EG310 - Pressure Relief Systems

8/13/2019 EG310 - Pressure Relief Systems

1/28

Occidental Oil and Gas Corporation

Engineering Guide

Title Document No.

PRESSURE RELIEF SYSTEMS EG-310

Revision No. Approved Effective Date Page No.

1 Bryan D. Hum !rie" 1#1#$001 1 %& $'

Please refer to EG-300 General to place this guide in context and for overall purpose and scope, general requirements, applica ilit!, variances, and glossar! ofterms"

1.0 THIS GUIDE IS U(DERG)I(G *DDITI)(*L RE+ISI)(, BUT SH)ULDBE USED I( THE PRESE(T F)RM.

$. S )PE

This document provides assistance on the design and selection of thepressure relief system for onshore oil and gas production and processingfacilities hile providing for the safe and rapid disposal of aste gas undercontrolled conditions so that personnel and ad!acent facilities are not e"posedto ha#ards.

This document includes vapor discharge to the atmosphere$ vapor dischargeto a closed pressure system and flare$ and vapor depressuring and li%uid&lo do n systems for nonto"ic hydrocar&ons.

Pressure relief systems for to"ic vapors and venting atmospheric are notcovered.

3. PURP)SE

The intent of the design philosophy is to produce the most economicalpressure relief system that ade%uately disposes of all emergency releasesfrom safety relief valves$ vapor depressuri#ing and &lo do n systems$process stream diversion$ e%uipment drainage$ etc.

. DESIG( RITERI*

Overpressure is the result of an un&alance or disruption of the normal flo ofmaterial and energy that cause material or energy$ or &oth$ to &uild up insome part of the system. The pressure relief system should &e designed toprotect the e%uipment and piping from pressures outside the operating limitsand therefore$ the appropriate means of relief must then &e selected and thesystem discharged to a safe place.

Although efforts have &een made to cover all ma!or circumstances$ theconditions descri&ed herein should not &e considered as the only causes ofoverpressure. Any circumstance that reasona&ly constitutes a ha#ard underthe prevailing conditions for a system should &e considered in the design.

Overheating a&ove design temperature may also result in overpressure$ dueto the reduction of allo a&le stress. A pressure relief valve cannot protectagainst this type of contingency.

PROPRIETARY INFORMATION For Authorized Company Only


2/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 $ %& $'

The &asis for design overpressure is related to the American 'ociety for(echanical Engineers )A'(E*$ Boiler and Pressure Vessel Code and theAmerican National 'tandards +nstitute )AN'+* ,- .-$ Code for PetroleumRefinery Piping . Compliance ith these codes is a re%uirement$ or isrecogni#ed as the e%uivalent of a re%uirement in many locations. /here codesthat are more stringent apply$ the local re%uirements must &e met.

0. Pressure Relief (ethods

There are three different methodologies to dispose aste gases and li%uids1)a* vapor discharge directly to atmosphere$ )&* discharge to a closed pressuresystem and )c* discharge to a lo er pressure system or vessel.

The most economical method of discharging vapors or li%uids from pressurerelief devices is to discharge vapors to the atmosphere$ nonvolatile li%uids toa se er$ and volatile li%uids to other e%uipment operating at a lo erpressure. 2i%uids shall not discharge to the vapor disposal system. Thesemethods are preferred to the closed pressure relief system or li%uid &lo do nsystem$ provided such disposal is not in conflict ith or restricted &y1 E"isting and anticipated regulations concerning air or ater %uality and

noise. Prevailing meteorological conditions.

Properties of the vapor that is discharged$ such as to"icity$ volatility$flamma&ility$ entrained li%uid$ and molecular eight.

Disposal re%uirements hen the addition of a ne process unit isplanned.

'pecial consideration should &e given if there is concern that tu&erupture in heat e"changers may cause release of volatile or to"ichydrocar&ons to the atmosphere.

0.3 Contingency ,asis

All contingencies hich may result in e%uipment overpressure should &econsidered$ this include e"ternal fire e"posure$ utility failure$ e%uipmentfailure and malfunctions$ a&normal processing conditions$ thermal e"pansion$startup and shutdo n$ and operator error.

