PROPRIETARY INFORMATION - For Authorized Company Use Only Date December, 1998 EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J. EXXON ENGINEERING CONTENTS Section Page SCOPE .................................................................................................................................................... 5 REFERENCES ......................................................................................................................................... 5 DESIGN PRACTICES (IN ADDITION TO OTHER SUBSECTIONS OF SECTION XV)........................ 5 INTERNATIONAL PRACTICES ........................................................................................................ 5 OTHER REFERENCES .................................................................................................................... 5 BACKGROUND ....................................................................................................................................... 5 DEFINITIONS........................................................................................................................................... 6 DESIGN FEATURES OF EMERGENCY BLOCK VALVES........................................................................ 8 INSTALLATION REQUIREMENTS FOR EMERGENCY BLOCK VALVES ................................................ 8 LOCATION AND OPERABILITY OF EBVS........................................................................................ 8 CHOICE OF VALVE BODY............................................................................................................... 8 SYSTEM FAILURE........................................................................................................................... 8 VALVE ACTUATORS ....................................................................................................................... 8 FIREPROOFING FOR EBVS ............................................................................................................ 9 ACTUATING CONTROLS................................................................................................................10 TESTING ........................................................................................................................................10 EMERGENCY ISOLATION......................................................................................................................11 LONG LINES...................................................................................................................................11 TOXIC MATERIALS ........................................................................................................................11 COMPRESSORS ............................................................................................................................11 PUMPS ...........................................................................................................................................12 VESSELS........................................................................................................................................12 FIRED HEATERS, BOILERS AND OTHER COMBUSTION DEVICES ..............................................13 VULNERABLE EQUIPMENT ...........................................................................................................14 BATTERY LIMITS ...........................................................................................................................14 TANK TRUCK AND RAIL LOADING AND UNLOADING FACILITIES ISOLATION.............................14 MARINE TERMINAL FACILITIES ISOLATION .................................................................................14 DUPLICATE ISOLATION.................................................................................................................14 WATER FLOODING PROVISIONS..........................................................................................................15 APPLICATION.................................................................................................................................15 DESIGN ..........................................................................................................................................15 Changes shown by
Transcript
PROPRIETARY INFORMATION - For Authorized Company Use OnlyDate
December, 1998
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
Figure 6 EBV Requirements for Battery Limits ......................................................................... 29
Figure A-1 Flow Factor for Close Clearance Bushings................................................................. 33
PROPRIETARY INFORMATION - For Authorized Company Use OnlyDate
December, 1998
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
CONTENTS (Cont)
Revision Memo
12/98 Page 5 Various references were updated.
Page 6 Added definitions for Combustible Liquids and ERPG-3.
Page 7 Added definitions for Flammable Liquids, Flammable Materials,
and Light Ends.
Page 7 Toxic Material: Removed reference to EBSI report; Updated thereference to the latest AIHA guidelines; Included the ERPG-3concentration in the definition of toxic materials.
Page 8 Relocated the DESIGN FEATURES OF EMERGENCY BLOCKVALVES and the INSTALLATION REQUIREMENTS FOR
EMERGENCY BLOCK VALVES to this page from their furtherback location in the previous document.
Page 8 Location & Operability of EBVs: Added reference to flexibleremote valve actuators.
Page 8 Valve Body: Added note that greater than NPS 4 soft-seatedvalves are not recommended if they're not fireproofed, while soft-
seated valves are preferred for manual isolation of burners; also,updated examples of accepted manufacturers.
Page 9 Electric Motor: Sentences deleted referencing connections to
different bus bars.
Page 9 Fireproofing of EBVs: Indicated acceptance of test method ASTME-1529 and lower heat flux of 50,000 Btu/hr-ft2.
Page 10 Revised the location of EBV actuating controls and addressed theidentification of the stations and buttons.
Page 11 Testing: Added reference to a CSC bypass valve to allow onlinetesting of EBVs.
Page 11 Long Lines: Added new paragraph.
Page 11 Toxic Materials: Added new paragraph.
Page 11 Compressors: Added sentence on EBV position switches fortripping the compressor.
Page 12 Pumps Figure 2: Removed requirement that a minimum of Type BEBV would be required if the material is toxic but a spill doesn't
result in ERPG-3 at the fence.
Page 12 Pumps-1: Clarified the criteria for installing EBV's at pump suctionlines to be consistent with the newly added definitions forflammable and combustible liquids.
Page 12 Pumps-2: Added reference to newly added APPENDIX.
Page 12 Pumps-4: Added note that EBVs are not required on flare
blowdown drum pump suction lines.
Page 12 Pumps-5: Added paragraph on EBV requirements for offsite pumpsuction lines.
Page 12 Vessels (general): Added reference to closed-cup (Pensky-Martens) flash point; added 250 gal (900 l) inventory in linerequirement; moved to first paragraph, from the last, the notes on
avoiding connections between vessel and EBV, and on the properlocation for the closed drain connection; added paragraph on worstcontingency evaluation for determining type of EBV to install; in
Figure 3, removed requirement that a minimum of Type A EBVwould be required if the material is toxic but a spill doesn't result inERPG-3 at the fence.
Page 12 Vessels-1 (and Figure 3): Removed requirement for Type A EBVif ERPG-3 cannot be reached at the fence.
Page 12 Vessels-2: Specified "offsites" vessel for light ends storage;
clarified type of EBV to be installed and indicated that EBVs shouldbe on lines located below the maximum working level.
DateDecember, 1998 PROPRIETARY INFORMATION - For Authorized Company Use Only
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
CONTENTS (Cont)
Page 13 Vessels-3: Specified location of EBVs to be on lines below themaximum working level; changed the requirement for Type A
EBVs to be on all lines (not just those normally open).
Added comment concerning Type A EBVs on normally closed lineswhen special factors apply.
Page 13 Vessels-3, 4, 5 and 6: Referenced item 7.
Page 13 Vessels-4: Replaced "normally open" lines with "all" lines andadded "below maximum working level."
Page 13 Vessels-5: Added reference to closed-cup (Pensky-Martens) flashpoint; replaced "normally open" lines with "all" lines and added"below maximum working level."
Page 13 Vessels-6: Replaced "normally open" lines with "all" lines, and
added "below maximum working level."
Page 13 Vessels-7: Added paragraph on lines between towers andassociated reboilers.
Page 14 Vulnerable Equipment: Clarified wording in Par. 1 to reflect thenewly added definition for flammable materials; in Figure 5removed requirement that a minimum of Type B EBV would berequired if the material is toxic but a spill doesn't result in ERPG-3at the fence.
Page 14 Battery Limits-5: Clarified wording to reflect newly added definitionfor flammable materials and combustible liquids.
Page 14 Added paragraphs on Tank Truck and Rail Loading and UnloadingFacilities and on Marine Terminal Facilities.
Page 15 Water Flooding Design: Clarified water flooding requirements.
Page 15 Emergency Depressuring: Indicated that liquid blowdown is nolonger recommended.
Page 15 Vapor Blowdown (VB): Clarified the services for which vaporblowdowns are installed; noted that facilities to stop feed shouldalso be provided when vapor blowdowns are installed.
Page 15 Design of VB-1: Added design to avoid plugging.
Page 16 Design of VB-2: Added restriction orifice requirement and tight-shutoff, fail-open control valve alternative.
Page 16 Design of VB-3a: Added feed and heater shutdown requirement.
Page 16 Equation (2): Included new equation for sizing control valves andupdated constants accordingly.
Page 17 Design of VB Release Systems: (1) added requirement for lockingopen release system until depressuring is complete; (2) indicatedthat VB may also discharge into a flare header.
Page 18 Added paragraph on MARINE TERMINAL SHUTDOWNSYSTEMS.
Page 19 Special Cases: Expanded section to include more emergency
shutdown systems details for Catalyst in-situ Conditioning andRegeneration, Unsaturated Naphtha Hydrofiners, C3 / C4 Splitters,and FCCU units.
Page 20 Added new section on Exothermic Reactors.
Page 21 Action for stop hydrogen make-up flow for unsaturated naphthahydrofiner changed to manual with note 2 added.
Page 23 Updated ERPG-3 table to include latest AIHA chemicals andvalues.
Pages 24-29 Figures 1-6: Updated as necessary to reflect text changes.
Page 30 Added APPENDIX, PROCEDURE TO ESTIMATE MAXIMUMPUMP SEAL LEAKAGE RATE.
PROPRIETARY INFORMATION - For Authorized Company Use OnlyDate
December, 1998
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
SCOPE
This section covers the requirements for emergency shutdown and isolation of compressors, pumps, vessels, combustiondevices, vulnerable equipment, and isolation at battery limits. Also covered is depressuring or displacement of the flammablematerial inventory of process units. Emergency shutdown and isolation for offsite facilities are covered further in Section XV-J.
� REFERENCES
DESIGN PRACTICES (IN ADDITION TO OTHER SUBSECTIONS OF SECTION XV)
Section II Design Temperature, Design Pressure and Flange Rating
Section XII-F Instrumentation
Section XXXI-I Safety Considerations for the Design of Marine Terminals
INTERNATIONAL PRACTICES
IP 3-2-3, Firewater Systems
IP 3-5-1, Fill and Discharge Lines, and Auxiliary Piping for Storage Tanks and Vessels
IP 3-6-1, Piping for Instruments
IP 3-6-3, Utility Connections to Piping and Equipment
IP 3-7-1, Piping Layout, Supports, and Flexibility
IP 3-12-1, Valve Selection
IP 14-3-1, Fireproofing
IP 15-1-1, Instrumentation for Fired Heaters
IP 15-1-2, Instrumentation for Compressors and Drivers
IP 15-7-1, Electric Power Branch Circuit Design for Instrumentation
IP 15-7-2, Protective Systems
IP 15-9-2, Electric Motor Operators for Valves
IP 15-10-1, Instrument Transmission Systems
IP 16-2-1, Power System Design
IP 16-3-1, Wiring Methods and Material Selection
IP 18-10-1, Additional Requirements for Materials
OTHER REFERENCES
1. Guidelines for Selection and Installation of Emergency Block Valves, Report No. EE.27E.84.
8. ANSI/FCI 70-2 1991, Quality Control Standard for Control Valve Seat Leakage.
BACKGROUND
Safety design philosophy is to eliminate foreseeable risks of fire, explosion or accident. However, it is recognized that suchincidents may still occur, therefore, plant designs must include features to minimize the resulting damage. Of major importancein this respect are emergency facilities to rapidly stop the uncontrolled release of toxics or of flammable material that is feedinga fire. These facilities comprise:
� Emergency isolation.
