Stresses and Displacement FEM Analysis on Biplane Disks

of the Butterfly Valves

MANESCU TIBERIU ŞTEFAN,

PRAISACH ZENO IOSIF,

POMOJA FLORIN,

AFRONIE EUGEN MARIUS,

STROIA MIHAELA DORICA

Department of Mechanical Engineering, Engineering Faculty

“Eftimie Murgu” University ReşiŃa

Traian Vuia Square, No 1 - 4, 320088 ReşiŃa, Caraş-Severin County

ROMANIA

t.manescu@uem.ro, z.praisach@uem.ro, f.pomoja@uem.ro,

e.afronie@uem.ro, m.stroia@uem.ro

http://www.uem.ro

Abstract: - This paper has the purpose to analyse the equivalent stresses and the displacements resulted at the

disk of butterfly valve. We used a butterfly valve ND2800 NP1.91 type, loading with the nominal water pressure of 1.91 MPa, using the Finite Element Method (FEM). After solving the FEM analyses, were obtained the equivalent stress von Misses, and the total deformation, for a half of the disk of the butterfly valve. The von

Misses equivalent stress determined values not exceed the given admissible value.

Key-Words: - von Misses equivalent stresses, displacements, biplane disks, butterfly valve, FEM

1 Introduction The Finite Element Method (FEM) is a powerful analytical tool that has applications in a multitude of

physical problems, such as acoustics, electrical and magnetic fields, fluid flow, heat transfer, micro

fluidics, stress analysis and others, and it remains the method of choice for complex systems.

In the Finite Element Method, the structural

system is modelled by a set of appropriate finite elements interconnected at points called nodes.

These elements may have physical proprieties [1]. Nowadays, in the design of hydro butterfly

valves are commonly used as body type Francis

turbine isolation or regulating the water flow. Due to the simple design, compact and robust

and low price, they are best used in hydropower. The butterfly valve is a safety element for the

turbine, having the role of tight closing of water admission into the turbine under normal operation conditions and emergency conditions.

The butterfly valves ND2800 NP1.91 types are mounted in the valve chamber of the hydropower

plant, between the penstock and the turbine spiral case.

In this paper we present some results obtained by

using Finite Element Method, to determine stresses

and main deformations on a butterfly valve ND2800 NP1.91 type.

Static analysis of the disk by the finite element method allows a quantitative and qualitative assessment of the state of stress and strain to

highlight critical areas.

2 The butterfly valve Main elements of butterfly valves are: the housing

and a jointly biplane disk mounted on two trunnion, which rotating in the cylindrical shell. The disk of the butterfly valve is shaped to the

direction of hydraulic flow, to ensure minimum hydraulic losses, and to balance the forces in the

housing of the valve. The modern solutions for this type of disks have

a 0.07 coefficient of hydraulic losses. The disk is done in welded construction; the

trunnion made of cast manganese steel, and rolled

steel for general use sheets. The valve body is made welded; hubs made of

cast manganese steel, and rolled steel for general

use sheets. Sealing seat is made by stainless steel.

The main valve seal is on the circumference of the

disk: a stainless steel chair located on the valve

Proceedings of the 4th WSEAS International Conference on Finite Differences - Finite Elements - Finite Volumes - Boundary Elements

ISBN: 978-960-474-298-1 88

body, and a rubber gasket. Disk trunnion area is

sealed with gaskets kit socket in V shape.

The main characteristics of this butterfly valve

are: nominal diameter Dn=2,900 mm, nominal

pressure Pn=1.91 MPa, hydraulic test pressure

Ph=2,856 MPa.

2.1 Main data for the disk calculations The disk has the cast hubs made from G20Mn5 QT

EN 10293, which has the yield strength Rc=240 MPa, the tensile strength Rt=450 MPa, and

admissible stress σa=150 MPa.

On the other hand, the S355J2+N EN 10025-2 rolled profile has the yield strength Rc=315 MPa,

the tensile strength Rt=470 MPa, and admissible

stress σa=156.6 MPa. For this butterfly valve the disk was calculated

using the finite element method – or FEM.

2.2 Boundary condition (BC) For considered disk, the boundary conditions are:

- frictionless support, symmetry for the half of

the disk (Fig. 1); - zero displacement in the axial direction on the

surfaces after contact with stopper and valve body (Fig. 2);

- zero displacement after X and Y directions

for a point located in the middle of the trunnion (Fig. 3).

