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SEVERE SERVICEVALVE SOLUTIONS
kentintrol
TECHNICAL BULLETINTSS – 0109
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KOSO KENT INTROLSUPPLIES A DIVERSERANGE OF PRECISION-MANUFACTUREDCONTROL, CHOKE,AND ROTARY VALVESFOR OIL AND GAS,PETROCHEMICAL ANDPOWER INDUSTRIES– WORLDWIDE
TABLE OF CONTENTS
– SEVERE SERVICE VALVES 2– SEVERE SERVICE APPLICATIONS 3– ENGINEERING TOOLS 4– MINIMUM FLOW PUMP RE-CIRCULATION VALVE 5– SERIES 51 & 57 TURBOTROL 6– FIRE WATER PROTECTION SYSTEM 7– ROTROL - SERIES 63 TO 66 8– SEPARATOR LEVEL CONTROL VALVES 9– SEVERE SERVICE CHOKE VALVES 10– FLASHING SERVICE 11– EROSION 12– AERODYNAMIC NOISE 13– SILENCERS 14– SURGE CONTROL 15– COMPRESSOR RE-CYCLE / ANTI-SURGE CONTROL VALVES 16– VECTOR LABYRINTH TRIMS 17– PERFORMANCE TESTING 18
PRODUCTRANGE
WWW.KENTINTROL.COM
TOP & BOTTOM-GUIDED CONTROL VALVESOur range of high-performance top and bottom-guided controlvalves includes single and double-seated valves suitable forlow and high-capacity applications, as well as three-way valvesfor mixing or splitting flows. Our control valves are designed tofacilitate pressure drops at all stages of transportation in the oil,gas and power industries. All valves are refined by our engineersto suit the needs of each application and all service conditions.
CAGE-GUIDED CONTROL VALVESThe Series 1200/7200 range of cage-guided control valves isKKI’s core product. The exceptional valves in this rangecombine high-integrity features, such as ASME VIIIbody/bonnet bolting design, a high flow capacity and a widerange of trim designs, from low-noise anti-cavitation tomulti-stage trims. These valves are ideally suited to the criticalservice process control requirements of a wide range ofindustry applications.
SURFACE CHOKE VALVESThe KKI Series 73 surface choke valve offers a unique solutionfor the majority of choke applications in the oil and gasindustry. The flexible valve design can incorporate manydifferent trim and body material options to suit differing flowrates and in-service conditions. Thousands of KKI Series 73surface chokes are installed around the world on projects forsome of the world’s leading oil and gas production companies.
ROTARY CONTROL VALVESThe Rotrol range of high-capacity butterfly valves has beendeveloped to overcome the problems associated with control,cavitation and noise in conventional butterfly valve designs.Lighter in weight and more compact than globe valvealternatives, this innovative valve performs especially well insevere-service applications, where pressure drops tend to behigh in the controlling position but where high-capacitythroughputs at low pressure drops are also required.
SEVERE SERVICE SOLUTIONSFor more than 45 years, KKI has built up a reputation fordelivering valve solutions for the most arduous serviceconditions. We have developed a range of advanced, high-qualitysevere service valve solutions for every type of problematicapplication, from high-pressure, high-temperature environmentsto sub-zero temperatures. Our valves are designed to combatthe effects of cavitation, flashing, erosion, contaminated fluids,corrosion, high velocity, vibration, noise and energy dissipation.
INSTRUMENTSKKI offers a wide selection of sophisticated instrumentation tosupport our comprehensive range of high-performance valvesand actuators. The instruments we supply include pneumaticand electro-magnetic positioners, airsets, volume boostersand airlocks. All instruments are specified to deliver optimumperformance for the service conditions and specific needs ofeach application. We also supply proprietary instruments tosuit individual customer preferences.
ACTUATORSOur range of robust, versatile and reliable pneumatic actuatorsincludes the ‘G’, ‘C’ and ‘D’ Series models. These have beendeveloped to meet the needs of all control valve applications,offering proven design and high reliability. They are usedextensively for on-shore, offshore and power installations. Inaddition, we supply various proprietary actuators – such aselectric, electro-hydraulic, pneumatic stepping and hydraulicstepping actuators – to meet customer requirements. All actuatorscan be supplied with hand-wheels and limit stop features.
TOP & BOTTOM-GUIDED CONTROL VALVES
SINGLE SEATED SERIES 10/71 DOUBLE SEATED SERIES 20 3-WAY MIXING AND DIVERTING SERIES 30
SURFACE CHOKE VALVES ROTARY CONTROL VALVES
INSTRUMENTS
ACTUATORS
SERIES 73 SERIES 60
SERIES C SERIES DSERIES G
SEVERE SERVICE SOLUTIONS
SERIES 1200/7200
CAGE-GUIDED CONTROL VALVES
02
SEVERE SERVICE VALVES
KKI have an unrivalled blend of proven expertise, innovativedesign technology and skilled engineering. This is the motivatingforce behind the development of the KKI range of high qualitySevere Service Control Valves, Surface Choke Valves andButterfly Valves. KKI has been manufacturing Severe ServiceValves for over 45 years.
