SSFFCC KKeeyy IInntteerrlloocckkss && PPrroocceessssMMaannaaggeemmeenntt SSyysstteemmss

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AApppplliiccaattiioonnss –– PPrreessssuurree PPrrootteeccttiioonn

PPrreessssuurree PPrrootteeccttiioonn

Whether onshore or offshore, maintenance procedures to Safety ReliefSystems on live plant cause concern in ensuring that an open path to reliefis maintained at all times during the work exercise.

Most modern piping arrangements include spare relief capacity enablingcontinuous production while such maintenance procedures are conductedon live plant eliminating the requirement to isolate and shut down theprocess.

Twin or multiple safety relief valve systems are usually fitted with isolationblock valves upstream and downstream of each safety relief valve - it isessential to ensure that the block valves isolating the spare relief valve areopened BEFORE the block valves of the workpiece relief valve are closed.This issue is a more acute problem if the respective relief valves and isolatingblock valves are distant or out of sight of each other.

Various AAPPII and AASSMMEE codes recognise this hazard and recommend the useof interlocks to eliminate this possibility. AAPPII RRPP 552200 (Pressure RelievingSystems for Refinery Services - Part II Section 4- Isolation ValveRequirements) and AAPPII RRPP 1144EE (Design and Installation of OffshoreProduction Platform Piping Systems - Para 5.8b [2] - Relief Device Piping)specifically recommend interlocks in this situation to ensure that(over)pressure protection of the vessel is not compromised. Theserecommendations are also in accordance with the requirements of AASSMMEE --SSeeccttiioonn VVIIIIII -- AAppppeennddiixx MM..

Fitting a valve interlock to the upstream and downstream isolating valves oneach safety relief valve (PSV) will ensure these recommendations areimplemented.

An initiating key, issued from a secure location (Control Room) commencesthe PSV changeover. Follow the step-by-step procedures in the diagram.

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....... 'apart from the possibility of death or injury topersonnel, or pollution of the locality, what other possibleimpact could an over-pressure explosion or rupture of one

of your main process vessels have on your business' ?TTyyppiiccaall ‘‘44 BBlloocckk VVaallvvee // 55 KKeeyy’’ IInntteerrlloocckk SSyysstteemm

IILLLLUUSSTTRRAATTIIOONN SSTTAATTUUSS::PPSSVV11 oonn lliinnee:: PPSSVV22 iissoollaatteeddBlock Valves VV11, VV22 & VV44** are Locked Open (LO.)Block Valve V3 is Locked Closed (LC)*Spare outlet (downstream) block valve normally LO especially iflower pressure rated than corresponding inlet (upstream) blockvalve

RReeqquuiirreemmeenntt::TThheerree iiss aallwwaayyss aann ooppeenn ppaatthh ttoo rreelliieeff..(Inlet block valves VV22 & VV33 must never be closed at the sametime)

MMaaiinntteennaannccee TTaasskk::TToo ccoommmmiissssiioonn PPSSVV22 iinnttoo sseerrvviiccee..TToo iissoollaattee aanndd ppeerrmmiitt rreemmoovvaall ooff PPSSVV11 ffoorr tteessttiinngg//sseerrvviicciinngg..

WWoorrkk SSeeqquueennccee::11.. Key 'DD' is issued from the Control Room to initiate the Permitto Work

22.. Key 'DD' unlocks and enables the opening of spare inlet blockvalve VV33

33.. VV33 is operated to open and is LO by removing Key 'CC' - PPSSVV22iiss nnooww oonn lliinnee.44.. Key 'CC' is transferred to unlock and close inlet block valve VV2255.. VV22 is LC by removing Key 'BB'66.. Key 'BB' is transferred to unlock and close outlet block valve VV1177.. VV11 is LC by removing Key 'AA'The return of Key 'AA' to the Control Room closes-out the workpermit and enables the issue of instructions for removal of PPSSVV11for testing and servicing.

TTwwiinn PPSSVV CChhaannggeeoovveerr SSeeqquueenncceeIt should be noted this interlock arrangement further ensuresthat the higher pressure rated inlet block valve VV22 is closedbbeeffoorree its corresponding lower pressure rated outlet block valve(VV11). Conversely, this key interlock arrangement would alsoensure opening of low pressure outlet block valves bbeeffoorreeopening of high pressure inlet block valves.

