applied sciences

Article Design of Laminated Seal for Triple Offset Butterfly ◦ Valve (350 C) Used in Combined Cycle Power Plants

Hyo Seo Kwak 1 , Hansaem Seong 2, Rivaldo Mersis Brilianto 3 and Chul Kim 3,* 1 Research Institute of Mechanical Technology, Pusan National University, Busan 46241, Korea 2 Department of Mechanical Convergence Technology, Pusan National University, Busan 46241, Korea 3 School of Mechanical Engineering, Pusan National University, Busan 46241, Korea * Correspondence: [email protected]; Tel.: +82-051-510-2489



Received: 26 June 2019; Accepted: 27 July 2019; Published: 31 July 2019


Abstract: In combined cycle power plants (CCPPs), the bypass butterfly valve is a key component to facilitate regulation of exhaust gas energy available at the turbine and to not produce too much boost pressure. The conventional damper valve causes leakage, back flow into the turbine, and damage of the blade, and the existing dual-layered seal with polytetrafluoroethylene (PTFE) and metal should be frequently replaced owing to its low durability and deterioration of mechanical properties under a high temperature. This study devised a triple offset butterfly valve with a new type of seal by alternatively laminating stainless steel and graphite to improve valve performance at the high temperature (350 ◦C). The slope angles of the seal contact surface to prevent friction were calculated using the mathematical models of the triple offset. Thermal-structure coupled analyses by varying the number of graphite and thickness were conducted, and the seven-layer model with the graphite thickness of 0.8 mm, which shows airtightness and smooth operation, was chosen. The contact stresses behaviors of the graphite at 350 C and at 196 C were investigated, and it was found that ◦ − ◦ the graphite is in charge of improving driving performance of the disc at the high temperature and sealing performance at the cryogenic temperature. The performance tests and the field tests of the suggested model verified its performance at the working temperature.

Keywords: bypass butterfly valve; laminated seal; graphite; triple offset; airtightness; thermal-structural coupled analysis; contact stress

1. Introduction As global warming and the depletion of energy resources have intensified, the growth in worldwide energy demand currently faces the difficulty of installing new power generation facilities as a result of limited funding and the strengthening of environmental regulations. Thus, combined cycle power plants (CCPPs), which consist of gas turbines and steam turbines, are becoming more important as the global demand for electrical power increases [1,2]. CCPPs manipulate discarded heat energy and store in hot gas into rotational energy, and the gas turbine compresses air and mixes it with fuel that is heated to a high temperature. The hot air–fuel mixture moves through the gas turbine blades to make them spin, and then the fast-spinning turbine drives the generator that converts a portion of the spinning energy into electricity [3–5]. With the stoichiometric burn, the power output of turbine drops sharply for flow rates above a critical value as a result of aerodynamic losses produced by the rotor blade stalling, and the turbine performs poorly in excessive load and exhaust gas pressure-states, which brings about a decrease in energy production. In order to prevent the above problems, the bypass system facilitates the regulation of the exhaust gas energy available at the turbine wheel, and thus allows the turbocharger to be controlled and to not produce too much boost pressure. In this system, the bypass valve, which is mounted between the

Appl. Sci. 2019, 9, 3095; doi:10.3390/app9153095 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, 3095 2 of 19

Appl. Sci. 2019, 9, x FOR PEER REVIEW 2 of 19 chamberAppl. Sci. 2019 and, 9, the x FOR atmosphere PEER REVIEW inparallel with the turbine, limits the maximum pressure in the chamber2 of 19 to prevent the instantaneous air flow rate through the turbine from exceeding the values above which inin thethe chamberchamber toto preventprevent thethe instantaneousinstantaneous airair flflow rate through the turbine from exceeding the aerodynamic stalling at the rotor blades would produce a severe fall in power output [6–8]. As the values above which aerodynamic stalling at the rotor blades would produce a severe fall in power modern CCPPs require an increase of exhaust pressure in order to fulfill the restrictions of pollutant output [6–8]. As the modern CCPPs require an increaseease ofof exhaustexhaust pressurepressure inin orderorder toto fulfillfulfill thethe emission and to improve energy productivity, the following complementary functions have to be taken restrictionsrestrictions ofof pollutantpollutant emissionemission andand toto improvimprovee energyenergy productivity,productivity, thethe followingfollowing complementarycomplementary into account while designing the bypass valve: resistance to the harsh engine boundary conditions functionsfunctions havehave toto bebe takentaken intointo accountaccount whilewhile dedesigningsigning thethe bypassbypass valve:valve: resistanceresistance toto thethe harshharsh (temperature of 350 C and working pressure of 1 MPa); smooth operation of the disc during opening engineengine boundaryboundary conditionsconditions◦ (temperature(temperature ofof 350 °C and working pressure of 1 MPa); smooth and closing; and maintenance of sealing in closed valve operation to maximize gas energy directed to operation of the disc during opening and closing; and maintenance of sealing in closed valve the turbine [9,10]. operation to maximize gas energy directed to the turbine [9,10]. In the damper valve, which had been used in the existing bypass system, thermal deformations InIn thethe damperdamper valve,valve, whichwhich hadhad beenbeen usedused inin thethe existingexisting bypassbypass system,system, thermalthermal deformationsdeformations and stress concentrations occurred at a high temperature because there is no offset of the disc rotary and stress concentrations occurred at a high temperature because there is no offset of the disc rotary axis from the seal. Also, a gap between the body and the disc due to absence of seal caused leakage, axis from the seal. Also, a gap between the body and the disc due to absence of seal caused leakage, back flow into the turbine, and damage of the blade, as illustrated in Figure1. back flow into the turbine, and damage of the blade, as illustrated in Figure 1.

FigureFigure 1.1. The existing damper valve.

TheThe dual-layered sealseal withwith polytetrafluoroethyl polytetrafluoroethyleneeneene (PTFE)(PTFE) andand metalmetal hadhad beenbeen adoptedadopted toto solve solve thethe above-mentioned above-mentioned problems, problems, but but PTFE PTFE shouldshould bebe frequentlyfrequently replacedreplaced replaced owingowing owing toto to itsits its lowlow low durability.durability. durability. MetalMetal hashas a worsea worse sealing sealing performance performance than PTFEthan [11PTFE,12], and[11,12], its mechanical and its mechanical properties areproperties deteriorated are atdeteriorated the high temperature at the high [temperature13], so new sealing[13], so material,new sealing particularly material, compositeparticularly material, composite is needed material, to improveisis neededneeded the toto improve sealingimprove ability thethe sealingsealing and durability abilityability andand of durabilitydurability other original ofof otherother seals. originaloriginal seals.seals. TheThe existing single and double offset offset butterflybutterfly valvesvalves (SOBV(SOBV andand DOVB)DOVB) havehave simple geometric structuresstructures tototo be bebe easily easilyeasily manufactured, manufactured,manufactured, but butbut rubbing rubbingrubbing and and friction friction between between the the seal seal and and the the disc disc cause cause life shorteninglifelife shorteningshortening and andand wear wearwear of the ofof seal thethe duringsealseal duringduring opening openingopening andclosing, andand closing,closing, as shown asas shownshown in Figure inin FigureFigure2. Therefore, 2.2. Therefore,Therefore, this study thisthis appliesstudystudy appliesapplies the triple thethe o tripletripleffset (radial offsetoffset eccentricity,(radial(radial eccentricity,eccentricity, axis eccentricity, axisaxis eccentricity,eccentricity, and cone andand axis conecone angle axisaxis eccentricity) angleangle eccentricity)eccentricity) butterfly valvebutterfly (TOBV), valve whose (TOBV), surface whose of surface the seal of is the in full seal contact is in fullfull when contactcontact thevalve whenwhen is thethe fully valvevalve closed. isis fullyfully This closed.closed. eliminates ThisThis gallingeliminateseliminates and gallinggalling minimizing andand minimizingminimizing seal wear and sealseal rubbing wearwear and for rubbing long life for and long tight life shut-o and tightff. shut-off.

FigureFigure 2. FrictionFriction and and rubbing rubbing occurring occurring at atthe the single single and and double double offset off butterflyset butterfly valves valves (SOBV (SOBV and andDOVB). DOVB).