� Emergency depressuring.
DateDecember, 1998 PROPRIETARY INFORMATION - For Authorized Company Use Only
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
BACKGROUND (Cont)
� Emergency shutdown systems.
� Liquid displacement and water flooding provisions.
Each of these four subject areas is covered in this section, along with minimum design requirements. Individual riskassessments on specific cases may justify a higher level of protection.
DEFINITIONS
For general definitions, see Section XV-A.
Battery Limits
Battery limits are the boundaries of the smallest geographical subdivisions of a processing equipment area which are separatedby at least 50 ft (15 m) from each other and from adjacent facilities, and which contain either a complete process or a group ofintegrated processes which may be shut down together for turnaround.
� Combustible Liquids
High-flash liquids [flash points 100�F (38�C) or higher] when handled at temperatures more than 15�F (8�C) below their closedcup (Pensky-Martens) flash point.
Emergency Block Valve (EBV)
Emergency Block Valves (EBVs) permit the control of hazardous situations. These are valves for emergency isolation or vapor
blowdown and are referred to as Type A, B, C or D (see DEFINITIONS, below). Requirements for these valves aresummarized in Table 1 and appropriate International Practices. Contingency considerations concerning a single EBV arealways limited to the source of the potential leak for which the EBV is installed.
The ERPG-3 is defined by the American Industrial Hygiene Association (AIHA) as: “the maximum airborne concentration belowwhich it is believed nearly all individuals could be exposed for up to one hour without experiencing or developing life threateninghealth effects.” There are also an ERPG-1 and an ERPG-2. These guidelines have been developed to aid in communityemergency response planning. Table 2 lists the ERPG-3's for all materials included in the AIHA 1998 Handbook. The mostrecent publication should always be checked when using this practice.
Equipment with High Fire Potential
Equipment with High Fire Potential shall include:
1. Pumps with a rated capacity over 200 gpm (45 m3/h) handling flammable liquids.
2. Compressors over 200 HP (150 kW) handling flammable gasses.
3. Fired heaters handling flammable liquids in tubes.
4. Vessels, heat exchangers, and other equipment containing flammable liquids over 600�F (315�C) or above their autoignition temperature, whichever is less.
5. Certain reactors that operate at high pressures or are capable of producing exothermic or runaway reactions.
Fire Hazard Area
A fire hazard area shall generally be considered as the area within a horizontal distance of 20 ft (6.0 m) from equipment withhigh fire potential with the following qualifications:
1. For tanks, spheres and spheroids, containing flammable material, the fire hazard area shall extend to the dike wall or 20 ft(6.0 m) from the storage vessel, whichever is greater.
2. For rotating equipment, the 20 ft (6.0 m) distance will be taken from the expected source of leakage.
3. For marine docks where flammable liquids are handled, the fire hazardous area shall extend 100 ft (30 m) horizontally fromthe manifolds or loading connections.
PROPRIETARY INFORMATION - For Authorized Company Use OnlyDate
December, 1998
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
DEFINITIONS (Cont)
� Flammable Liquids
Low-flash liquids [flash point below 100�F (38�C)], and high-flash liquids [flash point 100�F (38�C) or higher] when handled at
temperatures above or within 15�F (8�C) of their closed cup (Pensky-Martens) flash points.
� Flammable Materials
Flammable liquids, hydrocarbon vapors, and other vapors, such as hydrogen and carbon disulfide, that are readily ignitablewhen released to atmosphere.
� Light Ends
Light ends are volatile flammable liquids, which are significantly vaporized at normal ambient conditions. This indicates a typeof material of greater fire hazard than heavier hydrocarbons because of the large volume of vapor generated by a liquid leak orspill. For the purposes of this Design Practices Manual, the definition of light ends is a material having a Reid Vapor Pressure(RVP) of 15 psia (103 kPa) or greater, as determined by the standard ASTM D-323 test. By common usage, this covers thefollowing:
� Pentane and lighter hydrocarbons (either pure hydrocarbons or mixtures).
� Unstabilized naphthas, which meet the RVP criterion.
� Flammable chemicals which meet the RVP criterion.
When used as a criterion of hazardous properties for safety design purposes, the term is applied to the above materials onlywhen they are in the liquid phase or a combination of liquid and vapor phases.
A process unit is considered to be a light ends unit when a significant part of the equipment handles light ends. Pipestills andsidestream hydrofiners, for example, are not included in this category, but pipestill overhead gas recontacting and naphthafractionation systems are considered as light ends units.
� Toxic Materials
A toxic material is one which has the inherent ability to cause adverse biological effects. Some toxic materials are listed in TheAIHA (American Industrial Hygiene Association) 1998 Emergency Response Planning Guidelines (ERPGs) and WorkplaceEnvironmental Exposure Level (WEEL) Guides Handbook. Table 2 lists ERPG-3 for common chemicals. A material isconsidered to be toxic if the ERPG-3 concentration would be present in the vapor space at the stream temperature and oneatmosphere.
Type A Valve
A Type A EBV is manually operated and is installed at the equipment or vessel nozzle. Manual operation may be augmentedwith locally controlled power actuators in cases where valve size, flange classification or ergonomics is a factor (see Table 1).
Type B Valve
A Type B EBV is installed at least 25 ft (7.5 m) horizontally from the equipment it is to isolate. It is manually operated, 8 in.(200 mm) size or smaller, no higher than 15 ft (4.5 m) above grade, and up through flange class 300. Exception: Battery LimitType B EBV may be any flange class or any height (see Table 1).
Type C Valve
A Type C EBV is installed at least 25 ft (7.5 m) horizontally from the equipment it is to isolate. It is power operated with theactuating push button located at the valve. It is located no higher than 15 ft (4.5 m) above grade (see Table 1).
Type D Valve
A Type D EBV is power operated. Its actuating button is located at least 40 ft (12 m) horizontally away from the source ofpotential leak and such that it can be operated from grade. Consideration should also be given to locating the actuating buttonin the control house(see Table 1).
DateDecember, 1998 PROPRIETARY INFORMATION - For Authorized Company Use Only
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
S DESIGN FEATURES OF EMERGENCY BLOCK VALVES
Location, accessibility, and other design requirements for emergency block valves are summarized in Table 1.
The Design Specification shall identify all EBVs and indicate Type A, B, C, or D, as appropriate. When unknown layout couldeffect the type of EBV selected, the option should be specified. For example, if a pump could be located within 25 ft (7.5 m) ofits upstream vessel a Type D EBV would be necessary instead of a Type B. Design specification notes shall define thesetypes, or reference IP 3-7-1, and require color coding or signs to identify the EBVs and their actuating push buttons in the field.
S INSTALLATION REQUIREMENTS FOR EMERGENCY BLOCK VALVES
LOCATION AND OPERABILITY OF EBVs
Table 1 presents requirements for location, size and operability for EBVs. The distances stated in Table 1 are minimum valuesbased on experiences with average fires.
Access to Type B and C valves and to Type D push buttons must be direct and safe during an emergency. In addition todistance, other factors have to be evaluated carefully during detail design. For example, if a Type B or C EBV is located at theproper distance from a potential leak but is positioned near a catch basin that will drain that potential leak, then the valve shouldbe relocated or designated as a Type D since the intent of the spacing guideline is not met. Also, if the height limitation forType B and C EBVs is met but access is only possible from platforms elevated above the actual installation, then the valveshould be either relocated or designated as a Type D since easy access is not possible.
� Hand wheels for Type A and B valves as well as hand wheels for Type C and D actuators must be operable from either gradeor a platform. Chain wheels are not permitted on any EBV installation (IP 3-12-1), but flexible remote valve actuators may beconsidered for certain applications (Report 97 ECS3 20, SOC Communication 97-01).
� CHOICE OF VALVE BODY
The valve body choice for emergency block valves depends on application and on location. In areas where an EBV might beexposed to fire (such as in process areas) and must remain closed in an emergency, the valve body must be capable ofwithstanding prolonged fire impingement without leaking. Therefore, EBVs in isolation service should be either a gate valve, alubricated plug valve, or a high performance ball or butterfly valve. High performance ball or butterfly valves have metal seatswithout soft seals and are considered inherently fire safe. (As an example, here are some manufacturers that have beenaccepted in the past: Velan, Bray-McCanna, Tyco Valves (Vanessa), Neles Controls, Nordstrom, and Adams.) (IP 3-12-1)
Soft seated, fire-tested (fire safe) type ball, plug or butterfly valves greater than NPS 4 (100 mm) (IP 3-12-1) are only to be usedif they are fireproofed, because non-uniform flame exposure of the valve body may lead to only partial melting of the seal andsubsequent leakage. However, such “fire safe" soft seated valves are allowed in areas where there is only a remote chance offire. Such an area would be the shoreside end of a marine finger or T-head pier where the valves are at least 100 ft (30 m)from the source of potential leak (IP 3-12-1). Soft seated valves are preferred for manual isolation of burners.
