PRV Set Point Accuracy

ASME NRC Pump & Valve Symposium July 2008

Presenter: Chad Dupill

ReferencesReferences

The American Society of Mechanical Engineers The American Society of Mechanical Engineers (ASME) Pressure Relief Devices Performance (ASME) Pressure Relief Devices Performance Test Code 25Test Code 25--2001 (PTC 252001 (PTC 25--2001)2001)The National Board Inspection Code (NBIC)The National Board Inspection Code (NBIC)Plant testimonials Plant testimonials –– A special thanks to J. Alton Cox (Vice Chairman, NBIC A special thanks to J. Alton Cox (Vice Chairman, NBIC

SubSub--Group Pressure Relief Devices) for his Group Pressure Relief Devices) for his contributions in guidance, and experience.contributions in guidance, and experience.

DefinitionsDefinitionsDefinitionsDefinitionsNOTE: For the purpose of this paper we are going to define the NOTE: For the purpose of this paper we are going to define the following as:following as:High Volume test benchHigh Volume test bench –– PRV Test device with at a minimum capacity volume of 28 Liter [PRV Test device with at a minimum capacity volume of 28 Liter [1 1 cubic foot] test vessel and a minimum piping (between the Test Vcubic foot] test vessel and a minimum piping (between the Test Vessel and the Test Connection essel and the Test Connection for the Valve being tested) diameter of 5 cm [2 inches]. for the Valve being tested) diameter of 5 cm [2 inches]. Low Volume test benchLow Volume test bench –– PRV Test device with a test vessel less than 28 Liter [1 cubic PRV Test device with a test vessel less than 28 Liter [1 cubic feet] and feet] and a piping diameter (between the Test Vessel and the Test Connectia piping diameter (between the Test Vessel and the Test Connection for the Valve being tested) on for the Valve being tested) of less than 5 cm [2 inches]. of less than 5 cm [2 inches]. Set PressureSet Pressure –– The value of increasing inlet static pressure at which a pressuThe value of increasing inlet static pressure at which a pressure relief device re relief device displays one of the operational characteristics as defined underdisplays one of the operational characteristics as defined under opening pressure, popping opening pressure, popping pressure, startpressure, start--toto--leak pressure, burst pressure, or breaking pressure. (The applileak pressure, burst pressure, or breaking pressure. (The applicable operating cable operating characteristic for a specific device design is specified by the characteristic for a specific device design is specified by the device manufacturer.) PTC 25device manufacturer.) PTC 25--20012001Opening PressureOpening Pressure –– The value of increasing inlet static pressure of a PRV at whichThe value of increasing inlet static pressure of a PRV at which there is a there is a measurable lift, or at which the discharge becomes continuous asmeasurable lift, or at which the discharge becomes continuous as determined by seeing, feeling, determined by seeing, feeling, or hearing. (For liquid Service) PTC 25or hearing. (For liquid Service) PTC 25--20012001Popping PressurePopping Pressure –– The value of increasing inlet static pressure at which the diskThe value of increasing inlet static pressure at which the disk moves in the moves in the opening direction at a faster rate as compared with correspondinopening direction at a faster rate as compared with corresponding movement at higher or lower g movement at higher or lower pressures. PTC 25pressures. PTC 25--20012001StartStart--toto--Leak PressureLeak Pressure –– The value of increasing inlet static pressure at which the firsThe value of increasing inlet static pressure at which the first bubble t bubble occurs when a PRV is tested by means of air under a specified waoccurs when a PRV is tested by means of air under a specified water seal on the outlet. PTC 25ter seal on the outlet. PTC 25--20012001ChatterChatter –– abnormal rapid reciprocating motion of movable parts of a pressabnormal rapid reciprocating motion of movable parts of a pressure relief valve in ure relief valve in which the disk contacts the seat. PTC 25which the disk contacts the seat. PTC 25--20012001First Steady StreamFirst Steady Stream –– Set pressure for liquid Service Pressure Relief Valves. When gSet pressure for liquid Service Pressure Relief Valves. When gravity ravity overcomes cohesion the water drops straight off the Pressure Relovercomes cohesion the water drops straight off the Pressure Relief Valve outlet; an observable, ief Valve outlet; an observable, repeatable Phenomenon. NB 18repeatable Phenomenon. NB 18CohesionCohesion –– the attraction of like moleculesthe attraction of like moleculesNote: For the purposes of this paper Test Bench, Test Device, TNote: For the purposes of this paper Test Bench, Test Device, Test Stand, and/or Test Unit are est Stand, and/or Test Unit are interchangeable.interchangeable.

