Emergency Block Valves a Guide to Selection

8/10/2019 Emergency Block Valves a Guide to Selection

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AIChE Paper Number: 150c

EMERGENCY BLOCK VALVES

A GUIDE TO SELECTION

Prepared for Presentation at the 2012 Spring National Meeting

24th Ethylene Producers' Conference

Houston, Texas, April, 1 - 5, 2012

AIChE and EPC shall not be responsible for statements or opinions contained in papers orprinted in its publications


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Emergency Block Valves

A Guide to Selection

Abstract: An Emergency Block Valves (EBV) is used as a means of isolating flammable or toxicsubstances in the event of a leak or fire. The installation, and use, of EBV's in manyhydrocarbon services will significantly reduce the potential of fire and explosion damages

caused by loss of hydrocarbon containment situations; and a general improvement in overallplant safety for both capital assets, and operating and maintenance personnel. InHydrocarbon, and / or toxic services; EBV's will serve to mitigate the potential of significantenvironmental releases.

This paper is to be presented as a general design guide to aid in understanding of anEBV is, " is responsible of definition of selection basis, an EBV should beconsidered, " an EBV should be installed, and " Y" they should be installed. Theitems to be covered include the code basis of EBV's (API RP-553, NFPA 58 specificrequirements for LPG service), the types of valves to be used; the selection of manual or

automatic valve actuation; guidelines for determining if EBV's are recommended based onequipment services, and hydrocarbon inventories; general installation requirements;integration with other safety instrumented systems within the processing unit; and justificationof installation cost.


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Introduction

Safety. One word, one idea, should be foremost in our minds throughout our range ofdaily activities. We have heard it all before; "safety is number 1", "the person mostresponsible for safety is you". However, we need to be especially aware of the instanceswhen an individual's decision affects the safety of others. Similar to the selection and design

of any safety system; the selection, design, and installation of Emergency Block Valves (EBV's)may have long term impact on the safety of many individuals. The use of EBV's cansignificantly reduce the impact of an accidental release of hydrocarbons, by limiting thepotential of damage and personnel injury caused due to subsequent fire or explosion.

The primary purpose of EBV's is to limit the release of large quantities of dangerousmaterials, and the potential for damage or injury which may occur from such a release. Inaddition, limiting the quantities of materials released may also result in an economic benefit;both in loss of valuable process fluids, and reduced costs of subsequent repair / replacementof damaged capital items (equipment, piping, instrumentation, etc.).

The main basis of this paper is the definition of EBV requirements as defined in API RP-553. However, other codes and standards which also describe emergency isolation are alsoreferenced. The main codes and standards used to complete the basis of this paper are asfollows:

API RP-553 "Refinery Control Valves" NFPA 30 "Flammable and Combustible Liquids Code" NFPA 58 "Liquefied Petroleum Gas Code" API RP-2510 "Design and Construction of LPG Installations" NFPA 85 "Boiler and Combustible Systems Hazard Code" API RP-560 "Fired Heaters for General Refinery Service" API RP-556 "Instrumentation and Control Systems for Fired Heaters and Steam Generators" NFPA 497 "Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations In Chemical Process Areas" API RP-500 "Recommended Practice for Classifications of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Division 1 and Division 2" MSDS "Material Safety Data Sheets"

The intention of this paper is to use the 5 W's to develop a general guide to establish abasis for design and selection of EBV's by the following:

"What" is an EBV? (Definition and Valve Types Considered) "Who" defines the basis of design and selection? (Codes / Standards) "When" an EBV should be considered? (Hydrocarbon Volume Requirements) "Where" should an EBV be installed? (Locations relative to Equipment)


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"Why" should they be installed? (Safety / Cost Justification)

Asking these questions, and using the material presented; the reader can develop adesign basis for establishing if an EBV is needed, the type selected, and where it should beinstalled.

WHAT? - Definition of an Emergency Block Valve

This paper has been titled "Emergency Block Valves", or EBV. However it should beunderstood that many names are often used by designers, operators, owners; and evenvarious codes, standards, and recommended practices. NFPA 58, for LPG facilities, refers toEmergency Isolation Valves (EIV's). NFPA 85, for fired heaters, refers to "safety shutoffvalves" in fuel gas systems. Then there are the codes and standards which define variousother terms for storage, loading, and other fluid handling facilities. Across the petrochemicalindustry many other names, like "cutoff valve", "chopper valve", "trip valve", "SIS valve" and

various combinations of names including the words, safety, emergency, isolation, trip, and fireare used to identify devices used for the same purpose; reduction of the amount of dangerousmaterials (combustible, flammable, hazardous, toxic) released to the environment due to anaccident.