Whether it is for problematic applications relating to HighPressure, High Temperature, Sub Zero Temperatures,Cavitation, Flashing, Erosion, Solids Contaminated Fluids,Corrosion, High Velocity, Vibration, Noise or EnergyDissipation, KKI has proved it has the solutions. These issuesare discussed in the following sections together with CaseStudies, which present some of the solutions provided by KKIto handle potentially problematic applications. In addition tothis KKI has the proven Koso Vector (velocity control)Labyrinth Disk Stack design in it's product portfolio.
QUALITY MANUFACTURING
Maintaining the higheststandards of qualitythroughout design, productionand customer service is thecornerstone of Koso KentIntrol’s philosophy. Our plant isaccredited in accordance withQuality Management SystemISO 9001 and EnvironmentalManagement System ISO14001. In addition all products,where applicable, conform toATEX, PED and all otherapplicable EU Directives andare CE marked accordingly.
The company’s standardmanufacturing experienceincludes NACE MR01.75,NORSOK, API 6A specificationsand individual customerspecifications. Our in-houseinspection and testing facilitiesinclude hardness testing,NDE, PMI, gas and flowtesting. Safety is the keyelement in everything we do,with all employees undergoingboth general and specificHealth and Safety training.
Fig 01Vector (velocity control)Labyrinth disk stack trim design
Fig 02Turbotrol control valve
SEVERE SERVICEAPPLICATIONS
– Anti Surge – CompressorRecycle
– Pipeline Surge ReliefControl
– Centrifugal Pump MinimumFlow Re-circulation
– Over Board Dump– Fire Water Deluge System – Slug Catcher– Vent to Flare– Separator Level Control– Boiler Feed Water– Emergency Drains– Super Heater Spray– High Pressure HighTemperature (HPHT)
The following is a list of someof the issues that areconsidered in assessing theseverity of an application:
– High Noise– Severe Vibration– High Pressure Drop– Cavitation– Flashing– High Velocity– Contaminated Flow– Erosive / Corrosive Medium– Joules Thompson Effect
Fig 03HFL-3 high performanceMulti-sleeve / Multi-step trim
Fig 04Tungsten carbide plug for heavily contaminated fluids
Fig 06Vector ‘D’ disk – velocity controlLabyrinth trim design
Fig 05Cartridge trim with
Solid Tungsten Carbide Guide
The trims presented on this page are some examples of the SevereService Trims available from Koso Kent Introl.
TECHNICAL BULLETINTSS – 0109
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There is level of “mystique” surrounding specific applications encountered in the control valveindustry. Certain manufacturers try to differentiate themselves by specifying such applicationsas severe service. It should be noted that there is no definitive ruling as to what is and is notsevere service. In reality it really depends on the severity of the operating conditions and on theimportance of the valve to the operation of the plant.
KKI have over the years operated at the leading edge of the oil and gas industry and have assuch encountered ever increasing demands in terms of pressure drop, contamination andincreased flow rates.
In order to handle these arduous applications special selection criteria have been developed. Some applications that are frequently classified as “Severe Service” include:
KKI is committed to providing fully analysed and tested valveproduct for the Severest Service Applications. Our expertengineering staff continually design, develop and test productsto meet the ever-changing needs of the industry whilesupporting products that are already installed and operatingthroughout the world.
Our engineering staff utilise modern engineering tools, such as3D Modelling, Finite Element Analysis, and CFD analysis toensure that the products are designed to the highest level ofintegrity and reliability.
As a result of the continuous Research & Development and theutilisation of the most up to date Engineering Tools, the SevereService Valves supplied by KKI are at the cutting edge ofcontrol and choke valve technology.
ENGINEERINGTOOLS
04
Fig 08Plan view of a valve trim showing the sand particle trajectory
m/s
155
117
79
39
0
Fig 09CFD analysis of a valve trim
Fig 07CFD analysis of 5 stage multi-spline
Fig 10Choke body evaluation using Finite Element Analysis
1.569E-01
9.183E-02
8.478E-02
5.369E-02
1.003E-01
1.390E-01527E-01
The trim in the adjacent photographs illustrates the extremedamage that high levels of cavitation can produce on pumpminimum flow recirculation applications – it can literally tear atrim apart in minutes.
