and discharges it to a heat sink at a higher temperature. It uses a circulating liquid refrigerant as the medium which absorbs and removes heat from the space to be cooled and subsequently discharges the heat elsewhere. The system has four components: a compressor, a condenser, an expansion valve and an evaporator.

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The Refrigeration Cycle

Circulating refrigerant enters the compressor as a vapour and is compressed to a higher pressure, resulting in a higher temperature as well. The hot, compressed vapour is then at a temperature and pressure at which it can be condensed by cooling water or cooling air.

The hot vapour passes through a condenser where it is cooled and condensed into a liquid by flowing through a coil or tubes with cool water or cool air flowing across the coil or tubes. This is where the circulating refrigerant extracts heat from the system which is carried away by either the water or the air.

The condensed liquid refrigerant then passes through an expansion valve to reduce its pressure and evaporate the liquid refrigerant. This lowers the temperature of the liquid and vapour refrigerant mixture to where it is colder than the temperature of the enclosed space to be refrigerated.

The cold mixture is then routed through the coil or tubes in the evaporator. A fan circulates the warm air in the enclosed space across the coil or tubes carrying the cold refrigerant liquid and vapour mixture. That warm air

evaporates the liquid part of the cold refrigerant mixture. At the same time, the circulating air is cooled and thus lowers the temperature of the enclosed space to the desired temperature.

To complete the refrigeration cycle, the refrigerant vapour from the evaporator is again a saturated vapour and circulates back into the compressor.

Revision Questions

1. Outline the main hazards of steam.

2. Explain the mechanism of a steam explosion.

3. Outline the refrigeration cycle.

4. Describe the main two types of steam boiler.

(Suggested Answers are at the end of the book.)

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• Simple unfired pressure systems are specified in the UK’s Simple Pressure Vessels (Safety) Regulations 1991, applying to vessels which are intended to contain air or nitrogen under pressure and not intended to be exposed to flame. The following terms are important in understanding simple pressure systems: vessel; unfired; contents; shape, construction and materials; gauge pressure; operating conditions; transportable gas containers.

• Simple pressure vessels with a stored energy of over 50 bar.litres are subject in UK law to the essential safety requirements set out in Schedule 1 of the Regulations, which also specify standards for pressurised components, steel and aluminium vessels and non-pressurised components.

• Pressure systems may require a written scheme of examination.

Simple Unfired Pressure Systems

Key Information

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Pressure System

A pressure system is a means of storing and transporting energy for use in the workplace.

MeaningsSimple unfired pressure systems are specified in the UK’s Simple Pressure Vessels (Safety) Regulations 1991, applying to vessels which are intended to contain air or nitrogen under pressure and not intended to be exposed to flame. These Regulations specify standards for the design, manufacture and conformity assessment of simple pressure vessels.

The following terms used in the Regulations specify what is meant by a ‘simple pressure vessel’.

VesselA welded vessel made of steel or aluminium intended to contain air or nitrogen at a gauge pressure greater than 0.5 bar, not intended for exposure to flame.

UnfiredAn unfired pressure vessel is one that is not in direct contact with a heating flame. It is a closed metal container intended for the storage and transport of any compressed gas which is subjected to internal pressure. It does not include containers where steam or other vapour is generated or water or other liquid is heated.

ContentsSimple pressure vessels are vessels which are intended to contain air or nitrogen at a gauge pressure greater than 0.5 bar but less than or equal to 30 bar.

Gauge PressureGauge pressure is pressure relative to atmospheric pressure. Atmospheric pressure is approximately 1 bar. Therefore a gauge pressure of 0.5 bar means 0.5 bar above atmospheric pressure. (A gauge pressure of greater than 0.5 bar is part of the definition of a simple pressure vessel.)

Shape, Construction and MaterialsThe components and assemblies contributing to the strength of a simple pressure vessel are made either of non-alloy quality steel, or of non-alloy aluminium, or of non-age-hardening aluminium alloy.

The vessel itself consists either of:

• a cylindrical component with circular cross-section, closed at each end, each end being either outwardly dished or flat and being also co-axial with the cylindrical component; or

• two co-axial outwardly dished ends.

Operating ConditionsFor simple pressure vessels:

• The maximum working pressure (PS) is limited to 30 bar; PS.V should not be more than 10,000 bar.litres.

• The minimum working temperature should not be lower than -50°C.

• The maximum working temperature should not be higher than:

– 300°C, in the case of steel vessels; or – 100°C, in the case of aluminium or aluminium

alloy vessels.

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Maximum Working Pressure The maximum gauge pressure which may be exerted under normal conditions of use.

Minimum Working TemperatureThe lowest stabilised temperature in the wall of the vessel under normal conditions of use.

Maximum Working TemperatureThe highest stabilised temperature in the wall of the vessel under normal conditions of use.

Transportable Gas ContainersTransportsable gas containers are a type of transportable pressure equipment.

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Transportable Pressure Equipment

Transportable pressure equipment, in simple terms, includes pressure receptacles or tanks used for carriage by road or by rail or storage of compressed gases.

Included are valves or other accessories fitted to the equipment and having a direct safety function, and any permanent fitting to the equipment.