For simplicity, this paper will use the basic definition as provided in API recommendedpractice (RP) 553 - Refinery Control Valves (2007 edition).

In addition to a plethora of names; and EBV may also take on many forms. While APIRP-553 is titled "Refinery Control Valves", EBV's do not need to be actual control valves, or forthat matter, to even have any instrumented functions. The only requirement of RP-553 is thevalve used is of a fire-safe design as per API spec 6FA "Fire test for valves"; or an equivalentstandard. However, even this may not be a fixed requirement depending on the specificinstallation, valve location relative to the likely fire area, or the amount of other fire protection(such as water sprays) provided.

Practically any valve can be used to create an EBV; for the most crude to the highlysophisticated. Some refining services still use reverse mounted swing check valves; with afusible link and an external actuator. LPG service shut-off valves are also available withremote cable pulls and fusible links. Most EBV classifications in RP-553 are simply manual


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valves (gate / ball / butterfly), and may have a motor or pneumatic actuator. Excess flowcheck valves (spring type), and regulators (differential pressure based) are also used in someservices in various hydrocarbon process industries.

As unit capacity, and the valve diameter required, increases; standard type on / offvalves are more likely to be required. Often the design will require an actuator; and may

incorporate various instrumented functions. A typical basis for EBV's in today's olefins unitswould incorporate a fire-safe manual valve with a DCS enabled power actuator, and someadditional SIS functionality (open / close limit switches; interlocks; etc.). Additional fireprotection of power and control wiring would also be incorporated into the design.

API RP-553 paragraph 7.1 defines the general valve type as follows:

RP-553 classifies the selection on EBV's into four categories simply defined as types "A", "B","C" and "D". The definitions of each type are included in Table 1, and summarized as follows:

The RP-553 definition includes the valve be "fire-safe", installed at the equipment, andused when ignition of the leaking fluid is not expected. This implies an operator would needto enter the area where leaking fluid exists in order to operate the valve. A more appropriatedesign for a manual valve would be to locate the valve a safe distance from both the leaksource and the potential fire zone. A typical use of a Type "A" EBV would be a battery limitblock valve used to stop flow of hydrocarbons, or other dangerous material, from entering theunit after a breach of containment has occurred.

Essentially this is Type "A" with location requirements added due to the expectedignition of the leaking fluid. RP-553 states the valve should be installed a minimum of 25 feetfor the ignition source (a typical API fire radius), no larger than 8 inches in diameter, nopressure class rating greater than 300 lb. with access via platform with stairs and elevation no

greater than 15 feet. As with the type "A" valve; consideration should be given to having thevalve placed a safe distance from the potential leak and fire source; or more than 50 to 100feet away. Increased distance from the fire source should negate the size, pressure class, andelevation requirements; as these are likely based on the intensity of the fire, and thepersonnel exposure permissible at a 25 to 50 foot distance. As with a type "A" EBV, a typical


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use of a Type "B" EBV would be a battery limit block valve used to stop flow of hydrocarbons,or other dangerous material, from entering the unit after a breach of containment hasoccurred.

Essentially this is a manual valve with addition of an actuator. Although poweroperated is not specifically defined; later sections refer to selection and design of electricmotor and pneumatic actuators. The control initiation is still manual (local pushbutton) andlocated at / near the valve in an accessible location. Depending on the actual valve locationrelative to the fire zone, consideration needs to be given to fireproofing the actuator andpower wiring to allow operation during exposure to a fire. A pneumatic valve / actuatorcombination should be designed as a fair safe system; or fail closed on loss of air supply.

This type does not specify either the type of valve or the actuator; only that the control

is remote. It removes the valve location requirements and adds the control location should bea minimum of 40 feet from the leak source and outside the fire zone. Further definitionincludes that the actuator and portion of control wiring / tubing within the fire zone befireproofed. Fireproofing is later defined as being per API 2218 -

.

