Technical Recommendations
for Choke Valve
Specifications
Reference:
© 2004 by CCI. All Rights Reserved. This document has been
produced by Control Components Incorporated, Rancho Santa
Margarita, California
Technical Recommendations for 100D CUSTOM Choke Valve Specifications
1.0 Choke Body Design
1.1 Valve body shall be angle type.
1.2 Flow direction shall be flow-to-close (flow over the plug).
1.3 The internal transition from the valve trim to the valve outlet shall be a smooth taper (venturi type) with an included angle of no greater than 30°.
1.4 To provide further protection of the valve outlet a Stellite® outlet liner should be
provided.
1.5 To address fugitive emissions concerns redundant pressure boundary seals shall be provided.
2.0 Choke Trim Design
2.1 When NACE MR0175/ISO 15156 2003 is required the use of 17-4PH SS for the stem material is prohibited when H2S partial pressures are in excess of 0.5 psi.
2.2 Choke trim shall be cage type. Single stage cages are acceptable for low delta P or end of well life conditions. High delta P conditions require multiple stages and all of the stages must be solid tungsten carbide.
2.2.1 To minimize choke trim erosion one discrete stage shall be provided for every 30 bar (435 psi) pressure drop across the choke.
2.2.2 For short term or start up conditions one discrete stage shall be provided for every 50 bar (725 psi) pressure drop across the choke.
2.3 Trim designs that use a needle and seat or contoured plug should be avoided to minimize the risk of high velocities, excessive vibration, and excessive erosion. 2.4 The plug shall be solid tungsten carbide and shall reside and move inside the throttling
cage(s). To protect the balance seal tungsten carbide tipped plugs and metal sleeved plugs are not acceptable.
2.5 Plugs with metering holes for flow are not acceptable. The cage shall be the throttling device.
2.6 Balanced plug types are acceptable in order to reduce required actuator forces. 2.6.1 Trim designs with two balance seals (“double balanced” plugs) contain an
additional failure point and are not acceptable.
2.6.2 Balance seals shall be u-cup style made from PTFE with spring energization 2.6.3 Balance seals shall be protected by wiper rings on each side.
2.6.4 The dynamic surface for balance seal shall be solid tungsten carbide materials.
2.7 The stem material shall be compatible with the level of NACE specified.
2.8 The entire cage shall be made of tungsten carbide. All stages in multi-stage designs shall be made of tungsten carbide.
2.9 The seat ring shall be made of tungsten carbide. The tungsten carbide may be shrunk fit into a metal housing, provided all surfaces exposed to the fluid are tungsten carbide. 2.10 The cage (single or multi stage) shall be held under compression from the bonnet
bolting. Trim designs that are threaded into the pressure boundary components are not acceptable.
2.11 To minimize issues with corrosion threaded bonnets shall not be used. The body/ bonnet connection shall be a bolted connection.
2.12 In order to minimize the potential of blockage, flow passages through the choke trim shall be at least 6x6 mm for plug sizes larger than 25mm.
2.13 The choke trim shall be capable of withstanding an impact of 400 joules or greater, and after such an event, shall be capable of safely modulating so as to prevent over-pressurization of the downstream system.
2.14 To minimize the risk of seat bore erosion the fluid velocity and kinetic energy through the seat bore shall be controlled. When seat bore velocities are in excess of 122 m/s (400 ft/s) and kinetic energies are greater than 861 kPa (125 psi) the design should be reviewed for potential problems with erosion and vibration. In no case shall the seat bore velocities and kinetic energies exceed 183 m/s (600 ft/s) and 1724 kPa (250 psi) respectively.
2.15 To minimize the risk of valve outlet erosion the fluid velocity should be controlled. When valve outlet velocities are in excess of 46 m/s (150 ft/s) the design should be reviewed for potential problems with erosion and vibration. In no case shall the outlet velocity exceed 76 m/s (250 ft/s).
3.0 Noise
3.1 Vendor shall submit predicted noise calculations. These calculations shall conform to I.E.C. 60534-8.3 “Control Valve Aerodynamic Noise Prediction Method” and the requirements of this section.
3.2 Predicted noise levels shall have a tolerance of +0 / -5 dBA.
3.3 Vendor shall calculate noise per I.E.C. 60534-8.3 using only the gas component of the flow stream as shown on the data sheets.
3.4 Vendor may take a deduction from the result of the calculation in 3.2 based on the liquid component in the fluid stream. The table below depicts the maximum deduction allowable.