For depressuring systems, the situation is different since tight shutoff is needed during normal operation and the EBV isrequired to open in an emergency. In this case, an acceptable and economical solution would be a tight shutoff diaphragmoperated valve with a fail open action under fire exposure conditions. A gate valve may be used with an orifice plate, but if it isnot fail open, it shall be fireproofed as required below. (IP 3-12-1)
SYSTEM FAILURE
Consideration of system failure must be included in the design of EBV, both on a plant-wide and an individual basis. Thedesign used for many EBVs is such that the valve remains stationary upon loss of the control signal, the actuating medium or amechanical component failure. This design, also known as “Fail-Stationary," avoids nuisance trips of the valves.
In a “Fail-Safe" design, the valve would always move to the position considered safest in an emergency upon loss of the controlsignal or actuating medium. This design is generally recommended for EBVs in emergency depressuring systems or air tooxidation processes. No fireproofing is needed for such designs since loss of the control signal or actuating medium wouldresult in the valve moving to its “Fail-Safe" position. Such emergency block valves should mechanically lock in the “fail-safe"position regardless of whether the valve was purposely moved or failed to the “fail-safe" position.
VALVE ACTUATORS
Valve actuators for Type C and D valves can be energized by electric power, hydraulic oil, instrument air, nitrogen or naturalgas. The reliability of the energy source system at each location may influence the choice. Specific requirements andrestrictions for the different types of actuators are as follows:
PROPRIETARY INFORMATION - For Authorized Company Use OnlyDate
December, 1998
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
S INSTALLATION REQUIREMENTS FOR EMERGENCY BLOCK VALVES (Cont)
� 1. Electric Motor
Electric motor actuators in conjunction with gate valves have proven to be highly reliable in many locations and aretherefore recommended as a first choice (IP 15-9-2). However, since this system “Fails-Stationary," operation can only beguaranteed as long as it cannot be damaged by fire. Thus, within the presumed fire hazard area, the actuator and cablesmust be fireproofed. The power supply for the electric motor should be from a secondary selective power system. Motoroverload protection, if furnished, shall be deactivated. (IP 16-2-1)
2. Hydraulic Piston
Hydraulic pistons may be used for emergency isolation valves when a reliable hydraulic system has already been designedfor other use (e.g., slide valve actuation on some FCC units). Since hydraulic systems are expensive and needconsiderable maintenance, they may not be justified for power operated EBVs alone.
3. Air Drivers
Double-acting, heavy duty air piston operators have shown acceptable reliability and are therefore recommended if quarter
turn valves (requiring a 90� movement for closure) are used.
The instrument air system should be used to provide motive energy for driving EBV air pistons. The capacity of the main
air surge drum and system line sizes should be evaluated to ensure that there is adequate air available to move the valve,even with an air compressor failure. For retrofit cases, where there is insufficient air holdup capacity, installation ofindividual air surge drums, pressurized through a check valve, may be justified.
Rotary air motors and single acting air piston operators are not recommended in emergency service. They have been
installed in several locations and have demonstrated poor reliability.
Diaphragm operated valves are not acceptable for isolation purposes but they are allowed in “fail-safe" services asindicated previously. If a diaphragm operator is specified in isolation service where it is expected that the valve will remainclosed if exposed to fire, the spring, even if fireproofed, could relax its pressure due to overheating. This would lead toreopening of the valve, which cannot be tolerated.
FIREPROOFING FOR EBVs
EBVs are intended to operate during the first phase of a contingency when in some cases a fire may already have started.Therefore, from a safety standpoint, the best location for an EBV is outside the presumed fire hazard area. For most fires, thismeans 25 ft (7.5 m) away from the equipment where the leak might occur. However, for some offsite isolation situations, wherethe possibility of greater fire spread exists and where the impact of a fire can be significant, increased spacing for EBVs may bejustified. An example of this is a marine terminal where the valve should be located at least 100 ft (30 m) from the manifoldwhere the leak may occur. Beyond those distances no fireproofing would be needed.
1. D Type EBVs (not fail safe)
If it is not justified to locate an EBV 25 ft (7.5 m) or more from a potential fire source, a fireproofed Type D EBV may beinstalled. The installation has to be done in such a way that fire damage does not impair the operation of the valve.Therefore, the preferred cable routing and fireproofing for Type D EBVs are as follows:
� Underground routing of power and signal cables up to the point vertically below the valve actuator. If power and signalcables cannot be run underground from outside the fire hazard area to the point vertically below the valve actuator,they shall be fireproofed within the fire hazardous area of the protected equipment.
� Fireproofing of power and signal cables between grade and the actuator.
� Fireproofing of the actuator.
� Fireproofing shall not include the valve body and hand wheel. Fireproofing of power cables, signal cables, and the
actuator shall be designed so that the system will function for at least 15 minutes when exposed to a 2000�F (1100�C) firewith an incident heat flux of at least 50,000 Btu/hr-ft2 (160 kW/m2) at the conditions set forth in UL-1709, ASTM E-1529, orequivalent test method. For fireproofing details see IP 14-3-1. There shall be no uncovered sections at junctions, bends orterminal entries. Fire resistant cable that meets the above temperature, heat flux, and time criteria may be used withoutadditional fireproofing. For actuators, an easily installed or dismantled fireproof enclosure is recommended.
In hot services greater than 700�F (370�C) the functioning of a fireproofed electric motor can be impaired by heat transferthrough stem and yoke into the actuator. In such cases, the EBV should either be installed in a location where nofireproofing is needed or the valve should be refitted with a longer stem and yoke to facilitate cooling.
DateDecember, 1998 PROPRIETARY INFORMATION - For Authorized Company Use Only
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
S INSTALLATION REQUIREMENTS FOR EMERGENCY BLOCK VALVES (Cont)
If underground routing of power and signal cables is impractical, conduits should be routed via the shortest distancepossible away from the area of the potential leak. Normal cable banks should not be used for convenience if their useresults in enlarging the exposed EBV cable length. For dock installations, the system has to be fireproofed within ahorizontal distance of 100 ft (30 m) from the potential leak. Vulnerable parts in LPG storage vessel isolation valve systemshave to be fireproofed within and beyond the dike area. For all other installations, the above ground power and controlwiring associated with remote actuation has to be fireproofed within a horizontal distance of 25 ft (7.5 m) of the equipmentbeing protected, or further if the equipment fire hazardous area demands.
Depressuring systems and air to oxidation processes (actuators and cables), when not designed to be “Fail-Safe," have to
be fireproofed within battery limits if above ground. This increase in fireproofing is required since this system is counted onto be available assuming the fire can occur anywhere in the unit.
Careful engineering may result in a solution where aboveground power and signal cables are always routed outside otherpotential fire hazard areas (IP 15-10-1). However, if power and signal cables are routed through areas where they mightbe endangered by a fire not requiring the use of this EBV, they need not be fireproofed. It is not EXXON philosophy torequire reliability for EBVs regardless of cost to assure operability under all potential fires. Furthermore, it is reasonable toassume that one contingency does not necessarily result in another. Only when a hazard analysis reveals that one eventleads to another is additional fireproofing justified.
2. C Type EBVs
Type C EBVs by definition are installed at a horizontal distance of at least 25 ft (7.5 m) from the potential leak andtherefore do not need fireproofing. This implies that cables serving a Type C EBV are routed outside the presumed firehazard area associated with this valve. It would not be acceptable if cables for such valves were routed back through thepresumed fire hazard area. Even if fireproofed, this would not meet the intent for Type C EBV requirements. As with TypeD EBVs, it is preferable to route cables serving Type C EBVs underground.
ACTUATING CONTROLS
Actuating controls for Type C and D EBVs should consist of push buttons for moving the valve in the opening and closingdirections. Valve travel once initiated should continue until the valve has moved to its full travel position in the requireddirection. For testing purpose, a stop push-button shall be provided allowing the valve travel to be stopped at any intermediatepoint. All actuating buttons must be provided with a protective guard to prevent inadvertent operation.
With Type D EBVs, the actuation push buttons for remote operation should be located 40 ft (12 m) from the potential leak. Therationale for increasing the distance from the potential leak for Type D EBV push buttons is that this would reduce operatorexposure at little additional cost since the push buttons must be located remote from the Type D EBV in any event. Controlroom activation for Type D EBVs in toxic service should be considered because the field push button could be in the toxiccloud.
Additional push buttons for compressor, fired heater and depressuring system EBVs must be located in the control house(IP 3-7-1). These push buttons should be placed on the appropriate section of control panel covering the unit involved in alogical process relationship to the layout of the other instrumentation.
� All field mounted buttons should be grouped, located at battery limits and should not be less than 40 ft (12 m) away from thenearest potential leak. These unit EBV (D) actuation stations should be clearly marked (to enable personnel to locate during anemergency) and have the emergency action buttons (for example, the close button for a normally open EBV) clearly identified.Valve position indicating lights should be provided.
Local actuating buttons for Type D EBVs are desirable for startup and local testing of equipment such as compressors. It isrecommended to use the existing buttons at the valve actuator instead of installing additional buttons on the local control panel.However, if additional push buttons are installed on the control panel, the wiring for an actuating circuit shall be such thatremote operation will still function even though a local actuation point is lost. If this cannot be accomplished, the local actuatingsystem has to be fireproofed. (IP 14-3-1)
TESTING
The availability of an EBV installation is highly dependent upon how frequently the system is checked since valves can foul andcircuits can fail. For testing, the following is required as a minimum:
PROPRIETARY INFORMATION - For Authorized Company Use OnlyDate
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EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
S INSTALLATION REQUIREMENTS FOR EMERGENCY BLOCK VALVES (Cont)
� � The EBV system should be tested periodically by actuating all functions. Where it is not possible to test an EBV at afrequency suitable to ensure availability without impacting operations, facilities should be provided for on-line testing. Fornormally open, isolation EBVs (C or D) smaller than 8 in. (200 mm), a CSC (carsealed closed) bypass valve shall beprovided, because partial closing of the EBV online can restrict flow and hinder operations. The cost of a bypass valve isnot justified for EBVs equal to or greater than 8 in. (200 mm) which are normally open (isolation valves), provided the EBVcan be partially closed for on stream testing, and full closure is carried out periodically (e.g., during a turnaround). Anexception is made for normally open isolation EBVs installed in a furnace outlet. In this case, a CSC bypass valve shall beprovided around the EBV for onstream testing, regardless of its size.
