1.Colour Coding and Signs

8/8/2019 1.Colour Coding and Signs

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PG06disc3/JA/4 January 2011 1

10.0 COLOUR CODING AND SIGNS

It is sometimes necessary to follow a particular pipe run through the complexpipe system in a process area. Consequently, it is important to distinguishand identify one pipe and its contents from another. To make identification

easier the standardised colour code, using bright colours, is normally used.

A typical colour coding system for pipes is:

Category Colour

Storage tanks White

Surface piping oil, Browncondensate, diesel etc.

Natural gas, LPG, oxygen Yellow ochrehydrogen, sulphur,acetylene

Acids and alkalis Violet

Glycols, inhibitors Black

Instrument air Light blue

Water lines, industrial, Light greenpotable, cooling andcondensate

Steam and insulated lines Aluminium or silver grey

Fire-fighting lines and Fire redand foam piping

Special marking for danger Yellow with black diagonalstripes

Electrical services Orange

Direction of flow By arrow

In some cases the complete pipe run will be colour coded; in other cases thecolour will only be shown at key points. An arrow painted on a pipe indicatesthe direction of fluid flow.


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SAFETY SIGNS

10.1 Safety Colours and Signs

It is important that safety-signs such as illustrated in Figure17 are displayed.These signs may also include warning of danger (gas, explosive, etc.).Certain colours are reserved for a particular use, but of equal importance isthe shape of the sign. If colour and shape have a particular meaning peoplesuffering from colour blindness can still identify the sign.

red for danger and prohibit signs, yellow for cautionary (warning) signs, green for safety signs and treatment areas, blue for regulation signs.

Red is used on stop, danger, no entry, no smoking, prohibited area signs andgenerally anything related to fire.

The cautionary yellow signs relate to explosives, radioactivity, dangerouschemicals, toxic substances and fire risks. See Figure18.


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obvious. Consequently the use of personal protective equipment and

guidance by the supervisor are most important.

11.2 Hazardous Gases

Hazardous gases that may be encountered by the production operator are:

hydrogen sulphide (H2S), hydrocarbon gases, carbon monoxide (CO), carbon dioxide (CO2),

nitrogen (N2).

Some of these gases are toxic and affect the respiratory system. Some ofthe gases are particularly dangerous because they are either odourless orthey affect the sense of smell. See Figure 19.


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HAZARDOUS GAS SAFETY APPARATUS

HYDROGEN SULPHIDE LEVEL EFFECT

H2S - Hydrogen sulphide- 0.13 ppm Minimal perceptible odour.is a highly toxic, colourless(transparent) gas which isheavier than air.

Hydrogen sulphide is a poison 4.60 ppm Easily detectable, moderategas that can paralyse your smell.breathing system and kill youin minutes. In small amountsit is dangerous to your health.

At low concentrations H2S 10.00 ppm Maximum Acceptable limit.

has an offensive odour similarto rotten eggs.

At slightly higher concentrations 27.00 ppm Strong unpleasant smell, but notit may have a sick, sweet smell. intolerable

100.00 ppm Coughing, eyeirritation, loss of

smell in 2.5 minutesAt high concentrations no smell 200-300 ppm Marked conjunctivitis and

can be detected because H2S respiratory tract irritation after

rapidly deadens the sense of one hour of exposure.smell paralysis of the olfactorynerve. Consequently the senseof smell cannot be relied upon

to detect H2S.Hydrogen sulphide is formed 500-700 ppm Loss of consciousness and

by the decomposition of possible death in 30minutes to organic animal and/or vegetable one hour.matter by bacteria. So it isfound in natural oil and gas,sewers, septic tanks and in a

variety of industrial andbiological processes.

700-1000 ppm Rapid unconsciousness,cessation of respiration and

death.

H2S means that in each 1000-2000 ppm Unconsciousness at once, withmolecule of the gas there early cessation of respirationis one part sulphur atom and death in a few minutes.and two hydrogen atoms.

Death may occureven if the


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individual is removed to fresh airat once.

If you are in any doubt about the concentration of gas present GET OUTand arrange to carry out any necessary gas tests.

