Emergency Shutdown and Blowdown Valves - Nao-spc-d-pf-002

TALISMANE N E R G y

NAO ENGINEERING SPECIFICATIONS - PIPING FOR FACILITIES

EMERGENCY SHUTDOWN AND SLOWDOWN VALVESNAO-SPC-D-PF-002

EMERGENCYSHUTDOWN ANDSLOWDOWN VALVESIssue: 2011/01/01

Next Review Date:June 2011 Published by:

HSE/OI Staff Responsible: Talisman Energy Inc.Mechanical Technical Authority Operational Integrity Department

APPROVALS:Calgary

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VP-HSEOI: a retrieval system, or transmitted, in any form ormeans, without the prior written permission ofTalisman, or as expressly permitted by law.

Note: This is an existing specification currently being used by Talisman and has not beentechnically reviewed or signed off by the Technical Authority at this time. Over time, thesespecifications will be rebuilt and validated through a specification review process. Pleaseensure that you use the most current copy of the specs listed on the NAO Portal underEngineering Specifications. The Technical Authority identified on the cover sheet is the point ofcontact for this specification.

Attention: Paper copies are uncontrolled. This copy is valid only at time of printing, 12/15/2010.The controlled document is available on the Talisman NAO Portal.

Attention: Paper copies are uncontrolled. This copy is valid only at time of printing, 12/15/2010.The controlled document is available on the Talisman NAO Portal.

mTALISMANWorleyParsons ENE R G Y

resources & energy

GUIDELINEEMERGENCY SHUTDOWN AND BLOWDOWN VALVES

TABLE OF CONTENTSTABLE OF CONTENTS ...............................................................................................................................111

LIST OF FIGURES .......................................................................................................................................111

INTRODUCTION............................................................................................................................1

ESD VALVES.................................................................................................................................2

1.

2.

2.1

2.2

2.3

2.4

3.

3.1

3.2

Location of ESD valves.................................................................................................................. 2

Hydraulic vs. Pneumatic ESD Valve Actuators.............................................................................. 3

ESD Valve Hydraulic Circuitry .......................................................................................................4

ESD Valve Sizing ...........................................................................................................................6

BLOWDOWN VALVES.................................................................................................................. 7

Locating Blowdown Valves............................................................................................................ 7

Sizing Blowdown Valves................................................................................................................ 8

LIST OF FIGURESFigure 1: SCHEMATIC FOR BETTIS PRESSUREGUARD HYDRAULIC ESD SYSTEM ...........................5

EcoNomicsIncorprating Colt Engineering

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1. INTRODUCTION

This document describes the recommended design standards for emergency shutdown (ESD) valves andblowdown valves for the design of Talisman wellsites and facilities. The section on ESD valves is limitedto hydraulic and pneumatic types, as these comprise the vast majority of those used in the Talismansystem.

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2. ESD VALVESAn ESD (emergency shutdown) valve is a valve equipped with a spring return actuator, such that whenthe actuator pressure signal is released the valve is forced closed by the actuator spring. Generallyspeaking, ESD valves are quarter turn actuated ball valves, but they can also be sliding stem gate valvesor other types, although these are less common. The actuator types considered in this document arehydraulic or pneumatic. The actuator pressure signal can be tripped by a mechanical pilot assembly, asolenoid valve, or a combination of the two.

ESD valves are used to isolate the facilities in emergency situations. For single well tie-ins, a wellheadESD valve is usually suffcient. If the well is sour and fed with fuel gas for a line heater, then there shouldalso be a fuel gas ESD valve to shut off the fuel supply in the event of a line heater building fire. Onsingle well tie-ins, there is generally no need for an outlet ESD valve, as these installations usually arenot equipped with auto blowdown valves. Whenever an auto blowdown valve is added to a system, theoutlet check valve should be accompanied by an outlet ESD valve.

2.1 Location of ESD valves

Wellhead ESD valves should be placed close to the wellhead; generally a 5 m removable spool is placedbetween the ESD valve and the wellhead to facilitate dismantling the high line for downhole wirelineservice work.

