Figure 73.--Penstock and outlet pipes, station 17+48.00 to downstream end-- Manifolds.

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54. Hydraulic Design Data. Design requirements for the outlet works and powerplant specified bypassing past the dam a flow of not less than 30, 000 second-feet with a reservoir surface at elevation 5497.50. Hydraulic design capacities are given in section 33.

The penstock was designed for a total head of 346 feet, including water hammer. The maximum static head on the penstock and outlet pipe is 239 feet. Water hammer was computed on the basis of a turbine wicket gate closure time of 8 seconds from the fullopen position.

55. Economic Penstock Diameter. - With a rated head of 190 feet, the rated discharge for each of the four turbines is 2, 140 second-feet. With the turbine centerline at elevation 5380.00 and power generation required from elevation 5497. 50, friction losses in the penstock system must be limited. The 26-foot inside diameter of the penstock was sufficiently large to limit the velocity in the pipe to 25 feet per second, which was considered the maximum for proper turbine operation. The 26-foot-diameter outlet pipe, while of the same size as the penstock, was sufficiently large to pass the much greater required flows because much higher velocities were permitted (sec. 54).

56. Materials and Working Stresses. - Steel plates used in fabricating the penstock manifold and outlet pipe manifold conform to ASTM designation A 201, grade B, with a minimum tensile strength of 60,000 pounds per square inch and a minimum yield point of 32, 000 pounds per square inch. This is a "killed" steel, having, it is believed, a reduced notch sensitivity and good welding characteristics, so that it was considered to be the best suited for this job which required high resistance to brittle fracture. Steel plates used in fabricating the tunnel liners conform to ASTM designation A 7. Working stresses for the steel plate are as follows: for the penstock manifold, having a 95 percent joint efficiency with thermal stress relieving and radiographing required, 14, 250 pounds per square inch; for the outlet pipe manifold, having a 90 percent joint efficiency with radiographing only required, 13, 500 pounds per square inch; and for the tunnel liners, having an 80 percent joint efficiency with neither stress relieving nor radiographing required, 10, 120 pounds per square inch. Welding nozzles and flanges are of forged or rolled steel conforming to ASTM designation A 181 and A 105.

57. Design. The design of the penstock and outlet pipe manifolds conforms to the requirements of the 1951 edition, and the design of the tunnel liners conforms to the requirements of the 1943 edition of the API-ASME "Code for the Design, Construction, Inspection and Repair of Unfired Pressure Vessels for Petroleum Liquids and Gases." A basic design stress for the manifold plates of 15, 000 pounds per square inch was used with double-butt-welded joints, and for the tunnel liners a basic design stress of 12, 650 pounds per square inch was used with double-butt-welded joints or single-butt-welded girth joints with external backing strips. Radiographing of the manifold welded joints was required but not radiographing of the liner joints. Only the penstock manifold sections were thermal stress relieved as a whole after welding. Hydrostatic testing of the manifolds and liners was not required.

Stiffener rings are attached to the tunnel liners to provide rigidity during handling and support for external bracing during encasement concrete pouring. Field joints in the outlet pipe manifold and between plates less than 1-1/4 inches thick in the penstock manifold were designed for welding. Field joints in the penstock manifolds between plates 1-1/4 inches or more in thickness were designed with triple-riveted butt strips of the same thickness as the plates joined. Girders and tie rods are used to reinforce the manifold lateral branches and wyes. Flanged joints connect the penstocks and outlet pipes to adjacent downstream valve, gate, and turbine equipment.

Temporary test heads were shop installed at the upstream and downstream ends of the outlet pipe manifold for hydrostatically testing the manifold in the field. A temporary steel test head was shop installed about midway down the penstock manifold so that, in conjunction with the butterfly valves in the penstock lateral branches, the lower end of the penstock manifold could be hydrostatically tested in the field. After hydrostatically testing and encasing the lower end of the penstock manifold in concrete, the test head was removed and reinstalled at the upstream end of the penstock manifold for hydrostatically testing that portion of the manifold. The explanation for this testing procedure is given in section 61.

58. Pipe Fittings and Appurtenances. - Sleeve couplings are of the centersleeve and follower-ring types, with outside packed gaskets of a flexible material suitable for cold-water service. The couplings were designed for a pressure of 150 pounds per square inch.

A 20-inch manhole is located in the bottom of each turbine inlet pipe and an 18by 24-inch manhole is provided in each temporary test head. The 20-inch manhole is a type A, standard design, rated at 150 pounds per square inch working pressure, as shown on drawing 40-D-4556*, and the 18- by 24-inch manhole is of commercial design rated at not less than 150 pounds per square inch working pressure.

A combination air inlet and release valve is provided in the upper end of the penstock manifold and near the joint between the outlet tunnel liner and the outlet pipe manifold. The combination valve combines a 2-inch air release and a 6-inch air inlet, and is rated at not less than 150 pounds per square inch working pressure.

A 30-inch steel air vent pipe with 4-inch wall extends from the arch of each of the power and outlet tunnels just downstream from the fixed-wheel gates upward to louvered intakes on the roofs of the hoist houses. The pipe is embedded in the concrete of the intake structures and hoist houses.