� EBVs, which are normally closed (depressuring valves), should be provided with a CSO block valve upstream andadjacent to the EBV.
� It is required that the open/close position of an emergency valve can be clearly determined by visual observation of thevalve, even when the valve actuator is fireproofed. Extension rods on gate valve stems or indicators on quarter turn valvescan serve this purpose. (IP 3-7-1)
S EMERGENCY ISOLATION
Manually or power operated EBVs located at strategic points throughout the equipment (on both geographical and process flowbases), permit an affected section to be isolated from other sections of the plant, so that the inventory of fuel feeding a fire orrelease is limited. On a larger scale, in the event of a widespread fire, it is necessary to shut in the whole unit by closing valvesat battery limits. Mechanical failures of machinery, fired heater tubes, and other vulnerable equipment are recognized as acommon cause of major fires, and individual EBVs for this equipment are specified in the following paragraphs.
In order to simplify the selection process and insure the correct type of EBV is used, logic flow diagrams are provided inFigures 1 through 6. To use these figures, choose the figure corresponding to each piece of equipment in a system and followthrough the logic. For example, if you have a vessel and a pump, use both Figures 2 and 3. In this case if both pieces ofequipment require an EBV, see the section on Duplicate Isolation below.
When considering EBVs for equipment such as pumps and compressors, the intent is to provide an isolation capability wherethere is fire directly associated with that equipment. The approach is to provide valving and protection to maximize the isolationcapability for the designated risks at a reasonable added cost relative to reliance on normal process valving. It is not intendedto provide design features to insure operability under all possible fire conditions regardless of cost.
EBVs for isolation should be provided in accordance with guidelines given below. The method of isolation required in eachcase is referred to as Type A, B, C, or D. These types are defined above under DEFINITIONS. Detailed design requirementsare given in Table 1.
� LONG LINES
Where emergency isolation is needed in long lines, such as those present in marine loading facilities, consideration should begiven to the time it takes for the EBV to close fully. The possibility of creating a potentially damaging hydraulic pressure surgeshould be evaluated (Report No. EE.21E.89, Piping Vibration Evaluation Guide) and the valve closing time appropriate to thespecific situation should be used.
� TOXIC MATERIALS
Where toxic materials are present and a release to the atmosphere can occur, either due to a failure of a small connection [e.g.,3/4 in. (19 mm) bleeder] or a flange leak (one half of a flange gasket blows out), and the resulting toxic vapor concentration canexceed the ERPG-3 at the fence line, then either a Type D EBV should be installed, or alternative isolation means should beconsidered. When a Type D EBV is required for toxic service, control room activation should be considered because the fieldpush button could be in the toxic cloud.
COMPRESSORS
A simplified flowchart summarizing the EBV requirements for compressors may be found in Figure 1.
� 1. Type D EBVs are required in the suction and discharge of any compressor of 200 HP (150 kW) and higher handlingflammable or toxic gases. These EBVs should be equipped with position switches set to trip the compressor when theyare less than 50% open (see IP 15-1-2), but the EBVs should not be actuated (automatically closed) by the compressorshutdown system. For compressors less than 200 HP (150 kW), no EBV is required.
2. For compressors meeting the above criteria which have multiple suctions or discharges connected to different pressurestages, Type D EBVs are required in all suction and discharge lines that leave the compressor area and are normallyopen.
DateDecember, 1998 PROPRIETARY INFORMATION - For Authorized Company Use Only
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
S EMERGENCY ISOLATION (Cont)
3. For compressors meeting the criteria in (1), above, which have interstage circuits (e.g., condensers and K.O. drums), TypeD EBVs are required in the suction and discharge lines of each interstage, if that interstage’s equipment contains morethan 1000 gallons (4 m3) of flammable liquid at normal levels.
PUMPS
� A simplified flowchart summarizing the EBV requirements for pumps may be found in Figure 2.
� 1. A Type B, C, or D EBV according to size and location should be installed in the pump suction line when the inventory in a
pump suction vessel meets either of the criteria listed below. In the case of towers, inventory is calculated at the top of theworking level range, with the addition of tray and reboiler holdup if they are draining into the tower sump.
a. Inventory is over 2,000 gallons (7.5 m3) of flammable liquid.
b. Inventory is over 4,000 gallons (15 m3) of combustible liquid.
� 2. A Type D EBV shall be installed in the pump suction line if toxic liquid released from a seal failure would result inexceeding the Emergency Response Planning Guideline Level 3 (ERPG-3) at the fence line. Quantities resulting inERPG-3 can be determined by dispersion calculations specific to the plant. The APPENDIX summarizes a methodologyfor estimating maximum pump seal leakage rate in the event of a seal failure.
3. Where an EBV is installed in the suction line to a pump, or in the common suction line to two or more pumps, the EBV andall piping components between it and the pump(s) must have a pressure rating at normal operating temperature of not lessthan 3/4 of the pressure that will exist downstream of the pump when the EBV is shut. This requirement is the short timedesign basis for piping per ASME 31.3. The pressure in this situation is not necessarily the pump discharge pressure. Inmost cases, this will be the pressure in the vapor space of the first downstream vessel, which contains significant vapor.Should a change of flange rating be required in a pump suction system because of this consideration, it must occur at theupstream side of the EBV.
� 4. EBVs are not required in suction lines to flare blowdown drum pumps even when maximum liquid inventory is above thatnormally requiring an EBV on pump suctions because the risk reduction from the addition of such an EBV is negligible,since these pumps run infrequently, and there is normally no significant inventory in the vessel.
� 5. A Type A EBV shall be installed in the suction line if the pump is not located in an onsite process area. However, an EBVType B, C, or D would be required if spacing is substandard per Section XV-G, or if pump is located near other equipmentwhich is vulnerable to fire.
� VESSELS
Vessels containing more than certain inventories of liquid light ends, liquid heavier than light ends but above or within 15�F(8�C) of its closed cup (Pensky-Martens) flash point, or toxic liquids should be provided with EBVs at the vessel nozzles locatedbelow the maximum working level. These EBVs are to isolate the vessel contents from possible failures in the associated liquidpiping. Small piping is more vulnerable to mechanical damage and should be provided with EBVs in some cases where largelines are not. The volume of liquid is calculated at the top of the working level range with the addition of tray and reboilerholdup in the case of towers and neglecting line inventory, unless the inventory in the line exceeds 250 gal (900 l).Connections between EBVs and the vessel should be avoided. The connection to the closed drain header should be taken offdownstream of the isolation valve and the vessel.
In determining the type of EBV to install, the worst contingency should be evaluated. This may not always be the first or largestflange out of the vessel, e.g., a flange leak from an elevated drum under low pressure may have a lower leak rate at the first outflange than a smaller flange at grade, due to liquid head.
A simplified flowchart summarizing the EBV requirements for vessels may be found in Figure 3.
The type of EBV shall be as follows:
� 1. If a toxic liquid release can exceed the Emergency Response Planning Guidelines Level 3 (ERPG-3) at the fence linewhen one half of a flange gasket blows out from any normally open line below the maximum working level, then a Type DEBV is required in the respective line. The liquid inventory required to exceed ERPG-3 can be established by dispersioncalculations specific to the plant.
� 2. If the liquid inventory of any volume in an offsites storage vessel is light ends, then Type D EBVs are required on allnormally open lines below the maximum working level per IP 3-5-1, and a Type A EBV on all other lines below themaximum working level. Note that a failure in a line above the maximum working level will result in a long-lasting incidentas the contents slowly vaporize. This should be considered when assessing the need for EBVs in connections above themaximum working level.
PROPRIETARY INFORMATION - For Authorized Company Use OnlyDate
December, 1998
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
S EMERGENCY ISOLATION (Cont)
� 3. If the liquid inventory in a process vessel is more than 10,000 gal (40 m3) light ends, and there are any special factors suchas substandard spacing, congestion, stacking, substandard firefighting, etc., then a Type D EBV is required on all normallyopen lines below the maximum working level, and a Type A EBV is required on all normally closed lines below themaximum working level. If no special factors apply, then a Type A EBV is required on all lines below the maximumworking level (see Item 7).
� 4. If the liquid inventory is more than 1,000 gal (4 m3) but less than 10,000 gal (40 m3) light ends, then a Type A EBV shall beinstalled on all lines 2 in. (50 mm) or smaller below the maximum working level (see Item 7).
� 5. If the liquid inventory in a process vessel is over 10,000 gallons (40 m3) heavier than light ends at a temperature above or
within 15�F (8�C) of its closed cup (Pensky-Martens) flash point, then a Type A EBV is required on all lines below themaximum working level. This requirement may be applied to smaller inventories when there are special hazard factorsassociated with the vessel contents, e.g., high corrosion rates, high pressure, or cryogenic conditions (see Item 7).
� 6. If the liquid inventory is over 1,000 gallons (4 m3) but less than 10,000 gallons (40 m3) heavier than light ends and at a
temperature above or within 15�F (8�C) of its closed cup (Pensky-Martens) flash point, then a Type A EBV is required onall lines 2 in. (50 mm) or smaller below the maximum working level (see Item 7).
� 7. Lines between towers and associated reboilers need not have EBVs.
FIRED HEATERS, BOILERS AND OTHER COMBUSTION DEVICES
A simplified flowchart summarizing the EBV requirements for fired heaters, boilers, and other combustion equipment may befound in Figure 4.