InIn thethe previousprevious studiesstudies related related to to thethe TOBV,TOBV, ChenChenChen determineddetermineddetermined suitablesuitablesuitable tripletripletriple eccentricitieseccentricitieseccentricities toto improveimprove thethe sealseal performance,performance,performance, and and checkedchecked thethe staticststatic andand dynamicdynamic interferenceinterference throughthrough motionmotion simulationsimulation [14[14].[14].]. Liang LiangLiang developed developeddeveloped a computer aa computercomputer programs programsprograms for calculate forfor calculatecalculate the feasible thethe the feasiblefeasible three eccentricities thethe threethree andeccentricitieseccentricities the value andand of the thethe cone’s valuevalue half ofof thethe angle cone’scone’s [15 half].half Kan angleangle provided [15].[15]. KanKan a criterion providedprovided for aanon-interference criterioncriterion forfor non-interferencenon-interference for the metal sealforfor thethe pair metalmetal considering sealseal pairpair the consideringconsidering radial off set, thethe theradialradial diameter offsetoffset,, ofthethe valve diameterdiameter disc, ofof the valvevalve sealing didisc,sc, thickness, thethe sealingsealing and thickness,thickness, the cone angleand the of cone the sealing angle surfaceof the sealing [16]. Bodhayan surface [16]. validated Bodhayan the PTFE validated seal designthe PTFE for seal gas liftdesign valves for through gas lift checkingvalves through leakage checking amount andleakage performed amount finite and element performed analysis finite (FEA) element on the analysis seal design (FEA) under on the a highseal design under a high pressure to predict the sealing contact pressures [17]. Ping implemented FEA with different sealing ring surface using the numerical method of symmetrical penalty function. The sealingsealing ringring surfacesurface andand thethe sealingsealing ratioratio pressurepressure were suggested to enhancee thethe sealingsealing performanceperformance Appl. Sci. 2019, 9, 3095 3 of 19 pressure to predict the sealing contact pressures [17]. Ping implemented FEA with different sealing ringAppl. surfaceSci. 2019, using9, x FOR the PEER numerical REVIEW method of symmetrical penalty function. The sealing ring surface3 of and 19 the sealing ratio pressure were suggested to enhance the sealing performance of the rotating ball valve withof the double rotating direction ball valve metal with sealing double [18 ].direction Ahn proposed metal sealing a design [18]. criterion Ahn proposed to ensure a the design seat tightnesscriterion into whichensure the the contact seat tightness pressure in between which the the contact metal seal pressure and the between valve discthe wouldmetal seal be comparedand the valve with disc the fluidwould pressure, be compared and mechanical with the fluid behavior pressure, of a flexibleand mech solidanical metal behavior seal for of a a cryogenic flexible solid butterfly metal valve seal wasfor a investigated cryogenic butterfly [19]. However, valve was there investigated were deficiencies [19]. However, of previous there works were in deficiencies relation with of designprevious of laminatedworks in relation seal in with TOBV design to possess of laminated good sealing seal in TOBV property, to possess operability good of se thealing disc, property, and capability operability of withstandingof the disc, and high capability temperatures. of withstanding high temperatures. InIn thisthis paper,paper, a a study study on on performance performance enhancement enhancemen oft of the the triple-o triple-offsetffset butterfly butterfly valve valve used used in the in bypassthe bypass system system of a CCPP’sof a CCPP’s gas turbine gas turbine was conducted. was conducted. After calculatingAfter calculating the slope the angles slope ofangles the contact of the surfacecontact tosurface eliminate to eliminate rubbing onrubbing the seal on contact the seal surface, contact with surface, them, with the mathematic them, the mathematic model of triple-o modelffset of wastriple-offset generated. was Ingenerated. order to In solve orde ther to problems solve the ofproblems the existing of the valve, existing a laminated valve, a laminated seal was seal devised was bydevised substituting by substituting PTFE for graphite, PTFE for which graphite, is known which to excel is known in extreme to excel conditions, in extreme withstanding conditions, heat andwithstanding pressure. Theheat technique and pressure. for the The thermal-structural technique for the coupled thermal-structural analysis was establishedcoupled analysis to consider was established to consider thermal deformation because of exposure to the high temperature (350 °C), thermal deformation because of exposure to the high temperature (350 ◦C), and the maximum contact stressesand the atmaximum the contact contact surface stresses of the sealat the were contact derived surface by varying of the theseal number were derived of graphite by varying layers andthe number of graphite layers and thicknesses, slope angle of the contact surface (66.1° and 86.1°) thicknesses, slope angle of the contact surface (66.1◦ and 86.1◦) calculated and temperature (22 ◦C calculated and temperature (22 °C and 350 °C). On the basis of the analysis results, the seven-layer and 350 ◦C). On the basis of the analysis results, the seven-layer model with the graphite thickness ofmodel 0.8 mm with was the suggested graphite thickness to guarantee of 0.8 not mm only was airtightness, suggested to but guarantee also smooth not operationonly airtightness, of the disc, but andalso thesmooth structural operation reliability of the was disc evaluated., and the structural When the reliability contact stresses’ was evaluated. behavior When of the graphitethe contact at 350stresses’C was behavior compared of the with graphite that at at 196350 °CC, was it was compared found that with the that graphite at −196 is °C, in chargeit was found of improving that the ◦ − ◦ drivinggraphite performance is in charge ofof the improving disc at high driving temperature performance and sealing of the performancedisc at high attemperature cryogenic temperature. and sealing Theperformance internal pressure, at cryogenic leakage temperature. tests were The implemented internal pressure, based on leakage the international tests were implemented regulation, and based the actualon the verificationinternational experiment regulation, for and three the monthsactual veri provedfication the experiment durability andfor three suitability months for proved the actual the workingdurability environment. and suitability for the actual working environment.

2.2. Materials and Methods

2.1.2.1. Operating Principle and Theoretical AnalysisAnalysis ofof TripleTriple OOffsetffset ButterflyButterfly ValveValve

2.1.1.2.1.1. Structure of Triple OOffsetffset ButterflyButterfly ValveValve TheThe geometrygeometry ofof the the triple triple o ffoffsetset butterfly butterfly valve valv ande and its componentits component is shown is shown in Figure in Figure3. The 3. disc The rotatesdisc rotates by the by actuator the actuator to control to control amount amount of the exhaustof the exhaust gas, and gas, the and shaft the connects shaft connects the valve the body valve to thebody actuator. to the actuator. The sealing The part sealing consists part ofconsis the laminatedts of the laminated seal and seal the retainer.and the retainer.

Figure 3.3. Structural of triple-otriple-offsetffset butterflybutterfly valve.valve.

2.1.2.2.1.2. Sealing Mechanism of Laminated Seal ThisThis studystudy deviseddevised aa laminatedlaminated sealseal byby insertioninsertion ofof graphitegraphite withwith metalmetal (A240–316)(A240–316) toto aideaide inin strengthstrength andand stabilitystability forfor extremelyextremely highhigh temperaturetemperature applications,applications, asas shownshown inin FigureFigure4 4.. ToTo achieve achieve tighttight shut-oshut-off,ff, the the disc disc is is driven driven into into the the valve valve body body using using larger larger and and more more expensive expensive actuator actuator than than that that used with other valve designs, thereby it is necessary to design a shape of laminated seal to achieve the high sealing property and smooth driving with low torque [20]. Appl. Sci. 2019, 9, 3095 4 of 19 used with other valve designs, thereby it is necessary to design a shape of laminated seal to achieve the highAppl. Sci. sealing 2019, 9 property, x FOR PEER and REVIEW smooth driving with low torque [20]. 4 of 19

Appl. Sci. 2019, 9, x FOR PEER REVIEW 4 of 19

Figure 4. Existing dual seal and new laminatedlaminated seal. PTFE, polytetrafluoroethylene. polytetrafluoroethylene.

A working pressure of 1 MPa is imposed inside the valve and then produces contact stress on the A working pressureFigure 4. Existing of 1 MPa dual isseal imposed and new laminateinside dthe seal. valve PTFE, and polytetrafluoroethylene. then produces contact stress on contactthe contact surface surface between between the seal the and seal the and body the atbody the finalat the shut-o finalff shut-offposition. position. When the When working the working pressure (P ) is higher than the contact stress (Pcontact), the fluid is squeezed into the sealing clearance; pressureworking (PA workingworking) is pressurehigher thanof 1 MPa the iscontact imposed stress inside (P thecontact valve), the and fluid then isproduces squeezed contact into stress the sealingon otherwise,clearance;the contact otherwise, sealing surface performance sealing between performance the is guaranteed seal and isthe guaranteed asbody expressed. at the as final expressed. shut-off position. When the working pressure (Pworking) is higher than the contact stress (Pcontact), the fluid is squeezed into the sealing 2.1.3. Mathematical Modeling of TOBV Seal Pair 2.1.3. clearance;Mathematical otherwise, Modeling sealing of performance TOBV Seal is Pair guaranteed as expressed. Conventional single offset valve with center shaft, which penetrates a seal, is suitable for low Conventional2.1.3. Mathematical single Modeling offset valve of TOBV with Seal center Pair shaft, which penetrates a seal, is suitable for low temperature and low pressure services only, and double offset valve with eccentric shaft results in an temperature and low pressure services only, and double offset valve with eccentric shaft results in uninterruptedConventional seal that single can beoffset used valve at higherwith center pressures shaft, which and temperatures, penetrates a seal, but is the suitable friction for andlow seal an uninterrupted seal that can be used at higher pressures and temperatures, but the friction and seal wear deterioratetemperature sealingand low performance. pressure services only, and double offset valve with eccentric shaft results in wear andeteriorate uninterrupted sealing seal performance. that can be used at higher pressures and temperatures, but the friction and seal In the triple offset valve, both the seal and the disc are surfaces of a cone that is sectioned at an Inwear the deteriorate triple offset sealing valve, performance. both the seal and the disc are surfaces of a cone that is sectioned at an angle. The valve shaft is located slightly to one side of the seal center and above the plane of the seat, angle. TheIn valve the triple shaft offset is located valve, slightlyboth the toseal one and side the ofdi scthe are seal surfaces center of and a cone above that theis sectioned plane of at the an seat, and its rotation center is also offset from the axis of the imaginary cone that extends from the surface and itsangle. rotation The valvecenter shaft is also is located offset slightly from the to oneaxis side of the of the imaginary seal center cone and thatabove extends the plane from of the the seat, surface of the seat. When the valve is closed, the surfaces of the seal and the disc are in full contact at all of theand seat. its Whenrotation the center valve is also is closed,offset from the thesurfaces axis of theof the imaginary seal and cone the that disc extends are in from full the contact surface at all points,of andthe seat. opening When the the valve valve results is closed, in thethe discsurfaces moving of the away seal and from the the disc seal are at in all full points, contact eliminating at all points, and opening the valve results in the disc moving away from the seal at all points, eliminating gallingpoints, and minimizingand opening the seal valve wear results due to in non-rubbingthe disc moving sealing away from surfaces the seal for at long all points, life and eliminating tight shut-o ff. galling and minimizing seal wear due to non-rubbing sealing surfaces for long life and tight shut-off. The threegalling separate and minimizing offsets are seal designed wear due in to thenon-rubbing butterfly sealing valve, surfaces as shown for in long Figure life and5. tight shut-off. The three separate offsets are designed in the butterfly valve, as shown in Figure 5. OTheffset three 1 (H separate): The shaft offsets is are off setdesigned from thein th seale butterfly plane providingvalve, as shown an uninterrupted in Figure 5. sealing surface. Offset 1 (H): The shaft is offset from the seal plane providing an uninterrupted sealing surface. OffsetOffset 2 (E ):1 The(H): The centerline shaft is offset of disc from is otheffset seal from plane the providing centerline an uninterrupted of the shaft allowing sealing surface. the disc to OffsetOffset 2 (E ):2 The(E): The centerline centerline of ofdisc disc is is offset offset from from the centerlinecenterline of of the the shaft shaft allowing allowing the discthe discto to freely lift off and away from the seal during opening. freelyfreely lift off lift and off andaway away from from the the seal seal during during opening. opening. Offset 3 (γ): The centerline of seal cone with conical angle of 2α is offset by γ from the centerline OffsetOffset 3 (γ): 3 The(γ): The centerline centerline of ofseal seal cone cone with with conical conical angle of of 2 2αα is is offset offset by by γ° γfrom◦° from the thecenterline centerline of the body to eliminate rubbing on the contact surface during opening and closing, thereby rotating of theof body the body to eliminate to eliminate rubbing rubbing on on the the contact contact su surfacerface during opening opening and and closing, closing, thereby thereby rotating rotating the disc without interference [21]. the discthe withoutdisc without interference interference [21]. [21].