Table 1 - API RP-553 EBV Valve Types (Category)

ValveType

Fire-Safe(*)

Operation Pressure

Class

Diameter Distance from Source

(Valve) (Control)

"A" Yes Manual

(no ignition)

N.D. N.D. @Equipment

NA

"B" Yes Manual

(ignition)

300 # 8" 25 Ft NA

"C" Yes Power (**) > 300 # > 8" 25 Ft At Valve

"D" Yes Power (**) N.D. N.D. No

Restriction

Remote

40 Ft

* Fire-Safe valve may not be required if located outside the Fire-Zone

** Actuator, power, cables fire-proofed


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When positive isolation of the process stream is not likely; and the valve cannot belocated a safe distance from the potential leak source and fire zone; a type "D" valve is themost likely selection. In today's modern plant designs with advanced DCS control system, it islikely that remote actuation from the DCS operations panel in the control room, or remoteinstrument enclosure will be incorporated into the design. This will enable the board operatorsto keep control of the intended operation, as well as prevent the potential exposure of any

personnel to an area near the fire zone.

WHO? - Establishing the Basis for Needing an EBV

The first thing required in the review or development of a unit design is to determinethe basis to define the need for EBV's. Even though there are some specific servicerequirements for EBV's (LPG systems, Fired Heater Fuel Gas, Loading / Unloading operations,etc.); the majority of selection basis is defined by recommended practices, and goodengineering principles.

Many companies have their own engineering and safety standards for establishing whenan EBV is required. These may appear in a verity of design guides or standards; including fireprotection, piping, instrumentation, safety, operations. Establishing the need for an EBV mayalso be the result of a hazard review (Hazop, LOPA, SIL); or be required by HSE standards.

Various combinations of standards may also be required to define the complete design. As anexample; the need for an EBV may be defined by a safety standard, with fire protection of thedevice defined in the fire protection standards, and the actuation and controls defined in aninstrumentation standard.

The main point here is to check the standards of the facility owner first. Any designbasis or selection criteria contained in the owner's standards are likely to be compiled as theowner's interpretation of applicable codes. Local site requirements, insurance requirements,or even environmental permit requirements can affect the specific need in any particular unit.

If owner standards are not available, the designer can default to a number of selectionbasis documents from various NFPA sections or API Recommended Practices. For generalservice, RP-553 provides guidance on the hydrocarbon inventory which will suggest an EBV beinstalled; as well as the general selection basis of valve type. When the fluid processed is

considered to be LPG (mostly C3 or C4 hydrocarbons), NFPA 58 and API RP-2510 may beused. Requirements specific to the designs of fired heaters would utilize NFPA 85 and API RP-560.

When a wide range of flammable / combustible materials are encountered; NFPA 30can be used to establish the threshold value of fluid quantities which will trigger consideration


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of installing an EBV. NFPA 30 breaks down the maximum permitted storage volume offlammable liquids by combinations of flash points and boiling points.

It is also important to establish if the proposed EBV is located within a fire zone; andfire protection of the valve and instrument components is required. To establish if an EBV isto be installed within a fire affected zone, RP-553 basis can be used (25 foot radius typical of

many API based fire applications). A more conservative approach would be to use theclassification area as per NFPA 497/ API RP-500. This will establish a fire zone which willaccount for the fluid properties (flammable / combustible class) and source pressure. Ofcourse all EBV installations can simply be treated as requiring fire-safe valve designs with fireprotection of auxiliary components; negating the need for any detailed review or backupdocumentation.

When establishing the design basis for EBV requirements; the following should normallybe considered:

1. Check owner's design specification first

2. Use RP-553 for installations without owner specifications3. Consider NFPA 30 for more detailed treatment of fluid volume4. Consider NFPA 497 RP-500 for establishing fire protection requirements5. Use Additional standards for specific applications (NFPA 58 / API RP-2510 for LPG

service; NFPA 85 / API RP-560 /API RP-556 for fired heaters; review codes forspecial cases like loading / unloading at waterways; etc.)

Special consideration should be given to the need for EBV's when handling toxicmaterials. Although olefins units do not typically have streams with large quantities of trulytoxic materials; there are occasions where high concentrations of toxic components (such asH2S) may present a significant health hazard in event of a leak.