4or each contingency$ the resulting overpressure should &e evaluated and theneed for appropriately increased design pressure )to ithstand the emergencypressure* or pressure relieving facilities to prevent overpressure ) ithcalculated relieving rates* should &e esta&lished.

Every emergency arises from a specific cause or contingency. Thesimultaneous occurrence of t o or more contingencies should &e consideredunli5ely. 6ence$ an emergency$ hich can arise only from t o or more



3/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 3 %& $'

unrelated contingencies$ is normally not considered for si#ing safetye%uipment. 2i5e ise$ a simultaneous &ut separate emergencies are notconsidered if the contingencies causing them are unrelated. Contingencies$including fire e"posure$ are considered as unrelated if there is no process$mechanical$ or electrical relationship &et een them$ or if the length of timeelapsing &et een possi&le successive occurrences of these contingencies issufficient to separate their effects.

Every e%uipment item must &e studied individually and every contingencymust &e evaluated. The safety e%uipment for an individual item should &esi#ed to handle the largest load resulting from any possi&le singlecontingency. /hen analy#ing any single contingency$ one must consider alldirectly related effects that may occur from that contingency.

2i5e ise$ if a certain emergency ould involve more than one item$ then allaffected items must &e considered together.

The e%uipment !udged to &e involved in any one emergency is termed a7single ris57. The single ris5 hich results in the largest load on the safetyfacilities in any system is termed the 7largest single ris57 and forms thedesign &asis for the common collection system$ such as the flare header$5noc5out drum and flare. The emergency$ hich results in the largest singleris5 on the overall &asis$ may &e different from the emergency that forms the&asis for each individual item of e%uipment.

/hile generally only a single contingency is considered for design purposes$there may &e situations here t o or more simultaneous contingenciesshould &e ta5en into account8 e.g.$ if there is some remote relationship&et een them$ and pressures and temperatures developed could result incatastrophic failure.

Overpressure that may occur at normal or &elo normal pressures$ as aresult of reduced allo a&le stresses at higher than design temperaturesshould also &e evaluated and appropriate protective features applied in thedesign. 4or e"ample$ such conditions may arise from startup or upsetconditions. 2i5e ise$ lo metal temperature must also &e considered$ such asfrom autorefrigeration$ to ma5e sure that &rittle fracture conditions do notdevelop.

0.- Pressure Relief Devices

The function of a pressure relief device is to protect pressure vessels$ pipingsystems$ and other e%uipment from pressures e"ceeding the ma"imumallo a&le or5ing pressure )(A/P* &y more than a predetermined amount inorder to avoid ris5 to personnel and e%uipment. The permissi&le amount ofoverpressure )a&ove (A/P* is covered &y various codes and is a function ofthe type of e%uipment and the conditions causing the overpressure.



4/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 %& $'

+ndividual pressure relief devices and system depressuring loads should &ecalculated for each applica&le failure$ in accordance ith American Petroleum+nstitute )AP+* Recommended Practice 93 $ Guide for Pressure-Relieving andDepressuring Systems and American Petroleum +nstitute )AP+* RecommendedPractice 93:$ Sizing, Selection, and Installation of Pressure-Relieving Devicesin Refineries .

The essential steps in the design of protection against overpressure hich arecovered in other parts of this Guide$ or referenced documents as indicated$are summari#ed &elo 1

4rom the range of availa&le pressure relief valves and other devices$selection should &e made of the appropriate type for each item ofe%uipment su&!ect to overpressure. +nstrumentation$ chec5 valves$ andsimilar devices are generally not accepta&le as means of overpressureprotection.

'tandard calculation procedures should &e applied to determine the si#eof the pressure relief device re%uired for the ma"imum relieving rate$together ith other information necessary to specify the valve.

The pressure relief valve installation shall &e designed in detail$ includinglocation$ si#ing of inlet and outlet piping$ valving and drainage$ selectionof open or closed pressure relief$ and design of the closed pressure reliefsystem.