1. Fuel to Firebox
All fuel streams (including pilot gas, auxiliary fuel, offgas, etc.) to fired heaters, boilers and other combustion devicesshould be provided with an accessible Type B EBV located at least 40 ft (12 m) from the equipment. This increaseddistance recognizes that fired heaters have a higher risk for fires than do other process equipment. A battery limit valve orother EBV in the line may be considered to meet the fuel isolation requirement, provided that its closure would not createother hazards or conflict with other actions that might be necessary during a plant emergency. For example, a fuel gas linemight be required to be open as a depressuring route. This fuel isolation requirement is in addition (and is intended as aback-up) to tight shutoff valves provided for the emergency shutdown system.
2. Process Feed to Fired Heater
Means must be provided for stopping the flow of flammable process fluids to fired heater coils. This should consist of anaccessible Type B EBV in each stream, located at least 40 ft (12 m) from the fired heater. This increased distancerecognizes that fired heaters have a higher potential, both in magnitude and frequency, for fires than do other processequipment. Block valves for feed pumps, compressors, or control valves, which meet the above requirement, areacceptable for this purpose.
Means of emergency isolation in the outlet of a fired heater handling flammable materials is also desirable in cases wherebackflow of the downstream inventory would have a major effect on the extent and duration of a tube failure fire. However,this objective has to be balanced against the practical problems of coking and inadvertent closure of isolation devices.Factors associated with the downstream equipment which would favor the installation of fired heater outlet isolation includehigh pressure, volatile liquids, large inventory and absence of vapor blowdowns.
Fired heater outlet isolation is not normally provided unless coil outlet pressures exceed 200 psig (1400 kPa). Anexception to this is the case of POWERFORMING Unit fired heaters, where no check valves are used, because of thedifficulty of providing effective isolation with the series flow arrangement of the fired heater and reactors.
a. When isolation is required, a check valve is the normal method, provided that reliability can be expected consideringcoke deposition. The check valve must be of the swing-check type with no external actuation or dampeningmechanism. No additional overpressure protection is necessary as a result of the inclusion of this check valve.
b. Although isolation by check valve is recognized to have a degree of unreliability, use of a remote operated valve as anadditional means of isolation is not generally recommended, because of the possibility of inadvertent closure and theassociated problems of designing an effective safety relief system that will maintain continuity of flow through the coil.However, an exception is made in the case of a process fired heater operating at coil outlet pressures above 1,000psig (6,900 kPa) where the importance of isolation is considered sufficient to justify the installation of a positive shutoffof the Type D EBV in addition to a check valve in the fired heater outlet. Fired heater overpressure protection must beprovided in these applications, in accordance with Section XV-C (Overpressure in Specific Equipment Items).
DateDecember, 1998 PROPRIETARY INFORMATION - For Authorized Company Use Only
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
S EMERGENCY ISOLATION (Cont)
� VULNERABLE EQUIPMENT
Emergency isolation may be required for equipment, which is exceptionally vulnerable to fracture and uncontrolled release as aresult of mechanical or thermal shock (e.g., graphite heat exchangers). In these cases the type of EBV shall be as follows:
1. If the contents include flammable material, Type B, C or D EBVs (depending on the valve’s size and location) are requiredin the equipment inlet and outlet piping.
2. If the contents include toxic materials which if released from a hole 2 times the cross sectional area of a tube would result
in a level exceeding the Emergency Response Planning Guidelines Level 3 (ERPG-3) at the fence line, then Type D EBVsare required in the equipment inlet and outlet piping. The volume required to exceed ERPG-3 can be established bydispersion calculations specific to the plant.
The engineering safety specialists should be consulted on these applications. A simplified flowchart summarizing the EBVrequirements for vulnerable equipment may be found in Figure 5.
BATTERY LIMITS
Spacing requirements for battery limits from roadways, offsite pipe bands and other units are defined in Section XV-G. Batterylimit valve manifolds must be located at the battery limit, or if there is an adjacent offsite pipe band, location up to the neareredge of this pipe band is permissible. A simplified flowchart summarizing the EBV requirements for battery limits may be foundin Figure 6.
1. Emergency isolation is required in every process or utility line entering or leaving plant battery limits if the line is normallypressurized. For flare and closed release headers refer to Section XV-D.
2. A single valve in a line at battery limits may serve for both emergency and turnaround isolation.
3. Battery limit EBVs should be grouped into one or more manifolds provided with line identification.
4. Type B or Type C EBVs must be specified according to size and service and must meet the requirements for these valvesdefined in Table 1. Type C EBVs are only required in flammable or toxic service where the valve is larger than 8 in. (200mm).
� 5. Onsite equipment adjacent to the battery limit valve manifold must be located to provide the 25 ft (7.5 m) horizontalspacing required between Type B and C isolation valves and the equipment being protected (per Table 1). For batterylimit isolation, this is interpreted as 25 ft (7.5 m) from any onsite equipment except low fire-risk facilities, such as thosehandling non-flammable materials or combustible liquids, for which 15 ft (4.5 m) spacing is acceptable.
� TANK TRUCK AND RAIL LOADING AND UNLOADING FACILITIES ISOLATION
Refer to Section XV-J.
� MARINE TERMINAL FACILITIES ISOLATION
Refer to Section XXXI-I.
DUPLICATE ISOLATION
Where two pieces of equipment are involved, each requiring an EBV, sometimes the requirements may be combined and oneof these EBVs may be eliminated. An example of this is the suction line from a vessel to a pump, where emergency isolation ofeach piece of equipment requires an EBV. If the volume in the line exceeds the inventory requirements for pumps, two EBVsare required. However, if the volume in the line is less than the inventory requirements for pumps then only one EBV isrequired and it must meet the installation requirements of both the pump and vessel. Typically this will be the EBV at thevessel nozzle with the type being dictated by distance to the pump and size and location of the valve.
PROPRIETARY INFORMATION - For Authorized Company Use OnlyDate
December, 1998
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
S WATER FLOODING PROVISIONS
APPLICATION
Water flooding connections are sometimes provided on equipment to protect against uncontrolled release of flammablematerial at the bottom connections or at the pump withdrawing liquid from the vessel. In such a contingency, injected water willdisplace the liquid hydrocarbon up the vessel, so that only water escapes through the point of failure. This method requires asource of water at a pressure higher than the vessel operating pressure plus static head, and should not be provided if the
operating temperature is above 200�F (93�C) or below 40�F (5�C). Water flooding connections have limited application, butshould be considered for non-refrigerated, large volatile liquid inventories in addition to remote controlled isolation facilities.The engineering safety specialists should be consulted on such applications.
In some cases, such as for large liquid-filled water wash settling drums, water displacement may be used to remove liquidhydrocarbons. This method is conveniently used when enough water normally enters a liquid-filled vessel that the hydrocarboncan be displaced by shutting off both the hydrocarbon feed and the water outlet.
DESIGN
The injection point for water flooding should comply with the requirements of IP 3-6-3, and the water lateral should be suitablyprotected against freezing.
� All pressurized storage vessels handling flammable materials like LPG, Natural Gas Liquids (NGL), or other chemicals withsimilar vapor pressures not in refrigerated service (including horizontal drums used for storage, spheres, and spheroids) shallhave a connection installed to permit flooding of the vessel with firewater per IP 3-2-3.
Structures and foundations of vessels provided with water flooding connections must be designed for the associated hydraulic
loads.
S EMERGENCY DEPRESSURING
� It is possible to reduce the duration and intensity of a fire by providing a means to quickly remove the inventory of flammablematerial in the affected section of the plant. Generally, this involves depressuring equipment. Depressuring may beaccomplished by the use of normal process disposal mechanisms and routes, and/or by the use of special vapor blowdownfacilities. Although it is not necessary to be able to completely empty the equipment within a specified time, it is intended thatthe overall combination of emergency facilities and fire protection be capable of bringing the fire under control within one hour.See further discussion in Section XV-A. Liquid pulldown has been used in the past but it is no longer recommended becausethe equipment is not used frequently and may deteriorate due to lack of maintenance.
� VAPOR BLOWDOWN (DEPRESSURING) APPLICATION
Special emergency depressuring facilities (vapor blowdowns) are provided on certain high-pressure equipment so that vesselstresses, and hence the risk of failure under fire exposure or runaway reactions, may be reduced in an emergency situation.They also facilitate rapid shutdown of a plant in the event of mechanical failure and potential fire. Vapor blowdowns areinstalled as follows:
1. On equipment operating above 150 psig (1030 kPa) where there is no liquid inventory, or the liquid inventory is dispersedin a continuous vapor phase such as in a mixed-phase fixed-bed reactor.
2. For other equipment (for example large light ends fractionators or surge drums) operating above 250 psig (1,720 kPa)where the flammable liquid and vapor contents of a vessel or group of vessels (excluding piping and pumps) would exceed200,000 ft3 (5,600 m3), when flashed and expanded adiabatically from operating conditions to atmospheric pressure.
3. To arrest runaway chemical reactions.
In all cases where emergency depressuring facilities (vapor blowdowns) are provided, facilities should also be provided to stopall feeds to the system.
DESIGN OF VAPOR BLOWDOWN CONNECTIONS
� 1. Two or more vessels may be grouped for emergency depressuring purposes and fitted with a single blowdown connection,provided that the interconnecting piping and any control valves in this piping have adequate capacity to meet thedepressuring time requirement defined below, and are designed to avoid plugging. In addition, control valves must movetowards the open position as a result of both actuating medium failure and normal control response to the depressuringoperation.
DateDecember, 1998 PROPRIETARY INFORMATION - For Authorized Company Use Only
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
S EMERGENCY DEPRESSURING (Cont)
� 2. The connection shall have a restriction orifice (RO) and a Type D EBV actuated from the control room and shoulddischarge to the flare system. Where two or more vapor blowdown connections are installed in a process unit, separateactuation of the EBVs shall be provided. A tight-shutoff, Fail-Open control valve may be used as an alternative to theEBV/RO system. The control valve seat leakage rate should meet the Class VI specification, per ANSI/CFI 70-2 1991,unless the material temperature would exclude its use (see Section XII-F, Table 7).