Hydrocarbon Gases

In and around production and processing facilities several types ofhydrocarbon fractions are detectable. These are:

methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), pentane (C5H12),

hexane (C6H14).

These gases are highly flammable when concentrated as combustiblemixtures with air. They always present a fire hazard when vaporising in theatmosphere.

In atmospheres rich with hydrocarbon gas, as in oil storage tanks, there maybe little or no oxygen and an unprotected person will suffocate.

Carbon Monoxide (CO)This gas is present in the exhaust from internal combustion engines, gasturbines and the flue gas from fired heaters.

Carbon monoxide is odourless and heavier than air, consequentlyconcentration will build upwards from ground level. Although prolongedexposure can be fatal, its initial effect is similar to that of intoxication.

Areas where carbon monoxide might accumulate should always be wellventilated. For instance, never run an engine in an enclosed space.

Carbon Dioxide (CO2) and Nitrogen (N2)Both of these gases are odourless, colourless and nontoxic. Although theyaffect breathing they do not attack the respiratory muscles; they have asuffocating effect. Nitrogen is often used during certain work processes topurge oxygen, consequently lessening the chance of an explosive mixtureoccurring. Afterwards nitrogen is cleared by venting with air. A check mustthen be made to ensure oxygen levels have been restored.

11.3 Radiation Hazards

Certain materials radiate energy waves which, although undetectable by thehuman eye, are dangerous. One of the rays you may have heard about is the


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X-ray. However, the degree of danger depends on how long you areexposed to the radiation, how far you are from the source and the strengthof the radiation.

X-rays are used for medical purposes (radiography) and to much lesser

degree in the oil and gas industry. X-ray equipment is used to test pipewelds, pressure vessels and in some instances to detect well leaks. Any areawhere x-ray equipment is being used must be enclosed by a barrier and theapproved warning sign prominently displayed.

12.0 ELEMENTARY FIRST AID

All personal injuries sustained at work must be reported to the section head.

It is not the objective of this section to teach first aid as a subject in its ownright; that can only be done by properly qualified instructors. For safetypurposes, what an operator must be capable of is recognising that acolleague needs help and then being able to help until qualified assistancearrives.

An untrained, unqualified man 'trying to help' may cause more pain damageand suffering than if he was to do nothing. The one thing you can always dois SEND for qualified medical help.

12.1 Shock (Trauma)

A state of shock usually accompanies all but minor accidents. It must beremembered that shock alone can be fatal. Shock can be recognised by theperson being:

pale and having a clammy skin, frightened and shivering, probably semiconscious and not breathing normally.

The actions you take are:


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send for medical help, loosen tight clothing, keep the person warm.

Do not move the person unless you are absolutely certain he has no physical

injury.

12.2 Bleeding

Small cuts and grazed skin can be treated from the first aid box in the CCR.Make sure the wound is clean and apply a dry dressing/bandage. If thebleeding does not stop within a reasonable period of time or other problemsarise, consult the medic.


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WOUNDS

For more severe cuts, abrasion, possible internal bleeding or, the woundcannot be cleaned properly, then the medical services must be consultedimmediately. Four common wounds are illustrated in Figure 20.

After treatment protect the injured area as much as possible; for instance

wear the relevant protective clothing.

12.3 Heat

It is important when treating victims of heat to recognise the differencebetween heat exhaustion and heat stroke. The wrong treatment can be fatal.

Heat Exhaustion

This is a result of excessive activity in high temperatures. The victim will bepale and have a cold and sweating (clammy) skin; he will probably be

unconscious. Treat him by keeping him warm and quiet. If he is consciousgive him salt water to drink (two teaspoons to a glass of water).


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Heat Stroke

This is result of being overexposed, particularly the heat, to the sun. Thevictim will have a hot, dry and reddened skin; he will probably be delirious orunconscious. Treat him by sponging his whole body with cold water.

12.4 General Guidelines to First Aid

Until you know the extent of the injuries to a person:

Do not move him if you suspect fractures, neck or back injuries. Do not touch him unless you are certain he is not in contact withany electrical circuit.

NOTE:In the case of electrocution, switch off the power immediately or

remove the victim with dry clothing, a stick or anythingthat will insulate you from the electricity.

