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ASME Class 2 and 3 Nuclear Safety Related Air Service Butterfly Valves
Valve shall be either Henry Pratt Company Series 1200 or an approved equal. The valves shall be furnished under a current N-Stamp program, as applicable, and comply with the following details.
Valve Model & Sizes
Pratt 1200 (6" through 48")
Standard Pressure Class: ANSI 150 lb. Class for valves up to 24".
Standard Pressure Class: For valves larger than 24", 75 psig service class, as permitted by ASME Sec. III Code Case 1678.
Maximum Shut-off Pressure, for Bubble-tight Service: 200 psig for valves up to 24"; 75 psig for valves above 24".
Maximum Normal Service Temperature: 300oF.
Maximum Faulted Condition Temperature: 350oF.
Maximum Radiation Exposure: 1 x 108 Rad.
Class 1 for active and non-active service. The upset emergency or faulted conditions will be analyzed concurrently with 5g seismic load applied simultaneously along three major axes. The stress levels will be maintained within the Code allowables.
Valve Operability Assurance
The manufacturers shall submit a program for providing the valve operability assurance requirement meeting the intent of NRC Reg. Guide 1.48. The program shall be submitted with the proposal describing the valves to be tested, type of testing and test conditions.
Valve Body: Valve body shall be flanged or prepared for welding to the adjacent pipe. The weld end preparation will be in accordance with the customer's design specifications. Flanges for valves up to 24" will conform to ANSI B16.5. Flanges for valves larger than 24" will be in accordance with Code Case 1678, Code Case 1702 or Code Case 1744 as applicable. Valve bodies with drilled and tapped holes will be suitable for Class 2B. Alloy bolt thread through entire body thickness is not acceptable. All valves shall be suitable for dead-end service. Wafer style valves are not acceptable.
Valve Disc: Valve disc shall be of fabricated or cast steel construction with no external ribs perpendicular to the flow. The disc shall rotate 90o from full open to full close position. The disc shall be mechanically locked with the valve shaft.
Valve Seats: Rubber seats shall be either mechanically retained on the valve disc. The seat shall be adjustable and replaceable with access from flanged end of the valve. This rubber seat shall be suitable for specified conditions of pressure, temperature and radiation.
Valve Shaft: The valve shaft may be a one-piece construction extending through valve disc or may be comprised of two-piece shafts inserted into the disc hubs (stub shaft). If the shaft is of the two-piece design, each stub shaft shall be inserted in the valve disc hubs for minimum distance of 1o times shaft diameter. The shaft shall be finished to satisfy the requirements of the bearings and packing used. The valve shaft diameter shall not be reduced at the bearing or at the adaption of the actuator.
Valve Trim: The elastomeric components of valves, such as packing, seat and O-rings, shall be of material suitable for specified radioactive and temperature service. EPT materials for these components will be preferred.
Valve Bearing: Valve bearing shall be sleeve-type or roller bearing type, installed in the valve body trunnions. Bearing shall be corrosion resistant. If lubrication is required, accessible fitting shall be provided.
Shaft Seals: The packing shall be of the self-adjusting rubber chevron type with a minimum of three rings in a set. The valves normally containing radioactive fluid shall have two independent sets of packing separated by a lantern ring and a leak-off connection, tapped o" NPT and plugged. Shaft seals shall be replaceable without disturbing any part of the valve or valve actuator assembly.
Actuators: Manual actuators, unless otherwise specified, shall be capable of opening the valve against the design differential pressure and the resulting maximum dynamic torque with not more than 100 lb. pull on the handle or lever. Manual actuators shall have factory set travel limit stops at both ends of travel and shall be designed to withstand, without damage, a pull of 200 lbs. on the handwheel after stops are encountered.
Power operated valves shall have actuators sized for maximum differential pressures specified in the design specifications.
Materials of Construction
Valve Body: Valve body shall be constructed of material conforming to SA-516, Gr. 70.
Valve Disc: Valve disc shall be of material conforming to SA-516, Gr. 70. The seating surface which contacts the rubber seat shall be SA-479, Type 304 welded either to the valve body or to the valve disc. Code Case 1516 may be invoked for welding of seats.
Valve Shaft: Valve shaft shall be SA-564, Type 630 (Cond. 1150).
Valve Trim: The rubber seat and all other elastomeric materials for components, such as packing and O-rings, shall be suitable for continuous operations at design temperature and radiation conditions. Sealing shall be unimpaired by radiation exposure up to 1 x 10o Rad. EPT materials for these components will be preferred.
Fully machined valve bodies shall be hydrostatically tested in accordance with the requirements of ASME Sec. III. Tight shut-off of valve seat in both directions of travel will be demonstrated by bubble-tight testing with air in accordance with MSS-SP-67. Equivalent seat leakage shall not be greater than 2cc air per hour, per inch of nominal valve size at specified operating pressure.
The valves shall be tested at the maximum specified differential pressure and at some lower pressure to demonstrate that pressure-assisted sealing is not required for tight shut-off. A "go-no go" test may be substituted for a qualitatively measured leak test ifs the manufacturer demonstrates empirically that the "go-no go" test is sufficiently sensitive to indicate when acceptable leak rate is exceeded.
Fully assembled valves shall be cycled, opened and closed three times without pressure across the disc to check proper functioning of the actuators and proper setting of the travel limit stops. Power actuators shall be checked for conformance to speed of closure requirements, with a minimum specified motive power, in the design specifications.