Figure 5. Scheme of the triple-offset butterfly valve. Figure 5. Scheme of the triple-offset butterfly valve. A coordinate systemFigure is established 5. Scheme by of taking the triple-offset the apex of butterfly the cone, valve. and the geometry of the triple offset seal pair is shown in Figure 6. A coordinate system is established by taking the apex of the cone, and the geometry of the triple offset seal pair is shown in Figure 6.

Appl. Sci. 2019, 9, 3095 5 of 19

Appl. Sci. 2019, 9, x FOR PEER REVIEW 5 of 19 A coordinate system is established by taking the apex of the cone, and the geometry of the triple offset seal pair is shown in Figure6. ABCD : Seal cone surface Appl. Sci. 2019, 9, x FOR PEER REVIEW 5 of 19 D0 : Intermediate diameter of disc ABCDH0, H1, and H:2 Seal: Distancescone surface from the coordinate origin D0 : Intermediate(O) to N0 ,diameter N1 and N of2 disc H0, NH01,, Nand1 and H2 N:2 Distances: Intersections from the between coordinate cone origin center and (O) toS0 ,N S01, andN1 and S2 N2 N0, 𝑚𝑛N1 and N2 : Intersections: Centerline between of valve cone bod centery and O0 S:0 , S Rotation1 and S2 center of the disc 𝑚𝑛S 1 , S2 : Centerline: Upper ofand valve lower bod sectionsy of disc O0 S0 : Rotation: Section center of disc of the center disc S1 , TS 2 : U: pp Thicknesser and lower of sectionsdisc of disc S0 α : Section: Half of conical disc center ang le T : Thickness of disc α : Half conical angle Figure 6. Geometry of triple offset seal pair. Figure 6. Geometry of triple offset seal pair. Figure 6. Geometry of triple offset seal pair. The functions of cone where the disc is situated about y-axis are expressed in Equation (1), and the sectionsThe of functions the disc of(S conei) in Equation where the (2) disc depend is situated on H abouti, whichy-axis are arethe expresseddistances between in Equation the (1),coordinate and the The functions of cone where the disc is situated about y-axis are expressed in Equation (1), and the sectionsorigin (O of) and the N disci, given (Si) inby Equation Equation (2)(3) depend(i = 1, 2, onandH 3).i, which are the distances between the coordinate sections of the disc (Si) in Equation (2) depend on Hi, which are the distances between the coordinate origin (O) and N , given by Equation (3) (i = 1, 2, and 3). origin (O) and Ni, giveni by Equation (3) (i = 1,y 2 2,= andk 2 ⋅ z 3).2 − x2 , (1) = ⋅ + y 2== k⋅2 2⋅ z+2 − x22 , 2 2 = ⋅ + (1) z k0 y H0 for S0, z k0 yy =Hk1 forz S1x, ,z k0 y H 2 for S2, (2) (1) · − = ⋅ + = ⋅ + = ⋅ + z k0 y H0 for S0, z k0 y H1 for S1, z k0 y H 2 for S2, (2) z = k0 y + H0 for S0, z = k0 y + H1 for S1, z = k0 y + H2 for S2, (2) ·  T·  T ⋅i · H =  H −  + ! i  0 ⋅ γT  ⋅ γ T, i (3) =   − 2T cos( +)  T cos(i ) Hi H Hi =0 H0  +, · ,(3) (3)  2⋅cos(− 2γ ) cos cos((γ)γ ) cos(γ)  ·  where kk = tantan ( (𝛼α) and k00 == tantan ( (𝛾γ).). When When the the sealing sealing surface surface is is truncated truncated by by an an arbitrary arbitrary plane that is where k = tan (𝛼) and k0 = tan (𝛾). When the sealing surface is truncated by an arbitrary plane that is in parallel with yOz plane with its x-coordinate asas x00, the the equation equation of the hyperbola ( ajbckd) shown in in parallel with yOz plane with its x-coordinate as x0, the equation of the hyperbola (ajbckd) shown in Figure 77 is is obtainedobtained byby EquationEquation (4),(4), andand thethe coordinatecoordinate of of two two intersection intersection points points ( (xx,, yyii,, zzii) between Figure 7 is obtained by Equation (4), and the coordinate of two intersection points (x, yi, zi) between hyperbola and disc surface (Sii) is obtained by Equation (5). hyperbola and disc surface (Si) is obtained by Equation (5).

FigureFigure 7. Projection 7. Projection diagram diagram of disc of disc section. section.

z 2 z 2 2y 2 y 2 y2 −z − = 1 = 2 2 2 2 1 = 1 (4) x  x2 2  0x0 x0 0 x−0 x0 (4) (4)   k  kk    x = x0  q x = x=0  k2 k H k2 k2 x2+k2 H2 x2 x x0  − · 0· i± · 0· 0 · i − 0   yi = (5)  − 2 ⋅ ⋅ ± 2 ⋅ 2 ⋅ 2k2+k2 2 1⋅ 2 − 2   = k− k20⋅ H⋅i ±k k20 ⋅ x02 ⋅· k02−+H2i ⋅ x20 − 2 yi k k0=Hi k+ k0 x0 k Hi x0 (5) yi = zi k0 2y⋅i 2 −Hi   k· k20 ⋅ 12 − (5)  k k0 1 zi = k0 ⋅ yi + Hi  zi = k0 ⋅ yi + Hi  Appl. Sci. 2019, 9, 3095 6 of 19

Appl. Sci. 2019, 9, x FOR PEER REVIEW 6 of 19 The elliptical equations for the intersections between the disc cutting planes and the curved The elliptical equations for the intersections between the disc cutting planes and the curved surface of cone are expressed by Equation (6). surface of cone are expressed by Equation (6). x2 + y2 = (k k y + H )2, x2 + y2 = (k k y + H )2, x2 + y2 = (k k y + H )2 (6) 2 + 2 = ⋅ ⋅0 + 2 0 2 + 2 = ⋅ ⋅ + 0 2 21+ 2 = ⋅ ⋅ + 02 2 x y (k k· 0 y· H 0 ) , x y (k k0 y· H·1) , x y (k k0 y H· 2) · (6)

The intersections between the vertical lines of N0, N1, and N2 with the plane x = x0 are the The intersections between the vertical lines of N0, N1, and N2 with the plane x = x0 are the center center point of jk, bc, and ad, and apexes Ni of minor axis of the intersection constitutes the line NiO. point of jk, bc, and ad, and apexes Ni of minor axis of the intersection constitutes the line 𝑁𝑂. Friction Friction behavior of TOBV seal pair depends on the following five parameters: offset 1 (E), offset 2 (H), behavior of TOBV seal pair depends on the following five parameters: offset 1 (E), offset 2 (H), offset offset 3 (γ), half conical angle (α), and disc thickness (T). During the valve opening and closing, 3 (γ), half conical angle (α), and disc thickness (T). During the valve opening and closing, point P(y, point P(y, z), which is on the hyperbola ab, rotates about O with speed of PN→ perpendicular to O P, z), which is on the hyperbola ab, rotates about O0 with speed0 of 𝑃𝑁⃗ perpendicular to 𝑂𝑃, as shown0 inas Figure shown 8. in The Figure angle8. The of θ angle in Equation of θ in Equation (7) is the (7) friction is the frictionangle between angle between the seal the pair seal (𝑃𝑀 pair and (PM 𝑃𝑁and), andPN), the and angle the angleof β in ofEquationβ in Equation (8) is between (8) is between 𝑃𝑀 andPM theand axial the line axial crossing line crossing the seal thepoint seal and point parallel and withparallel y-axis. with They-axis. angle The of angleθ1 in Equation of θ1 in Equation (9) is between (9) is between 𝑂𝑃 andO the0P and vertical the verticalline crossing line crossing the rotary the centerrotary ( centerO0). The (O 0higher). The highertical line tical crossing line crossing the rotary the rotarycenter center(allel with (allel fiv, with which fiv, which means means that the that disc the candisc rapidly can rapidly be disengaged be disengaged from fromthe valve the valve seal, seal,and the and friction the friction moment moment decreases decreases [15]. [15].