The design specification should include a ta&ulation of all contingenciesconsidered$ together ith their relief re%uirements.

Pressure relief devices should &e located to discharge from the vapor space oroverhead line of the protected vessel to minimi#e li%uid entrainment in therelief vapors.

Pressure relief devices can &e classified as follo s1

0.-. 'afety ;alves

An automatic$ spring


5/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 / %& $'

'afety relief valves are further su&divided in1

#onventional $afet! %elief &alve > this type of valve has its springhousing vented to the discharge side of the valve. The operationalcharacteristics )opening pressure$ closing pressure and relieving capacity* aredirectly affected &y changes in &ac5 pressure on the valve.

'ello(s $afet! %elief &alve > this valve incorporates a means of isolatingthe process fluid from the &onnet$ spring$ stem$ and stem &ushing. The&ello s is vented through the &onnet to atmosphere$ and in ha#ardous orto"ic service$ the vent must &e piped to a safe location. The &ello s design is

recommended hen the process stream ould effect the moving partscausing a &inding &et een the stem and the stem &ushing. A valve ith aruptured &ello s ill have a reduced capacity and a higher reseat pressure.

'alanced 'ello(s $afet! %elief &alve > a variation of the &ello s valvethat minimi#es the effect of &ac5 pressure on the operational characteristics)opening pressure$ closing pressure and relieving capacity*. The opening andclosing pressures are maintained ith increasing &ac5 pressure &y using apitch diameter of the &ello s e%ual to the seat diameter of the valve. The&ello s is vented to the atmosphere and must &e piped to a safe location forha#ardous and to"ic materials. A valve ith a ruptured &ello s ill have areduced capacity and a higher reseat pressure.

0.-.- 2i%uid Relief ;alvesA spring


6/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 %& $'

0.0 Guidelines for ?se of Pressure Relief Devices

Application guidelines are as follo s1 Conventional pressure relief valves should only &e used hen the &uilt ell suited for tall structures su&!ect to strong inds.6o ever$ they are the most e"pensive to erect and maintain.

Self-supporting Stac! > designed so that the flare riser pipe has no lateralsupport structure support. 4or short flares$ this type is the least e"pensive toerect and maintain.



11/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 11 %& $'

0. .-.3 Ground 4laresGround flares are partially enclosed &urners that are mainly utili#ed henluminosity and noise have &ecome o&!ectiona&le. Radiation energy isminimi#ed &y the retaining structure and$ smo5eless operation can &eachieved provided the design gas rate to the flare is not e"ceeded. 6o ever$since the flame is near ground level$ dispersion of flared gases may result insevere air pollution or ha#ard if com&ustion products are to"ic or in the eventof a flame


12/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 1$ %& $'

Ta 4e 1a 5 *44%6a 4e T!erma4 Radia7i%n E8 %"ure Le9e4" :;


13/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 13 %& $'

Environmental imitations > emissions such as smo5e formation$malodorous$ or to"ic com&ustion products$ noise$ hich may &e &asedon statutory and=or pu&lic relations re%uirements.

/aintenance ccess > for multiple flares$ maintenance access toelevated platforms or grade located e%uipment may affect spacing andheight.

The flare operating performance is in turn determined &y the flo rate$material properties$ and smo5ing characteristics of the flame.

0. .0.3 ConstructionThere are three &asic construction types of flares$ and they should &e selected&ased on the follo ing guidelines1 Elevated lares > the most common method of reducing e"posure to

thermal radiation and concentration of com&ustion products. Theyre%uire little real estate and are relatively ine"pensive.

Ground lares > also 5no n as com&ustor cham&ers. Ground flaresare special types of ground &urners used primarily for continuous ventstreams. They are enclosed to eliminate noise and thermal radiation.Typically$ they have e"tensive smo5e occurs hen there is a sudden release of large%uantities of gas into the relief system. Typically$ ith short durationflaring$ there is a rapid increase to a pea5 follo ed &y a larger period of



14/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 1 %& $'

flo decay. 'hort periods of high flaring flo s normally occur as a resultof plant shutdo n or emergencies.