Toxic materials need to be covered on a case by case basis. The need is likely to betriggered by a HSE review of materials being processed in the unit, and concentrations abovesafe exposure limits. Material Safety Data Sheets (MSDS) for the component considered willgive both the safe and health threatening concentrations. Once a high concentration of a toxiccomponent is identified, and estimate of the leak quantity would need to be determined (suchas the escape rate via a 3/4 inch bleed valve). The leak rate would then be used to establisha concentration profile within a reasonable distance from the leak point. The need for an EBV

would be determined based on comparison of allowable emergency exposure concentration tothe calculated dispersion profile.


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WHEN? - Establishing if an EBV is needed?

Determining when an EBV should be considered may be the most difficult question toanswer in review of plant design. Since the process streams of most plants, and especiallyolefins units, are comprised of flammable/ combustible hydrocarbons; how is the need for anEBV determined? Should there be a different basis for various fluids? Should other design

factors be addressed? These questions, and others, are likely to require answers fromindividuals design a unit. In addition, documentation defining the selection criteria will likelybe required for input to safety and hazard reviews.

To develop a basis of design and selection, various standards will need to be consulted.Each may yield a different basis; and the designer will need to select the most applicable tothe specific application considered. In order to make a selection the basis of standards andcodes presented in the previous section should be used. The steps taken would then be asfollows:

This is where the designer needs to do a little legwork, and crack open the books. Aspreviously mentioned, many owners have available standards. When a specific EBV / isolationstandard is not available; check Safety, HSE, Instrumentation, and Fire Protection standards.

A little time to review them can result in a clear design basis, and prevent having to re-designafter HAZOP or other reviews.

When specific owner's standards do not exist; the first source of information would beRP-553 (Section 7 of this RP contains the basis for EBV design). Separate design criteria areincluded for compressors, pumps, vessels, and fired heaters. A summary of the criteriacontained in RP-553, and some interpretation of the requirements, is as follows:

: EBV's should be considered for installation when the following criteria are met.

a) Install suction and discharge EBV when horsepower is greater than 200.b) Install EBV's on interstage equipment when liquid inventory is more than 1000

gallons (4 cubic meters).

The installation of EBV's on compressor lines is generally to allow isolation of significant

high pressure gas volumes in event of damage or failure of the seal system. The EBV can alsoact as equipment isolation, and prevent need for removal of process system inventory toperform repairs. EBV's should also be considered on any induction / extraction lines as foundin many C2 or C3 refrigeration systems. An EBV would not normally be considered for selfcontained interstage equipment (no side stream flows); other than liquid removal lines whenliquid volume is greater than 1000 gallons.


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: For pumps with seals, EBV's should be considered for installation when the followingcriteria are met.

a) Install an EBV in the pump suction line when the liquid inventory in the upstreamvessel is more than 2000 gallons (8 cubic meters) of either light ends, hydrocarbonswith an operating temperature above the auto-ignition point, or hydrocarbons with

an operating temperature above 600 degrees F ( xx degrees C).b) Install an EBV in the pump suction line when the liquid inventory in the upstreamvessel is more than 4000 gallons (16 cubic meters) of liquid hydrocarbons.

The pump suction EBV is mainly installed to prevent the release of fluids from theupstream vessel. Therefore, the default basis would be to install a single EBV close to thevessel liquid outlet. For services with multiple pumps (either multiple operating or operating /spare configurations); consideration should be given installing an EBV on each individual pumpsuction line. The use of individual EBV's would be more likely as pump flow increases, pumphorsepower increases, the flash point of the material processed decreases, or an unplannedfailure (closure) of the EBV can lead to a major unit upset / relief scenario. Individual EBV's

may also be desirable if they are part of an SIS system, and require periodic testing.

: EBV's should be considered when the following criteria are met.

a) Install an EBV on vessels containing light ends or toxic materials.b) Install an EBV on vessels containing liquids heavier than light ends; with their

operating temperature above their flash point.

Vessel EBV's will generally be installed on the liquid outlet lines only. RP-553 does notspecify a volume for vessel inventory; but the pump suction vessel criteria can be assumed toapply.

For vapor lines, or vessels in vapor only service, total vessel isolation from the normalvapor path would be considered where an upset condition could lead to a vessel failure(exclusive of normal relief conditions). A prime example of this would be olefins plantacetylene reactor systems, where normal flow path isolation would be used to prevent addingreactive materials. These would normally be used in conjunction with other safety systems,such as a flare dump valve.