Figure 8. Contact angle of seal pair during closing and opening. Figure 8. Contact angle of seal pair during closing and opening.

θ =θ − β θ1= θ 1 β (7) (7) −       y   β = arctan  y   (8) β = arctan  q    2 22 2  (8)  k ⋅ xk + yx + y   0· 0      k y k y     0  θ1 = arctan⋅ − ·⋅ −q ·  (9) θ =  k y k y0   1 arctan  k z x2 + y  (9) ⋅ − 0 2 + 0  k z0 · x0− y    2.1.4. Calculation of Slope Angle at Contact Surface

2.1.4. WhenCalculation the TOBV of Slope with Angle the inner at Contact diameter Surface of 200 mm is subjected to the temperature of 350 ◦C and the internalWhen the pressure TOBV ofwith 1 MPa, the theinner diameter diameter and of the200 thickness mm is subjected of the disc, to the outertemperature diameter of and350 the°C andthickness the internal of the pressure seal, the of three 1 MPa, offsets the ( Ediameter, H, and anγ),d andthe thickness the half conical of the disc, angle the (α )outer are given diameter from and the theinternational thickness regulationsof the seal, the (API609 three and offsets ASME (E, B16.10).H, and γ On), and the the basis half of conical the dimensions angle (α shown) are given in Table from1, thethe international geometry of theregulations disc surface (API609 was created and ASME using B16.10). commercial On the software, basis of GEOGEBRA, the dimensions as follows. shown in Table 1, the geometry of the disc surface was created using commercial software, GEOGEBRA, as (Step 1) Cone surface is generated by inputting α (13.9◦) using Equation (3), as shown in Figure9a. follows. (Step 2) When γ (10◦), disc thickness (15 mm) is given, H0 = 369.9 mm, H1 = 377.5 mm, (Step 1) ConeH2 =surface362.3 mmis generatedand rotary by inputting center of α disc (13.9°) is obtainedusing Equation from Equation(3), as shown (5), in and Figure then 9a.S0 , (Step 2) WhenS1, and γ (10°),S2 are disc generated thickness using (15 mm) Equation is given, (4), H as0 shown= 369.9 inmm, Figure H1 =9 377.5b. mm, H2 = 362.3 mm and rotary center of disc is obtained from Equation (5), and then S0, S1, and S2 are generated using Equation (4), as shown in Figure 9b. Appl. Sci. 2019, 9, 3095 7 of 19

Appl. Sci. 2019, 9, x FOR PEER REVIEW 7 of 19 (Step 3) The cone surface is cut by x = x0 (0.05, green plane) to obtain hyperbola in Equation (6), (Step 3)which The cone enables surface the is outer cut by diameter x = x0 (0.05, of discgreen to plane) be 190.1 to obtain mm, hyperbola and then in the Equation disc surface (6), is obtainedwhich enables as shown the in outer Figure diameter9c. of disc to be 190.1 mm, and then the disc surface is (Step 4) Rotaryobtained center as shown of the in disc Figure moves 9c. by the eccentricity H (23 mm) and E (2.5 mm) to avoid (Step 4) Rotary center of the disc moves by the eccentricity H (23 mm) and E (2.5 mm) to avoid interference between the seal and the disc during opening and closing, as shown in Figure9d. interference between the seal and the disc during opening and closing, as shown in Figure (Step 5) The9 (d). eccentric angle of 10◦ (γ) of the final triple offset model results in the variation of the (Step 5)slope The angle eccentric of the angle contact of 10° surface (γ) of the from final 66.1 triple◦ (minimum offset model angle) results to 86.1 in the◦ (maximum variation of angle) the in theslope tangential angle of direction, the contact as surface shown from in Figure 66.1° (minimum9e. angle) to 86.1° (maximum angle) in the tangential direction, as shown in Figure 9e.

(a) Step 1 (Generation of cone surface)

(b) Step 2 (Generation of S0, S1, and S2)

(c) Step 3 (fit the outer diameter of disc using hyperbola)

Figure 9. Cont. Appl. Sci. 2019, 9, 3095 8 of 19 Appl. Sci. 2019, 9, x FOR PEER REVIEW 8 of 19

(d) Step 4 (move the rotary center of disc by H and E to avoid interference)

(e) Step 5 (final model with variation of slope angle of the contact surface (66.1°~86.1°)

Figure 9. Procedure for generation of slope angle of the contact surface. Figure 9. Procedure for generation of slope angle of the contact surface.

Table 1. The value of triple offset butterfly valve (TOBV) parameters.

DiameterTable 1. ofThe the valuedisc (mm) of triple offset190.1 butterfly valveOffset (TOBV) 1, E parameters. (mm) 2.5 Thickness of disc, T (mm) 15 Offset 2, H (mm) 23 Diameter of the disc (mm) 190.1 Offset 1, E (mm) 2.5 Outer diameter of the seal (mm) 218 Offset 3, γ (°) 10 Thickness of disc, T (mm) 15 Offset 2, H (mm) 23 Thickness of seal (mm) 7 Half conical angle, α (°) 13.9 Outer diameter of the seal (mm) 218 Offset 3, γ (◦) 10 Thickness of seal (mm) 7 Half conical angle, α (◦) 13.9 2.2. Finite Element Analysis

2.2. Finite2.2.1. Geometry Element Analysis and Analysis Conditions

2.2.1. GeometryOn the basis and Analysisof the above Conditions generated geometry, 2D modeling of the sealing part at final shut-off position was conducted using a commercial software, Inventor 2019, as shown in Figure 10. The Oncontact the basisstress ofrises the with above the generated increase of geometry, the slope 2Dangle modeling based on of the the Hertzan sealing theory part at shown final shut-oin ff positionEquation was conducted (10) and Figure using 11, a so commercial simulations software, were carried Inventor out only 2019, in the as showncase of minimum in Figure 10(66.1°). The and contact stressmaximum rises with angle the (86.1°). increase of the slope angle based on the Hertzan theory shown in Equation (10) and Figure 11, so simulations were carried out only in the case of minimum (66.1◦) and maximum F ϕ Pcontact = 0.798 , F = Pworking× cos angle (86.1◦). 1 v2 1 v2 (10) luv( 1 )+( 2 ) tE1 EF2 Pcontact = 0.798 , F = Pworking cos ϕ (10) 1 v2 1 v2 × l( − 1 ) + ( − 2 ) E1 E2 Appl.Appl. Sci. Sci.2019 2019,,9 9,, 3095 x FOR PEER REVIEW 9 of9 of 19 19 Appl. Sci. 2019, 9, x FOR PEER REVIEW 9 of 19

Appl. Sci. 2019, 9, x FOR PEER REVIEW 9 of 19

Figure 10. Two-dimensional (2D) geometry of triple offset butterfly valve (TOBV). FigureFigure 10.10. Two-dimensionalTwo-dimensional (2D)(2D) geometrygeometry of triple ooffsetffset butterflybutterfly valve (TOBV).

Figure 10. Two-dimensional (2D) geometry of triple offset butterfly valve (TOBV).

Figure 11. Scheme of normal load (F) acting on the contact surface. Figure 11. Scheme of normal load (F) acting on the contact surface. Figure 11. Scheme of normal load (F) acting on the contact surface. In order to investigateFigure contact 11. Scheme stress of behaviornormal load according (F) acting on to the contact seal design, surface. a series of finite element (FE) simulationsIn order to investigate were performed contact with stress the behavior different according total number to the of se sealal design, layers bya series laminating of finite alternately element In order to investigate contact stress behavior according to the seal design, a series of finite element the(FE) American simulationsIn order Society towere investigate performed for Testing contact with and stress the Materials behaviordifferent (ASTM) according total number A240 to the of Grade se sealal design, layers 316 stainlessa byseries laminating of steelfinite (SS)element alternately and the the(FE) American simulations Society were performedfor Testing withand theMaterials different (A totaSTM)l number A240 Grade of seal 316layers stainless by laminating steel (SS) alternately and the graphite(FE) (G)simulations (1-layer were (SS), performed 3-layer (SS with/G the/SS), different 5-layer tota (SSl number/G/SS/G of/SS), seal 7-layerlayers by (SS laminating/G/SS/G /alternatelySS/G/SS)) and graphitethe American (G) (1-layer Society (SS), for Testing3-layer (SS/G/SS),and Materials 5-layer (A STM)(SS/G/SS/G/SS), A240 Grade 7-layer 316 stainless (SS/G/SS/G/SS/G/SS)) steel (SS) and and the thicknessthe American of graphite Society (0.6 for mm~1.2 Testing mm and at Materials the interval (ASTM) of 0.2 A240 mm), Grade as shown 316 stainless in Figure steel 12 (SS). Full-thickness and the thicknessgraphitegraphite (G)of graphite(G) (1-layer (1-layer (0.6 (SS), (SS), mm~1.2 3-layer 3-layer mm (SS/G/SS), (SS/G/SS), at the interval 5-layer5-layer of (SS/G/SS/G/SS),(SS/G/SS/G/SS), 0.2 mm), as shown 7-layer 7-layer in (SS/G/SS/G/SS/G/SS)) Figure (SS/G/SS/G/SS/G/SS)) 12. Full-thickness and and (7 (7 mm) of the seal is fixed, so thickness of 1-layer stainless steel depending on that of the graphite was mm)thicknessthickness of the of sealgraphite of graphite is fixed, (0.6 (0.6 mm~1.2so mm~1.2 thickness mm mm ofat at the 1-layerthe intervalinterval stainless ofof 0.2 0.2 mm), steelmm), asdepending as shown shown in inFigureon Figure that 12. of 12.Full-thickness the Full-thickness graphite (7 was (7 calculated according to the number of laminated layers, as listed in Table2. The analysis models were calculatedmm)mm) of the of according theseal seal is fixed,is tofixed, the so numberso thickness thickness of laminatedof of 1-layer1-layer stlayeainlessrs, as steel steel listed depending depending in Table on 2. on thatThe that of analysis theof thegraphite modelsgraphite was were was simulatedsimulatedcalculatedcalculated according accordingaccording according tototo thetothethe the temperaturestemperatnumber number ofures of laminated laminated (the room laye temperature rs,rs, as as listed listed in of ofin Table 22 22Table °C◦ C2. and and2.The The theanalysis the analysis high high models temperature temperature models were were of of 350350simulated◦ °C)C)simulated usingusing according commercialaccording to tothe finitethe finite temperat temperat elemen elementuresurest software, software, (the(the room ANSYS ANSYS temperaturetemperature workbench workbench of of 22 22 °Cver. °C ver.and 18.and the18. the high high temperature temperature of of 350 °C)350 °C)using using commercial commercial finite finite elemen element tsoftware, software, ANSYS workbench workbench ver. ver. 18. 18.