Either incorrect specification of the operating conditions or theincorrect design of trim are the underlying factors in such anapplication. In this particular instance the incorrect outletpressure specified at 6 bar, was in fact atmospheric, resulting inthis extreme level of erosion. The valve operated for only a fewhours before it had to be taken out of service.
The original trim design incorporated 5 stages (10 turns) ofpressure let-down, but the pressure drop apportionment did noteliminate cavitation, due to the much lower downstreampressure. In order to handle this pressure drop and eliminatecavitation, the trim design needed an additional 4 stages oflet-down, giving a total of 14 turns within the existing valvebody design, see HFL-9 Stage Anti-Cavitation trim.
The area increase through the trim resulted in lower pressuredrops in the outlet stages of the trim and thereby eliminatingcavitation, even though the outlet pressure was close toatmospheric. This design is a hybrid of the KKI Turbotrol valvethat is used on similar applications and discussed in thefollowing section.
CASE 1SPECIALIST APPLICATION MINIMUM FLOW PUMPRECIRCULATION VALVE
CAVITATION EXPLAINED
Cavitation is the phenomenonthat can occur in controlvalves on liquid duties. In itsmost severe form cavitationcan destroy a control valvetrim in a matter of hours. It istherefore important to controlthe level of cavitation whenselecting a control valve.
Cavitation occurs on liquidapplications when the fluidstatic pressure firstly reducesbelow the fluid vapourpressure (Pv) andsubsequently rises (recovers)above the fluid vapourpressure. This results firstly inthe creation of small vapourbubbles (cavities).
Subsequently these cavitiescollapse producing localisedshock wave micro-jets. Ifthese impact on the metallicsurface of the valve thensevere pitting and erosiondamage can occur. Acomplete explanation ofcavitation and the KKImethod of calculating theCavitation Index is given inthe Technical SelectionManual TS 20 available atwww.kentintrol.com
Fig 12 and 13Original trim with severecavitation damage
Fig 11HFL-9 stage Anti-Cavitation trim
Pv
P2
Pvc
P1
VALVE INLET VALVE OUTLET
}
STA
TIC P
RESSURE
HIGHRECOVERY
VALVE
9 STAGES (14 TURNS)PRESSURE REDUCTION
CAVITATING FLOW
Fig 14Comparison betweenlow and high recoverytrim designs
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SERIES 51 & 57 TURBOTROLSEVERE SERVICE VALVES
MULTI-SPLINE TRIMSThe multi-spline trim is designed to extend the Turbotrol rangefor high-pressure drop liquid services for applications with lowflow rate requirements. These trims are supplied in valve sizesup to 2" (50mm) diameter. In common with the larger Turbotroltrims, the flow sleeve and plug are constructed as an insert-ablecartridge, with up to 5 stages of pressure drop to ensure thatcavitation does not occur throughout the stated flow range.
The multi-spline trim option has an excellent rangeability. Rangeabilities in excess of 100 to 1 can be achieved due tothe very precise fit of the plug within the seat. The standard trimmaterial is generally Full Stellite Grade 6. However, there arealso the options for tungsten carbide and advanced ceramic forpressure drops greater than 100 bar (1450 psi). Typicalapplications are low flow high-pressure drop services MEGInjection, Methanol Injection & other low flow requirements.
Fig 15Illustration ofa 9 stageTurbotrol trim
Fig 16Illustration of a
Multi-spline trim
TURBOTROL VALVE DESIGN
The patented ‘Turbotrol’ valve design is utilised on very high-pressure drop liquid applications to eliminate the potentiallyerosive effects of cavitation. This design was first introducedby KKI in the mid 1980’s and was specifically developed forminimum flow re-circulation pump protection. This design istypically employed on applications where the pressure droprequirement is in excess of 200 bar and the downstreampressure is close to Pv.
The design incorporates between 4 and 9 stages (9 and 14turns). The flow is directed through a series of radial and axialflow paths, where the fluid is firstly split into many small flowsand then recombines into an axial flow. This occurs repeatedlyas it passes through the trim ensuring controlled dissipation ofthe fluid energy. The control of the velocity through the trimreduces the high wear rates normally associated with highpressure drop applications.
An additional feature of the Turbotrol is the plug seating face,which is protected from the effects of wire-drawing anderosion at low flows. A dead band is introduced adjacent to theseat, which ensures that the seating faces are positionedoutside the high velocity turbulent flow streams prior to theflow stream holes being exposed.