The EBV criteria contained in the vessel section of RP-553 is the only mention of toxicmaterial control. When toxic materials are encountered, several things should be checked to

determine if emergency isolation is required. The first thing is to know the concentration andvolume of material contained within the process equipment. Secondly, establish a potentialleak path and location (likely to be a bleed valve). Check with owner HSE for exposure guides,or check applicable Material Safety Data Sheets (MSDS). The MSDS will usually containinformation on allowable short term / emergency exposures. Additional information may alsobe indicated on an evacuation radius. The NFPA 497 / RP-500 classification areas could beused as the initial distances for calculation of exposure concentration resulting from a leak. A


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simple basis would be to uniformly distribute the leak volume over the volume covered by theclassification area. A more refined method would be to use dispersion modeling to determinethe concentration gradients.

Systems containing toxic materials will likely require a controlled access area. Theboundary of this area will be the location of the maximum allowable concentration without

protective equipment. Additional access control may also be required for maximum allowableconcentrations when protective equipment (respirator) is used.

: EBV's should be considered when the following criteria are met.

a) Install an EBV on each fuel gas or oil lineb) Install an EBV on each feed line which contains a flammable fluid.

Isolation of fuel and feed lines for fired heaters are covered in detail in NFPA 85, APIRP-560 / 556. The recommendation here is to default to these other documents, in additionto any applicable owner's standards on combustion control and burner management.

While the criteria included in RP-553 will cover the majority of design cases likely to inany particular process unit; other applications for EBV installations may exist. The mostsignificant of these would be lines crossing the unit battery limits.

The typical battery limit manual block valve would be considered an EBV by RP-553.However the valve size, class, and location may not be strictly within the complete criteria.Typical pipe spec valves used for the battery limit block may also not be of a fire-safe design.In today's modern highly automated plants with remotely located control rooms, and few fieldoperators; consideration should be given to including power actuated EBV's on hydrocarbonfeed lines to the unit.

Table 2 - API RP-553 Design Criteria

EquipmentType

Power Inventory Notes

(HP) (Gallons) (Cubic Meter)

Compressor 200 1000 4

Pump - 2000 8 Light Ends / Auto-IgnitionTemperature> 600 F

- 4000 16 Liquid Hydrocarbons

Vessel - YES YES Light Ends / Toxics

YES YES Operating Temperature aboveFlash Point


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Fired Heater - YES YES Each Fuel Gas / Fuel Oil Line

YES YES Each Flammable MaterialFeed Line

When the contents of a facility are mainly large quantities of combustible, or flammablehydrocarbons; additional definition (above that of RP-553) may be in order. NFPA 30 is agood source to use for establishing a consistent design basis. This code can be used toclassify the fluids into several categories, as well as establishing both a volume criteria, and afire affected zone.

The primary basis is to use the data provided in NFPA 30; referencing storagelimitations for outside storage. The assumption is the released material is in an area with nospecial fire protection (sprinklers, deluge, etc), other than hydrant / monitor stream coverage.Therefore, the released quantity would be equivalent to a storage volume. The valuesincluded in NFPA for minimum separation distances to a property line (or uncontrolled access),

is interpreted as the area affected by the resultant fire, or fire zone. The storage volumevalues from NFPA 30 are tabulated in Table 3; and NFPA liquid classification basis in Table 4.

Table 3 - NFPA Storage Volume and Separation Distance

Liquid Class Maximum Volume Separation Distance

(Gallons) (Cubic Meters) (Feet) (Meters)

IA 1,100 4.2 50 15.2

IB 2,200 8.4 50 15.2

IC 4,400 16.8 50 15.2II 8,800 33.6 25 7.6

III 22,000 83.3 15 3

Table 4 - NFPA Flammable / Combustible Class Definition

Liquid Class Flash Point Boiling Point

(F ) (C ) (F ) (C ) (F ) (C )

IA < 73F < 22.8C < 100F < 37.8C

IB < 73F < 22.8C 100F 37.8C

IC 73F 22.8C < 100F < 37.8C

II 100F 37.8C < 140F < 60C

III 140F 60C


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From the above, it is readily seen that for lighter hydrocarbons (class I), the limitingvolume is typically similar to the RP-553 values of 2000 or 4000 gallons. However, use of theNFPA basis will allow larger volumes of heavier hydrocarbons (class II and III) beforeconsidering installation of an EBV.