An 18-inch outside diameter filling and drain line connects the outlet pipe manifold and penstock manifold to a turbine pump located in a pit below the manifold elevations and discharges into the outlet works stilling basin. An 18-inch welding type nozzle in the outlet pipe manifold and a similar nozzle in the penstock manifold provide connections for the drain and filling line. An 8-inch welding type nozzle in the penstock branch for unit 1 and a similar nozzle in the outlet pipe manifold provide connections for supplying the water supply and fire-protection systems in the powerplant. Six-inch welding type nozzles upstream and downstream from the butterfly valve in the penstock branch for unit 2 provide connection for pitot tubes for use in determining leakage through the butterfly valve and the turbine wicket gates and in measuring other turbine characteristics. Three-quarter-inch standard pipe thread piezometer connections are provided in the penstock branch for unit 2 and in each of the discharge outlets of the outlet works.

Shop painting or painting at the time of fabrication of the penstock and outlet pipe manifolds was not required. Painting and coating after installation is discussed in section 61.

59. Concrete Anchors.

The reinforced concrete encasement of the penstock and outlet pipe manifolds provides anchorage of these manifolds against hydraulic forces acting on the manifolds at the outlet discharge opening and the turbine inlet pipes. The anchor blocks (figs. 60 and 62) were placed on and against the diversion channel concrete floor and lining. The spaces between and over the concrete encasements of the discharge outlets is backfilled and surfaced with gravel. Drains are provided in the backfilled

areas.

60. Fabrication. - Because of their size the liners and manifolds were fabricated at the damsite. In addition to the fabrication requirements of the API-ASME "Code for the Design, Construction, Inspection, and Repair of Unfired Pressure Vessels for Petroleum Products and Gases," the following provisions and conditions were required. The entire penstock manifold, including the two penstock bypasses, was thermally stress relieved; however, stress relieving was not required for the outlet-pipe manifold nor for the tunnel liners, except that the 26-foot-diameter three-way branch was stress relieved in parts and all other wyes were stress relieved as a whole. Hydrostatic testing of the manifold sections was not required at the time of fabrication, but was performed on the outlet pipe and penstock manifolds after erection. Each course of the outlet pipe and penstock manifolds is constructed with not more than three longitudinal joints and is not more than 6 feet long, unless otherwise shown on the drawings. No welding was permitted when the metal temperature was lower than 32o F.

Plates of each pipe course were rolled to two circular sections with curvature continuous from the edges of the plates, and correction of curvature by blows was not permitted. The ends of pipe sections lay in planes normal to the axis of the section, with allowable deviation from the plane of one-sixteenth inch maximum on either side of

*Not included.

the plane. The edges and ends of adjoining plates and courses were matched when welding so that the outer surfaces of the plates are in continuity with a maximum allowable offset at any point of one-sixteenth inch. The stiffener rings for the turbine inlet pipes are fabricated from not more than six circumferential sections which are joined by butt welds staggered from the longitudinal joints in the pipe sections. Final machining of the faces of the pipe flanges was performed after the flanges were welded to the pipe, and all points on the finished faces of the flanges were required to lie in a plane normal to the longitudinal axis of the pipe within a maximum deviation of 1/64 inch on either side of such plane.

61. Installation and Coating. - After installation of the tunnel liners and their encasement in concrete, the tunnel walls were grouted from pipe connection in the liner shell. Grouting operations caused some inward bulging of the liner shell. This was corrected by flame cutting through the shell from the inside, chipping out concrete as necessary and replacing the removed shell plate or jacking out the bulged section to its original position. Butt welding of the plate in the repaired shell was from the inside with a backing-up strip tack welded to the outside of the shell. The plate in the repaired shell was then tapped and grout pumped in at low pressure to fill the void.

After erection of the penstock and outlet pipe manifolds, debris was removed from within the manifolds and they were hydrostatically tested. Because the full diversion capacity of both the power tunnel and the outlet tunnel was required when erection of the penstock manifold was started, the lower portion downstream from the initial position of the temporary test head was hydrostatically tested and then encased in concrete before diversion through the power tunnel was stopped. While work of erection, testing, and encasement of the lower portion of the penstock manifold was being done, the water diverted through the power tunnel was deflected into the outlet tunnel diversion basin.

The manifolds were hydrostatically tested at 1-1/2 times the working pressure. Because of the greater pressure on the penstock manifold, it was heated for testing to a 60° F. minimum temperature by heating the testing water with a steam boiler. A recording thermometer provided a record of temperature during the tests.

Indicating pressure gages were located at various points in the manifolds during the hydrostatic testing. A recording pressure gage and a diaphragm type pressure cell was located at each end of the manifold during the tests to provide a permanent record of the pressure and to record any high-frequency transient waves. During testing, localized strains in the shell plates and in the wye and lateral branch reinforcement girders and tie rods were measured by strain gages located to give maximum values in the various component parts.

After completion of the hydrostatic testing, the manifolds were encased in concrete while still under pressure. After encasement, the test heads were removed and closing sections were installed between the manifolds and liners and between the outlet pipes or penstock bypasses and the transition pieces for the outlet guard gates.

After satisfactorily completing all erections, hydrostatic testing, and concrete encasement, the liners and manifolds were drained and coated with coal-tar enamel on the interior surfaces. Exterior surfaces to be embedded in concrete were unpainted and uncoated.