3. A blowdown connection is typically sized to reduce the pressure in the equipment from its operating pressure to 50% of itsdesign pressure in 15 minutes for fire emergency. Higher rates may be required to contain runaway reactions. Forgrouped vessels, the pressure of each vessel must be reduced to a pressure no higher than this requirement. Oversizingblowdown connections should be avoided since this can result in an excessive large flare system and, for some reactors,the possible lifting of the catalyst bed (see Section VII-B). Depressuring rates are calculated on the following basis:
� a. Process flow and heat input to the process has stopped (may require feed and heater emergency shutdownactuation). Liquids are not vaporizing.
b. Flow through the valve or orifice is critical.
c. Credit may be taken for water cooling (but not air fin cooling) if the depressuring connection is located downstream ofa cooler or condenser.
d. Credit is taken for simultaneous depressuring through normal process disposal routes, if criteria as stated in (1) aboveare met.
e. Back-flow from connected equipment during depressuring may be disregarded if automatic shutoff is provided bymeans of a check valve or control valve which closes as a result of both actuating medium failure and normal controlresponse to the depressuring operation.
f. Following formulas should be used for sizing restriction orifices and control valves.
Sizing restriction orifices
���
����
�
���
����
�
�
���
����
�
�
1k
1k
2
1
1k
2k
M
TZRC
P
PlnV
Ad Eq. (1)
Sizing control valves (Cv method)
�
�
�
���
� ����
����
� �
���
����
�
��
M
TZ
Xk142.21N
P
Pln
R
V
C
T8
2
1
v Eq. (2)
where: A = Constant: 4.95 x 10-2 (10.28 for metric units)
C = Orifice coefficient, dimensionless
Cv = Flow coefficient, dimensionless
d = Orifice diameter, in. (mm)
k = Ideal Heat Capacity ratio of vapor, dimensionless
M = Vapor Molecular weight, dimensionless
N8 = Constant (see Section XII-F): Rpsiahr
lb3.19 ��
�
���
� or
�
���
���
���
�KkPa
hr
kg948.0 �
P1 = Initial system pressure, psia (kPa)
P2 = Final system pressure, psia (kPa)
PROPRIETARY INFORMATION - For Authorized Company Use OnlyDate
December, 1998
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
S EMERGENCY DEPRESSURING (Cont)
R = Gas Constant:Rlbmole
psiaft73.10
3
�
or
�
�
���
�
Kkgmole
kPam314.8
3
�
T = Absolute Temperature at inlet conditions, �R (�K)
V = Total system volume, ft3 (m3). When the system gas is cooled before the depressuring
valve, the system volume should be adjusted for the reduction in temperature due to
cooling. Reductions in pressure due to cooling are usually small and are neglected.
XT = Constant for valve type. It is the pressure drop ratio factor empirically determined for
each valve (see Section XII-F).
Z = Compressibility factor at inlet conditions, dimensionless
� = Time for depressuring, hours
� =���
����
�
��
���
�
1k
k
1k
21 , dimensionless
Note: Eq. (2) applies for 40.1
Xk
P
PP T
1
21 �
and 1.25 � k � 1.40.
For conditions outside this range of k consult with ER&E’s INSTRUMENTATION SPECIALISTS.
The compressibility factor (Z) has been assumed constant for simplification of the integration while, in fact, it is a functionof pressure. For practical design purposes, however, an average estimated value will not contribute appreciable errorfor moderate pressures.
� DESIGN OF VAPOR BLOWDOWN RELEASE SYSTEMS
1. When actuated, the vapor blowdown release system needs to lock open until depressuring is complete.
2. Blowdown connections may discharge into a flare header or other closed release system. In either case, the principles ofheader sizing, layout and blowdown drum selection are the same as for closed release systems (see Section XV-D).
3. For header sizing, the contingency considered is a fire in a single fire hazard area, with all vapor blowdowns in that areareleasing simultaneously, along with all safety relief devices in the same fire hazard area which meet all of the followingcriteria:
a. They are on equipment not provided with vapor blowdowns.
b. They are tied into the same header as the vapor blowdowns.
c. They discharge as a result of fire exposure on equipment.
Each fire hazard area is examined on this basis, and the header is sized such that during the largest single contingencyrelease, back pressure on all safety relief devices tied into the header does not exceed the limitations applying to thedesign of normal closed release headers.
4. Vapor blowdowns may be discharged to the atmosphere if all the criteria applying to the atmospheric discharge of pressurerelief valves are satisfied (including pollution considerations), and provided that the material released can only be vaporunder any foreseeable emergency conditions.
LOW-TEMPERATURE IMPACT STRENGTH
Vessels containing volatile liquids, with vapor blowdown piping, must be designed to withstand the low temperatures resultingfrom auto refrigeration during emergency depressuring, in accordance with the requirements of Section II and IP 18-10-1.
CONTINGENCY OTHER THAN FIRE
If depressuring facilities are required for the control of exothermic or runaway process reactions, these conditions must beconsidered separately. If blowdown facilities are required for both fire and process depressuring, the larger requirement mustgovern.
DateDecember, 1998 PROPRIETARY INFORMATION - For Authorized Company Use Only
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
S EMERGENCY DEPRESSURING (Cont)
USE OF NORMAL DISPOSAL ROUTES AND CONTROLS
For process plant equipment which does not meet the criteria for installation of special vapor blowdown facilities as describedabove, it is assumed that in a fire situation some of the normal disposal mechanisms and routes are still functional andaccessible to the operators, so that they can remove as much as possible of the flammable inventory. These may include:
� Depressuring by releasing vapors to the fuel gas header or associated plants.
� Pumping or pressurizing liquids from vessels by normal routes out of the plant to tankage, to other units, or to slop.
These functions can often be carried out using the valve, manifolding, and process controllers provided for normal, startup andshutdown operations. Note this type of flammable inventory reduction is not quick. Valves which are critical for these functions(e.g., product diversion to slop), should be located in a low fire-risk area, such as at the battery limit piping manifold.Emergency conditions must be analyzed to avoid dangerous situations in tankage or equipment receiving disposal materials.For example, debutanizer bottoms routed to naphtha tankage could be contaminated with light ends or could be followed bylight hydrocarbon gases after all the liquid has been discharged.
INSTRUMENT FAILURE CONSIDERATIONS
Considerations of instrumentation failure must be included in the design of emergency systems, both on plant-wide andindividual bases. Overpressure protection considerations for instrument failures are covered in Section XV-C.
S EMERGENCY SHUTDOWN SYSTEMS
Emergency shutdown systems enable the operators to perform the quick shutdown of a plant in an emergency situation byremotely carrying out functions such as shutting down major machinery, stopping heat input to fired heater and reboilers, andshutting off air to oxidation processes. They also serve as a means by which machinery may be remotely shutdown in theevent of mechanical malfunctions when there is a possibility of catastrophic failure.
Emergency shutdowns are required for:
DRIVERS
1. On all compressors over 200 HP (150 kW). (Actuation from the control house.)
2. On steam driven pumps and compressors that handle combustible liquid or flammable materials. (Actuated remotely.)
3. On other machinery where there are particular factors which increase the potential for mechanical failure and majorrelease of flammable materials, e.g., large multistage pumps.
FIRED HEATERS, BOILERS, AND OTHER COMBUSTION EQUIPMENT (FUEL TO FIRE BOX)
The ability to close from the control house the main fuel shutdown valves and pilot gas valves to combustion equipment isrequired. These valves should be tight shutoff, dedicated only to safe shutdown of the equipment. These are the same safetyshutoff valves referred to in IP 15-1-1. An additional EBV (Type B) in all fuel lines (including pilot gas) shall be provided asdiscussed under EMERGENCY ISOLATION.
AIR INJECTION / OXIDIZER STREAMS TO PROCESS
A shutdown valve actuated from the control house is required for an air injection or oxidizer stream to process where immediateshutoff is a stage in the emergency shutdown procedure, which is essential to making the unit safe. Besides a tight shutoffvalve, the installation should include a check valve and a vent valve to depressurize the air/oxidizer stream. (See also SectionXV-B.)
REFRIGERATED LIQUID / GAS FACILITIES
The required Type D EBVs shall be tied into an emergency shutdown system so that refrigerated liquid tanks, pumps,compressors, loading facilities and processing units can be segregated from each other. Refer also to special Report79.ECS.729, Suggested Design Considerations for Refrigerated Liquefied Gas Facilities.
� MARINE TERMINAL SHUTDOWN SYSTEMS
Refer to Section XXXI-I and to Report No. EE.108E.98.
PROPRIETARY INFORMATION - For Authorized Company Use OnlyDate
December, 1998
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
EXXON
ENGINEERING
S EMERGENCY SHUTDOWN SYSTEMS (Cont)
� SPECIAL CASES
Further application of remote shutdowns may be justified in special cases, to enable other process functions or equipment to bestopped, thus accelerating the shutdown procedure. Factors, which should be taken into account in such cases, include plantsize, complexity and operator manning levels. For example, catalytic cracking units are provided with a special emergencysystem, which diverts feed and closes slide valves to isolate the reactor and regenerator. The unit can therefore be rapidly putinto a “safe" condition during an emergency. Other examples for application of emergency shutdown systems are Claus plants,gas turbines, air preheaters and the combination of process EBV with the driver trip system on large rotating machines.
Following are some examples of cases where special emergency shutdown systems should be considered:
� In-Situ Conditioning of Fresh Catalyst in Fixed Bed Reactors: Normally catalysts are pretreated or conditioned beforeprocess use by treating with hydrogen, hydrogen sulfide, etc. to activate the catalyst. These treatments are usuallyexothermic. Due to the transient nature of the operation, high temperature moving fronts can be generated that couldunder certain circumstances potentially exceed the reactor design temperature. This thermal front can occur with singlephase and mixed phase (gas/liquid) pretreatments and the front may be trapped in the bed under certain trip scenarios.The Reactive Chemistry group of ER&E should be consulted for each specific reactor case to be designed. A computermodel is available to help analyze situations.