(a)( a1-la) 1-layeryer (SS) (SS) ((bb) )3-la 3-layyerer (SS/G/SS) (SS/G/SS) (a) 1-layer (SS) (b) 3-layer (SS/G/SS)

(c) 5-layer (SS/G/SS/G/SS) (d) 7-layer (SS/G/SS/G/SS/G/SS) (c) 5-layer (SS/G/SS/G/SS) (d) 7-layer (SS/G/SS/G/SS/G/SS) Figure 12. (Analysisc) 5-lay ermodel (SS/G/SS/G/SS) with the different number (d of) 7layer.-layer SS, (SS/G/SS/G/SS/G/SS) stainless steel; G, graphite. FigureFigure 12.12. AnalysisAnalysis model with the different different number of layer. layer. SS, SS, stainless stainless steel; steel; G, G, graphite. graphite. Figure 12. Analysis model with the different number of layer. SS, stainless steel; G, graphite. Appl. Sci. 2019, 9, 3095 10 of 19

Table 2. Thicknesses of graphite and stainless steel according to the number of layers.

1-Layer Model 3-Layer Model 5-Layer Model 7-Layer Model Stainless Stainless Stainless Stainless Steel Graphite Graphite Graphite Steel Steel Steel 0.6 3.20 0.6 2.13 0.6 1.45 Thickness 0.8 3.10 0.8 2.07 0.8 1.39 7 (mm) 1.0 3.00 1.0 2.00 1.0 1.55 1.2 2.90 1.2 1.93 1.2 1.36

The chemical composition and mechanical properties of the ASTM A240 Grade 316 stainless steel are listed in Table3. Thermal and mechanical properties of A240–316 (retainer and steel layer), A216 Wrought Carbon with Grade B (WCB) (body), and graphite according to the temperatures (25 ◦C~350 ◦C) are listed in Table4[16,22,23].

Table 3. Chemical composition of (American Society for Testing and Materials) ASTM A240 Grade 316 Stainless Steel.

Carbon 0.08% Silicon 1.0% Manganese 2.0% ≤ ≤ ≤ Phosphorous 0.045% Sulphur 0.030% Nickel 10~14% ≤ ≤ Chromium 16%~18% Molybdenum 2%~3% Iron 61.8%~72%

Table 4. Nonlinear material properties according to temperature.

(a) Thermal Conductivity

Thermal Conductivity (W/m ◦C) Temperature (◦C) · A240–316 A216 WCB Graphite 25 14.1 11.5 108.4 100 15.4 12.7 106.5 200 16.8 13.8 102.5 250 17.6 14.3 100.3 300 18.3 14.9 98.3 350 19.0 15.4 88.9 (b) Thermal Expansion 6 Thermal Expansion (10− m/m ◦C) Temperature (◦C) · A240–316 A216 WCB Graphite 25 0 0 0 100 1.3 1.0 0.8 200 3.1 2.3 1.8 250 4.0 3.0 1.8 300 4.9 3.7 1.8 350 5.9 4.5 1.8 (c) Mechanical Property Elastic Modulus (GPa) Poisson’s Ratio Temperature ( C) ◦ A240–316 A240–316 A216 WCB Graphite Graphite A216 WCB 25 195 202 9.83 100 189 198 9.53 200 183 192 9.53 0.29 0.21 250 179 189 9.53 300 176 185 9.53 350 172 179 6.619 Appl.Appl. Sci. Sci.2019 2019, 9,, 30959, x FOR PEER REVIEW 11 of11 19 of 19 Appl. Sci. 2019, 9, x FOR PEER REVIEW 11 of 19

Thermal-structural coupled analysis was conducted to calculate contact stress considering Thermal-structuralThermal-structural coupledcoupled analysisanalysis waswas conductedconducted to to calculate calculate contact contact stress stress considering considering deformation caused by the thermal loads and the working pressure (1 MPa). In the thermal analysis, deformationthe convective caused heat by transfer the thermal coefficient, loads 3.675 and the × 10 working−3 W/mm pressure2·°C, was (1 employed MPa). In to the the thermal edges analysis,of the the convective heat transfer coefficient, 3.675 × 10−33 W/mm2·°C,2 was employed to the edges of the the convective heat transfer coefficient, 3.675 10− W/mm ◦C, was employed to the edges of the body, the retainer and the seal, which was exposed× to the room· temperature, and the thermal load of body, the retainer and the seal, which was exposed to the room temperature, and the thermal load 350 °C was imposed on the edges, where contact with the working fluid occurred, as shown in Figure of 350 C was imposed on the edges, where contact with the working fluid occurred, as shown in 13a. Friction◦ coefficients between the disc and the seal were 0.3 for stainless steel and 0.21 for graphite, Figure 13a. Friction coefficients between the disc and the seal were 0.3 for stainless steel and 0.21 for respectively, as shown in Figure 13b [19]. graphite, respectively, as shown in Figure 13b [19].

FigureFigure 13. 13.Analysis Analysis condition condition ofof thermalthermal simulation.simulation. ( (aa)) Temperature Temperature and and convection, convection, (b ()b friction) friction Figure 13. Analysis condition of thermal simulation. (a) Temperature and convection, (b) friction coecoefficient.fficient. SS, SS, stainless stainless steel; steel; G, G, graphite. graphite. coefficient. SS, stainless steel; G, graphite. The global hexagonal grid size of the disc, the body, and the retainer was 1 mm, and that of the The global hexagonal grid size of the disc, the body, and the retainer was 1 mm, and that of the seal was 0.5 mm. The denser sizing of 0.1 mm was set up to the edges of the seal and the body at seal was 0.5 mm. The denser sizing of 0.1 mm was set up to the edges of the seal and the body at whichwhich contact contact stress stress occurs occurs as as shown shown in in Figure Figure14 14a,a, and and thethe numbernumber of nodes nodes was was 555,953 555,953 and and that that of of elementselements was was 182,554. 182,554. The The orthogonal orthogonal qualityquality of 98.9% was was close close to to 1, 1, and and skewness skewness ofof 92.8% 92.8% was was closeclose to to 0 as0 as shown shown in in Figure Figure 14 14b,b, which whichverifies verifies thethe FEFE model.

(a) Edge sizing

(b) Orthogonal quality and skewness Figure 14. Generation of mesh. FigureFigure 14.14. Generation of of mesh. mesh. Appl. Sci. 2019, 9, 3095 12 of 19

Appl. Sci. 2019, 9, x FOR PEER REVIEW 12 of 19 The modeling and outputs of the thermal analysis were coupled to the static structural analysis, The modeling and outputs of the thermal analysis were coupled to the static structural analysis, as shown in Figure 15a. In this step, deformations at the disc, which were caused by torque applied as shown in Figure 15a. In this step, deformations at the disc, which were caused by torque applied on the shaft to rotate the disc and to maintain it at the desired position, should be considered [24]. on the shaft to rotate the disc and to maintain it at the desired position, should be considered [24]. Moment load condition is usable for only axisymmetric geometry in 2D analysis, but is inapplicable Moment load condition is usable for only axisymmetric geometry in 2D analysis, but is inapplicable because the 2D model is asymmetric because of its eccentricities, thus the maximum deformation in because the 2D model is asymmetric because of its eccentricities, thus the maximum deformation in the y-axis ( 5.5 10 3 mm) at the disc, which was obtained from the 3D simulation, was considered the y-axis (−−5.5 ×× 10−3− mm) at the disc, which was obtained from the 3D simulation, was considered inin the 2D simulation, simulation, as as shown shown in in Figure Figure 15b. 15 b.Also, Also, the the temperature temperature distribution distribution with with the maximum the maximum value ofof 350350◦ C°C and and the the minimum minimum of of 36.5 36.5◦C °C was wa importeds imported to theto the boundary boundary condition, condition, and and the workingthe pressureworking pressure (1 MPa) (1 was MPa) applied was applied as shown as shown in Figure in Fi 15gurec. The 15c. body The body and theand retainer the retainer were were fixed, fixed, and the 4 xand-displacement, the x-displacement, which waswhich a relativelywas a relatively very small very small value value (1.7 (1.710 −× 10mm),−4 mm), was was not not considered. considered. ×

(a) Coupling model and result of thermal analysis to static analysis

(b) Analysis conditions and y-axis deformation distribution caused by torque in 3D simulation

(c) Load conditions (temperature, working pressure, and y-displacement)

FigureFigure 15. 15. AnalysisAnalysis conditions conditions of thermal-structural of thermal-structural coupled coupled simulation. simulation.