Normally$ the largest %uantity from a single contingency &asis is used andshall &e esta&lished after determining the ma"imum relief condition of eachsafety valve and the %uantities to &e relieved in each of the generalemergency cases of cooling ater failure$ po er failure$ instrument air failure$steam failure$ and fire conditions cited in American Petroleum +nstitute )AP+*Recommended Practice 93:$ Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries .

?nder fire conditions$ calculations of pressure relief loads should &e &ased ona minimum fire area of 3 : m 3 )-$::: ft 3* and a minimum height of . m )39ft* a&ove any level at hich the fire may &e &ased$ in conformance ithAmerican Petroleum +nstitute )AP+* Recommended Practice 93:$ Sizing,Selection, and Installation of Pressure-Relieving Devices in Refineries, Part and American Petroleum +nstitute )AP+* RP 93 $ Guide for Pressure-Relievingand Depressuring Guides .

0. .0.0 ,ac5 Pressure and Pressure Drop Considerations4lare selection and si#ing of flare systems for lo pressure plants such assta&ili#ers$ spheroids and 2PG tan5s need special considerations. 2i%uidaccumulation in flare lines$ especially in vertical sections$ should have specialattention &ecause of a possi&le pressure &uild


15/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 1/ %& $'

0. .0. Air +ngression PreventionPurging and sealing are necessary to prevent air penetration in the headerand flare stac5 to avoid flash&ac5 and the possi&ility of e"plosions. Purgingand sealing provide complementary functions.

Purging is used either in lieu of a seal or as a supplement to the seal. Purging&y itself may prevent air infiltration &ut is e"pensive due to the volume ofpurge gas re%uired. Therefore$ the purge rate may &e reduced &y a sealdepending on the seal design and its location. 'ome seals are effective formost circumstances ith little or no purge gas$ hile other seals re%uire afi"ed purge rate to &e effective. 'ealing is provided &y mechanical e%uipmentthat prevents air ingress. The type of seal is determined &y its location in thesystem.

Purging and seals are further discussed in 'ections and J respectively.

0. .0. 2i%uid 6andling+f large amounts of li%uid are present in the flare stream$ li%uid carryover canresult in ha#ardous conditions. Thus$ the flare header shall &e provided ith a5noc5out drum to remove li%uid surges in the flare header so as to preventli%uid slug damage to piping and vessels and 5noc5out li%uid droplets hich

ould other ise proceed to the flare tip$ ignite and may create a ha#ard &yfalling as &urning hydrocar&on droplets onto the plant area.

0. .0.J NoiseNoise can &ecome a pro&lem$ particularly at high flo rates and if steam oranother medium is &eing used to ma5e it smo5eless. Noise is not a safetypro&lem8 ho ever$ pu&lic concerns may &e a pro&lem.

0. .0. : +gnition 'ystemsAn ignition system to light the pilot$ or re


16/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 1 %& $'

are either automatic or manual. /ith the latter$ the operator mustmonitor the pilot for re fuel gas is added to the line leading to theigniter tip$ hich is located &eside the pilot at the tip of the flare. Aneductor in the line aspirates air that mi"es ith the fuel gas$ such that asource of compressed air is not re%uired. A spar5ing device after theeductor ignites the mi"ture$ and the flame front travels up the line intothe igniter tip$ and lights the pilot. The eductor is located a&out -: m) :: ft* from the pilot. Air aspiration igniters are either automatic ormanual. /ith manual igniters$ the operator must monitor the pilot forre compressed air and pilot fuel gas are added to thepilot$ here it is ignited &y an electric igniter device located at the flarepilot. The flare pilot may &e operated in a continuous mode or anintermittent mode$ if permitted &y regulations. +n the continuous mode$the pilot &urns continuously$ &ut is re


17/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 1 %& $'

'mo5e is reduced &y higher com&ustion efficiency and chemicalmeans. 'team and ater spray reduces smo5e chemically &ycom&ining ith car&on to form car&on mono"ide$ car&on dio"ide$ andhydrogen. /ater may also reduce smo5e caused &y crac5ing andpolymeri#ation &y cooling and adding a source of o"ygen.