Help that can be given includes:

Moving victims overcome by gas into a clean air area, taking thenecessary precautions to ensure you are not affected. For example, wearingbreathing apparatus. Stopping bleeding by applying slight pressure to the injured areawith a cloth pad. Applying cold water or ice to burns, do not apply cream orattempt to remove clothing stuck to the victim. Making sure a victim's nose and mouth are clear. Victims ofchemical splashes must shower immediately, removing their clothes only aftermost of the chemicals have been washed away, paying special attention tothe washing of the eyes. Giving artificial respiration where a victim has stoppedbreathing.


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PREPARATION OF VESSELS FOR MAINTENANCE

This section on operational safety discusses the procedures involved whenvessels and equipment containing hydrocarbons require shutting down, andopening to the atmosphere to make repairs or perform other maintenance

work. These procedures are conducted by the operator after a shutdown tomake equipment 'safe to work' for the maintenance crew.

13.1 Removal of Hydrocarbons

The two main hazards from opening equipment to the air are:

Hydrocarbons leaking from the equipment, creating a dangerousatmosphere. Hydrocarbons leaking into equipment when personnel arepresent.

All hydrocarbons, liquid and vapour, must be removed safely and replacedwith air before equipment can be safely entered or worked on. In addition,each hydrocarbon connecting line must be isolated to prevent the possibilityof leakage into the equipment.

13.2 Vessel Isolation

A closed valve is not a positive means of stopping or isolating flow into avessel. Valves can pass or leak. The double block and bleed valvearrangement shown in Figure 21 can safely isolate flow, when the blockvalves are both closed and the bleed valve is open to the atmosphere. A leakthrough the upstream block valve will flow out of the bleed valve and not enterthe vessel or equipment.

FIGURE 21DOUBLE BLOCK AND BLEED VALVE ISOLATION

Lines frequently only have one block valve. Correct isolation is made byinstalling a metal plate into a downstream flange or the downstream valveflange. The metal plate is called a spade or blind and must be of sufficient

thickness to withstand the full upstream pressure on the line, or it may ruptureif the block valve fails. See Figure22.

HP

CLOSED CLOSED

BLOCK

VALVE

BLOCK

VALVE

OPEN

BLEED

VALVE

TO SHUTDOWN

VESSEL OR

EQUIPMENT


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SPADE OR BLIND ISOLATION

On high pressure lines a safer arrangement is to install a spacer between theblind and the downstream side flange face. This allows valve leakage to flow

out of the flange at the spacer. See Figure23.

FIGURE 23SPACER AND BLIND ISOLATION

The double block bleed or spacer can be used when little or no leakage isexpected from the upstream blockage. If leakage is expected to create ahazard, a full thickness blind must be installed.

Plan the Entry

Prior to conducting a confined space entry, the job must be planned. Thisincludes a review of the confined space entry check list and insuring all of thelogistic considerations have been made. i.e. If nitrogen is used for purging, isenough on board? Are all tools and equipment available? Have all of thehazards associated with the confined space been identified and appropriatecontrols as safeguards in place?

Issue Work Permits

Issue all work permits prior to commencement of the job. Refer to the Permitto work procedures for detailed requirements. All permit condition must be

met and all precautions must be identified on the permits.

Pre-Job Safety Briefing

All of the individuals involved in the confined space entry must be informed ofthe hazards and limitations on their work. It is most important that people donot proceed with the next step until all of the prerequisite work has beencompleted.

Shutdown Process

TO SHUTDOWN

VESSEL OR

EQUIPMENT

SPACER

BLIND

CLOSED

BLOCK

VALVE

HP


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The operating authority is responsible for shutting down the process. Properauthorisation must be obtained before taking a vessel out of service.

Depressure

Depressure the vessel through the flare or closed drain system. Uncontrolledventing of gas creates a hazardous situation.

Purge Out of Service

The vessel must be purged out of service to avoid forming an explosivemixture of gas and air. A vessel can be purged with an inert gas, water orsteam. If water is considered, check with an engineer to insure the weight ofthe water will not cause a problem with the structure or foundations.