2.2.2. Results Results of of the the Thermal-Structural Thermal-Structural Analysis Analysis High contact contact stress stress improves improves sea sealingling performance, performance, while while it does it doesnot allow not allowthe smooth the smooth driving drivingof ofthe the disc. disc. It is It thus is thus necessary necessary to find to find an aneffect effiveective trade-off trade-o betweenff between needs needs for good for good operation operation and and prevention of leakage. Contact stress, which is a little higher than the working pressure, could guarantee prevention of leakage. Contact stress, which is a little higher than the working pressure, could guarantee not only airtightness, but also smooth rotation of the disc. Tables 5 and 6 represent the maximum contact not only airtightness, but also smooth rotation of the disc. Tables5 and6 represent the maximum stresses for the different seal designs, temperatures (25 °C and 350 °C) and slope angles (66.1° and 86.1°). contact stresses for the different seal designs, temperatures (25 C and 350 C) and slope angles (66.1 SS and G indicate stainless steel and graphite, and min and max◦ mean the◦ minimum (66.1°) and ◦ andmaximum 86.1◦). (86.1°) SS and slope G indicate angles. stainless steel and graphite, and min and max mean the minimum (66.1◦) and maximum (86.1◦) slope angles. Appl. Sci. 2019, 9, 3095 13 of 19

Table 5. Maximum contact stresses of stainless steel.

Graphite SSmin (66.1◦) SSmax (86.1◦)

Thickness (mm) 22 ◦C 350 ◦C 22 ◦C 350 ◦C 1-layer - 2.00 282.17 0.64 199.71 0.6 2.05 169.22 1.16 129.86 0.8 2.13 154.37 1.16 128.81 3-layer 1 2.14 124.61 1.51 115.68 1.2 2.26 115.37 1.60 95.33 0.6 3.40 118.94 1.92 104.14 0.8 3.62 116.61 2.26 85.61 5-layer 1 3.73 113.53 2.66 79.56 1.2 3.98 104.82 2.67 76.53 0.6 3.46 122.55 2.71 68.67 0.8 3.66 97.15 2.99 66.81 7-layer 1 5.09 74.50 4.33 64.33 1.2 6.33 74.13 4.90 63.02

Table 6. Maximum contact stresses of graphite.

Graphite Gmin (66.1◦)Gmax (86.1◦)

Thickness (mm) 22 ◦C 350 ◦C 22 ◦C 350 ◦C 0.6 0.26 12.33 0.16 5.03 0.8 0.28 13.01 0.17 5.67 3-layer 1 0.22 8.71 0.16 4.03 1.2 0.24 7.07 0.15 3.75 0.6 0.26 8.12 0.16 3.11 0.8 0.19 7.20 0.15 2.56 5-layer 1 0.22 5.93 0.15 2.14 1.2 0.21 5.72 0.13 2.10 0.6 0.24 7.52 0.18 2.40 0.8 0.21 4.90 0.18 1.74 7-layer 1 0.17 3.60 0.15 0.81 1.2 0.19 2.73 0.14 0.79

For both stainless steel and graphite, the models with the slope angle of 66.1◦ showed lower contact stresses than those of 86.1◦, which proves that the increases of the contact surface led to a reduction of the peak contact stress, and sealing performance was improved with increasing temperature as a result of thermal expansion. In respect to the graphite layers, leakages were expected for the all models at 25 ◦C (Gmin: 0.19~0.28 MPa,Gmax: 0.14~0.18 MPa), and there were small changes in contact stress by varying the amount of the graphite, whereas at 350 ◦C, the larger contact stresses (Gmin: 12.33~4.73 MPa, Gmax: 5.03~0.79 MPa) beyond the working pressure were observed. This means that the graphite displayed a sealing effect at high temperature rather than at room temperature, and the contact stress decreases with increment of the number of laminated layer. In respect to the stainless steel layers, the graphite did not withstand the contact force at 25 ◦C, so the contact stress at the stainless steel increased with more amount of the graphite (SS : 2.0 MPa 6.3 MPa, SSmax: 1.2 MPa 4.9 MPa) because the min → → contact force was intensively applied on the stainless steel. On the other hand, at 350 ◦C, the contact force was distributed to the graphite, so more graphite leads to a reduction of the peak contact stress at the stainless steel (SS : 169.2 MPa 74.13 MPa, SSmax: 129.9 MPa 63.0 MPa). min → → The 1-layer model with the slope angle of 86.1◦ showed leakage (SSmax: 0.61 MPa) at 25 ◦C, while the excessive contact stresses (SSmin: 282.17 MPa, SSmax: 199.71 MPa) at 350 ◦C would disturb smooth operation of the disc. In the 3-layer and 5-layer models, the contact stresses of the stainless steel (SSmin: 169.22~115.37 MPa and SSmax: 129.86~95.33 MPa for 3-layer, SSmin: 118.94~94.82 MPa and SSmax: 104.14~76.53 MPa for 5-layer) decreased compared with those of the single layered model Appl. Sci. 2019, 9, x FOR PEER REVIEW 14 of 19 Appl. Sci. 2019, 9, x FOR PEER REVIEW 14 of 19

282.17 MPa, SSmax: 199.71 MPa) at 350 °C, but they were still too large. The 7-layer model with the 282.17 MPa, SSmax: 199.71 MPa) at 350 °C, but they were still too large. The 7-layer model with the graphite thickness of 1.2 mm showed the lowest contact stresses of the stainless steel (SSmin: 74.13 Appl.graphite Sci. 2019 thickness, 9, 3095 of 1.2 mm showed the lowest contact stresses of the stainless steel (SSmin: 74.1314 of 19 MPa, SSmax: 63.02 MPa) at 350 °C, but the maximum contact stresses of the graphite were below the MPa, SSmax: 63.02 MPa) at 350 °C, but the maximum contact stresses of the graphite were below the working pressure (Gmax: 0.79 MPa). Therefore, the 7-layer model with the graphite thickness of 0.8 working pressure (Gmax: 0.79 MPa). Therefore, the 7-layer model with the graphite thickness of 0.8 mm was suggested to guarantee not only airtightness, but also smooth rotation of the disc, and its (SSmmmin was: 282.17 suggested MPa, SSto maxguarantee: 199.71 not MPa) only at airtightness 350 ◦C, but, but they also were smooth still too rotation large. of The the7-layer disc, and model its contact stress distributions are shown in Figures 16 and 17. withcontact the graphitestress distributions thickness ofare 1.2 shown mm showedin Figures the 16 lowest and 17. contact stresses of the stainless steel (SSmin: Analyses results of the new laminated seal at 350 °C were compared to those at the 1-layer, 3- 74.13 MPa,Analyses SSmax results: 63.02 of MPa) the new at 350 laminated◦C, but theseal maximum at 350 °C contactwere compared stresses ofto thethose graphite at the were1-layer, below 3- layer, and 5-layer models in Table 7. The maximum contact stresses in case of the slope angle of 66.1° thelayer, working and 5-layer pressure models (Gmax in: Table 0.79 MPa). 7. The Therefore,maximum co thentact 7-layer stresses model in case with of the the graphite slope angle thickness of 66.1° of were reduced by 65.5%, 42.6%~15.8%, and 18.3%~7.3%, and those in case of the slope angle of 86.1° 0.8were mm reduced was suggested by 65.5%, to guarantee42.6%~15.8%, not and only 18.3%~7.3%, airtightness, and but those also smoothin case of rotation the slope of theangle disc, of and86.1° its were reduced by 66.5%, 48.8%~29.9%, and 35.8%~12.7%, respectively, which means that the shape contactwere reduced stress distributions by 66.5%, 48.8%~29.9%, are shown in and Figures 35.8%~12.7%, 16 and 17 respectively,. which means that the shape design of the laminated seal allows to mitigate the excessive contact stress. design of the laminated seal allows to mitigate the excessive contact stress.

(a) Slope angle of 66.1° (b) Slope angle of 86.1° (a) Slope angle of 66.1° (b) Slope angle of 86.1° Figure 16. Contact stress distribution at stainless steel of the 7-layer model with graphite thickness of FigureFigure 16. 16.Contact Contact stressstress distributiondistribution atat stainless steel of the the 7-layer 7-layer model model with with graphite graphite thickness thickness of of 0.8 mm. 0.80.8 mm. mm.