TURBOTROL DESIGN SPECIFICATION– Sizes – 11⁄2” to 8" (40mm to 200mm)– Ratings – ANSI 600 to 4,500 / API 3,000 to 15,000– Design – ISO 10423 / API 6A / API 17D / ANSI B16.34 /ASME VIII
– Standards – PED / ATEX / NACE MR01.75 / ISO 15156 / NORSOK– End Conns. – ISO 10423 / API 6A / API 17D / ANSI Flanges /Hub type connections
– Stages of let-down 4 to 9 (9 to 14 turns)
CASE 2SPECIALIST APPLICATION FIRE WATER PROTECTIONSYSTEM
Diesel firepump
Fire Water controlvalve
Fire wallOverload dump(Atmos, pressure)
Inlet pressure6 bar
10 20 30 40 50 60 70 80 90 100
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
VALVE CV (% OF MAXIMUM)
CAV
ITAT
ION C
OEFF
ICIE
NT
Rotrol vane
Standard vane
Rotrol vane andbaffle plate
Fire waterring main
Ring mainpressure5 bar
The fire water system on offshore platforms, see fig 18, hasproven to be an extremely onerous duty. KKI became involvedin this application when a competitors Butterfly Valve sufferedsevere vibration, resulting in a failure of the system and causinga Health & Safety issue due to the fact that both the sprinklerand deluge system would not function correctly. On closerinspection of the valve, erosion (resulting from cavitation) of thevane, valve body and seating area was discovered.
On investigation it was noted that the valves were originallyspecified to be operating with an inlet pressure of 6 bar and a pressure drop of 1 bar. Following installation it was revealedthat the operating pressure drop under test conditions wassignificantly higher. The pressure drop was actually 5 bar andthe flow rate had increased from 250 to 340 m3/hr. This meantthat the existing Butterfly Valve had a calculated cavitationIndex of + 2.0 bar, which is classified as “severe”.
The photograph below shows the type of damage thatoccurred on this application. The majority of the damage wasto the outer edge of the vane, there was also severe cavitationerosion damage to the valve body.
Although it was clear that a larger globe type valve fitted with alow pressure recovery trim would be suitable for the operatingpressures, the operator required a valve that would fit into theexisting pipework configuration. KKI provided the Rotrol HighPerformance Butterfly Valve as the solution. This product hadundergone extensive tests both on KKI’s water test facility and atBrown Boveri Corporation (Baden) research facility. The special lowrecovery vane enables high-pressure drops to be handled withoutthe onset of cavitation.
A comparison between the respective pressure recoverycharacteristics of a Standard Vane and a Rotrol vane ispresented in Fig 19. The Cavitation Index (CI) for the Rotrolvalve under the most extreme condition was - 0.5 bar. The valvewas installed and operated without the previous problems ofcavitation and unstable control. This valve is now an acceptedsolution to what is still an onerous application.
Fig 18 Fire Water System
Fig 19 Pressure Recovery Comparison
Fig 17Cavitation damage to Butterfly valve
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ROTROL – SERIES 63 TO 66
Fig 20Comparison of pressure recovery betweenLow and High Recovery vane designs
THE ROTROL BUTTERFLY VALVE
The Rotrol Butterfly Valve range was developed to overcome theproblems associated with control, cavitation and noise thatwould otherwise cause premature mechanical wear and failureof components on conventional Butterfly and Ball Valve designs.
The innovative design, refer to Fig 21, incorporates a profiledvane that has cowls on its leading and trailing edges. Thecowls are drilled with a series of holes to allow flow to passthrough the cowl.
Thus, at low valve openings when the cowls are most effectivethe flow passes through these holes, producing smallerturbulence scale and a similar low pressure recovery to that ofa cage style trim, refer to Fig 20. This allows the valve to handlehigher pressure drops and higher velocities without the onsetof cavitation and noise.
This specialised valve performs exceptionally well in severe serviceapplications with its variable resistance trim, where the pressuredrop tends to be high in the controlling position but where highcapacity through puts at low pressure drops are also required.
For applications that are particularly severe, an integral diffuserpack would be supplied, refer to Fig 21. The diffuser packgenerally consist of one baffle plate fitted into the outlet of thevalve body, but can consist of upto 3 baffle plates for the moreextreme applications. The diffuser pack becomes effectivewhen the flow rate through the valve increases.
Thus, as the valve opens beyond 30o open and the influence ofthe cowls on the flow is reduced, the baffle plates start togenerate a back pressure. KKI will consider all valve openingswhen selecting the Rotrol valve and diffuser pack, to ensurecavitation is eliminated at all valve openings.
Fig 21Rotrol valve withoutlet baffle plate
Pv
P1
P2
VALVE INLET VALVE OUTLETTRIM INLET
STA
TIC P
RESSURE
STANDARDDISC (HIGHRECOVERY)
ROTROL DISC(LOW DISCOVERY)
CAVITATION
Fig 24Patented solid tungsten carbideLCV trim after two years operation
Fig 25Fully stellited cage guided trim after two weeks operation
Deadband
LCV design (patented)Seating point
Over the next two years KKI developed the LCV trim design,see Fig 23, by introducing various design enhancements toensure that the trim would withstand the erosive nature of themedium. These enhancements included the introduction of adead-band, sacrificial plug nose, a shrouded seat facearrangement and solid tungsten carbide for the main trimcontrol elements.