� In-Situ Catalyst Regeneration in Fixed Bed Reactors: The burning of coke from catalyst or the hydrogen treatment torejuvenate catalyst occurs as an exothermic moving front in the fixed bed. The corresponding heat front that will begenerated has to be monitored and controlled to keep the temperature within the reactor design bounds. Design andoperating guides for the specific catalyst should be consulted for monitoring and shut down guidelines or the ReactiveChemistry Group in the Reactor and Fluid Dynamics Section of ER&E should be consulted.
� Unsaturated Naphtha Hydrofiners: Provide Priority 1 THA in reactor inlet to prevent initiating olefin saturation and largeexotherm (THCO needed).
� C3 / C4 Splitters: Provide LL(CO) to avoid sending C3 into the C4 storage.
Emergency shutdown systems for Fluid Catalytic Cracking (FCC) Units (see Report No. EE.67E.97) and various otherexothermic reactor systems are shown below.
FCCU EMERGENCY SHUTDOWN (ESD) SYSTEMSPRESSURE BALANCE CONTROL FCC UNITS
Minimum ESD Requirements
TRIP INITIATOR AUTOMATED SHUTDOWN SYSTEM ACTIONS
� Low Reactor Temperature
� Low Stripper Level
� Low Overflow Well Level
� High Reactor Temperature
1. Close the Regen Cat slide valve
2. Close the Spent Cat slide valve
3. Close all hydrocarbons to the reactor
4. Divert feed to the fractionator
� Low Air Flow to Regenerator 1. Close the Regen Cat slide valve
2. Close the Spent Cat slide valve
3. Close all hydrocarbons to the reactor
4. Divert feed to the fractionator
5. Inject steam in the air lines
� Main air line
� Spent cat riser or control air riser or sparger air line
6. Assist in the closure of check valves in the air lines
7. Shut-off torch oil
8. Shutdown fuel to the auxiliary burner
9. Stop any oxygen injection
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S EMERGENCY SHUTDOWN SYSTEMS (Cont)
FCCU EMERGENCY SHUTDOWN (ESD) SYSTEMSSLIDE VALVE CONTROL FCC UNITS
Minimum ESD Requirements
TRIP INITIATOR AUTOMATED SHUTDOWN SYSTEM ACTIONS
� Low Reactor Temperature(1)
� Low Spent Cat Slide Valve �P
� Low Regen. Cat Slide Valve �P
� High Reactor Temperature
1. Close the Regenerator Cat slide valve
2. Close the Spent Cat slide valve
3. Close all hydrocarbons to the reactor
4. Divert feed to the fractionator
� Low Air Flow to Regenerator 1. Close the Regenerator Cat slide valve
2. Close the Spent Cat slide valve
3. Close all hydrocarbons to the reactor
4. Divert feed to the fractionator
5. Inject steam in the main air line
6. Assist in the closure of check valve in the air line
7. Shut-off torch oil
8. Shutdown fuel to the auxiliary burner
9. Stop any oxygen injection
Note:
(1) For those units with two feed risers, a low temperature trip on any one riser should initiate the closure of allhydrocarbon sources to that riser and also trip the regenerated catalyst shut-off slide valve. However, should bothrisers have trips on low temperature, then the shut-down system response should be the same as for a single riser as
summarized above.
� EXOTHERMIC REACTORS
Exothermic reactors with the potential for temperature runaways must be protected from excessively high metal temperatures,which can result in vessel, line, or equipment failure. This applies to all processes in which there is the possibility of exceedingthe reactor vessel design temperature as a result of uncontrolled exothermic reactions caused by process upsets,maldistribution, decomposition, or other reaction mechanisms. Protection of such reactors is usually achieved by high-temperature cut-outs that automatically depressure the reactor system when the reactor temperature reaches a pre-determinedlevel. The reactor temperature is normally monitored with multiple thermocouples within the reactor bed and occasionally withreactor skin thermocouples or maximum temperature monitoring bands connected to a Programmable Logic Controller (PLC)based protective system. There may be other initiators in addition to high reactor temperature tied into the system. In additionto depressuring the reactor system, there may be other responses that depend on the configuration of the individual unit. Suchresponses may include shutting-off the flow of reactants, tripping feed and/or treat gas heaters and others. The choice, numberand location of temperature monitoring or other responses can be aided by the application of existing reactor computer modelsavailable in the Reactive Chemistry Group in the Reactor and Fluid Dynamics Section.
Following are some examples of emergency guidelines used for exothermic reactors now in operation. These guidelines arefor typical situations. Each new design or modification of an operating unit must be examined for specific requirements. TheReactive Chemistry Group in the Reactor and Fluid Dynamics Section should be consulted for each specific case. Computermodels are available to help analyze specific situations.
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S EMERGENCY SHUTDOWN SYSTEMS (Cont)
� EMERGENCY GUIDELINES FOR SOME EXOTHERMIC REACTORS
ACTION
HYDROCRACKER,
H.P. GOFINER,RESIDFINER,
AROMATIC SATUR.
DIENEHYDROGENATOR(LIQUID PHASE)
UNSATURATEDNAPHTHA
HYDROFINER METHANATOR
Depressure Reactor A M or A M A
Stop Hydrogen Make-up Flow A A M(1) NA
Stop Feed Flow A NA A(2) NA
Bypass & Isolate Reactor NA M or A NA A
Shutdown Furnace A NA NA NA
Stop Wash Water Flow A NA NA NA
Stop Lean MEA Flow A NA NA NA
Legend:
A = Automatic Activation
M = Manual Activation (remote)
NA = Not Applicable
Notes:
� (1) If the system is "once-through," makeup Hydrogen flow should not be stopped.
(2) The action is automatic once the manual system has been initiated.
DESIGN FEATURES OF EMERGENCY SHUTDOWN SYSTEMS
� Shutdown controls must be provided with suitable guards to prevent accidental operation. They should be designed for themaximum possible extent of on stream testing without actually shutting down the equipment (see IP 15-7-1 and IP 15-7-2).
� Shutdown signal systems to machinery drivers should normally be de-energized while the protected equipment is inoperation. All other shutdown instrument systems must be normally energized as per IP 15-7-2.
DateDecember, 1998 PROPRIETARY INFORMATION - For Authorized Company Use Only
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S TABLE 1LOCATION, SIZE AND OPERABILITY REQUIREMENTS FOR EMERGENCY BLOCK VALVES (IP 3-7-1, IP 3-12-1)
APPLICABLE RESTRICTIONS FOR VALVE TYPEREQUIREMENT
A B C D
VALVE LOCATION
� Horizontal distance from source ofpotential leak
At equipment > 25 ft (7.5 m)(1)(4) > 25 ft (7.5 m)(1)(4) No restrictions
VALVE SIZE & FLANGE RATINGS
� Recommended for All sizes and classes � 8 in. (200 mm) orClass 300 and lower(3)
> 8 in. (200 mm) orAbove Class 300(3)
All sizes and classes
� Valve can be reached withoutpassing the source of potential leak
closer than
Not applicable 25 ft (7.5 m)(4) 25 ft (7.5 m)(4) Not applicable
Notes:
(1) This distance increases to 40 ft (12 m) for manually operated block valves in process, fuel and pilot gas lines to fired heaters.
(2) If the valve is more than 75 ft (23 m) horizontally from source of potential leak, or identified as “Battery Limit (BL)" valve, there are no
restrictions on elevation or flange class.
(3) EBVs located at Battery Limits normally are either Type B or C. Type C EBVs are required at the battery limit only in flammable or toxic
services for valves larger than 8 in. (200 mm).
(4) For marine pier facilities, this distance is 100 ft (30 m)
(5) For pressurized and refrigerated storage facilities (e.g., LPG) the push-button should be located outside of the dike.
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�S TABLE 2AMERICAN INDUSTRIAL HYGIENE ASSOCIATION (AIHA) ERPG-3's 1998(1)
(1) For other chemicals which may be potentially toxic, or for updated values of the chemicals listed above, refer to the latest AIHA
Emergency Response Planning Guidelines (ERPGs) and Workplace Environmental Exposure Level Guides Handbook (the list isupdated periodically), or contact Exxon Biomedical Sciences, Inc. (EBSI).
DateDecember, 1998 PROPRIETARY INFORMATION - For Authorized Company Use Only
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� FIGURE 1EBV REQUIREMENTS FOR COMPRESSORS
Start
Is the
Compressor
200 HP orLarger ?
Is ItHandling
Flammable orToxic Material
?
EBV Type D
Between Stages
and Interstage Equipment
EBVs Type DIn All Inlets, Discharges
And all Sidestream Lines
EBV
Not Needed
for Interstage
EBV
Not
Needed
EBV
NotNeeded
No
No
No
Yes
Yes
Yes
Metric Equivalent
200 HP 1,000 Gal
150 kW 4 m 3
Is There
an Interstage Vessel
(Drum/Condenser) withmore than 1,000 Gal
Liquid?
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� FIGURE 6EBV REQUIREMENTS FOR BATTERY LIMITS
Is the
Stream Flammableor Toxic
?
Is the Valve
Greater than
8 in. (200 mm)
?
EBV Type C
No
Start
DP15Ff06
No
Yes
EBV in Every NormallyPressured Line Entering
or Leaving the Plant.
Exception: Flare or Closed
Release Header.
Select Type
EBV Type B
EBV Type B
Yes
DateDecember, 1998 PROPRIETARY INFORMATION - For Authorized Company Use Only
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� APPENDIX -PROCEDURE TO ESTIMATE MAXIMUM PUMP SEAL LEAKAGE RATE
ASSUMPTIONS
1. No reduction in total leakage has been included due to flow restriction from internal throat bushings or seal flush plan. (Inmost pumps, an internal throat bushing might provide some restriction to the flow, which proceeds from the back side ofthe impeller, into the seal chamber, and then to the environment through the throttle bushing. Likewise, the amount of flowinto the seal chamber from any flush system or API flush arrangement might be restricted by the size of the hole drilled inthe gland plate.)