(a) Slope angle of 66.1 (b) Slope angle of 86.1° (a) Slope angle of 66.1 (b) Slope angle of 86.1° Figure 17. Contact stress distribution at graphite of the 7-layer model with graphite thickness of 0.8 Figure 17. Contact stress distribution at graphite of the 7-layer model with graphite thickness of 0.8 Figuremm. 17. Contact stress distribution at graphite of the 7-layer model with graphite thickness of mm. 0.8 mm. Table 7. Comparison of peak contact stress at the new seal with those at the 1-layer, 3-layer, and 5- Table 7. Comparison of peak contact stress at the new seal with those at the 1-layer, 3-layer, and 5- Analyseslayer models results (350 of °C). the new laminated seal at 350 ◦C were compared to those at the 1-layer, 3-layer, layer models (350 °C). and 5-layer models in Table7. The maximum contact stresses in case of the slope angle of 66.1 ◦ were Comparison Graphite Reduction of Peak Contact Stress reduced byComparison 65.5%, 42.6%~15.8%, Graphite and 18.3%~7.3%,Reduction and those of in casePeak ofContact the slope Stress angle of 86.1◦ were Model Thickness (mm) Slope Angle of 66.1° Slope Angle of 86.1° reduced by 66.5%,Model 48.8%~29.9%, Thickness and (mm) 35.8%~12.7%, Slope respectively, Angle of 66.1° which Slope means Angle that the of shape86.1° design of 1-layer - 65.6%↓ 66.5%↓ the laminated1-layer seal allows to mitigate- the excessive contact 65.6%↓ stress. 66.5%↓ 0.6 42.6%↓ 48.6%↓ 0.6 42.6%↓ 48.6%↓ 0.8 37.1%↓ 48.1%↓ Table 7. Comparison3-layer of peak contact0.8 stress at the new37.1% seal with↓ those at the 1-layer,48.1% 3-layer,↓ and 5-layer 3-layer 1 22.0%↓ 42.2%↓ models (350 ◦C). 1 22.0%↓ 42.2%↓ ↓ ↓ 1.2 15.8%↓ 29.9%↓ 1.2 15.8% Reduction of Peak Contact29.9% Stress Comparison Model Graphite0.6 Thickness (mm) 18.3%↓ 35.8%↓ 0.6 18.3%↓ 35.8%↓ 0.8 16.7%Slope↓ Angle of 66.1◦ Slope22.0% Angle↓ of 86.1◦ 5-layer 0.8 16.7%↓ 22.0%↓ 5-layer1-layer 1 -14.4%↓ 65.6% 16.0%66.5%↓ 1 14.4%↓ ↓ 16.0%↓ ↓ 1.2 0.67.3%↓ 42.6% 12.7%48.6%↓ ↓ ↓ ↓ ↓ 1.2 0.87.3% 37.1% 12.7%48.1% 3-layer ↓ ↓ 1 22.0% 42.2% ↓ ↓ 2.2.3. Discussions—Effect of Graphite on1.2 Sealing Ability 15.8% 29.9% 2.2.3. Discussions—Effect of Graphite on Sealing Ability ↓ ↓ On the basis of the previous study 0.6in relation with the cryogenic 18.3% triple-offset butterfly35.8% valve with ↓ ↓ On the basis of the previous study 0.8in relation with the cryogenic 16.7% triple-offset butterfly22.0% valve with the laminated5-layer seal, which is installed in liquefied natural gas (LNG)↓ marine engine,↓ to control the the laminated seal, which is installed in1 liquefied natural gas 14.4% (LNG) marine engine,16.0% to control the flow of liquid nitrogen (−196 °C) to liquefy natural gas [25], the ↓contact stress behaviors↓ under the flow of liquid nitrogen (−196 °C) to liquefy1.2 natural gas [25], 7.3%the contact stress behaviors12.7% under the three different temperatures (−196 °C, 25 °C, and 350 °C) were analyzed↓ to discover the↓ graphite effect three different temperatures (−196 °C, 25 °C, and 350 °C) were analyzed to discover the graphite effect 2.2.3. Discussions—Effect of Graphite on Sealing Ability On the basis of the previous study in relation with the cryogenic triple-offset butterfly valve with the laminated seal, which is installed in liquefied natural gas (LNG) marine engine, to control the flow Appl. Sci. 2019, 9, 3095 15 of 19 Appl. Sci. 2019, 9, x FOR PEER REVIEW 15 of 19 at each temperature. In the stainless steel layer, the contact stress was increased at 350 °C as a result of liquid nitrogen ( 196 ◦C) to liquefy natural gas [25], the contact stress behaviors under the three of undergoing thermal− expansion, while in the graphite layer, the larger contact stresses were different temperatures ( 196 ◦C, 25 ◦C, and 350 ◦C) were analyzed to discover the graphite effect at observedAppl. Sci.at 3502019, °C9, x andFOR PEER −−196 REVIEW °C rather than 25 °C, which indicates that the graphite is a favorable15 of 19 for each temperature. In the stainless steel layer, the contact stress was increased at 350 ◦C as a result of sealing property at severe temperature. As more laminated layers of the graphite, the contact stresses undergoingat each temperature. thermal expansion, In the stainless while insteel the layer, graphite the contact layer, stress the larger was increase contactd stressesat 350 °C were as a result observed at both graphite and stainless steel decrease at 350 °C, but opposite behavior was observed at −196 at 350of◦ Cundergoing and 196 ◦thermalC rather expansion, than 25 ◦whileC, which in the indicates graphite that layer, the the graphite larger iscontact a favorable stresses for were sealing − property°C. It observedis worth at severe atnoticing 350 temperature. °C andthat − the196 graphite°C As rather more thancontributes laminated 25 °C, which layersimproving indicates of the drivin graphite,that theg performance graphite the contact is a favorableof stresses the disc for at at both the high temperature and sealing ability at the cryogenic temperature, as shown in Table 8. graphitesealing and property stainless at severe steel decrease temperature. at 350 As ◦moreC, but laminated opposite layers behavior of the graphite, was observed the contact at stresses196 ◦C. It is at both graphite and stainless steel decrease at 350 °C, but opposite behavior was observed− at −196 worth noticingTable 8. Comparison that the graphite of contact contributes stress behavior improving of laminated driving seal performance at 350 °C withof that the at disc−w96 at °C. the high temperature°C. It is worth and sealing noticing ability that the at graphite the cryogenic contributes temperature, improving asdrivin showng performance in Table8. of the disc at the high temperature and sealing ability at the cryogenic temperature, as shown in Table 8. Change of Contact Stress as More Table 8. Comparison of contact stress behavior of laminated seal at 350 C with that at w96 C. TemperatureTable (°C) 8. Comparison ofLayers contact stressof Graphite behavior of laminated seal at 350 °CPurpose◦ with that of at Graphite −w96− °C. ◦ ChangeStainless of Contact Steel Stress as Graphite More Layers of Graphite Temperature (◦C) Change of Contact Stress as More Purpose of Graphite 350 ↓ ↓ For improving driving performance Temperature (°C) StainlessLayers Steel of Graphite Graphite Purpose of Graphite −350196 ↑ ↑ For improvingFor improving sealing driving performance performance Stainless↓ Steel Graphite ↓ 196 For improving sealing performance − 350 ↓↑ ↓ ↑ For improving driving performance 2.2.4. Verification−196 of Structural↑ Safety of the Proposed↑ TOBV For improving sealing performance 2.2.4. Verification of Structural Safety of the Proposed TOBV In order to verify the reliability of the TOBV with the proposed laminated seal, the 3D thermal- 2.2.4. Verification of Structural Safety of the Proposed TOBV structuralIn order coupled to verify analysis the reliabilitywas conducted of the as TOBV shown with in theFigure proposed 18. The laminated simulation seal, conditions the 3D (convectivethermal-structuralIn heatorder transfer to coupled verify coefficient, the analysis reliability was thermal of conductedthe TOBV load, withfriction as shown the proposedcoefficients, in Figure laminated 18and. The torque) seal, simulation the were 3D thermal- the conditions same as (convectivein thestructural 2D analysis. heat coupled transfer Table analysis 9 coe comparesfficient, was thermalconductedthe maximum load, as shown friction equivalent in coe Figureffi stresscients, 18. at The and each torque)simulation part with were conditions the the allowable same as (convective heat transfer coefficient, thermal load, friction coefficients, and torque) were the same as strengthin the 2D [26], analysis. and it Table is expected9 compares that the all maximum components equivalent are not stressyielded at eachat 350 part °C. with Also, the the allowable contact in the 2D analysis. Table 9 compares the maximum equivalent stress at each part with the allowable surfacesstrength [of26 the], and final it ismodel expected showed that allthe components sticking status are notas shown yielded in at Figure 350 C. 19, Also, so deboning the contact of surfacesthe seal strength [26], and it is expected that all components are not yielded at ◦350 °C. Also, the contact layersof thesurfaces finaldue to model ofthe the different showed final model theexpans showed stickingion coefficientsthe status sticking as shown status does as innot shown Figure occur. in19 Figure, so deboning 19, so deboning of the seal of the layers seal due to thelayers different due to expansion the different coe expansfficientsion does coefficients not occur. does not occur.

(c) (Discc) Disc (a) Body(a) Body ( (bb)) ShaftShaft

(d) Laminated seal—stainless steel (e) Laminated seal—graphite (d) Laminated seal—stainless steel (e) Laminated seal—graphite FigureFigure 18. 18.Equivalent Equivalent stress stress distribution distribution in each each part part of of proposed proposed model. model. Figure 18. Equivalent stress distribution in each part of proposed model.

Figure 19. Contact status between stainless and graphite layers. Figure 19. Contact status between stainless and graphite layers. Appl. Sci. 2019, 9, x FOR PEER REVIEW 16 of 19 Appl. Sci. 2019, 9, 3095 16 of 19

Table 9. Structural safety of the proposed TOBV. Table 9. Structural safety of the proposed TOBV. Part Allowable Strength (MPa) Maximum Equivalent Stress (MPa) Yielding BodyPart Allowable184.25 Strength (MPa) Maximum Equivalent 158.30 Stress (MPa) Yielding No ShaftBody 385.25 184.25 143.19 158.30 No No DiscShaft 137.35 385.25 117.51 143.19 No No Disc 137.35 117.51 No SS SS137.35 137.35 56.50 56.50 No No G G4.69 4.69 0.24 No No

3. Prototype Prototype and Performance Test

3.1. Internal Internal Pressure and Leakage Tests The performanceperformance tests tests of theof proposedthe proposed TOBV TOBV were conducted were conducted using the using experimental the experimental equipment, equipment,based on the based regulation on the of regulation KS B 2304:2001 of KS B (General 2304:2001 rules (General for inspection rules for ofinspection valves). Theof valves). boiler andThe boilerthe temperature and the temperature sensor controlled sensor thecontrolled temperature the temperature of 350 ◦C, and of 350 the °C, pressure and the gauge pressure checked gauge the checkedinternal the pressure. internal In pressure. the internal In the pressure internal test,pressu there valvetest, the body valve was body filled was with filled the with water the atwater the athalf-shut the half-shut position, position, and then and the then internal the internal pressure pressure of 1.7 MPa, of 1.7 which MPa, exceeded which exceeded the working the pressureworking (1pressure MPa) (11.5 MPa), was × maintained1.5, was maintained for 182 s. Infor the 182 leakage s. In the test, leakage the valve test, body the valve was filled body with was the filled water with at × the fullywater shut-o at theff fullyposition, shut-off and theposition, internal and pressure the in ofternal 1.15 pressure MPa, which of 1.15 exceeded MPa, thewhich working exceeded pressure the (1working MPa) pressure1.1, was (1 maintained MPa) × 1.1, for was 125 maintained s. The results for of125 the s. The flowrate results measurement of the flowrate exhibit measurement that there × wereexhibit no that leakage there andwere exudation no leakage in and both exudation tests, as shown in both in tests, Table as 10 shown and Figurein Table 20 10. and Figure 20.