The features of this design were patented and form the basisof the Koso Kent Introl Severe Service Choke Trim design aswell as being an option within the globe control valve productrange. The success of the trim design utilising tungstencarbide as presented in Fig 24 shows a relatively small amountof erosion to the sacrificial elements after two years operation.
This development lead KKI into the design and manufacture oftheir highly regarded choke valve product range.
Fig 22Separator levelcontrol schematic
Fig 23 LCV design principle
CASE 3SPECIALIST APPLICATION SEPARATOR LEVEL CONTROLVALVESIn 1974 Koso Kent Introl supplied a number of control valvesfor a separator level control system schematic representedbelow in the Separator Level Control Schematic.
The original trim was a HFD cage guided design with anoperating pressure drop of 100 bar (1450psi). In the early 1980’sthe client introduced water injection, the additional water cutresulted in the fluid being contaminated with sand. Within twoweeks of operation of the valve, the trim was being severelyeroded, due to the excess sand contamination.
Second stage levelcontrol valve
Tothird stage levelcontrol valve
First stage levelcontrol valve
Wellhead
First stageseparator
Test separatorcontrol valve
First stageseparator
Testseparator
Productionchoke
Gas Gas
LIC LIC
TECHNICAL BULLETINTSS – 0109
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High velocity flow
10
Fig 26In-line choke withHydraulic actuator
SEVERE SERVICE SURFACECHOKE VALVES
CHOKE DESIGN SPECIFICATION
Examples of be-spoke designs supplied by Koso Kent Introlare illustrated above, with special piping configurations, blockvalves and electro-hydraulic actuated units.
SIZES1" to 16" (25mm to 400mm).
RATINGSANSI 600 to 4,500 / API 3,000 to 15,000.
DESIGN STANDARDSISO 10423 / API 6A / API 17D / ANSI B16.34 / ASME VIII
STANDARDSPED / ATEX / NACE MR01.75 / ISO 15156 / NORSOK.
END CONNSISO 10423 / API 6A / API 17D / ANSI Flanges / Hub typeconnections. Other end connections available on request.
TRIM DESIGNHF, LCV, Microspline, Multi-spline, Vector and various Multi-stagetrim options. Other special trim configurations available onrequest.
ACTUATIONA wide range of actuator options are available, including manual, pneumatic spring opposed diaphragm, pneumatic piston, pneumatic stepping, hydraulic stepping, electric, and electro-hydraulic.
BE-SPOKE DESIGNED SEVERE SERVICE CHOKE VALVES
Koso Kent Introl has been supplying high technology surfacechoke valves since 1975. The design of the severe service trimincorporated in this valve was discussed in the previous section.
To date thousands of Kent Introl Series 73 surface chokes havebeen installed around the world on projects for some of theworlds leading oil and gas companies.
Fig 27Competitor’s torturous path trim design that failed on a SevereService application due to contamination and Interstage flashing
Fig 29A competitors trim which has
been replaced by a KKItungsten carbide trim design
CASE 4SPECIALIST APPLICATION FLASHING SERVICE
Through experience of supplying valves into the most arduousconditions found, i.e. in the North Sea, where there is also sandcontamination to contend with, KKI has over the last 20 yearsdeveloped a successful selection criteria for these applications.
From the on-set, KKI used multi-stage trim designs on suchapplications, however, it soon became apparent that thisresulted in premature failure of the valve trim. The reason forthis was that as soon as there was any pressure drop in thetrim, the fluid started to ‘flash’, i.e. since the fluid was no longerin equilibrium, some of the liquid was converted to vapour. Theresultant two phase flow has a significantly higher specificvolume than the single phase flow leading to higher velocitiesand higher erosion rates. Thus the respective flow paths ineach stage of let-down will subsequently see higher velocitiesand higher erosion rates. For this reason KKI will generallyoffer single stage let-down, in hardened materials, for flashingservice applications. On higher pressure drops tungstencarbide is utilised to reduce erosion rates.
KKI have retro-fitted a large number of competitors valvesoperating on such duties with single stage tungsten carbidedesigns. On heavily contaminated services, the LCV trim designhas been supplied. This protects both the control and seatingsurfaces on the valve plug and seat from the erosive flow.
The image below shows a competitors multi-stage trim thathas suffered from flashing erosion damage. The illustration inFig 28 presents a tungsten carbide trim designed to replacethe Fig 27.