IntroductionIntroduction

Testing methods and devices vary widely Testing methods and devices vary widely within the industry when testing for the within the industry when testing for the set point of Pressure Relief Valves. set point of Pressure Relief Valves. Testing devices within Nuclear Plants Testing devices within Nuclear Plants range from:range from:–– Shop built devicesShop built devices–– Hand PumpsHand Pumps–– Manufacturer built test devicesManufacturer built test devices–– OthersOthers

PurposePurpose

To discuss some of the different design To discuss some of the different design characteristics and how those design characteristics and how those design characteristics can affect your set point characteristics can affect your set point when testing for the set point of Pressure when testing for the set point of Pressure Relief Valves in both gas and liquid Relief Valves in both gas and liquid service. service.

OverviewOverview

Importance of following NBIC and ASME PTC-25-2001 recommendations on Internal Contours of Fittings, Adapter’s, and Reducers between Test Vessel and Test DeviceRecommended Volume CapacityRecommended Volume Capacity–– PRV Seat AlignmentPRV Seat Alignment

Air EvacuationAir Evacuation

Internal Contours of Fittings, AdapterInternal Contours of Fittings, Adapter’’s, and s, and Reducers between Test Vessel and Test DeviceReducers between Test Vessel and Test Device

ASME PTC 25ASME PTC 25--2001 states that 2001 states that ““The pressure relief device to be The pressure relief device to be tested shall be installed on a test vessel with adapter fittingstested shall be installed on a test vessel with adapter fittings(flanged, screwed, welded, etc.).(flanged, screwed, welded, etc.).””The NBIC also states that The NBIC also states that ““any intervening piping between the test any intervening piping between the test vessel and the pressure relief valve should be as short and stravessel and the pressure relief valve should be as short and straight ight as possible and be of adequate size to minimize inlet pressure as possible and be of adequate size to minimize inlet pressure drop.drop.””ASME PTC 25ASME PTC 25--2001 goes on to state that 2001 goes on to state that ““Other adapter fittings Other adapter fittings may be used provided may be used provided the accuracy of the test is not affectedthe accuracy of the test is not affected..””ASME PTC 25ASME PTC 25--2001 and the NBIC recommend that when testing a 2001 and the NBIC recommend that when testing a PRV on a test bench the piping, adapters, and fittings leading uPRV on a test bench the piping, adapters, and fittings leading up to p to the test valve need be taken into account in order to minimize tthe test valve need be taken into account in order to minimize the he pressure drop as well as minimize the affect of flow turbulence pressure drop as well as minimize the affect of flow turbulence on on the final test results.the final test results.

PTC 25PTC 25--2001 Recommended Internal 2001 Recommended Internal Contours of fittings, adapters, and reducersContours of fittings, adapters, and reducers

PTC 25PTC 25--2001 Recommended Arrangements 2001 Recommended Arrangements for Testing Valves with Incompressible fluidsfor Testing Valves with Incompressible fluids

Tapered Inlet Adaptor

Test Plate

Test Plate

Sharp Corner Adaptor

Sharp Corner

Test PlateAir Flow

Sharp Corner on Inlet may cause turbulence in flow path and result in poor performance from SRV including Flutter or Chatter.

Tapered Inlet

Test Plate

Radius on Inlet eliminates turbulence in flow path and results in consistent performance from SRV without Flutter or Chatter.

