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A full range of special pipe and fittings is available to satisfy project requirements. They are custom fabricated at the pipe manufacturing facility and delivered with the pipe to the construction site in proper sequence for installation in the pipeline. Fittings can be designed to fit almost any configuration. Special pipe and fittings of all sizes can be supplied with various end configurations including flanged ends for flanged joints, steel plate plain ends for mechanical coupling joints or for butt-strap closures, and steel bell and spigot ends for joints sealed with a standard round rubber ring. When practical, fittings are attached to sections of pipe to reduce the number of field joints and for ease of handling, transport and installation.
Special Pipe
Special pipe sections including short pipe, bevel pipe, angle pipe and outlet pipe are generally fabricated by modifying a standard section of pipe.
Pipe sections with spigot end beveled up to 5 degrees are available in all diameters to accommodate
changes in pipeline direction. Beveled pipe sections are fabricated by cutting the steel cylinder at the desired mitre angle and welding the spigot ring to the cut end.
Angle pipe is available to accommodate changes in pipeline direction for angles up to 22.5 degrees. Angle pipe is fabricated by making a mitered girth seam of the desired angle in a section of pipe.
Outlets of any size up to the pipe diameter can be built into the wall of a pipe for manholes, air valves,
blow offs and other connections. The steel cylinder at the outlet opening is reinforced with either a steel collar, a wrapper plate or a crotch plate, depending on cylinder thickness, pipe and outlet diameters, and operating conditions.
 Fittings
Custom-fabricated fittings include elbows, tees, wyes, closures, reducers, and connections to mainline valves and appurtenances. They are fabricated from welded steel plate or sheet and lined and coated with cement mortar. The cylinder diameter for the mainline portion of the fitting is equal to the cylinder diameter of standard pipe.
Fittings Design
The design and manufacture of fabricated steel fittings conform to the applicable section of AWWA Standard C303; their dimensions conform to AWWA Standard C208. Flanges conform to International Standard ISO 2531.
The design thickness of the steel cylinder used in a fabricated fitting is:
Ty = Pd Dy
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2000fs
where Ty=steel cylinder thickness, mm
Pd = design pressure, kPa
Dy = inside diameter of steel cylinder, mm
fs = circumferential stress in the steel cylinder at design pressure,
MPa
The design stress in the steel cylinder of fabricated fittings is limited to 103
MPa or one-half the minimum specified yield strength of the steel used. The minimum steel cylinder thickness used in fabricated fittings to assure adequate stiffness for handling and for resisting normal external loads are:
| Fittings Diameter Range
(mm) |
Minimum Thickness of Sheet
or Plate (mm) |
| 300-500 |
3.4 |
| 600-900 |
4.6 |
| 1000-1200 |
6.7 |
| 1300-1500 |
7.9 |
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