On larger facilities, the ESD valves should be placed near the pipeline riser, with 15 meters separationbetween the ESD valves and the closest process building. The idea is to create an ESD "boundary",whereby all the piping and vessels on the "facility side" of the ESD valves would be de-pressured in anemergency condition and the ESD valve is located far enough away from probable fire areas to ensurethe valve is not enveloped in the fire. The risers would remain pressurized. Ideally, all of the risers wouldbe clustered in a common area close to one side of the facility lease, and the surface area of piping thatwould remain pressurized in an emergency condition would be minimized. This idealized layout is notalways practical to achieve. Depending on the piping layout, it may be advisable to clad the exposedpressurized piping with fireproof insulation to mitigate risk to this piping in an ESD condition if theidealized layout can not be achieved.

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2.2 Hydraulic vs. Pneumatic ESD Valve Actuators

If a reliable pneumatic medium is available, pneumatic actuators should be used in preference tohydraulic actuators because they are less expensive, more reliable, cleaner, and simpler. "Reliablepneumatic medium" must be instrument air from a system equipped with a proper air dryer, or pipelinespec sweet fuel gas (dehydrated to 4 Ib water per MMSCF or dryer). Note that any system that usesprocess gas as the pneumatic instrument medium, such as sweet single well tie-ins, will not qualify forthis definition of "reliable pneumatic medium". In these cases the ESD actuators must be hydraulic,UNLESS the ESD valve in question is located inside the heated facility building.

The one advantage of hydraulic actuators is that they do not require an instrument operating medium,and can therefore be used at sites that do not have instrument air or fuel gas. Also, the hydraulic fluid istotally impervious to cold temperature. The disadvantage of hydraulic systems is that they are reliant ona perfect seal in the actuator, leak free check valves on the hydraulic pump, and leak-free tubing from thehydraulic pump to the actuator. If a leak develops in a hydraulic system, the actuator spring will push thehydraulic fluid out of the leak, and this leaking hydraulic fluid will cause the valve to "creep" closed. Thisleak may also be a clean-up issue. Small hydraulic leaks can be managed by having the operatorsregularly pump the actuator back up to keep the valve open, and mopping up as needed with rags.

In a pneumatic system, small leaks are replenished by the pneumatic supply on a continual basis, andthe leak does not spill material on the ground. From this standpoint the pneumatic system is superior.

Another advantage of hydraulic systems is that each stroke of the pump handle will move the valve apredictable few degrees, and on smaller systems the hydraulic ESD valve would not require a car sealedclosed bypass. The same can not be said of pneumatic ESD valves. Generally speaking, pneumaticESD valve's should have a bypass to equalize the pressure across the valve prior to opening, unless thesystem is small and there is a means of throttling flow elsewhere on the piping system.

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2.3 ESD Valve Hydraulic Circuitry

Detailed design of hydraulic ESD circuitry is generally beyond the scope of this document. However, oneaspect of hydraulic ESD circuitry bears mention because there is chance of making the ESD circuitcompletely unresponsive with the prescribed design. Refer to Figure 1, Schematic for the Bettis''PressureGuard'' hydraulic ESD System. The system shows a solenoid valve (20) between a highllowhydraulic pressure switch (14) and the reset valve (23). The reset valve is a latching relay that can bereset to enable the ESD valve to be pumped open before the conditions on the system are satisfied forthe highllow pressure switch. A reset valve of this type is quite normal, as you would otherwise run into a"catch 22" where you can't open the ESD valve because pressure is too low, but you need to establishminimum pressure by opening the ESD valve. However, the problem with the design as drawn is thatunless the solenoid valve is energized, the high/low pilot would be shut out of the system. A betterdesign would be to install the solenoid valve (20) on the hydraulic feed to the highllow pilot, between theaccumulator (27) and the reset valve (23). See Figure 1 below. The reason for modifying the vendor'srecommended design is that their design would disable the ESD system if the operations people did notenergize the solenoid valve before jacking the ESD valve open. The recommended procedure requiresthe reset valve to be latched to enable the actuator to be opened. If the solenoid valve is not energized,then this latching relay will never "arm" itself even when pressure comes up to normal to arm the pressurepilot. If the pressure then goes above the high trip on the pilot, the system is not going to respond andthe ESD safety feature is disabled.

If on the other hand the solenoid valve is placed upstream of the reset valve, the procedure would be tofirst energize the solenoid valve, then latch the reset valve, and then pump the valve open. Energizingthe solenoid valve with pressure below the low pressure shut down should be a feature that would beprogrammed into the site control system. Low pressure shut down should be configured as a class Cshut down, which means that the control system ignores low pressure until system pressure rises abovethe trip point, after which the shut down is enabled. In this case, both the site control system (PLC orRTU or electric relay panel) and the hydraulic pressure pilot would be activated as soon as systempressure rises above the low trip points, and it would never be possible to inadvertently shut out thepressure switch and disable the ESD functionality.