Fig. 1 BC – Frictionless support

Fig. 2 BC – Displacement in stopper

Fig. 3 BC – Displacement inside middle of the trunnion

2.3 Loads At normal pressure on the disk surface Pn=1.91 MPa, the load on the disk is shown in figure 4.

Proceedings of the 4th WSEAS International Conference on Finite Differences - Finite Elements - Finite Volumes - Boundary Elements

ISBN: 978-960-474-298-1 89

Fig. 4 Normal pressure on the upstream surface

2.4 Meshing of the butterfly valve’s half disk After the boundary condition was established it is

necessary to mesh the 3D model. For mesh was considered tetrahedral elements

with the average size of 38 mm, with smooth transition. After meshing we obtained 999,044 nodal points and 683,474 finite elements.

The mesh results of the 3D model are presented in the figure 5.

Fig. 5 Mesh view

3 FEM analyses and results The FEM static analyze was used to obtain the stress and displacements.

Fig. 6 The von Misses equivalent stress

After solving the FEM analyses, were obtained

the von Misses equivalent stress (Fig. 6), and the

total deformation (Fig. 9), for a half of the disk of the butterfly valve.

It can be observed that the maximum von Misses equivalent stress not exceeds the allowable stress

150 MPa. The maximum values (Fig. 7 and Fig. 8) for the

equivalent stress appear in the transition area

between trunnion and disk hub.

Fig. 7 Maximum von Misses stress on the upstream side

The major parts of equivalent stresses do not

exceed σ=225 N/mm2, which are smaller than

admissible stress value σa=1.5x150=225 N/mm2.

The maximum deformation value for disk in closed position is 5.7263 mm at lower side of the disk.

Proceedings of the 4th WSEAS International Conference on Finite Differences - Finite Elements - Finite Volumes - Boundary Elements

ISBN: 978-960-474-298-1 90

Fig. 8 Maximum von Misses stress on the downstream side

4 Conclusion As we pointed, the static analysis of the disk for the

butterfly valve using the finite element method allows a quantitative and qualitative assessment of the state of stress and strain to highlight critical

areas.

Fig. 9 The total deformation of the disk

The equivalent stress von Misses not exceed the

admissible value: σ=225 N/mm2<σa=1.5x150=225

N/mm2, in accordance with ASME Code Section VIII/Division 2/Appendix 4.

The maximum deformations appear in the bottom of the disk and not exceed the value of

5.73 mm. The butterfly valve disk type ND2800 NP1.91 as

critical areas were highlighted areas for connection

to the hub disk spindles.

Acknowledgement The authors gratefully acknowledge the support of:

the Managing Authority for the Operational Program “Competitiveness and performance quality of doctoral research programs”

POSDRU/88/1.5/S/61178, and also the support of the Managing Authority for Operational Programme

for Human Resources Development (MASOPHRD), within the Romanian Ministry of Labour, Family

and Equal Opportunities by co-financing the project “Excellence in research through postdoctoral programmes in priority domains of the knowledge-

based society (EXCEL)” ID 62557, for creating the possibility to perform these researches.

References:

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structurală prin metoda elementelui finit,

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[2] Davis, C.V., Sorensen, K.E., Hand book of

applied hydraulics, McGraw-Hill Book Company, Third edition, 1969.

[3] Mănescu, T.S., Cîmpian, V., Praisach, Z.I., Pinca, C.B., FEM analyses applying on biplane

disk of butterfly valves, Classics and Fashion in

Fluid machinery, Belgrad Weekend Conference October 18-20, 2002 - pg. 195-202.

[4] Raabe, J., Hydraulische Machinen und

Anlagen, Dusseldorf, VDI Verlag, 1989. [5] X.G. Song, L. Wang, Y.C. Park, Analysis and

optimization of a butterfly valve disc, Proceedings of the Institution of Mechanical

Engineers, Sage Publications, Vol. 223, 2/2009. [6] *** Hydraulic gate and penstock association,

Toranamon Jitsugyokaikan, Tokyo, Japan. [7] http://www.mece.ualberta.ca/tutorials/ansys [8] http://www.tpub.com/fireman/69.htm

Proceedings of the 4th WSEAS International Conference on Finite Differences - Finite Elements - Finite Volumes - Boundary Elements

ISBN: 978-960-474-298-1 91