These methods are augmented &y flame retention rings that promotetur&ulence and 5eep the flame erect8 thus ma5ing the flame moresta&le at higher tip velocities. /ind guards placed around the tip canreduce ind


18/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 1' %& $'

ha#ardous condition can result if a flameout occurs. 4laring of gases ith high6 3 ' level should &e done in an elevated flare.

0. .0. 3 ;elocity 2imitations for 4lare TipsThe criterion for flare tip velocity is a function of assist gas and net heatingvalue. The criteria must &e met during periods of start


19/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 12 %& $'

the seal$ and the type of air assist. 4orced air assist$ ith concentric piping$can no accommodate a molecular gas seal.

A properly designed seal at the tip of the flare stac5 protects &oth the flareheader and the flare stac5. Therefore$ it is recommended that all flare stac5s&e protected ith a seal at the top of the flare$ ith the follo ing e"ceptions1 +f sufficient purge )minimum velocity* gas is provided to prevent air

infiltration for the flare scenarios and material. +f the stac5 is designed to ithstand a credi&le design scenario

e"plosion.

+f provided$ the seal is to &e located &elo the flare tip and &elo therefractory used to protect the tip.

0. .3 'eals at 4lare 'tac5 ,ase )2i%uid 'eal*

'eals placed at the flare stac5 &ase protect the header &ut not the flarestac5s. They are located at the &ase since they are too heavy to place at theflare tip. The typical li%uid used is ater.

The general principle is that the gas must pass through the li%uid seal as aseries of &u&&les$ each separated &y ater. The ater &arrier acts to cool thegas and prevent flame flash&ac5 into the header.

2i%uid seals offer protection from air infiltration and e"cellent protection fromflash&ac5. The seal internals must &e designed for pressure surges.Disadvantages of li%uid seals are e"pense and lac5 of protection for the flarestac5.

There are several configurations for li%uid seals8 the follo ing are e"amples ofthem1 'eals are most commonly separate vessels located after the 5noc5out

drum and &efore the flare stac5. They are located as close to the flarestac5 possi&le. They may &e vertical or hori#ontal depending on theamount of seal li%uid re%uired.

'eals are sometimes com&ined ith the 5noc5out drum in a hori#ontalvessel to avoid the design of t o separate vessels and connectingpiping. +n this design$ the seal is the first compartment so that the inletpiping may &e designed as a seal leg. The second compartment isdesigned as the 5noc5out drum.

2i%uid seals are often com&ined ith the 5noc5out drum in proprietarycyclone designs. These designs incorporate t o cham&ers in onestructure. The flare gas enters the 5noc5out drum$ and passes throughthe ater seal into the flare stac5.



20/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 $0 %& $'

A li%uid seal should &e considered hen1 There is a high possi&ility that the purge gas may fail. A li%uid seal

provides positive header protection even ithout purge gas. 6o ever$provision for retention of the seal must &e provided for scenarios such ascooling of the flare header.

Detonating gases e"ist in the flare stream. Gases that are suscepti&le todetonation )e.g.$ ethylene o"ide$ hydrogen$ etc.* may not &e protected&y a seal at the tip of the flare since flare


21/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 $1 %& $'

6ave a de point &elo the lo est e"pected temperature. 'team andgases heavier than &utane are seldom used &ecause of their high depoint.

Contain insufficient o"ygen to support com&ustion.

Typically$ the purge gas is fuel gas or nitrogen. 6igh molecular eight gasesencounter less mi"ing ith air than lighter gases$ essentially acting as a purgepiston$ and thus re%uires a lo er purge rate.

A seal may re%uire purge gas here air may &e dra n into the flare stac5

&elo the tip. The minimum purge gas re%uirements for different types ofseals$ thus the seal manufacturer should &e consulted for the stac5 velocitydesign rate.