KKI have a great deal of experience of supplying valves that operate on flashing fluids, bothcontaminated and un-contaminated. Flashing service applications range from relatively benignconditions, i.e. when the downstream pressure is just below the fluid vapour pressure, to severe,i.e. when the fluid is flashing at inlet to the valve and with pressure drops in excess of 20 bar.
Fig 28Illustration of a Tungsten
Carbide trim that replaced acompetitors torturous path
trim design
TECHNICAL BULLETINTSS – 0109
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, , , ,
EROSION When high velocity jets of liquid impinge against a solid surfacesome of the material will be eroded, the amount is dependanton the hardness and resilience of the material and on theimpact velocity and angle of impact. The inclusions of abrasiveparticles in the liquid aggravate the erosive process.
High velocity jets of fluid emerging from the controlling orificesof the valve trim may result in the erosion of any surface onwhich they impinge and the effects of this will be enhanced ifthe fluid contains abrasive particles such as sand. High velocityjets of gas or vapour containing droplets of liquid can alsoproduce severe erosion damage.
As with cavitation, predictive calculations are difficult becausethere are so many variables affecting the rate of erosion.
Research at universities and within the industry has producedsome proposals and arguably the most user friendly of thesefrom the valve applications engineers viewpoint is from the workcarried out by M.M. Salama, E.S. Ventakesh and E. Rabinowicz.
The graph below relates erosion rate versus velocity for differentmaterial grades. This shows the significant improvements thatcan be made by utilising stellite or tungsten carbide onpotentially erosive services.
EROSION DUE TO CLEAN FLUIDS
EROSION RATES FOR VARIOUS MATERIAL GRADES
Three years predicted erosion for clean liquids with an SG of 1 and an incidence angle of 90 Degrees
Inconel (cladding)Stainless 316Stellite No6Stainless 17/4PHStainless 420Tungsten carbide
1.00E-06 5 10 15 20
1.00E-07
1.00E-08
1.00E-09
1.00E-10
1.00E-11
1.00E-12
1.00E-13
1.00E-14
1.00E-15
MATERIAL β
Inconel (cladding) 175
Stainless 316 223
Stellite No 6 304
Stainless 17/4PH 334
Stainless 420 407
Tungsten Carbide 801
V = volume of material eroded mm3/mm2
u = velocity of fluid jet m/sec
ρ = density of fluid kg/m3
t = duration hours
β = coefficient depending on materialhardness (refer to adjacent table)
θ = angle of incidence of a jet with surface degree
(min. for use in the equation = 20o)
MATERIAL HARDNESS COEFFICIENTS
Volume erosion (m
m3/mm2)
Jet velocity (m/s)
AERODYNAMIC NOISEThe control of this noise generation has been a majorundertaking over many years. Over this period KKI haveundertaken a number of Research Projects in order to gain abetter understanding of this process.
Aerodynamic noise generation is attributed to the presence ofhigh turbulence levels and shock waves in the valve,downstream of the flow restriction. The high levels ofturbulence are a result of dissipating high levels of energy bythrottling the flow. The turbulence energy is converted by anon-linear process into internal and acoustic energy, andsubsequently the acoustic energy is propagated downstreamwith a small percentage being transmitted through the pipewall and into the surroundings as acoustic sound waves.
Aerodynamically generated noise usually seems to emanatefrom a point in the downstream pipe-work approximately 1 to 2pipe diameters from the exit of the valve. This distance isrelated to the pipe-work configuration and outlet flow velocity.
KKI has been providing solutions for high noise level applicationssince the 1960’s. The development of these trims has advancedconsiderably with the aid of experimental researchprogrammes and more recently Computational Fluid Dynamics.
KKI undertook an extensive research program during the1980’s into Aerodynamic noise generation within control valves.This resulted in the successful introduction of the low noisetrim designs referred to as HFQ1 and HFQ2. These complementedthe already proven HFD (Double Stage) and HFT (Triple Stage)trim designs previously used for low noise applications.
The preferred flow direction is “under” the plug for the HFQ trimdesign. This enables the optimum flow area increase as theflow passes through each stage of the trim. The result is a verylow trim exit velocity and very high levels of noise attenuation.The flow geometry means that the process fluid enters the cageradially and passes through the subsequent sleeves in atorturous path resulting in high frictional and impingementlosses. Shock wave formation is controlled by jet impingementon the sleeves, this has been shown to have a major(advantageous) bearing on the noise generation process.
The KKI family of HF trims (HF, HFD, HFT, HFQ1 & HFQ2)provide high levels of dynamic attenuation (upto 40dBA),whilst avoiding the problems of erosion and vibration.