2. The gland plate remains intact and does not separate from the pump back plate.
3. Single arrangement seals utilize a throttle bushing, dual seals do not.
4. Upon failure, all restriction from the seal faces is removed.
SEAL LEAKAGE CALCULATION PROCEDURE
1. Determine the applicable throttle bushing clearance from Table A-1 based on the seal arrangement (single or dual) andstandard to which the seal was designed. If the standard to which the pump/seal were built are unknown or do not appearin Table A-1, assume the seal has no throttle bushing and utilize a diametrical clearance of 0.025 in. (0.63 mm).
2. Determine the applicable throttle bushing length. Use the actual throttle bushing length as measured/provided for the seal.If an actual dimension is not available, use 0.25 in. (6.35 mm).
3. Determine the seal chamber pressure to be used for the leakage calculation. Use the highest differential pressure from thefollowing choices to calculate the maximum leakage rate:
a. The estimated seal chamber pressure using PC program SealExx, CPEE-042 or the formulas in Table A-2 based onthe pump construction style and pump differential pressure. Use of this pressure will provide the estimated leakagefor a pump that is operating. Note that the formulas in Table A-2 are identical to those used in PC program SealExx,available from ER&E. SealExx may be used in lieu of Table A-2 if desired.
b. Rated discharge pressure for the pump. The rated discharge pressure is the normal or usual discharge pressure withnormal suction pressure. This is the pressure that the seal will be exposed to if:
� The leaking pump is NOT running AND
� The spare pump IS running AND
� The leaking pump suction block valve is closed AND
� The leaking pump discharge check valve is bypassing AND
� The leaking pump does not have overpressure protection on the seal chamber per IP 3-3-2.
This pressure DOES NOT account for the maximum 10% of rated flow assumed in the Design Practices for leakagepast a check valve.
c. Seal chamber pressure equal to the overpressure protection setpoint (per IP 3-3-2) on the suction of the pump. Thispressure DOES NOT account for the maximum 10% of rated flow assumed in the Design Practices for leakage past acheck valve.
4. Using the throttle bushing clearance, length, and seal chamber pressure, calculate the estimated seal leakage rate usingEq. (A-1), Table A-3, and Figure A-1. Figure A-1 is applicable for oil viscosity range between 75-150 SSU.
gpm = Flow Factor x Bushing Length Factor x in. Diameter of Shaft Eq. (A-1)
where: Flow Factor = Determine from Figure A-1
Bushing Length Factor = Determine from Table A-3
Differential Pressure = Differential pressure between seal chamber pressure and ambient
pressure
Diametral Clearance = Diametral clearance of throttle bushing from Table A-1
Note that Eq. (A-1) is for water at 70�F (21�C). If the fluid being leaked is a hydrocarbon with a viscosity between 75 and150 SSU (14 cSt to 32 cSt) then multiply the result of Eq. (A-1) by 0.12.
If the viscosity of the hydrocarbon is below 75 SSU (14 cSt) use Eq. (A-1) without any viscosity correction and realize thatthe expected leakage will probably be somewhat less than predicted.
If the viscosity of the hydrocarbon is above 150 SSU (32 cSt) use Eq. (A-1), multiply the result by 0.12, and realize that theexpected leakage will probably be somewhat less than predicted.
PROPRIETARY INFORMATION - For Authorized Company Use OnlyDate
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TABLE A-1CLEARANCE IN THROTTLE AND THROAT BUSHING
THROTTLE BUSHING CLEARANCE (CLR)APPLICABLE SEAL DESIGNSTANDARD
SHAFT DIAMETER THROTTLE BUSHING DIAMETRAL CLR
API 682
First Edition, Oct. 94 for Sealregardless of Pump Design Standard
0 - 2.00 in. (0 - 50 mm)
2.01 - 3.00 in. (51 - 80 mm)
3.01 - 4.75 in. (81 - 120 mm)
0.007 in. (180 �m)
0.009 in. (225 �m)
0.011 in. (280 �m)
API 610
Fifth Edition, Mar. 71 and all priorAPI editions
NA 0.025 in. (635 �m)
API 610
Seventh Edition, Feb. 89
0 - 2.00 in. (0 - 50 mm)
For shaft diameter larger than2.00 in. (50 mm)
0.025 in. (635 �m)
0.025 in. + 0.005 in. for each additional in. of
diameter (635 �m + 127 �m for each additional25 mm of diameter)
API 610
Eight Edition, Aug. 95
0 - 2.00 in. (0 - 50 mm)
2.01 - 3.00 in. (51 - 80 mm)
3.01 - 4.75 in. (81 - 120 mm)
over 4.75 in. (120 mm)
0.007 in. (180 �m)
0.009 in. (225 �m)
0.011 in. (280 �m)
0.0025 in./in. diameter (2.5 �m/1.0 mmdiameter)
Dual Seal, pressurized or
unpressurized, any edition
All 0.025 in. (635 �m)
ANSI Pump All 0.025 in. (635 �m)
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TABLE A-2SEAL CHAMBER PRESSURE ESTIMATION BASED ON PUMP TYPE
In all the following equations:
� P1 = pump suction pressure,
� dP = normal pump differential pressure, and
� Psc = Sealing chamber pressure.
Pumps are assumed to have normal API clearance throat bushing.
1. Horizontal, Overhung, Single stage, no balance holes.
Psc = P1 + 0.3 dP or
Psc = P1 + 50 psi (345 kPa) whichever is lower.
2. Horizontal, Overhung, Single stage, WITH balance holes.
Psc = P1 + 0.1 dP or
Psc = P1 + 10 psi (69 kPa) whichever is lower.
3. Horizontal, Between bearing, single impeller double inlet.
Psc = P1 + 0.1 dP or
Psc = P1 + 10 psi (69 kPa) whichever is lower.
4. Horizontal, multistage with balance line between seal chambers at each end.
Suction End:
Psc = P1 + 0.1 dP or
Psc = P1 + 10 psi (69 kPa) whichever is lower.
Non Suction End:
Psc = P1 + 0.5 dP or
Psc = P1 + 100 psi (690 kPa) whichever is lower.
5. Vertical single impeller less than 3600 rpm with no balance holes, API Plan 11 and 13.
Psc = P1 + 0.9 dP with API Plan 11 and 13.
6. Vertical single impeller less than 3600 rpm with balance holes with API Plans 11 and 13.
Psc = P1 + 0.4 dP with API Plan 11 and 13.
7. Vertical single impeller greater than 3600 rpm.
Psc = P1 + 0.55 dP with API Plan 11 and 13.
8. Vertical multistage API Plan 11 and 13.
Psc = P1 + 0.25 dP or
Psc = P1 + 100 psi (690 kPa) whichever is lower.
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FIGURE A-1FLOW FACTOR FOR CLOSE CLEARANCE BUSHINGS
Differential Pressure (psi)
Conversion: 1 psi = 6.895 kPa
1 10 100 1000
0.1
1
10
100
(From Dura Seal Manual; Reproduced with Permission of FlowServe Corporation)
1000
0.025" Diametral Clearance
0.020" Diametral Clearance
0.015" Diametral Clearance
0.010" Diametral Clearance
0.005" Diametral Clearance
DP15FA1
TABLE A-3BUSHING LENGTH FACTOR
LENGTH (in.) FACTOR
0.250 2.00
0.375 1.60
0.500 1.40
0.625 1.30
0.750 1.20
0.875 1.10
1.000 1.00
1.250 0.90
1.500 0.80
1.750 0.75
2.000 0.70
2.500 0.65
3.000 0.60
Conversion: 1 in. = 25.4 mm
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EXAMPLE OF LEAKAGE CALCULATION IN THE EVENT OF PUMP SEAL FAILURE
Information Available
Pump = Horizontal, overhung single impeller pump build to API 610 Eight Edition.
Shaft diameter = 2.5 in. (63.5 mm).
Shaft Sealing = Type A, Plan 11 seal with no balance hole.
Operating speed = 1780 rpm.
Suction Pressure = 50 psig (345 kPa).
Discharge Pressure = 110 psig (760 kPa).
Seal failure is assumed to occur while pump is in operation.
Pump product is water.
Solution
1. From Table A-1 the Throttle Bushing Diametral Clearance for the above pump is 0.009 in. (225 �m).
2. Determine the Actual Throttle Bushing Length from actual part or seal drawing if available. If not available, use 0.25 in.(6.4 mm). In this example, assume 0.25 in. (6.4 mm).
3. From Table A-2 the Seal Chamber Pressure (Psc) is the lower of:
50 + 0.3 x (110-50) = 68 psig (470 kPa), or 50 + 50 = 100 psig (690 kPa)
Psc, therefore, is 68 psig (470 kPa).
4. From Figure A-1, with differential pressure between Psc and ambient of 68 psi (470 kPa) and Throttle Bushing
Diametral Clearance of 0.009 in. (225 �m), the Flow Factor is approximately 2.
5. Using Table A-3, the Bushing Length Factor is 2 for a Bushing Length of 0.25 in. (6.4 mm).
6. From Eq. (A-1), therefore, the Leakage Rate (gpm) is approximately:
gpm = Flow Factor X Bushing Length Factor X in. Diameter of Shaft
= 2 x 2 x 2.5
= 10 gpm (2.3 m3/hr)
If the viscosity of the hydrocarbon is below 75 SSU (14 cSt), use Eq. (A-1) without any viscosity correction and realize that theexpected leakage will probably be somewhat less than predicted.
If the viscosity of the hydrocarbon is above 150 SSU (32 cSt), use Eq. (A-1), multiply the result by 0.12, and realize that theexpected leakage will probably be somewhat less than predicted.