Air Flow

Recommended Volume CapacityRecommended Volume Capacity

Test vessels, piping size, and the size of test port vary to Test vessels, piping size, and the size of test port vary to a large degree a large degree –– DeLucaDeLuca Test standard model test benches are offered with 56 Test standard model test benches are offered with 56

Liter [2 cubic foot] stainless steel test vessel, 7.6 cm [3 inchLiter [2 cubic foot] stainless steel test vessel, 7.6 cm [3 inch] ] piping and test port piping and test port

–– well known Test bench manufacturerwell known Test bench manufacturer’’s PRV test benches is s PRV test benches is offered standard with a 4 liter [less than .2 cubic feet], 1.3 coffered standard with a 4 liter [less than .2 cubic feet], 1.3 cm m [[½½ inch piping] and test port inch piping] and test port

Recommended Volume CapacityRecommended Volume Capacity

The size of the vessel, piping, and test The size of the vessel, piping, and test port affects the volume that the test port affects the volume that the test bench has the capability to act on the bench has the capability to act on the valve which can affect the results of the valve which can affect the results of the test. test. –– may affect the results of the test specifically may affect the results of the test specifically

when conducting liquid service PRV testwhen conducting liquid service PRV test’’s and s and possibly damage the PRV seat by inducing possibly damage the PRV seat by inducing chatter when testing with air.chatter when testing with air.

Recommended Volume CapacityRecommended Volume Capacity

Liquid Service PRV TestLiquid Service PRV Test–– Visually determining when you have achieved a first steady Visually determining when you have achieved a first steady

stream stream –– If the test bench being utilized does not have sufficient volumeIf the test bench being utilized does not have sufficient volume it it

can be difficult for the operator to determine when they are can be difficult for the operator to determine when they are actually achieving set pressure. actually achieving set pressure.

–– it can be very difficult, on a low volume test bench, to it can be very difficult, on a low volume test bench, to differentiate between a differentiate between a ““PrePre--leakleak”” where cohesion causes the where cohesion causes the water to curve back toward the PRV inlet (which is not the PRV water to curve back toward the PRV inlet (which is not the PRV opening pressure) and a first steady stream. opening pressure) and a first steady stream.

Liquid Service PRV TestingLiquid Service PRV Testing*It is necessary to have sufficient volume and flow path*It is necessary to have sufficient volume and flow pathto accurately perform liquid service PRV Testing to accurately perform liquid service PRV Testing

““First Steady StreamFirst Steady Stream””

LIQUID SERVICE PRV

INLET

OUTLET

PIPE NIPPLE

Opening Pressure

When Gravity overcomesCohesion, the Water dropsStraight off the PRV outlet.This is Set Pressure. It is an observable, repeatablePhenomenon.

Preleak

Recommended Volume CapacityRecommended Volume Capacity

TestimonialsTestimonials–– Rich Booth, with Vermont Yankee, has experience with both Low anRich Booth, with Vermont Yankee, has experience with both Low and d

High volume test benches and stated that:High volume test benches and stated that:““Accuracy and repeatability of new relief valve test equipment (HAccuracy and repeatability of new relief valve test equipment (High igh Volume) exceeds the capabilities of the old equipment (low volumVolume) exceeds the capabilities of the old equipment (low volume test e test unit). A three (3) inch test bench port and accumulator now prounit). A three (3) inch test bench port and accumulator now provides the vides the volume to control relief valve lift at set point more accuratelyvolume to control relief valve lift at set point more accurately versus the versus the previous reciprocating pump test bench and 3/8 inch tube. The lprevious reciprocating pump test bench and 3/8 inch tube. The low volume ow volume test bench could in some instances only test bench could in some instances only ““burpburp”” the valve before dropping the valve before dropping below the lift point. Determination of manufacturerbelow the lift point. Determination of manufacturer’’s set points (i.e. first s set points (i.e. first steady stream) was subjective, susceptible to inconsistencies ansteady stream) was subjective, susceptible to inconsistencies and sometimes d sometimes not achievablenot achievable””..

