Control Valve Specification For Steam Turbine Bypass

CONTROL VALVE SPECIFICATION FOR TURBINE BYPASS (FOSSIL DRUM & SUPERCRITICAL) 1. SCOPE OF WORK 1.1.

Equipment and Services Furnished by the Seller Shall Include: 1.1.1. Design, fabrication, testing and delivery of all valves, complete with operators, solenoid valves, and accessories, per attached valve data sheets. 1.1.2. In case of pneumatic actuator, all interconnecting instrument air tubing and fittings between valve operator, positioner (if required), and air filter regulator. 1.1.3. Any special tools required for assembly, disassembly and maintenance. 1.1.4. Valve drawings, including outline dimensions, weights, circuit diagrams, section drawings, and parts lists. 1.1.5. Installation, Operation, and Maintenance Manuals, including instructions for any sub-suppliers. 1.1.6. Recommended spare parts lists.

1.2.

Equipment and Services Furnished by the Buyer or End-Customer Shall Include: 1.2.1. Receiving, unloading, storage, and installation of all equipment supplied by Seller. 1.2.2. Electrical wiring for power, position indicating lights, solenoids, and control stations. 1.2.3. All external piping, tubing, valves, and fittings, except as specified to be furnished by the Seller.

2. APPLICABLE CODES AND STANDARDS All valves and associated equipment shall be designed and constructed in accordance with: 2.1.

ANSI/ASME B31-1, Power Piping

2.2.

ANSI B16.34, Valves - Flanged, Threaded, and Welding End or equivalent DIN/TRD rules.

3. TECHNICAL REQUIREMENTS 3.1.

HP Bypass Valve Design Criteria 3.1.1. Each control valve shall be sized and selected to provide reliable operation and control at the specified operating and design conditions. Valve body shall be designed to withstand thermal cycling. Thin walled sections shall be provided in areas after pressure reduction to reduce thermal fatigue. Transions between thick and thin wall sections shall be gradual. The operating and design conditions are specified on the attached Control Valve Data Sheets. 3.1.2. The material and design of the seat, trim and stem shall be sufficient to resist wear under severe service conditions. Cage material shall be of a high alloy material X20CrMoV121 for good thermal cycling and erosion resistance. Cylindrical cages shall not be provided.

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CONTROL VALVE SPECIFICATION FOR TURBINE BYPASS (FOSSIL DRUM & SUPERCRITICAL) 3.1.3. The valve trim shall be of removable type without requiring removal of valve body from the line. Valve body shall be protected from damage due to water injection by means of multi-function contoured cage. The cage shall be firmly attached at one end, and located radially at the other end to provide good guiding and allow axial growth due to thermal differentials. 3.1.4. The valve plug type shall be channel slotted design for acoustic attenuation and passage of nominal contamination. Plugs of multiple hole design and contoured plug designs shall not be provided. 3.1.5. Water spray shall be fully atomized within 1 m of valve outlet to ensure uniform temperature of cold reheat. Water injection shall be at a fixed point inside the valve with spray into the turbulant steam flow. Water shall not be injected through the stem or seat to prevent thermal cracking. 3.1.6. Bolted bonnets are preferred. If pressure seal bonnets are used, seal areas shall be inlayed with corrosion resistant materials to minimize leakage potential. 3.1.7. Valve packing shall be selected for the design conditions of the service intended. Teflon packing shall not be used in applications with operating temperature of the application above 450 F. Packing box design shall consist of two independent sets of rings separated by a metallic spacer. Packing shall be compressed by means of a bolted flange design. Screwed type gland packing retainers shall not be provided. 3.2.

LP Bypass Valve Design Criteria 3.2.1. Each control valve shall be sized and selected to provide reliable operation and control at the specified operating and design conditions. Valve body shall be designed to withstand thermal cycling. Thin walled sections shall be provided in areas after pressure reduction to reduce thermal fatigue. Transions between thick and thin wall sections shall be gradual. The operating and design conditions are specified on the attached Control Valve Data Sheets. 3.2.2. The material and design of the seat, trim and stem shall be sufficient to resist wear under severe service conditions. 3.2.3. The valve trim shall be of removable type without requiring removal of valve body from the line. If required, conical diffusers shall be provided to provide higher mechanical strength, and to allow for optimum velocity distribution downstream of the diffuser. Cylindrical diffusers shall not be provided. The diffusers shall be removable through bonnet to allow for inspection and maintenance. Cages or diffusers to be of wrought construction. No components may be screwed or welded inside the valve body for easy maintenance. 3.2.4. Plugs of multiple hole design and contoured plug designs shall not be provided. A combination of cage guiding and top guiding for plugs shall be provided to eliminate possibility of vibration.

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CONTROL VALVE SPECIFICATION FOR TURBINE BYPASS (FOSSIL DRUM & SUPERCRITICAL) 3.2.5. Water injection shall be down stream of pressure reduction to maximize evaporization. Water shall not be injected through the stem or seat to prevent thermal cracking. Water injection shall be performed through spring loaded spray nozzles. 3.2.6. Bolted bonnets are preferred. If pressure seal bonnets are used, seal areas shall be inlayed with corrosion resistant materials to minimize leakage potential. 3.2.7. Valve packing shall be selected for the design conditions of the service intended. Teflon packing shall not be used in applications with operating temperature of the application above 450 F. Packing shall be compressed by means of a bolted flange design. Screwed type gland packing retainers shall not be provided. 3.3.