Not included are:

• Aerosol dispensers.

• Gas cylinders forming a component part of a breathing appliance.

Essential Safety RequirementsSimple pressure vessels with a stored energy of over 50 bar.litres should:

• Meet essential safety requirements.

• Have safety clearance (which involves checking by an approved body).

• Bear CE marking or other specified inscriptions.

• Be accompanied by manufacturer's instructions.

• Be safe.

The essential safety requirements are specified in Schedule 1 of the Simple Pressure Vessels (Safety) Regulations 1991 and cover the design, manufacturing processes and material requirements. They establish good practice to ensure the safety of pressure vessels and the more important requirements are summarised below.

More...

The essential safety requirements in Schedule 1 of the Simple Pressure Vessels (Safety) Regulations 1991 can be accessed from:

http://www.legislation.gov.uk/uksi/1991/2749/schedule/1/made

Pressurised ComponentsThe non-alloy quality steel, non-alloy aluminium or non-age hardening aluminium alloy used to manufacture the pressurised components should:

• Be capable of being welded.

• Be ductile and tough, so that a rupture at the minimum working temperature does not give rise to either fragmentation or brittle-type fracture.

• Not be adversely affected by ageing.

For steel and aluminium vessels, the materials should in addition meet the requirements set out below.

Steel and Aluminium VesselsNon-alloy quality steels should meet standards for composition and mechanical strength.

Non-alloy aluminium should meet standards for composition, mechanical strength and resistance to intercrystalline corrosion at the maximum working temperature.

Welding materials used to make the welds on or of the vessel must be appropriate to and compatible with the materials to be welded.

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Accessories contributing to the strength of the vessel (bolts, nuts, etc.) must be made either of a material meeting the specification for the vessel or of another kind of steel, aluminium or aluminium alloy which:

• Is appropriate to and compatible with the materials used to manufacture the pressurised components.

• At the minimum working temperature has an appropriate elongation after rupture and toughness.

Non-Pressurised ComponentsAll welded non-pressurised components should be of a material which is compatible with that of the parts to which they are welded.

Welded Materials Must be Compatible

Types of Inspection, Frequencies and Statutory Basis for Examination of Simple Pressure SystemsGood practice for pressure vessels, pipework and protective devices is presented in UK legislation - the Pressure Systems Safety Regulations 2000. These Regulations place obligations on anyone who manufactures or constructs a new pressure system, and anyone who repairs or modifies a new or existing pressure system or part of it, to ensure that no danger will arise when it is operated within the safe operating limits specified for that plant.

The other main requirements of the Regulations are that the user must:

• Establish the safe operating limits of the system.

• Have a written scheme of examination for the system.

• Maintain the system.

• Have operating instructions and ensure that the system is only operated in accordance with the instructions.

The concept of the written scheme of examination is important. It should be compiled before a pressure system can be operated. Details of the pressure vessels,

protection devices and pipework should be included in the scheme. It should specify the nature and frequency of examinations and the measures necessary to prepare the system for safe examination.

A report of the periodic examination by the competent person should be given to the user or owner of the system within 28 days. However, if there is imminent danger from the continued operation of the system, the report should be provided within 14 days and a copy should be provided to the enforcing authority. The UK Regulations also require that records are retained.

Revision Questions

5. Simple unfired pressure systems are specified in the UK’s Simple Pressure Vessels (Safety) Regulations 1991. What sort of vessels are classed as simple unfired pressure systems and what is the purpose of regulation of such vessels?

6. Outline what is meant by an unfired pressure vessel.

7. Explain what is meant by gauge pressure.

8. Outline the essential safety requirements for Simple Pressure Vessels (Safety) Regulations 1991.


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• A pressure system is a means of storing and transporting energy for use in the workplace.

• Three types of pressure system are commonly defined:

– A system comprising a pressure vessel, its associated pipework and protective devices. – Pipework, with its protective devices, to which a transportable pressure receptacle is connected. – A pipeline with its protective devices.

All of the above must contain (or be liable to contain) what is called a “relevant fluid”

• A relevant fluid is:

– Steam (at any pressure) – Any fluid or mixture of fluids which is at a pressure greater than 0.5 bar above atmospheric and which is:

– A gas. – A liquid which would have a vapour pressure greater than 0.5 bar above atmospheric when in

equilibrium with its vapour at either the actual temperature of the liquid or at 17.5°C. – Any gas dissolved under pressure in a solvent, contained in a porous substance at ambient temperature and

which could be released from the solvent without the application of heat, e.g. acetylene.

• The key components and safety features of pressure systems include: temperature, pressure, level indicators; pressure relief valves; fuel cut-off systems; bursting discs; level replenishment systems and water treatment.

• A pressure system is a means of storing and transporting energy for use in the workplace. Hazards stem from:

– The use or misuse of this energy. – The possible failure of the system.

Pressure Systems

Key Information

What Constitutes a ‘Pressure System’Three types of pressure system are commonly defined:

• A system comprising a pressure vessel, its associated pipework and protective devices.

• Pipework, with its protective devices, to which a transportable pressure receptacle is connected.