–– Gary Caudill with VC Summer is also a strong proponent of high vGary Caudill with VC Summer is also a strong proponent of high volume olume testing:testing:

Has seen improved results by using his high volume test bench (3Has seen improved results by using his high volume test bench (3 inch inch diameter piping along with a 4 cubic foot Stainless Steel test vdiameter piping along with a 4 cubic foot Stainless Steel test vessel) when essel) when compared to the previous method of testing with a low volume tescompared to the previous method of testing with a low volume test bench. t bench.

PRV Seat AlignmentPRV Seat AlignmentOne of the primary issues with performance within a PRV design iOne of the primary issues with performance within a PRV design is s Seat alignment Seat alignment Seat and Disc alignment is critical for PRV performanceSeat and Disc alignment is critical for PRV performanceOEMs routinely employ radial surfaces called OEMs routinely employ radial surfaces called ““bearing pointsbearing points””Allows for movement between the disc and the disc holder Allows for movement between the disc and the disc holder (commonly referred to as (commonly referred to as ““disc rockdisc rock””))Following a bench test or system pressure excursion, movement Following a bench test or system pressure excursion, movement allows disc to reallows disc to re--align with the nozzle upon reseat forming a tight align with the nozzle upon reseat forming a tight sealsealLow Volume Test Benches do not generate the lifting forces Low Volume Test Benches do not generate the lifting forces required to permit the disc to realign upon closure required to permit the disc to realign upon closure Consequently result in a leaking PRV Consequently result in a leaking PRV PRV may have come out of the system tight, but as a result of a PRV may have come out of the system tight, but as a result of a low low volume test bench, the volume test bench, the ““as foundas found”” condition is condition is ““leaking below set leaking below set pointpoint””

PRV Seat AlignmentPRV Seat Alignment

Alton Cox (NBIC SubAlton Cox (NBIC Sub--Group Pressure Relief Group Pressure Relief Devices) recently participated in a liquid test Devices) recently participated in a liquid test with an ASME Consultant for a with an ASME Consultant for a ““UVUV”” Certificate Certificate Holder which highlights the importance of Holder which highlights the importance of volume in regards to PRV seat alignment. volume in regards to PRV seat alignment. –– Alton stated that they Alton stated that they ““had to gush a liquid PRV had to gush a liquid PRV ……. to . to

get it to stop leaking. We had 31 drops per minute get it to stop leaking. We had 31 drops per minute (allowable was 2.5 (allowable was 2.5 dpmdpm) after three successful lifts. ) after three successful lifts. Then we gushed the valve (sent into overpressure) Then we gushed the valve (sent into overpressure) and the PRV had zero drops after that.and the PRV had zero drops after that.””

Air Evacuation Air Evacuation The The ““Air BubbleAir Bubble”” trapped in the nozzle between the disc and the trapped in the nozzle between the disc and the water water Causes the first Test to give an inaccurate readingCauses the first Test to give an inaccurate readingThe trapped air beneath the seat of a PRV installed on a test beThe trapped air beneath the seat of a PRV installed on a test bench nch skews the first skews the first ““As FoundAs Found”” testtestGoal: Utilize the first pop as an actual documented Set Point Goal: Utilize the first pop as an actual documented Set Point Reading Reading Eliminate the Air pocket Eliminate the Air pocket Compressed Air generates a Compressed Air generates a ““burpburp”” of compressible fluid just ahead of compressible fluid just ahead of the liquid which follows it out of the PRV (Pre Conditioning)of the liquid which follows it out of the PRV (Pre Conditioning)Has the effect of yielding something other than a steady stream Has the effect of yielding something other than a steady stream as as required by PTC 25required by PTC 25““As FoundAs Found”” set point may be different from expectedset point may be different from expected