Table 10. Results of performance tests.

InternalInternal Pressure Pressure (MPa) Duration Duration Time Time (s) (s) Result Result RegulationRegulation 1.5 1.5 160 160 InternalInternal pressure pressure test test NoNo leakage leakage ActualActual 1.7 1.7 182 182 RegulationRegulation 1.1 1.1 125 125 LeakageLeakage test test NoNo leakage leakage ActualActual 1.15 1.15 30 30

(a) Internal pressure and duration time (left: pressure test, right: leakage test)

(b) Visual inspection and leakage measurement

Figure 20. Conditions and results of the performance tests.

3.2. Field Field Test of Proposed TOBV in CCPPs The prototype of the proposed TOBV was installedinstalled at the gas turbine in the CCPPs and was operated for three months to eval evaluateuate durability and suitability suitability for for the the actual actual working working environment. environment. Leakage could not be measured at the rear end of the turbine, so sealing performance of the new Appl. Sci. 2019, 9, x FOR PEER REVIEW 17 of 19 Appl. Sci. 2019, 9, 3095 17 of 19 model was predicted by comparing its temperature with that of the conventional valve, as shown in Figuremodel was21. Perfect predicted sealing by comparing blocks the itshot temperature gas flow into with the thatoutlet of thepipe, conventional which allows valve, the temperature as shown in inFigure the rear 21. Perfectend to decrease. sealing blocks The measurement the hot gas flow result intos show the outlet that the pipe, gas which (350 °C), allows which the temperatureentered into thein the inlet rear pipe end during to decrease. the disc The opening, measurement elevated results sharply show the that temperature the gas (350 at the◦C), rear which end entered from 27 into °C tothe 100 inlet °C. pipe After during then, the the disc temperature opening, elevateddecreased sharply at fully the shut-off temperature position, at the and rear it kept end fromin an 27 almost◦C to 100steady◦C. state. After The then, time the temperatureto be required decreased for openin at fullyg and shut-o closingff position, the disc and was it 4.25 kept s, in and an almostits cycle steady was onestate. day. The Temperature time to be required of the fornew opening model and(32 closing°C) decreased the disc by was 20%, 4.25 compared s, and its cycle with was that one of day.the Temperatureconventional ofone the (40 new °C), model which (32 demonstrates◦C) decreased that by the 20%, proposed compared laminated with that seal of improved the conventional the sealing one (40ability◦C), of which the TOBV. demonstrates that the proposed laminated seal improved the sealing ability of the TOBV.

Figure 21. TemperaturesTemperatures at rear end of the new TOBV and the conventional one. 4. Conclusions 4. Conclusions This study developed the laminated seal to enhance sealing performance and operability of the This study developed the laminated seal to enhance sealing performance and operability of the TOBV. Our conclusions are summarized as follows. TOBV. Our conclusions are summarized as follows. (1) WhenWhen the the TOBV TOBV has has the the inner inner diameter diameter of of the the pi pipe:pe: 200 200 mm, mm, the the diameter diameter of disc: of disc: 190.1 190.1 mm, mm, the outerthe outer diameter diameter of seal: of seal: 218 218 mm, mm, and and the the thickness thickness of ofdisc: disc: 15 15 mm, mm, the the three three eccentricities eccentricities (offset (offset 1:1: 2.5 2.5 mm, mm, offset offset 2: 23 23 mm, mm, offset offset 3: 10°) 10◦) were were specified specified based based on the international regulation, andand the the slope angles of contact surface (66.1(66.1°◦ (minimum(minimum angle)~86.1angle)~86.1°◦ (maximum angle)) for eliminatingeliminating rubbing rubbing were were calculated. calculated. (2) Thermal-structuralThermal-structural coupled analysesanalyses werewere conducted conducted for for the the di differentfferent seal seal designs designs (the (the number number of ofseal seal layers layers and and graphite graphite thicknesses), thicknesses), temperatures temperatures (25 (25◦C and°C and 350 350◦C), °C), and and slope slope angles angles (66.1 (66.1°◦ and and86.1 ◦86.1°),), and theand maximum the maximum contact contact stresses’ stresses’ behaviors behaviors at the contact at the surfaces contact were surfaces investigated were investigatedas follows: as follows: - It was observed that the increases of contact surface led to a reduction of the peak contact - It was observed that the increases of contact surface led to a reduction of the peak contact stress, so that sealing performance was improved with increasing temperature as a result stress, so that sealing performance was improved with increasing temperature as a result of thermal expansion. of thermal expansion. - In respect to the graphite layers, leakages were expected for the all models at 25 °C (Gmin: - In respect to the graphite layers, leakages were expected for the all models at 25 ◦C (Gmin: 0.19~0.28 MPa, Gmax: 0.14~0.18 MPa), and there were small changes in contact stress by 0.19~0.28 MPa, Gmax: 0.14~0.18 MPa), and there were small changes in contact stress by varying the amount of the graphite, whereas at 350 °C, the larger contact stresses (Gmin: varying the amount of the graphite, whereas at 350 ◦C, the larger contact stresses (Gmin: 12.33~4.73 MPa, Gmax: 5.03~0.79 MPa) beyond the working pressure were observed, which 12.33~4.73 MPa, G : 5.03~0.79 MPa) beyond the working pressure were observed, means that the graphitemax showed a sealing ability at the high temperature rather than at the which means that the graphite showed a sealing ability at the high temperature rather room temperature. than at the room temperature. - In respect to the stainless steel layers, the graphite did not withstand the contact force at 25 - In respect to the stainless steel layers, the graphite did not withstand the contact force at °C, so it was intensively applied on the stainless steel whose surface was decreased as the 25 C, so it was intensively applied on the stainless steel whose surface was decreased as amount◦ of the graphite was increased, and then the contact stresses at the stainless steel the amount of the graphite was increased, and then the contact stresses at the stainless were increased (SSmin: 2.0 MPa → 6.3 MPa, SSmax: 1.2 MPa → 4.9 MPa). While at 350 steel were increased (SSmin: 2.0 MPa 6.3 MPa, SSmax: 1.2 MPa 4.9 MPa). While at °C, the contact force was distributed to→ the graphite, and the peak→ contact stress at the 350 C, the contact force was distributed to the graphite, and the peak contact stress at stainless◦ steel was reduced (SSmin: 169.2 MPa → 74.13 MPa, SSmax: 129.9 MPa → 63.0 MPa) as the amount of graphite was increased. Appl. Sci. 2019, 9, 3095 18 of 19

the stainless steel was reduced (SSmin: 169.2 MPa 74.13 MPa, SSmax: 129.9 MPa → → 63.0 MPa) as the amount of graphite was increased. - The 7-layer model (graphite thickness: 0.8 mm, stainless thickness: 1.15, total thickness of seal: 7 mm, the slope angles of contact surface: 66.1◦ and 86.1◦) was suggested to guarantee not only airtightness, but also smooth rotation of the disc.

(3) More laminated layers of the graphite decreased the contact stresses in both graphite and stainless steel at 350 C, but opposite behavior was observed at 196 C, which means the graphite is in ◦ − ◦ charge of improving driving performance of the disc at the high temperature and sealing ability at the cryogenic temperature.

(4) In the field test, which was implemented for three months in CCPPs, the temperature (32 ◦C) in the rear end of the new model decreased by 20%, compared with that of the conventional one (40 ◦C), which demonstrates that the proposed laminated seal improved the sealing ability of the TOBV, and its durability and suitability for the actual working environment were verified.

The TOBV with the new laminated seal could improve turbine performance in the high temperature and production of electricity; furthermore, it could be widely applied to various industry fields under the server environments.

Author Contributions: H.S.K., H.S.S., and R.M.B. conceived design method/FEA, analyzed the data, and performed the experiments; R.M.B. performed design and FEA; H.S.K. wrote the manuscript; H.S.S. assisted with FEA; C.K. was in charge of the whole trial. All authors read and approved the final manuscript. Funding: This research was funded by the research development business funded by the KOREA SOUTHERN POWER CO., LTD (KOSPO)—2017-02. The authors gratefully acknowledge this support. Acknowledgments: The authors would like to express gratitude to KOREA SOUTHERN POWER CO., LTD (KOSPO for funding and for critical discussion and technical assistance. Conflicts of Interest: The authors declare no conflict of interest.

Abbreviations

CCPP Combined Cycle Power Plants SOBV Single Offset Butterfly Valve DOBV Double Offset Butterfly Valve TOBV Triple Offset Butterfly Valve PTFE Polytetrafluoroethylene ASME The American Society of Mechanical Engineers API American Petroleum Institute

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