• A pipeline with its protective devices.

All of the above must contain (or be liable to contain) what is sometimes called a ‘relevant fluid’ (for example, steam).

Meaning of ‘Relevant Fluids’What is considered a ‘relevant fluid’ for the purposes of any local regulations is likely to vary in detail. However, as an example, here is what is considered within the scope of the term in the UK regulations:

• Steam (at any pressure).

• Any fluid or mixture of fluids which is at a pressure greater than 0.5 bar above atmospheric and which is:

– A gas.

– A liquid which would have a vapour pressure greater than 0.5 bar above atmospheric when in equilibrium with its vapour at either the actual temperature of the liquid or at 17.5°C.

Examples of fluids in the above sub-categories could include compressed air, LPG, pressurised hot water, SCBA sets (excluding the transportable gas cylinder).

• Any gas dissolved under pressure in a solvent contained in a porous substance at ambient temperature, which could be released from the solvent without the application of heat, e.g. acetylene.

Steam At Any PressureThe primary concern regarding pressure systems is the risk created by a release of stored energy through system failure, rather than the hazardous properties of the contents released following system failure. Consequently, 0.5 bar above atmospheric pressure is set as the hazardous pressure level, regardless of the nature of the fluid. The exception to this is the scalding effects of steam and consequently this is addressed by including ‘steam at any pressure’ in the definition of relevant fluid.

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Key Components and Safety Features of Pressure Systems

Temperature, Pressure, Level IndicatorsPressure systems should have measuring or indicating devices to give clear indications of relevant critical conditions within the system such as temperatures, pressures, liquid levels. The display of any measuring equipment should be clearly visible. It should be possible to see when safe operating limits are being reached.

Equipment, such as boilers, in which a low level (or into which a low flow rate) of water could lead to unsafe conditions should be fitted with at least one suitable water level indicator and an alarm which sounds when the water level drops to a predetermined value. The indicator should be connected directly to the equipment. Fusible plugs should only be used as the sole low water alarm when other types of low water alarm are not practicable. They should be fitted at the point or points where overheating is first likely to occur if the water level drops. The gauge glasses of tubular water level gauges should be effectively protected to prevent injury from the effects of the glass breaking and the contents being ejected.

Pressure Relief ValvesPlant items in which the pressure can exceed the safe operating limit (i.e. those which have not been designed to withstand the maximum pressure that can be generated within the system) should be protected, whenever operational, by at least one pressure-relieving or pressure-limiting device. The device should be suitable for its intended duty and should be fitted as close as practicable to the plant item it is designed to protect. Sufficient devices should be fitted at other points to ensure that the pressures inside the system do not exceed the safe operating limits. In the event of a pressure relief device operating, the design should enable the contents to be released in as safe a manner as is practicable.

Where part of the system has a lower safe operating limit than other parts, suitable pressure-reducing valves, safety valves, pressure relief and indicating devices should be provided.

Pressure relief valves must be suitable for purpose

Fuel Cut-OffIf a boiler is operated without water in it, it can cause overheating, with possible rupture and catastrophic failure. A fuel cut-off is needed to turn off the burner or shut off fuel to the boiler to prevent it from running once the water goes below a certain point, usually activated by a float switch.

Bursting DiscsA bursting disc is a non-reclosing device that is designed to burst or rupture at a predetermined pressure, thus relieving a dangerous build-up of pressure. Bursting discs:

• Protect plant, pipework or vessels from overpressurisation that could cause failure and dangerous release of stored energy.

• Provide an instantaneous response to an increase in system pressure, but once the disc has ruptured it will not reseal.

Advantages of the use of bursting discs over pressure relief valves are leak-tightness and cost.

Level ReplenishmentIt is important to control the water level in a boiler because if it drops too low and the boiler tubes are exposed, the boiler tubes could overheat and fail, causing an explosion. For this reason, automatic level controls are used with probes that sense the level of water in the boiler. At a certain level, a controller will send a signal to the feedpump, which will operate to restore the

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water level, switching off when a predetermined level is reached. The probe will incorporate levels at which the pump is switched on and off, and at which low or high level alarms are activated.

Water TreatmentOrdinary untreated water is not entirely suitable for boilers. The major problems are:

• Scale (tube failures from excessive deposition of precipitated salts or particulate contaminants).

• Corrosion (severe pitting, gouging and embrittling of the tube metal can occur, which will ultimately lead to failure).

• Boiler water carryover (contaminant that leaves a boiler steam drum with the steam).

• Sludge deposition (build-up to a point where heat transfer is severely restricted and the boiler can overheat and fracture).

The water must therefore be treated with chemicals to reduce the impurities it contains. These chemicals include:

• Water softeners.

• Oxygen scavengers to absorb oxygen, preventing oxygen corrosion.

• Sludge conditioners to help prevent suspended solids baking onto heat transfer surfaces causing loss of efficiency.

• pH control products to help prevent corrosion.

Revision Questions

9. What is meant by the term “relevant fluid”?

10. What is meant by the term “pressure system”?

11. Explain the use and application of a bursting disc.

12. What are the main problems with using untreated water in boilers and what types of water treatment might be appropriate?


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