Ta 4e 3.2-1 5 S7a>; +e4%>i7y De"ign Ra7e

'tac5 velocity ithout a seal . cm=s to J .0 cm=s ):.3 ft=s to -.: ft=s*

'tac5 velocity ith air reversing seal .3 cm=s to 0. cm=s ):.:0 to :. 9 ft=s*

'tac5 velocity ith molecular seal :.- cm=s to :.J cm=s ):.: ft=s to :. :- ft=s*

(inimum velocity should &e maintained for all a&ove scenarios. ,esides theminimum purge rate$ facilities to add supplementary purge gas are oftenprovided.

Purge gas may &e added at any location upstream or do nstream of the seal.6o ever$ the typical location is at the &eginning of the header so it mays eep it completely. Purge gas lines are often fitted ith lo flo alarms to

arn of lac5 of sufficient purge gas. This is particularly true if the purge gas isused as a diluent for flared material.

/. *TM)SPHERI +E(TI(G

The most economical method of discharging vapors from pressure relief

devices is to discharge to the atmosphere. This method is preferred to theclosed pressure relief system$ provided such disposal is not in conflict ith orrestricted &y the follo ing1 Present and anticipated regulations concerning air %uality and noise.

Prevailing meteorological conditions.

Properties of vapor discharged$ such as to"icity$ volatility$ flamma&ility$entrained li%uid and molecular eight.



22/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 $$ %& $'

Discharges to the atmosphere should &e in the vapor state and &elo theautoignition temperature. The discharges should also meet one of thefollo ing property re%uirements$ su&!ect to air %uality control regulations1 4lamma&le vapors are either e%ual or lighter than air.

4lamma&le vapors are heavier than air$ molecular eight is less than :and the minimum velocity at discharge is 93 m=s )9:: ft=s*$ &ased onthe ma"imum capacity of the relief valve. (a"imum velocity should note"ceed : percent of sonic velocity ):. (AC6*.

4lamma&le vapors have a molecular eight greater than :. ;elocity atdischarge is as specified in the a&ove item$ su&!ect to managementapproval.

;apors$ of any molecular eights$ hich are non


23/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 $3 %& $'

4lame arrestors shall not &e installed on atmospheric vents &ecausearrestor elements may &ecome plugged ith atmospheric dust$ processproducts$ corrosion$ or ice during cold eather. The system shall &edesigned to preclude internal &urning and=or e"plosions.

Atmospheric vents shall terminate at least1

. m ) ft* a&ove the highest ad!acent structure or e%uipment.

0. m ) 9 ft* a&ove a dec5 or a&ove grade.

9 m )9: ft* or 3: pipe diameters$ hichever is greater from thenearest structure or e%uipment hen located at an elevation lo erthan the structure or e%uipment.

Any flamma&le material should &e discharged at more than -: m)J .0 ft* hori#ontal distance from heaters$ air inta5es$ hot spots$etc.

Atmospheric vents should &e si#ed to handle the ma"imum individual reliefload. /here more than one pressure relief valve lead is connected to a vent$the vent should &e si#ed for the largest anticipated individual relief load or forthe simultaneous loads from one cause$ hichever is greater.

'pecial consideration should &e given to purging or design the entire system

to handle flash&ac5s in case of ignition. Thermal radiation levels should also&e considered in case of ignition )i.e.$ lightning$ static electricity$ etc.*.

. L)SED PRESSURE RELIEF SYSTEM

/here the atmospheric discharge is not permissi&le or practica&le$ vaporshould &e discharged to a closed pressure relief system that terminates in avent or flare. The design of the closed relief system should meet there%uirements of air %uality regulations as ell as$ the release of com&ustionproducts to a safe location.

Closed vent systems should &e used only for emergency relief and &lo do n.Closed flare systems should &e used for continuous discharge from pressure

control systems.Consideration should &e given to grouping high pressure and lo pressurerelief into t o separate systems. This may reduce piping costs and ensure&etter operating conditions for venting and flaring.