PPSSVV 11VV11 -- KKeeyyss AA && BB

VV22 - KKeeyyss BB && CC

VV44 -- KKeeyyss EE && DD

VV33 -- KKeeyyss CC && DD

PPSSVV 22

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AApppplliiccaattiioonnss –– PPrreessssuurree PPrrootteeccttiioonn

MMeecchhaanniiccaall PPrriinncciipplleess

((BBlleeeedd ddeevviicceess ffiitttteedd iinnttoo cclloossuurree ooppeenniinnggmmeecchhaanniissmmss aarree aalloonnee aann uunnrreelliiaabblleessaaffeettyy aarrrraannggeemmeenntt ttoo ddeetteecctt tthheepprreesseennccee ooff rreessiidduuaall pprroodduucctt.. TThheeyy aarreepprroonnee ttoo wwaaxx oorr hhyyddrraatteess ffoorrmmaattiioonnsswwhhiicchh ccaann oobbssttrruucctt tthhee bblleeeedd cchhaannnneelliinnssiiddee tthhee vveesssseell tthheerreebbyy mmiisslleeaaddiinngg tthheeooppeerraattoorr ttoo bbeelliieevvee IItt IIss ssaaffee ttoo ooppeenn tthheecclloossuurree}}..

SFC interlocks can be specified to ensure the minimum safetyarrangement of interlocking the vessel vent valve with the pig trapclosure. This arrangement ensures (to the exclusion of all othermethods) the vessel VENT valve is OPEN before any attempt can bemade to open the closure.

With interlocks fitted to both the vent valve and pig trap closure, a key isreleased when the vent valve is opened - removing the key from the ventvalve locks the valve in the open position This key is coded in common withthe closure lock - only by opening and locking the vent valve can the operatorsecure the correct key to proceed to unlock and open the closure.

PPiigg TTrraappss

PPiigg ttrraapp aacccciiddeennttss iinnvvoollvviinngg ooppeerraattoorr iinntteerrvveennttiioonn ccaann bbeepprreevveenntteedd bbyy SSFFCC ccooddeedd--ccaarrdd kkeeyy iinntteerrlloocckk ssyysstteemmss..

DNV TN B 302 Technical Notes for Fixed Offshore Installations describes pigtraps as 'primary grades sources of hazard'. ASME and API codes equallyrecognise pig trap hazards - especially in relation to the risk of openingclosures while the vessel remains under pressure. The Pipelines SafetyRegulations 1996 enacted into UK law in April 1996 requires operators ofpipelines to provide safety systems that ensure persons are protected fromrisk to their health and safety - again describing the hazard of opening pigtrap vessels under pressure.

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SSaaffee LLooaaddiinngg aanndd UUnnllooaaddiinngg ooff PPiigg TTrraappss

PPiigg TTrraappss

Further procedure sequences can be regulated by interlocks toinclude drain valves, nitrogen purge and water flush valves,corrosion inhibitor and isotope functions, and indeed maininlet/outlet and kicker valve functions - every system is designedto meet clients' unique operating conditions/requirements.

Key interlocks can be integratedinto pig trap control systems evenwhere the main inlet/outlet valvesand kicker valve are actuated(MOV's). In this situation,launching or receiving pigs is asemi-automatic process withoperator intervention limited topush-button action either througha local control panel or effectedfrom a remote control station.

Indeed, these valves may even beprogrammed with ESD functions.

However, when it comes toloading or unloading of pigs, anabnormal condition arises where

software or electronic interlocking arrangements between thesevalves are suspended through the necessity to isolate thesevalves both from 'Remote' and 'Local' settings to the 'Off'position. An SFC coded-card key interlock system can be fitted tothese valves to mechanically prove their 'closed and isolated'

status - releasing a key which thenenables operation of manually-operated valves related to vent,drain, N2 purge and water flushprocedures before enabling anyattempt to unlock and open the pigtrap closure.

Only an SFC coded-card keyinterlock system can achieve thecondition of creating a positive linkthat makes the operation/status ofMOV's and manually-operatedvalves completely interdependentand absolutely reliably ensurestotal isolation, venting and drainingof the vessel BEFORE any attemptcan be made to open the vesselclosure!

....."Imagine the consequences of opening a pig trapclosure with product in the barrel"

....."Imagine the effect of attempting to pass a pig througha partially open outlet valve"

....."Imagine getting a sniff of H2S "

.....tthheessee tthhiinnggss ccaann hhaappppeenn -- hhaavvee hhaappppeenneedd!!