Since the primary purpose of most EBV installations is to prevent the spread offlammable / combustible materials, most EBV's are likely to be subject to fire exposure. Thiswould be especially true for EBV's installed in vessel outlet lines (as close to / or on, the vesseloutlet flange), or individual pump suction lines. As stated earlier in this document, RP-553recommends that EBV's be of a fire-safe design (low leakage post fire exposure), andactuators / control cable / power cable be fire proofed as required. However, all EBV's maynot be located with an area reasonably affected by a fire resulting from the service they areprotecting. In order to determine if the EBV is within the fire affected zone several criteria canbe used. These are as follows:

API General Criteria 25 Ft radius from leak source / fire (40 Ft minimum for remote control)

NFPA 30 Separation Distance 50 Ft for Class I Liquids 25 Ft for Class II Liquids 15 Ft for Class III LiquidsNFPA 497 / API RP-500 Various based on material

(typically between 15 Ft and 25Ft - more for shelters, ornon-ventilated areas)

The primary purpose of establishing the fire zone is to determine the requirements forfire-safe design of the EBV, and the need for fire proofing of control components. Any sitespecific fire protection requirements, or owner safety standards, should always be consultedbefore using general code values. An EBV located within the fire affected area, which isprotected by deluge or water spray (potential for large pumps / compressors) a fire-safe valvemay not be required. Control and power wiring would need to be reviewed on an individualbasis. If the potential for the EBV to be affected by a fire case is questionable, or theboundyies of the fire affected zone are unclear; a full fire-safe valve selection and fire proofedcontrol and power systems should be used.

Specific attention should be given to design situations which may be interpreted as anLPG installation. NFPA 58 defines Liquefied Petroleum Gas (LPG) as:


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This definition can apply to some of the light hydrocarbon systems within ethylene

units. As always, the designer should check with owners standards, including site operatingpermits and local requirements, to see if any systems could be classified as LPG. If this is thecase; the volume limits associated with NFPA 58 / RP-2510 would be used to determine if anEBV is required. The criteria for NFPA 58 compatibility is as follows:

Install an Emergency Shutoff Valves when:a) Storage system capacity greater than 4000 gallons (15.1 cubic meters)b) Liquid Transfer Line 1-1/2 inch or largerc) Vapor equalizing line 1-1/4 inch or larger

The NFPA 58 criteria above (4000 gallons capacity threshold) is somewhat less stringentthen either API-553 (2000 gallons for light ends), or NFPA 30 (1,100 gallons of class IAliquids). However, if the system in question is legally classified as LPG, the NFPA 58 criteriawould likely meet the minimum code requirements.

If a system is classified as LPG, the designer should note that other requirements forexcess flow check valves, and isolation may be needed. Especially for loading / unloadingsituations (either loading arms or hoses), or system designs interfacing with transportationsystems (containers, tank trucks, rail cars, barges, or ships) and beyond the intention of thispaper.

This paper has been created based on using general criteria from API RP-553 as astarting point to guide the designer in determining the selection of EBV installation. It is notintended to cover every design case or any site specific requirements. Every plant site is likelyto have some degree of owner specifications, local regulations, and maybe evenenvironmental permit or insurance requirements.

In previous sections, codes and standards other than RP-553 have been mentioned.

When determining if an EBV is required for a specific design, some questions to ask would be;

Can the system be classified as LPG? Can the system be classified as a process fired heater / steam generator? Can the system be classified as a thermal oxidizer / incinerator? Does the system involve loading / unloading facilities? Does the system include transportation facilities (DOT / Coast Guard / etc)?


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Does the system process toxic / hazardous / radioactive materials?

These are just some special circumstances which may be involved in determining thecorrect criteria for establishing EBV design basis. A yes answer to any of the above questionscould add additional specific design requirements to the system.

WHERE? - Establishing the location to install an EBV

Once it has been determined an EBV should be included in a system design; the nextstep is to determine where the valve should be installed. Guidance from RP-553, and otherreferences, is limited. The decision is left more to the designer, and various practices may beutilized depending on the specifics of the individual installation.