Fig 30 HFQ class low noise trim
Fig 32Plan view of a HFQ2 low noise trim
Flow path
Fig 31 5 stage (9 turns) low noise trim design
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SILENCERS
Fig 33Baffle plate
In solving aerodynamic noise generation problems it must alsobe recognised that there is a need to control downstreamvelocities, otherwise high pipeline velocities can producesecondary noise which could be significantly higher than thatproduced by the valve trim.
It is generally accepted that to achieve a low noise solution, thedownstream velocity should be restricted to less than 0.3 timesthe fluid sonic velocity. This coincides with the velocity atwhich compressibility effects start to become noticeable. Inorder to address this problem KKI utilise down stream silencers,these take the form of a taper pipe fitted with a number ofbaffle plates (circular plates with a number of drilled holes).
These are used to produce a back-pressure to the valve andare selected so that the velocity from the trim exit to the valveoutlet is less than 0.3 times sonic velocity (0.3 mach).
In utilising baffles the correct allocation of pressure drop to thetrim and each baffle stage is important. At least 30% of thetotal pressure drop should be allocated to the valve trim, theremainder divided through the various pressure drop stages.
If a number of baffles are required, then it is advisable toallocate the pressure drop in diminishing magnitudesas they are located further away from the valve inlet,so that the last baffle takes the lowest pressure drop.
In selecting these devices it is necessary to ensure that thetrim silencer system operates effectively over the full range ofoperating conditions. This approach has been usedsuccessfully by KKI for in excess of 30 years.
Certain valve manufacturers will endeavour to exclude the useof battle plates as dynamic attenuators because of thecommercial advantage it provides against larger valvesolutions. However, there is no valid technical reason whysilencers/baffles should not be used, on the proviso that alloperating conditions have been considered in their selection.
Fig 34Control valve c/w taper
pipe and baffle pack
CASE 5SPECIALIST APPLICATION SURGE CONTROL(INCOMPRESSIBLE FLUIDS)
Fig 35Alaska pipeline Anti-surge Severe Service control valves
TECHNICAL BULLETINTSS – 0109
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If there is a sudden closure of a valve or a trip out of a pump,either at the start or the end of pipeline or at an intermediarypump station, the flow at that point will be brought to rest orsignificantly reduced. The fluid upstream and down stream isnot “aware” of this stoppage and continues to flow under itsmass momentum.
The fluid upstream is compressed causing a pressure surgeand downstream there will be a rarefaction in pressure, whichwill encourage reverse flow. Pressure surges and reverse flowsare extremely dangerous causing damage to pumps andpossible to fracture to the pipeline. A surge on a long pipelineoperating at a normal pressure of 17.5 bar can generate atransient pressure of 96 bar if uncontrolled.
EXAMPLE OF SEVERE SERVICE SURGE CONTROL APPLICATIONThe customer was experiencing severe vibration due to cavitationwith a competitors control valve.
KKI were asked to a provide a trial valve that would eliminateall the cavitation, provide stable control while the valve wouldbe subjected to extremely high velocities and the valve had tofit into the existing space on the pumping station.
Seven Stages of pressure drop were used to ensure that thepressure of the medium did not drop below the vapourpressure, thus preventing cavitation and eliminating both thenoise and vibration that were previously being experiencedwith one of our competitors valves.
Great care was also taken to control the velocity through the valve.Although the valve was described as a 16" angle design, the trimcomponents and size were the same as used on a 24" valve.
Prior to shipment to Alaska the valve was fully tested in housefor confirmation of both the CV and flow characteristic.
After successful extensive customer trials Koso Kent Introlreceived an initial order for 36 Anti-surge Pipeline ControlValves, each one specifically designed around the flowconditions of each individual pump. KKI subsequently receivedand delivered a further order for 10 more units.
In 2009 the valves continue to function satisfactorily withminimum service requirements.
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CASE 6SPECIALIST APPLICATION COMPRESSOR RE-CYCLE/ANTI-SURGE CONTROL VALVES(COMPRESSIBLE FLUIDS)Although all control valve applications are sized considering allthe operating conditions and ensuring adequate valve openingsfor control, the anti-surge does require particular attention.
Usually, the valve specification states the exact requirements,i.e. the maximum range of the valve design Cv. These arespecified to ensure that when the valve is brought into serviceit can control the flow so that the compressor does not movetowards a surge condition.
An additional requirement for this application is for the valve to respond quickly under either a trip or modulatingcondition. This requires a sophisticated instrumentationconfiguration utilising volume booster and trip valves. Thesehave to be set up to ensure a stable control in operation.
Another problem that has to be considered on this particularapplication is vibration, many valve manufacturers have overthe years encountered such problems on this particularapplication. One of the main contributors to this is the adversepiping configurations that are created in an attempt to minimisethe footprint of the plant. This together with adverse operatingconditions, i.e. high pressure drop can result in problematicvibration problems. In order to counter this KKI apply a specificset of rules in the selection of the valve for this application.