MMeecchhaanniiccaall KKeeyy SSaaffeettyyMMeecchhaanniiccaall kkeeyy ssaaffeettyy iinntteerrlloocckkiinngg iiss tthhee OONNLLYY tteecchhnnoollooggyy tthhaatt ccaann aassssuurree tthhee uunniivveerrssaallllyy aacccceepptteedd rreeqquuiirreemmeenntt iinn tthhee llooaaddiinnggaanndd uunnllooaaddiinngg ooff ppiigg ttrraappss tthhaatt tthhee vveesssseell iiss vveennttiinngg BBEEFFOORREE iitt iiss ppoossssiibbllee ttoo ooppeenn tthhee vveesssseell cclloossuurree.. AA kkeeyy iiss rreelleeaasseedd wwhheenntthhee vveenntt vvaallvvee iiss uunnlloocckkeedd aanndd ooppeenneedd wwhhiicchh tthheenn eennaabblleess uunnlloocckkiinngg ooff tthhee cclloossuurree mmeecchhaanniissmm.. TThhiiss iimmppeerraattiivvee iiss ddeeffiinneeddvvaarriioouussllyy iinn tthhee ffoolllloowwiinngg ssttaannddaarrddss aanndd rreegguullaattiioonnss::-- ASME VIII - Division 1 1996 No. 825 - (UK) Pipeline Safety Regulations (Section 6 - Para. 37 of Guidance on Regulations - UK Health & SafetyExecutive). US DoT - Pipeline Safety Regulations - Part 195 Transportation of Hazardous Liquids by Pipeline (§195.426 Scraper & SphereFacilities). Shell DEP 31.40.10.13 - Gen : Design of Pipeline Pig Trap Systems.

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AApppplliiccaattiioonnss –– CCOO22 FFiirree DDeelluuggee SSyysstteemmss

FFiirree DDeelluuggee SSyysstteemmss

International concern over the environmental effect of widespread use ofCFC gases has led to the phasing out of HALON (Halon 1301) as a fireextinguishing medium and its substitution with Carbon Dioxide (CO2) or otherinert gases.

CO2 is a very effective extinguishing agent and works by reducing oxygenlevels to a point where combustion cannot be sustained. It is a naturallyoccurring substance and has no corrupting or polluting effect when releasedinto the atmosphere - unlike HALON which is a CFC compound.

Automatic CO2 fire extinguishing systems when activated are designed todeluge an area within seconds. Typical installations includeturbine/generator enclosures, plenum chambers, computer rooms, archivesor any other enclosed area designated as being not-normally-occupied. Suchareas are occupied only on an occasional basis usually for the purposes ofinspection, maintenance or repair.

MMeecchhaanniiccaall PPrriinncciipplleess

CCOO22 iiss ppootteennttiiaallllyy ffaattaall -- aannyyoonnee wwhhoo mmaayybbeeccoommee ttrraappppeedd iinn aann eenncclloosseedd ssppaacceeffllooooddeedd wwiitthh CCOO22 wwoouulldd vveerryy qquuiicckkllyyssuuffffooccaattee..

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.......'what's colourless, odourless, is all around us andcan kill a person in less than 2 minutes' ? .......

key(s) which enable isolation of the CO2 supply. Based on a keyexchange principle, further keys are released which enableunlocking of the access door(s) and permit the entry of theworker(s) to undertake the task at hand.

TThhiiss ssaaffeettyy ssoolluuttiioonn ffrroomm SSFFCC ffuullffiillllss tthhee ssaaffeettyy rreeqquuiirreemmeennttss ooffNNFFPPAA1122 ** aanndd BBSS 55330066.. ##

* National Fire Protection Association (USA) - Carbon DioxideExtinguishing Systems - 1993 Edition

# British Standard - Part 41986 - Specification for CarbonDioxide Systems

FFoorr tthhee ppeerriioodd iinn wwhhiicchh wwoorrkkiiss bbeeiinngg ccaarrrriieedd oouutt iinnssiiddeetthhee eenncclloosseedd ssppaaccee,, tthheeCCOO22 SSuuppppllyy iiss iissoollaatteedd aannddtthhee wwoorrkkeerr((ss}} ccaannnnoott bbeelloocckkeedd iinn.. HHoowweevveerr,, ttooeennssuurree ttoottaall wwoorrkkeerr ssaaffeettyyeeaacchh iinntteerrlloocckkeedd aacccceessssddoooorr wwiitthhiinn tthhee ssyysstteemm iissffiitttteedd wwiitthh aa ffaaiillssaaffeeeemmeerrggeennccyy oovveerrrriiddee eessccaappeemmeecchhaanniissmm wwhhiicchh ppeerrmmiittss aawwoorrkkeerr ttoo ssttrriikkee aa ppaanniiccbbuuttttoonn oorr ccrraasshh rraaiill tthhaattmmeecchhaanniiccaallllyy oovveerrrriiddeess tthheeddoooorr llaattcchh mmeecchhaanniissmm..

SSaaffee PPrraaccttiiccee

Safe practice requires an arrangement which prevents casual orunauthorised access into a (CO2) protected space and alsoenables emergency exit at all times from the protected area. Thesafety arrangements should also ensure that all doors andaccess hatches remain locked during periods of normaloperations and that access to the protected area is controlledand authorised only by the appointed authority.

SFC interlock systems can be applied for maximum effect topermit access only under the strictest conditions. Access forinspection or maintenance purposes is only possible by theissue of an initiating 'permit key' by the appointed authority. Thiskey may be used to activate visual or audible alarms whichdenote 'work in progress' and / or the release of secondary

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SFC Key Interlocks& Process Management Systems

Edition Date 2008