Test Plate

Liquid Test Liquid Test ––Trapped Air in PRV Nozzle Trapped Air in PRV Nozzle

Liquid Test Media

Air compressed by liquid entering flow path will exhibit “pop” action

on PRV initial lift

Air Evacuation Air Evacuation There are a couple methods commonly used to evacuate There are a couple methods commonly used to evacuate the compressed air out of the PRV prior to initiating the the compressed air out of the PRV prior to initiating the test. test. –– One of these methods is to literally rotate the entire valve andOne of these methods is to literally rotate the entire valve and

clamping station 180 degreeclamping station 180 degree’’s in order to allow the air to escape, s in order to allow the air to escape, sometimes referred to as presometimes referred to as pre--conditioning the valve. conditioning the valve.

This method is effective but can be tedious and time consuming.This method is effective but can be tedious and time consuming.–– Another method commonly used is to implement a test plate Another method commonly used is to implement a test plate

adapter with a bleed valve that is placed in between the test adapter with a bleed valve that is placed in between the test plate itself and the test valve. One then would pressurize the plate itself and the test valve. One then would pressurize the system with the bleed valve open until all of the air is evacuatsystem with the bleed valve open until all of the air is evacuated. ed. After all air is evacuated one would then close the bleed valve After all air is evacuated one would then close the bleed valve and initiate the test. and initiate the test.

–– DeLucaDeLuca incorporates a standard air evacuation tube design incorporates a standard air evacuation tube design developed by Gary Caudill at VC Summerdeveloped by Gary Caudill at VC Summer

Method 3:Method 3:Air EvacuationAir Evacuation

Incorporates a standard Air Evacuation Incorporates a standard Air Evacuation tube design tube design Completely eliminating the air pocketCompletely eliminating the air pocketSaves timeSaves timeValidates the first Validates the first ““As FoundAs Found”” testtest

*Gary Caudill developed idea of the Air Evacuation method currently used by DeLuca to validate the “As Found” Set Pressure Test

Liquid Test Air EvacuationLiquid Test Air Evacuation

WATERSUPPLY

NITROGENSUPPLY

INSERT ¼”PLASTIC

TUBE

REMOVE PLASTIC

TUBE

Open Air Evacuation Valve, Insert Plastic Tube

Air EvacValve

Install Test PRV, Clamp in Position

J-TubeVent

Water Fill

Valve

Open J-Tube Vent and Water Fill Valve

Green Arrow OPENRed Arrow CLOSE

Close Water Fill Valve, Open Bypass ValveWater fills test connection and forces air out tubeWhen water flows out tube, remove tube, close air evac valve

ConclusionConclusionThe National Board Inspection Code along with The The National Board Inspection Code along with The ASME PTC 25ASME PTC 25--2001 provide input and recommendations 2001 provide input and recommendations in regards to bench testing Pressure Relief Valves and in regards to bench testing Pressure Relief Valves and gives a basic guide on test bench layout and gives a basic guide on test bench layout and characteristics. Although these recommendations characteristics. Although these recommendations provide a base to follow they can still be open to provide a base to follow they can still be open to interpretation. These interpretations will be evident in interpretation. These interpretations will be evident in the differences in both the designthe differences in both the design’’s and capabilities of s and capabilities of PRV test benches found throughout the industry.PRV test benches found throughout the industry.PRV test bench users should be at least aware of these PRV test bench users should be at least aware of these differences and the impact they could have on the differences and the impact they could have on the accuracy of their set point results.accuracy of their set point results.

AcknowledgementsAcknowledgements

Richard Booth, Vermont YankeeRichard Booth, Vermont YankeeGary Caudill, V.C. SummerGary Caudill, V.C. SummerJ. Alton Cox, Vice Chairman, NBIC SubJ. Alton Cox, Vice Chairman, NBIC Sub--Group Pressure Relief DevicesGroup Pressure Relief DevicesCurt Dupill, Dupill Group / Curt Dupill, Dupill Group / DeLucaDeLuca Test Test EquipmentEquipmentDean Mathews, Dean Mathews, DeLucaDeLuca Test EquipmentTest Equipment

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