The graphs shown in Figs 36 and 37 present traces of theactual valve opening conditions during a re-cycle operation.Under most of the operational range the valve control remainedstable. However, under certain instances the response of thevalve was eratic as shown in Fig 36. The green and red lines arethe input (instrument signal) and output (valve position) of thedevice. This shows that although the input signal (green) isrequesting the valve to close, the valve actually remains openas shown by the red trace. Corresponding with this occurrencewas a sudden increase in SPL. This was not aerodynamic noisegeneration, it was a result of high vibration levels at a discretefrequency due to fluid induced resonance.
Numerous attempts at resolving the problem only partlyresolved the issue. This was largely due to the unpredictablenature of the problem. A complete review of the process wasundertaken, and various modifications to the trim design andguiding were incorporated into the replacement trim design. The valve was put back into service and retested. In order toverify the performance of the modification a slight sinusoidalsignal was incorporated into the input signal, Fig 37 representsthe results obtained from this test. The excellent correlationbetween the input signal and output signal indicate how themodifications have improved the control system. Several otherproblem re-cycle applications were resolved using the samedesign philosophy.
Fig 36 Eratic response due to vibration
Fig 37 Trace after modification
TIME
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VECTOR LABYRINTH TRIMSKKI supply the Koso VeCTor Severe Service Labyrinth Trims.These trims extend the capability of KKI to offer trim designsfor the most severe operating conditions now found in thevarious industries served.
KKI are in the enviable position of being able to supply themost appropriate design for the specified application whetherhigh pressure drop cavitating, high pressure drop flashing orhigh pressure drop gas application, this proven trim designdelivers accurate control, long life, free from cavitation,erosion, vibration and noise problems.
The design has evolved through many decades of experiencein solving severe service applications where durability,reliability, repeatability and accurate / precise control arerequired. The advanced design velocity control trim preventsgeneration of noise and / or cavitation at the source.
The typical applications that the Koso Vector Labyrinth trimhas been supplied on are basically the same as listed on page3 of this document, and include compressor re-cycle, turbineby-pass and pump recirculation.
The Koso Vector Labyrinth trims limit harmful flow velocities byseparating the flow into smaller individual channels, and thenstage the full pressure drop across multiple turns in the fluidpath. This is the basic principle of the HFL trim design, however,on the Vector designs the allowed pressure drops aresignificantly lower, leading to much lower velocities that are wellwithin any threshold for erosion for the majority of trim materials.
In addition to the Vector D Labyrinth trim shown in Fig 40 Kosohas also developed the Vector M Multi-step trim, shown below.This gives a smooth and continuous increasing flow over the fulltravel of the valve. This eliminates the inherent stepped flowthat occurs in most stacked disc designs, see Fig 38.
Fig 40Vector D Labyrinth disc
Fig 38Flow characteristic comparisonbetween D and M Vector
D
M
TECHNICAL BULLETINTSS – 0109
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Fig 39Vector M trim design
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Fig 42Choke valve during cryogenic testing
Fig 43Control valve during flow testing
Fig 41Turbotrol valve on 480 bartest loop – undergoing FAT
PERFORMANCE TESTINGKKI continually tests their products to ensure that the unitsmeet the ever-changing requirements of the specific Industrythat the units will be used in.
Some of the tests that are carried out include the following:
– Flow Testing – To verify valve size and the trim characteristic– Bend Testing – To verify the end loads– High Temperature Testing – To verify suitability at elevatedoperating temperatures
– Noise Testing – To confirm our noise prediction techniques– API 6A / 17D Testing – To ensure the products are inaccordance with the standards
– Vibration Analysis – To verify the stability of the valve underhigh-energy applications
– Erosion Qualification & CFD reports – To provide anindication of the life expectancy of a valve trim
– Cryogenic / Low Temperature test – to verify Control Valveoperation at sub zero temperatures
– Life Cycle Testing – To simulate and verify the lifeexpectancy of the valve components
– Trim Impact Testing – To verify that the trim will not collapsewhen hit by large solid contaminants travelling at high velocity
– Emission Testing – To prove that the valve integrity issuitable to prevent leakage to the atmosphere.
KOSO KENT INTROL LIMITEDARMYTAGE ROADBRIGHOUSEWEST YORKSHIREHD6 1QFUK
TELEPHONE+44 (0)1484 710311
FACSIMILE+44 (0)1484 407407
WEBSITE WWW.KENTINTROL.COM
Koso Kent Introl Limited is part of the KOSO Group of companies.
The company’s policy is one of continual development and the right isreserved to modify the specifications contained herein without notice.
Copyright © 2014All rights reserved Koso Kent Introl Limited