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FIGURE 1: SCHEMATIC FOR BETTIS PRESSUREGUARD HYDRAULIC ESD SYSTEM

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2.4 ESD Valve Sizing

The ESD valve generally matches line size. Wellhead ESD valves should always be full port valves, asthese types would be less prone to erosion damage from sand that may come up hole. Port sizes onother ESD valves would match what one would use on manual isolation valves on the same line. Forexample, if it is acceptable to use a reduced port ball valve for a manual isolation valve on a line, then theESD valve would also be a regular port valve. In some cases, such as larger piping systems, it may beacceptable to reduce down to the next line size for the valve, but in this case the process engineer shouldcheck flowing fluid velocities and ensure that a reduced size will be acceptable.

The pressure rating of the valve matches the highest line classification that the valve is connected to.The actuator sizing is done by Instrumentation, but the process engineer should check to ensure that themaximum differential pressure used for sizing the actuator matches the full cold flange rating of thehighest pipe classification. This ensures that the ESD valve can be re-used for any application thatmatches the pipe classification when the facility is abandoned or modified.

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3. BLOWDOWN VALVES

Blowdown valves are fail-open valves that allow the piping system to be de-pressured in an emergencycondition. The actuator on the valve is usually a pneumatic actuator, tripped by either a pneumatic pilotor a solenoid valve. The trip device (pneumatic pilot or solenoid valve) is configured such that loss ofsignal to the device will vent the blowdown valve actuator, causing the valve to go to its fail position.

The valve is usually a control valve, although an actuated ball valve can be used. The advantage ofusing a control valve is that the blowdown rate can be accurately predicted based on the wide open flowcoefficients as published by the valve manufacturer. If a ball valve is used as a blowdown valve, arestriction orifice should be installed between the downstream valve flange and the pipe flange tocreate a predictable flow through the valve.

3.1 Locating Blowdown Valves

Blowdown valves should be located so that all segments of piping and vessels between the inlet andoutlet ESD valve's are de-pressured, with no pockets of pressurized piping remaining. This requires athorough review of the system P&ID to determine where blowdown valves need to be added, along withconsideration of all possible scenarios that might arise during the emergency condition.

For example, consider a simple compressor installation consisting of an inlet ESD valve, an inlet controlvalve, a separator, a compressor package, and an outlet ESD valve. Let's say that the compressorpackage is equipped with an auto blowdown valve. However, it is located upstream of the unit checkvalve, and would therefore not serve to de-pressure the piping from the unit check valve to the outlet ESDvalve. This would mean it would be necessary to add an auto blowdown valve to the piping between theunit check valve and the outlet ESD valve.

Under normal operation, when the compressor is running, these two blowdown valves would serve to de-pressure all piping between the inlet and outlet ESD valve's. However, let's say the compressor packagecan be double block and bleed isolated from the separator in order to perform maintenance. (The idea isto save the gas in the separator, so it is not blown down during maintenance.) Now if an ESD conditionarose during the time when the compressor was isolated for maintenance, the two blowdown valvesmentioned above (one in the compressor package, the other on the outlet line upstream of the outlet ESDvalve) would not be able to blow down the site as needed, so another blowdown valve would be added tothe separator package to blow it down.

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One could assume that the segment of piping from the inlet ESD valve to the inlet control valve would bede-pressured by the separator blowdown valve. One could specify that this control valve remains onpressure control during the blowdown sequence, and as long as the signal and pneumatic supply to theinlet control valve were in tact, this assumption would be true. Usually, however, the inlet control valve isfail closed. One could not guarantee that the signal and pneumatic supply would remain in tact during theESD condition. Therefore, it would be necessary to add either a blowdown valve on the inlet pipingbetween the inlet ESD valve and inlet control valve, or a fail open bypass around the inlet control valve toenable this piping to blow down via the separator blowdown valve in an emergency condition. If there is aspec break at the inlet control valve, the fail open bypass should be sized such that the wide opencapacity is not greater than the vessel PSV capacity at the highest possible pressure upstream of thecontrol valve. In some cases, the inlet control valve is located close to the inlet ESD valve. In thesecases, it is not necessary to add a blowdown valve or fail open auto bypass around the inlet control valve,but consideration should be given to having a manual bypass and pressure gauges to confirm if thesystems have been de-pressured.