Determining the location to install an EBV involves a bit of application of common sensedesign. Remembering the primary definition and purpose of an EBV (

the first choice for installing would be directlymounted on the outlet flange of the source equipment. While this may be a reasonable choicefor many vessels, it will likely be incompatible for EBV's connected to pumps, compressors, orfired equipment. The location of the valve needs to address the maintenance and operationrequirements of the hydrocarbon containing equipment, as well as the same for the EBV itself.If the EBV is to be part of a SIS; consideration will also need to be given to system testing.

In order to minimize the release of materials, the EBV should be located as close aspossible to the source volume, and upstream of the potential leak point. On this basis, theequipment nozzle flange would be the most ideal location. However, this is often a pooroverall design choice, when considering unit operation, maintainability, and evenconstructability. The EBV is therefore, likely to be located a reasonable distance from thematerial source, and the following should be considered in setting the location.

Minimize the volume contained in the piping between the source and the EBV

Prevent installing any piping takeoffs (other than isolation blinds and bleeds) between the source and the EBV

Install the EBV in a position which facilitates construction, operation, and maintenance (usually in a horizontal pipe run - depending on valve and actuator style)

Is the valve in the fire zone? / Can it be within deluge - water spray area of the equipment?

Will an unintended EBV closure cause a major plant upset? (separate lines / multiple EBV's?)


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Does the valve installation allow for periodic stroke / control system testing?

Going through this simple set of questions will aid in determining the best location forthe specific EBV application. Tradeoffs will always be a part of the design process, andknowing which criteria are the most important for the specific application will help guide thedecision making process.

WHY? - The Benefits of Installing EBV's

This is the easiest question to answer. Directly from our definition of an EBV, thepurpose is to control the flow of dangerous materials. With regard to flammable / combustiblematerials this means having the ability to isolate fuel from a fire (or fuel from a potential fire).

Almost any hazard review will establish that being able to control, or stop, the release of fuelto a fire will result in a safer design; or safer with respect to potential injury of personnel,potential of damage to capital installations, or even potential environmental impact. Clearly

the benefit of installing EBV's can be summarized as follows:

Reduce the potential for injury to personnel due to limiting the magnitude or duration of a plant fire

Reduce the potential for damage to capital equipment. piping, instrumentation, etc., due to limiting the magnitude or duration of a plant fire

Reduce the potential for damage caused by environmental release of hydrocarbons, or products of combustion

Reduce the potential for injury to personnel in the unit, adjacent units, or outside a facility boundary due to limiting the quantity of toxic, hazardous materials

The need for EBV's from a hazard review / safety standpoint is not likely to be debated.However the installation of can by justified solely from a capital standpoint. This evaluationcan be made by using either published safety review criteria, or developing project specificguidelines. A review of this type may result in indicating an EBV could reduce the potentialdamage to the affect area of a facility by as much as 10 percent; and reduce repair time byseveral days.

Using one published source, a review of a typical C3 splitter system indicated amanually actuated EBV would reduce the expected fire damage by 2 percent, and save 1 dayof repair time. If the EBV installation is coupled with SIS control and fire and gas detection;the expected facility damage could be reduced by as much as 10 percent, and downtimereduced by 2 to 4 days. Using this basis, the following tabulation (Table 5) is presented astypical cost analysis.


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Table 5 - Cost Analysis of EBV Installation (fire damage basis)

Installed Value Damage Value

(*)

Savings

No EBV With EBV With EBV/SIS 1 day downtime

(**)

$1,000,000 $700,000 $14,000 $70,000 $300,000

$5,000,000 $3,500,000 $70,000 $350,000 $300,000

$10,000,000 $7,000,000 $140,000 $700,000 $300,000

* Damage value is estimated @ 70% of Installed Value (Typical)

** Daily Production Value of $300,000 assumed

From this analysis, it is readily seen that selection and installation of EBV's can be a costeffective method of providing increased safety within hydrocarbon processing units.

Concluding Remarks

From the preceding, it can be readily seen that the selection of EBV installation can be asimply process. It only requires the following a few steps, including the answers obtained by

asking WHAT, WHO, WHEN, WHERE, and WHY. The answers obtained, with the use ofestablished codes and recommended practices form the basis of a typical design.

While the first goal of installing any EBV is the increased safety of an operating plant;the installation can be viewed as insurance to limit facility damage cost.

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