The joints that connect each length of water or sewer pipe are as important as the pipes themselves. They must be specified to meet watertightness and thrust conditions, and then properly installed to ensure long-term performance of the pipeline as a whole.
Steel and rubber gasketed joints are watertight, flexible, easy to assemble, economical, self-centering, and versatile. This article provides an overview of each, beginning with the most common. All images are courtesy of Hanson Pressure Pipe.
CONCRETE PRESSURE PIPE: 6 OPTIONS
Details of concrete pressure pipe joints, including material specifications and mechanical and physical properties for steel and gaskets, are covered in American Water Works Association (AWWA) standards C300, C301, C302, and C303; and in AWWA Manual M9.
Concrete Pressure Pipe/Standard Joint (Unrestrained)
Assembly: a steel bell and a Carnegie spigot ring combined with a rubber O-ring gasket. The rubber gasket is volumetrically sized and enclosed by the steel joint rings, providing a completed joint with sufficient compression to form a pressure-tight seal. Joint rings are tested for dimensional accuracy and are self-centering when installed.
Grouting the exterior joint recess with portland cement grout protects the steel components from corrosion. Experience has shown that zinc metallizing of the joint rings or applying mortar into the interior joint recess is adequate protection for joints used in raw, fresh water, or potable water systems. For sewage applications, supplemental protective coatings are available.
Snap Ring (Restrained)
The Snap Ring is a patented, mechanically restrained joint system that consists of a steel bell and steel spigot and a snap ring with rubber gasket for water-tightness. It manages unbalanced thrust conditions in pipe diameters from 16 inches to 60 inches.
Once installed, the voids on both sides and above the insert are filled with a portland cement grout. After curing and under load, the grout compresses slightly to permit minor adjustments in alignment. Because the joint’s thrust-resisting components are housed within the steel bell ring and surrounded by grout, they’re protected from corrosive elements in the surrounding soil.
When exposed to thrust conditions, the lip of the bell ring bears against the Snap Ring insert. The insert and field-applied grout, in turn, bear against the back side of the spigot ring gasket groove. The joint is locked in position and prevented from opening.
This design eliminates the problem of point loading that’s possible with set screw-type restrained joints and permits some deflection during installation for slight directional changes or corrections. It’s also easier to assemble than any other restrained joint: The installer tightens a 3/8-inch bolt using a speed wrench.
Concrete Pressure Pipe/Harnessed Clamp (Restrained)
A two-part harness clamp for large diameters. After the pipe is installed, the clamp halves are positioned around the joint and secured together by tightening bolts on each side. The clamp assembly engages full-circumference steel bars on the bell and spigot rings. Grout is then poured into the grout band over the joint before the line is pressurized. The cured grout distributes thrust loads around the joint and protects the joint from corrosion.
Concrete Pressure Pipe/Welded
Restrains pipe against unbalanced thrust. Depending on pipe diameter and contractor preference, welding can be done either internally or externally. Welding from the inside must be full-circumference due to the absence of a rubber gasket. For smaller diameters and where external welds are used, this method requires using a filler rod or similar device rolled to the proper joint diameter. Diagram shows a welded C-303 and L-301 pipe joint.
Concrete Pressure Pipe/Testable
Also known as a double-gasketed joint, allows air testing of assembled joint seals individually at installation. This enables the contractor to confirm watertightness at installation when it’s easiest to fix any problems. Testing can be conducted internally or externally, depending upon the pipe diameter, using a compressed air supply and gauge to verify the gasket seal. Shown above is this joint for an E-301 pipe.
Concrete Pressure Pipe/Bonded
Bonding provides electrical continuity across joints, which allows corrosion, if any, to be monitored after installation. The manufacturer provides terminals or steel plates for test stations at each end of the pipe and fittings at appropriate locations along the pipeline. Diagram shows a joint with C-303 and L-301 pipe.
CONTINUED: STEEL PRESSURE PIPE: 4 OPTIONS