3.2 Sizing Blowdown Valves

The blowdown valves are sized based on two constraints: flare system capacity and time to blowdown.

3.2.1 Flare System CapacityDuring an ESD event, one assumes that all of the blowdown valves open at the same instant in time.The peak flow to flare can be modeled using Aspen Flare System Analizer (formerly Flarenet), and theflow specified for each blowdown valve would correspond to the wide open flow capacity of the blowdownvalve at the maximum system operating pressure. This creates a large initial peak flow rate to flare,which must be within the allowable flow capacity of the flare system. In some cases, with existing flaresystems, it may be necessary to stage the opening of blowdown valves or installing travels stops to limitthe maximum opening of the blowdown valve in order to limit the instantaneous rate such that the peakcapacity of the existing flare system capacity is not exceeded. Another consideration is that theblowdown valve on a separator or other vessel should not exceed the maximum gas capacity of theseparator or vesseL.

Most of Talisman's newer compressor packages are equipped with electronic control panels thatautomatically open the compressor recycle valve on unit shut down. This creates a condition where thepressure in the compressor system settles out to an average pressure that is higher than normal suctionpressure, but substantially lower than the normal discharge pressure. This would in turn result in muchlower pressure at the inlet of the compressor blowdown valve, and hence much less flow. However, forthe purposes of calculating the initial peak flow rate to flare, this settle-out phenomenon should beignored, as we can't guarantee that the recycle valve opens quicker than the blowdown valve.



The maximum possible system operating pressure is something that the individual process engineershould assess and make reasonable judgments on a case by case basis. By illustrative example, let'sconsider the separator/compressor scenario discussed in section 2.1 above. On a compressor, themaximum possible discharge pressure should be taken as the high discharge pressure shut down setting.The maximum suction pressure would correspond to the highest set point of the pressure controller onthe inlet control valve, which should be determined by the compression engineer, as it is dependent oncylinder loading.

3.2.2 Time to BlowdownThe other design parameter regarding blowdown valve sizing is time to blowdown. The standard forblowdown time is to follow API STD521, which indicates "de-pressured rate to achieve 100 psig or 50percent of vessel design pressure, whichever is lower, in 15 minutes or less".

The time to blowdown from a given pressure can be estimated using the spreadsheet "IBU-TLM-CLC-EM-PE-003 Depressuring Time.xls located at SharePoint\Prime Operating Manual\StandardCalculations\Engineering Management - Process. Note that this spreadsheet includes a feature wherebythe valve percent open can be specified. In most cases this would be 100 percent. In some cases, theblowdown rate must be limited by the use of actuator travel stops, which limit the opening of the valve bythe setting of the stop. If possible, the system should be designed without travel stops. Travel stopsintroduce a possibility of operator intervention such that the capacity of the system would be exceeded,and also add cost. A valve with a certain orifice size is much more difficult to tamper with and from thisstandpoint is more desirable in order to ensure that we don't exceed flare capacity.

For purposes of estimating the blowdown time (NOT FOR DETERMINING THE PEAK RATE OF THEVALVE), the settle out pressure should be used as valve inlet pressure in a compressor situation(provided it is certain that the recycle valve opens on compressor shut down). This is because the timerequired to open both the blowdown valve and the recycle valve is small in relation to the time needed tode-pressure.

The other pertinent parameter to specify for using this spread sheet is the system volume. For purposesof estimating blowdown times, assume that any separators or scrubbers are empty. This would give aconservative blowdown time, as any liquid would reduce the volume of gas present. Piping volumes canbe estimated by estimating total length from the piping GA's or plot plan. If the project is being done inAutoplant, the piping designer can provide an accurate estimate of piping lengths by line number. Usefulspreadsheets for determining the vessel volumes are:

"IBU-TLM-CLC-EM-PE-006 Horizontal Vessel Volume" located at SharePoint\Prime OperatingManual\Standard Calculations\Engineering Management - Process

"IBU-TLM-CLC-EM-PE-007 Vertical Vessel Volume" located at SharePoint\Prime OperatingManual\Standard Calculations\Engineering Management - Process


Emergency Shutdown and Blowdown Valves - Nao-spc-d-pf-002

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