Hydraulic Oil System 3.3.1. The hydraulic power unit shall be supplied with redundant pumps and power supply units. 3.3.2. Accumulators shall be sized so that all valves can be operated 2 times on power failure, before the oil pressure goes below the required system pressure. 3.3.3. Proportional valves shall be used for generating hydraulic signal. Servo valves shall not be used since they are very sensitive to paticulates in oil and is prone to leakage. The proportional valves shall be designed such that there is no overshoot during actuator movement. Proportional valves shall be mounted on the actuator so that the response time is faster. 3.3.4. The actuators shall be dual acting without the help of springs. Oil pressure on both sides of the actuator shall be controlled by the help of the proportional valve.

3.4.

Spray water valves 3.4.1. Velocity of water at trim exit shall not exceed 30 m/s. calculations and reference list.

Vendor shall provide

3.4.2. Valves shall be provided with rated cavitation index(Kcr) above cavitation index for the process (Kc) where Kc = (P1-P2)/(P1-Pv). 3.4.3. Valves shall be free of cavitation. Should process condition produce cavitation, valve design shall be upgraded to eliminate cavitation. 3.4.4. Valves shall be provided with hydraulic or pneumatic actuation. 3.5.

Turbine Bypass Control System 3.5.1. Control system shall be state of the art, digital type. 3.5.2. Control system shall have redundant power supply to ensure reliability. 3.5.3. Input/output modules, power supply modules and CPU modules shall have HOT SWAP feature and shall be replaceable while the plant is in operation without any disturbance of the other modules.

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CONTROL VALVE SPECIFICATION FOR TURBINE BYPASS (FOSSIL DRUM & SUPERCRITICAL) 3.5.4. Input/output modules, power supply modules and CPU modules shall have no slot dependencies for easier use. 3.5.5. Interface with main DCS shall be MODBUS. 3.5.6. Input/output modules shall have separate field wiring terminal strips. For easy maintenance, no field wiring shall be required for replacement of modules. 3.5.7. All modules shall be equipped with SAFE SWAP feature consisting of module fail state operation. In the event of a communication failure it shall be possible to configure all output modules to one of the three fail modes. Module shall be designed to be replaceable while the plant is in operation without any disturbance of the power plant and the other modules. 3.5.8. Desk insert shall be touch panel type with video display. MOSAIC type touch panel shall not be supplied. 3.5.9. Control system shall be supplied with upto seven levels of password protections. 3.5.10. Temperature control shall be performed by means of state controller with observer. Predefined algorithms in the state controller with observer shall minimize temperaure swings inside and outside of the valve, and the valve outlet temperature shall be controlled within +5 degree C under all operating conditions. PID or PIP control shall not be provided. 3.6.

Valve Operators 3.6.1. The valve operators (actuators) shall be hydraulic for the HP and LP Bypass Control Valves. The spray control valve actuator shall be hydraulic, pneumatic diaphragm or pneumatic piston type. 3.6.2. The valve actuator yoke design shall be such that it will accept installation of all required accessories, such as air sets, limit switches, and position indicators. 3.6.3. The plant air supply pressure shall be per attached Control Valve Data Sheets. 3.6.4. All control valve shall be designed to provide tight shut-off. The minimum specified seating force load per circumferential inch shall be: 300 lbf (5.3 kg/mm) for ANSI B16.104 Class IV shut-off; 500 lbf (9.3 kg/mm) for ANSI B16.104 Class V shut-off; 1000 lb. (18 kg/mm) for MSS-SP61 and pressure drops less than 3000 psi (21 Mpa); and 1500 lb. (21 kg/mm) for MSS-SP61 and pressure drops greater than 3000 psi (21 Mpa). linear inch of seat ring circumference (27 kg/mm)

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CONTROL VALVE SPECIFICATION FOR TURBINE BYPASS (FOSSIL DRUM & SUPERCRITICAL) 3.7.

Valve Control Accessories for pneumatic actuators 3.7.1. Positioners shall be of the pneumatic type and shall be provided with pressure gauges for indicating the positioner outlet and control signal pressures. Positioners shall be designed for a control signal input range as specified on the valve data sheets. 3.7.2. All positioners shall be equipped with filter regulator air sets and shall be mounted on the valve yokes. If the positioner can accept the maximum air supply pressure, then the positioners shall be equipped with an air filter in place of a filter regulator. 3.7.3. The positioner action shall be field changeable without additional parts. 3.7.4. The positioners shall be of the force balance type, employing positive cam type feedback to provide accurate control positioning. 3.7.5. All other accessories such as handwheels, limit switches, solenoid valves etc. shall be in accordance with the specifications in the attached valve data sheet.

4. QUALITY ASSURANCE

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4.1.

All valves shall be hydrostatically tested by the Seller in accordance with ANSI B16.37 or DIN/TRD rules.

4.2.

All valves shall undergo seat leakage testing in accordance with ANSI B16.104. The seat leakage test criteria will be per the attached Control Valve Data Sheet.

4.3.

All valves shall undergo functional tests to verify operability and stroke speed. The Seller shall document the test results and test criteria.

4.4.

The Seller shall obtain all pressure boundary materials with Certified Material Test Reports (CMTRs).

4.5.

The Seller shall maintain records of material traceability. All pressure boundary and trim components shall be identified by heat number and manufacturer production order number.

4.6.

The Seller shall provide the Buyer with a QA Data Package which will include, at a minimum, Certificates of Conformance and Valve Test Reports in accordance with paragraphs 4.1, 4.2, and 4.3.

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