There are 2 methods of purging with an inert gas. The dilution method whichis to pressure up the vessel with an inert gas to 45 psig from atmosphericpressure. The vessel is then taken back down to atmospheric. Inert gas isagain used to pressure up to 45 psig. The vessel needs to be pressured upto 45 psig 3 times. This will dilute the gas to a level that an explosive mixturecannot be formed.

The second method is the displacement method. It is simply injecting an inertgas into one end of a vessel and venting out the other. The method is lesseffective and is more suitable for pipelines and piping systems. Refer toFigure24.

Spade and/or Blank

A spade list should be developed at the planning stage. All spade/blankingpoints must be identified. Spades and blanks should be installed at thenozzles of the vessel to eliminate the need to blank various branches ofpiping. Double Block and Bleed is not an acceptable alternative toSpade/Blinding.

LockoutAll energy isolating devices must be locked out by both the operating authorityand the performing authority. Refer to the Lockout/tag out procedure fordetailed information.


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PURGE GAS FLOW PATTERNS

Open the Vessel

After purging, the vessel can be opened. A first step should be to remove the

PSV (pressure relief valve) and install an air extractor to ventilate the vessel.After the ventilator and all of the aforementioned safety conditions have beencomplied with can the vessel be opened. At this point the vessel cannot beentered.

Ventilate

An air extractor must be used to positively ventilate the vessel. Therecommended type of extractor is the venturi type. It is air operated, has nomoving parts and is intrinsically safe. The purpose of the ventilation is toremove any inert gas from purging as well as dilute any remaining

hydrocarbons to below the LEL (lower explosive limit).Tenorm Monitoring

LIGHT PURE GAS

PURGE GAS FLOW

IS FROM THE TOP

TO THE BOTTOM

WHEN GAS IS

LIGHTER THAN AIR

VENTHEAVIER

PURGE

GAS

VENT

PURGE GAS FLOW

IS FROM THE BOTTOM

TO THE TOP WHEN GAS

IS HEAVIER THAN AIR

VENT

VENT

PURGE GAS

PURGE GAS ENTERS THE

MIDDLE OF THE VESSEL

AND VENTS FROM TOP TO

BOTTOM AT THE SAME

TIME


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The safety department must be contacted to arrange for a radiation specialistto check for radiation levels from scale or sludge. The radiation specialist willdetermine if the TENORM radiation is below acceptable levels and if specialprotective clothing is required. Refer to the Tenorm procedures for further

information.

Gas Testing

The atmosphere inside the vessel must be tested before any person canenter. The initial testing must be done with a probe from outside the vessel.If the vessel is still full of an inert gas, a combustible gas detector will not besuitable for this testing.

Acceptable Limits

If the initial gas test is below 10% LEL, the gas tester may enter the vesselwith SCBA to complete the gas test. If toxic gas is expected, these must alsobe measured. If the inside of the vessel is below 10% LEL and the toxicgases are below their TLVs, the vessel can be entered for final cleaning.

Breathing Apparatus

All workers who initially enter the vessel must wear either SCBA or an Airlineset with an escape bottle. Only after the vessel has been cleaned thoroughlyand repeated gas tests shown negative, can entry be made without breathingapparatus, providing that the oxygen level is at least 20%.

Do the Work

Once the vessel is safe for entry, the work of inspection, coating repairs or hotwork may be completed.

LightingOnly low voltage, 12v or 24v DC lighting systems can be used. Batteryoperated or air driven lights are also acceptable. All lighting equipment must

be explosion proof or intrinsically safe. 110v or 220 v AC lighting systems arenot allowed.

SupervisionVessel entry requires close supervision. Always station a safety watch at theman way of the vessel while people are inside. It is this person'sresponsibility to assist the person inside and to summon assistance in theevent of a problem.

Button Up


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Once the work has been completed and all tools, equipment and people havebeen removed or exited, the vessel can be buttoned up.

Purge Into Service

The air inside the vessel must be purged out before gas is introduced into thevessel. This can be done in a similar method to purging out of service. At notime can an explosive mixture of gas and air be allowed to form.

Remove Locks and Blanks

The locks and blanks can now be removed as part of re-commissioning thevessel. Refer to the lockout procedure for further information.