A typical closed pressure relief system consists of1

. Pressure Relief ;alves

Pressure relief devices shall &e selected in accordance ith 'ection -.- of thisGuide.



24/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 $ %& $'

.3 'ystem Piping

'ystem piping should &e designed in accordance ith 'ection -.9 of thisGuide. +n addition$ the follo ing considerations should &e made1 The inlet piping &et een the protected e%uipment and the inlet flange of

the pressure relief valve should &e designed so that the total pressureloss does not e"ceed - percent of the set pressure of the valve.

Closed system piping should &e anchored and designed to resist thefor ard$ lateral and up ard dynamic forces developed at &ends due tothe high velocity vapors and condensed li%uids. The piping shouldinclude e"pansion loops to accommodate sudden thermal e"pansion orcontraction. E"pansion !oints should not &e used.

Pressure relief piping shall &e free of poc5ets and shall slope do n ardto ard the scru&&er or 5noc5out drum for good draina&ility. The totaldrop in elevation &et een any t o


25/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 $/ %& $'

The use of cyclone or inertial type separators$ and serpentine or otherinternals$ may only &e considered ith management approval. (isteliminators and other internals should generally not &e used unless thesavings in space and eight are significant. 'afety authorities may seethese internals as potential o&structions. 'pecial precautions may haveto &e made to ensure that &loc5age of the internals cannot occur.

'cru&&ers should &e provided ith heating coils to prevent free#ing$ tosta&ili#e volatile li%uids$ or hen re%uired &y process and=orenvironmental conditions.

.0 4lares

4lares should &e designed in accordance ith 'ection -. .3 of this Guide. +naddition$ the follo ing considerations should &e made1 The flare stac5 is generally si#ed on a velocity &asis$ although pressure

drop should &e chec5ed. The flare stac5 location should &e determined &y allo a&le radiant heat

intensities at critical points of the facility. Additionally$ flares should &echec5ed to ensure that sulfur dio"ide concentration levels from the flaredo not e"ceed pollution restrictions.

The ma"imum &urner tip e"it velocity for pipe tip flares should not

e"ceed :.9 of sonic velocity at ma"imum emergency relief load flaring. The &urner tip should &e designed to prevent flame lic5 or e"cessive

heat radiation to the tip assem&ly during periods of lo e"it gas velocity. Prevailing ind direction should &e considered hen locating the stac5.

The stac5 and stac5 structural support mem&ers should &e designed inaccordance to appropriate codes and criteria to ithstand environmentaland e%uipment loading conditions. The effects of radiant heat on thestructure and shielding should &e considered.

6igh temperature materials should &e specified for the flare &urner tipand pilot assem&ly to ensure long service life.

/here practical and considered economical$ radiant heat shielding may&e installed at selected points to protect personnel and e%uipment fromradiant heat intensities.

.9 'eals

'eals should &e designed in accordance ith 'ection -. of this Guide.

. Purging

4lares should &e designed in accordance ith 'ection -.J of this Guide.



26/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 $ %& $'

. +*P)R *(D LI?UID DIS H*RGES T) * L)


27/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 $ %& $'

.3. .0 2i%uid DisposalOnsite li%uid 5noc5out drums shall &e provided ith a pump and a spare eachsi#ed to empty a half


28/28


Engineering Guide

Title Document No.



1 Bryan D. Hum !rie" 1#1#$001 $' %& $'

.3.0. Pressure Relief ;alvesRelief valves shall &e selected to meet the re%uirements of 'ection -.- of thisGuide.

.3.0.3 PipingPiping shall &e designed to meet the re%uirements of 'ection -.9 of thisGuide.

Primar! %eferences are directly relevant to the design. "t#er References aredocuments hich are either referred to &y Primary References or hich only parts ofmay &e applica&le. The applica&le document)s* should &e consulted for specificapplications.

Primary ReferencesAP+ 93: 'i#ing$ 'election$ and +nstallation of Pressure

Date post:	04-Jun-2018
Category:	Documents
Upload:	ipi
View:	227 times
Download:	0 times

EG310 - Pressure Relief Systems

Documents