% by weight of
liquids Allowable deduction from gas only aerodynamic noise calculation
1-2% 2 dBA 3-5% 4 dBA 6-10% 7 dBA 11-15% 10 dBA 16-20% 14 dBA 21-25% 20 dBA > 25% 25 dBA
1.0 Choke Body Design
1.1 Valve body shall be angle type.
1.2 Flow direction shall be flow-to-close (flow over the plug).
1.3 The internal transition from the valve trim to the valve outlet shall be a smooth taper (venturi type) with an included angle of no greater than 30°.
1.4 To address fugitive emissions concerns redundant pressure boundary seals shall be provided.
2.0 Choke Trim Design
2.1 When NACE MR0175/ISO 15156 2003 is required the use of 17-4PH SS for the stem material is prohibited when H2S partial pressures are in excess of 0.5 psi.
2.2 Choke trim shall be cage type. Single stage cages are acceptable for low delta P or end of well life conditions. High delta P conditions require multiple stages and all of the stages must be tungsten carbide.
2.2.1 To minimize choke trim erosion one discrete stage shall be provided for every 100 bar (1450 psi) pressure drop across the choke.
2.3 Trim designs that use a needle and seat or contoured plug should be avoided to minimize the risk of high velocities, excessive vibration, and excessive erosion.
2.4 The plug shall be solid tungsten carbide and shall reside and move inside the throttling cage(s). To protect the balance seal tungsten carbide tipped plugs and metal sleeved plugs are not acceptable.
2.5 Plugs with metering holes for flow are not acceptable. The cage shall be the throttling device.
2.6 Balanced plug types are acceptable in order to reduce required actuator forces. 2.6.1 Trim designs with two balance seals (“double balanced” plugs) contain an additional
2.6.2 Balance seals shall be u-cup style made from PTFE with spring energization 2.6.3 Balance seals shall be protected by wiper rings on each side.
2.6.4 The dynamic surface for balance seal shall be solid tungsten carbide materials. 2.7 The stem material shall be compatible with the level of NACE specified.
2.8 The entire cage shall be made of tungsten carbide. All stages in multi-stage designs shall be made of tungsten carbide.
2.9 The seat ring shall be made of tungsten carbide. The tungsten carbide may be shrunk fit into a metal housing, provided all surfaces exposed to the fluid are tungsten carbide.
2.10 The cage (single or multi stage) shall be held under compression from the bonnet bolting. Trim designs that are threaded into the pressure boundary components are not acceptable. 2.11 To minimize issues with corrosion threaded bonnets shall not be used. The body/bonnet
connection shall be a bolted connection.
2.12 In order to minimize the potential of blockage, flow passages through the choke trim shall be at least 6x6 mm for plug sizes larger than 25mm.
2.13 The choke trim shall be capable of withstanding an impact of 400 joules or greater, and after such an event, shall be capable of safely modulating so as to prevent over-pressurization of the downstream system.
2.14 To minimize the risk of seat bore erosion the fluid velocity and kinetic energy through the seat bore shall be controlled. When seat bore velocities are in excess of 122 m/s (400 ft/s) and kinetic energies are greater than 861 kPa (125 psi) the design should be reviewed for potential problems with erosion and vibration. In no case shall the seat bore velocities and kinetic energies exceed 183 m/s (600 ft/s) and 1724 kPa (250 psi) respectively.
2.15 To minimize the risk of valve outlet erosion the fluid velocity should be controlled. When valve outlet velocities are in excess of 46 m/s (150 ft/s) the design should be reviewed for potential problems with erosion and vibration. In no case shall the outlet velocity exceed 76 m/s (250 ft/s).
3.1 Vendor shall submit predicted noise calculations. These calculations shall conform to I.E.C. 60534-8.3 “Control Valve Aerodynamic Noise Prediction Method” and the requirements of this section.
3.2 Predicted noise levels shall have a tolerance of +0 / -5 dBA.
3.3 Vendor shall calculate noise per I.E.C. 60534-8.3 using only the gas component of the flow stream as shown on the data sheets.
3.4 Vendor may take a deduction from the result of the calculation in 3.2 based on the liquid component in the fluid stream. The table below depicts the maximum deduction allowable.
% by weight of
liquids Allowable deduction from gas only aerodynamic noise calculation
1-2% 2 dBA 3-5% 4 dBA 6-10% 7 dBA 11-15% 10 dBA 16-20% 14 dBA 21-25% 20 dBA > 25% 25 dBA