Pressurise

Pressurise the vessel in stages. Insure all blanking locations, PSV and allflanges are tight and to not leak. Pressuring-up too quickly can causedamage to the coatings or cause chilling problems with the steel.

Close Out

Once all of the above steps have been completed, the process can berestarted. Insure all work permits are closed out and that restarting theprocess does not create a hazard to other work which may be going on.

13.4 Pressure Testing for Leaks

After purging air from gas plant vessels and equipment the system must betested for leaks using gas. The tightness of the system flanges, valves, manways, etc., is tested first during purging at 15 psig. pressure, then again at50% normal operating pressure and finally at full normal operating pressure.A pressure test is conducted using the tape and soap method. Flanges aretaped and a small hole punched into the top or side of the tape. A soapysolution is then used on the hole to detect gas leaks which show when thesoap solution bubbles.

Liquid leaks are detected by punching a hole in the tape at a low point andwatching for liquid dripping out of the hole. See Figure25.

All leaks must be stopped as they are found.

Pressuring and Depressuring Vessels

During pressuring and depressuring operations of gas process equipmentconsideration must be given to the high operating pressures and highvelocities of gas. Caution must be taken to prevent damage to vessel internal


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13.5 Venting

When venting a vessel or item of process equipment to atmosphere all the

components for fire are present. Fuel and air are present, and heat forignition is possible from static electricity or a spark that may come from ametal tool striking the vent line. The safest way to vent equipment is into aflare or vent system. Vent lines sometimes discharge directly to theatmosphere at a safe distance above or away from the vessel or equipment.Venting vessels directly to the atmosphere can be hazardous when thevapours are heavier than air. Heavy gas falls to the ground and accumulatesin clouds, if a heat source is present nearby the vapour cloud will ignite andthe fire will 'flashback' to the vent on the vessel. Heavy vapours shouldalways be vented to a flare and burnt-off safely.

FIGURE 25

TAPE AND SOAP TEST

13.6 Miscellaneous Equipment Safety Practices

When a pump, compressor or generator is shutdown for repair,ensure that the driver cannot be started during maintenance. Electric motors,should be electrically isolated by 'locking off' at the master power supplyswitch and attaching a 'Do Not Operate' warning tag. If the driver is anengine, lock the fuel valves in the 'closed' position and attach warning tags. Process instrument must be checked for correct operationbefore startup. An instrument control loop is functionally checked byimposing a process input signal to the controller, and observing themovement of the control valve. Before vessels are closed after repair, the operator shouldvisually inspect inside them, to ensure that all tools and maintenance

equipment have been removed.

TAPE IS WRAPPED AROUND THE MATING

FLANGES. HOLES PUNCHED TO DETECT

GAS AND LIQUID LEAKS.

SOAP BUBBLE

TAPE

JOINT


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If electric motor cables have been disconnected during repair,the motor should be checked for correct direction of rotation before startup.

13.7 Valve Security

Certain valves in a process system might be locked in a permanently open orclosed state. This may be to prevent flow into an area which is not ready foruse; there are many possible reasons. Unauthorised alteration of thisarrangement could change a safe condition into a potentially hazardouscondition.

To secure these valves the hand wheel, or the securing lever is chained andpadlocked to prevent it being altered. The key is kept by the productionsupervisor and will only be issued to authorised personnel, along with apermit to work and isolation certificate. If the valve is closed and locked for avessel or equipment inspection a spade or blind must also be fitted.

NOTE:Safety or relief valves must never be tampered with. If a relief valve is

seen to be leaking this must be reported.

13.8 Emergency Shutdown Devices (ESD)

ESD devices are mentioned here because of their safety aspects. The ESDprocedures and systems are not the concept of this unit and are to be foundin process operations manuals. ESD devices perform a vital function inshutting down platforms, units or equipment under conditions when continuedoperations could cause damage or endanger personnel. The devices areoperated automatically by sensors; however, manual operation is possiblefrom the control room and site locations.

If ESD devices are deactivated for any purpose the control room must beinformed and the devices clearly tagged. A safety system by pass certificatemust be issued.


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SAFETY FACTORS IN PRODUCTION EQUIPMENT

Safety factors are built into all gas production equipment to prevent failureunder the most extreme operating conditions. All pressure vessels andequipment, such as separators and contactors, pumps and compressors, are

built to strict specifications. They are designed to operate at a pressure atleast 10% above normal operating pressure, and at temperatures muchhigher than normal operating temperatures.

14.1 Pressure Vessels

During the design stage, the construction specification for process vesselsusually requires a safety factor of 4. The safety factor represents 4 times theminimum thickness of metal required to contain the design pressure of thevessel. Most pressure vessels are designed with the safety factor of 4, at astandard operating temperature of 650F, this is mu ch higher than most gas

field operating temperatures.

The final stage in the manufacture of pressure vessels is a hydrostaticpressure test at 1 times the design pressure. The pressure test is held onthe vessel for usually 24 hours, if a leak is detected, it is repaired and the testrepeated.

For example, a gas field production separator with internal diameter of 36inches is required to operate at a pressure of 800 psig. The design pressurewill be 10% higher than operating pressure, or 880 psig. The minimumthickness of steel plate required to contain 880 psig. is 0.23 inch. With asafety factor of 4 the vessel thickness must be 4 x 0.23 = 0.92 inch thick.Steel plate is made in thickness of 1/16 inch increments, the closest standardplate size to 0.92 inch is 0.94 inch, which will be used in the final manufactureof the separator. After completion of fabrication, the separator will behydrostatically pressure tested at 1.5 x 880 = 1320 psig. Refer to Figure26.

FIGURE 26

PRESSURE VESSEL SAFETY FACTORS14.2 Pressure Safety Valves

FEED INLET

VENTVALVE

TO ATMOSPHERE

OR FLARE

36 inch

PRESSURE SAFETY

VALVE SET AT

968 psig

GAS

PLATE THICKNESS

WITH SAFETY FACTOR 4

0.92 inch. CLOSEST

STANDARD PLATE 0.94 inch

CONDENSATE

DRAIN

OPERATING PRESSURE

800 psig

DESIGN PRESSURE

880 psig


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All pressure vessels are equipped with pressure safety valves (PSV) or safetyrelief valves (SRV) that are designed to open and relieve the pressure if itreaches 10% above the design pressure. PSV's are also sized to release thetotal fluid inlet flow to the vessel to prevent pressure continuing to increase

after the PSV has opened.

14.3 Metal Fatigue

Vessel failure is usually due to metal fatigue caused by one or more of thefollowing:

heating, cooling, corrosion, vibration from pumps and compressors, and wind action.

Metal fatigue failure usually occurs around a nozzle connection wherecorrosion frequently occurs, or vibration is concentrated. Small cracks appearlong before a major rupture occurs.

14.4 Piping

The piping safety factor depends on location. Gas plant piping, where thereis continual exposure to personnel has the same safety factor as pressurevessels. Piping in wellhead areas and flow lines because of less exposure topersonnel, usually has a safety factor rating of 2.

14.5 Rotating Equipment

Process pump and compressor casings are made of cast iron which has ahigh resistance to corrosion and wear, but it is not ductile and will thereforebreak if subjected to piping strain or continuous vibrations.

Excessive operating conditions of pressure and temperature will damagerotating equipment packing, seals, valves and pistons. The casing will not bedamaged by excessive pressure or temperature as long as correct lubrication

is maintained.

14.6 General

The maximum limits of pressure and temperature that can safely be toleratedby gas vessels and equipment is generally 10% above the design parameter.The design parameter is usually stated on Piping and Instrument Diagrams (P& ID's) which the operator uses as a reference and guidance. If an operatingcondition increases above the 10% point the operator should report itimmediately to his supervisor for operating and engineering advice. Thedesign pressure and temperature are stamped on the name plate on the

individual item of equipment.


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14.7 Safety Considerations

SeparatorsOne of the most important controls on separator vessels is level. A failure or

malfunction of level control devices can cause serious operational problems.

A high liquid level will cause liquid carry over in the gas outletstream. Liquid in the gas stream will cause foaming in the glycol dehydrationunit, which could result in liquid in the fuel gas system as well asunacceptable glycol losses. A low liquid level will cause gas to flow out of the condensateliquid line and over pressure the downstream stabilising equipment.

The Level Gauge (Refer to Figure 27)

Level gauges are the simplest form of level measuring devices, they enablethe operator to see the level of fluid in a vessel. The level gauges in use inthis area are the "reflex type", consisting of a steel housing and a glass slab.The glass is flat on the outside and has 90groove s on the inside, down itsvertical length. The level gauge is in open communication with the vessel andthe level in the gauge is therefore the same as the level in the vessel.

Light rays entering the gauge glass are reflected where gas is present andare absorbed where the liquids come in contact with the glass. This meansthat the part of the gauge glass which is in contact with gas will show a clearsurface, as all light is reflected and the part of the gauge glass that is incontact with the liquid will show a dark surface, as practically all the light isabsorbed.

Most gauge glasses are fitted with offset type gauge valves that have a balland seat safety device which seals off the pressure in the vessel from theoutside, in the event of the glass breaking. Figure28.

When putting the level gauge in service the operator should start with bothgauge cocks in the closed position. The gauge cocks should then be backedoff slowly from the seat in quarter turn increments until a level is obtained in

the sight glass. Once the level is obtained the gauge cocks must be openedfully.


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SIGHT GLASS LEVEL MEASUREMENT

When draining the sight glass it is best to close the gauge cocks fully, performthe draining operation and then put the level gauge back in operation asdescribed in the previous paragraph. The reason for this is that if the gaugecocks are left open during draining operations the ball check will seat itselfand give the operator the incorrect impression that the gauge cocks areclosed.

FIGURE 28GAUGE COCK

Wellhead Assemblies

The numerous valves, fittings and pressure gauges on a wellhead assemblyare all a possible source of leakage. All valves on the wellhead are lubricatedso that they are free to move when required. Valves that are not connectedto lines are plugged (bull plug) and have a pressure gauge and bleed valveattached. With this arrangement, pressure on the plugged side can be safelybled off and indicated on the gauge before the plug is removed. It is unsafeto fit bull plugs to unconnected valves without a gauge and bleed valve. Aslight leakage in the valve will produce wellhead pressure inside the plug,

which if loosened will blast with great force.Before removing a fitting from a wellhead or changing a bean in a choke, twopressure gauges must be installed on the fitting and the pressure vented.Many serious injuries to operators have occurred on high pressure gauge orbleed valves when they have become blocked with debris and the operatorthought the fitting had depressured. A second pressure gauge reduces thishazard.

Rotating EquipmentPumps

GLASS

GAS SECTION OF SIGHT GLASS

LIGHTRAYS REFLECTED

GLASS

METAL HOUSING

REFLEX GAUGE

LIGHTRAYS ABSORBED

GLASS

LIQUID SECTION OF SIGHT GLASS


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The main hazard from gas plant process pumps is that of leaking seals orpacking. Repairs must be made promptly, because the leak quickly becomesworse if no action is taken. Packing usually lasts for about a year in mostapplications; mechanical pump seals are safety and more efficient and last alot longer before requiring maintenance.

Compressors

The majority of gas compressors in the field are driven by gas engines or gasturbines, which have proven safety and reliability. The main hazard from acompressor, like pumps, is a fire resulting from gas leaking from packing orseals that is ignited by the engine or hot exhaust stack.

The packing on a compressor is enclosed in a housing or packing box. Thisis vented to atmosphere a safe distance away from the engine. If the housingcovers are removed to check the condition of the packing, leaking gas can

drift towards a ignition source. Operators must be aware of the fire hazardsinvolved in operating gas compressors.

Atmospheric Storage Tanks

Fuel storage tanks operate at, or near, atmospheric pressure. There is apossibility of air entering into the tanks and creating a combustible mixture.

When the level in a fuel tank falls, pressure also falls and air enters the tank,creating a possibly hazardous combustible mixture of hydrocarbon vapourand air. As the level rises the combustible mixture is forced out of the tankvent and could be ignited by lightning or static electricity. The flame at thevent could travel back into the tank causing an explosion. See Figure 29.


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ATMOSPHERIC VESSEL OPERATIONS

Flame ArrestorsAtmosphere storage tanks usually have 'flame arrestors' installed in the ventconnections. A flame arrestor is a cooler. If the vapour leaving the tankignites, the flame will move through the flame arrestor, where it cools to belowthe ignition temperature and extinguishes. Flame arrestors should beinspected regularly by operators and cleaned as necessary.

FIGURE 30FLAME ARRESTORBlanket Gas

Air can also be excluded from atmospheric tanks by using a 'blanket gas'system, where a stream of gas (fuel gas) is introduced in the top of the tankto maintain a slight positive pressure inside at all times. A pressure regulatorin a supply blanket gas line maintains constant pressure of a few inches watergauge inside the tank. A vent or pressure safety valve allows excessive gaspressure to exit the tank. The pressure in the system must be monitoredfrequently to ensure that the pressure regulator and PSV are functioning

correctly. See Figure 31.

BLANKET GAS

Vacuum

Another problem that can occur with storage tanks is that of vacuum. Tankscan collapse under a vacuum. A vacuum can occur when pumping out atank, if the blanket gas system or air vent is not functioning, or if the operatorpumps out too quickly. A vacuum can also occur on a storage tank that isalmost completely drained, some of the vapour will condense and a vacuumcan result. Vacuum can be prevented by connecting the tank to a source of

VENT

AIR ENTERS

VAPOUR + AIR

PUMPING

VENT

COMBUSTIBLE

MIXTURE

VAPOUR + AIR

FILLING

IF THE COMBUSTIBLE MIXTURE

IGNITES THE FLAME WILL TRAVEL

BACK INTO THE TANK

CONDENSATE IN

CONDENSATE OUT

PRV

VACUUM

VENT

POSITIVE PRESSURE

PSV

GAS


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pressure or, as a last resort, opening a vent line. A vacuum breaking valve isusually fitted to the tank top to prevent a vacuum condition occurring.

Pressurised Equipment

Although gas production and process facilities are designed and constructedwith a high margin of safety, failures will occur. Part of an operator's duty is tobe aware of the possibility of a failure occurring on the equipment he isoperating. This is especially true when working on wellhead assemblies or onthe high pressure gas plant facilities.

For example, because of the high operating pressure of gas plants even asimple task like greasing a valve can be dangerous. Stand to one side whenapplying grease so that if the grease fitting fails, it will not blow out into yourface. Apply the same safe technique when opening or closing valves,draining level glasses or performing other duties - stand to one side.

Pressure gauges are useful operating aids, but they can give a false sense ofsecurity. Gauges can fail just like any other item of equipment. Because apressure gauge indicates 'O' psig (zero) it does not necessarily mean thatthere is no pressure in the equipment it is attached to.

The gauge may:

have failed, be plugged. have moved the pointer full scale around the dial so that itappears to indicate zero.Pressure gauges on wellheads and flow lines frequently plug with sand andgive false readings.

ElectricityWhen an electrical short circuit occurs, the heat generated often melts theconduit or housing containing the damaged cable, and may be a source ofignition to a combustible mixture in the area.

Electric switches and switch gear must be enclosed in explosion and spark-proof housings to prevent sparks, that occur when the switch is operated,from igniting a combustible mixture that may have leaked into the vicinity. Aswitch must never be operated if the explosion proof housing has beenremoved.

The condition of electric motor drivers must be checked periodically to ensurethat no sparking is occurring on the motor, this could also be a source ofignition.

Whenever any electrical work is being carried out, the master switch on the

equipment should be locked-off (padlock) and a 'Do Not Operate' tagattached to the equipment and switch gear.


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ChemicalsThe effects of exposure to gas field treating chemicals varies from mild skinirritation, from corrosion inhibitors, to severe burns from acids. In most cases,

the more hazardous chemicals are also the most corrosive.

Plastic gloves, aprons, rubber boots and full face shields must be available forthe safe handling of chemicals. Even so, most accidents and injuries occurfrom improperly handled chemicals. The operator must be aware of the safehandling techniques, wear the correct protective clothing and be able to givethe appropriate First Aid treatment before using chemicals.

Chemical storage drums and containers can corrode on the inside andchemical injection piping systems can fail because of internal corrosion. Awater 'body and face' safety shower should be available on-site so the

operator can quickly wash off any chemical that accidentally splashes, spraysor spills on him.

1.Colour Coding and Signs

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