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How have pipe joints developed? |
 The caulked joint dates as far back as 1785 and was invented in Europe. One of the earliest recorded iron pipe installations in the United States was in Philadelphia in the early 1800s. That pipe was cast in 9-foot lengths and was joined by caulked lead joints. In an 1823 document titled Report of the Watering Committee to the Select and Common Councils of the City of Philadelphia, there is a detailed and glowing account of this pipe and the "ease" of assembling the joints: "(The joint) ... is first caulked in with a ring of plaited hemp, to prevent the lead (from) running into the Pipes; then a pair of nippers, with a joint in the lower part to fit all round the Pipes — so as to prevent the lead coming out in front, which is further secured by a ring of clay, outside the nippers and formed into a cap at top, into which melted lead is poured. When the lead is cold, the clay and nippers are removed, and then (the lead) is upset with a hammer and chisel, which completes the joint."
As difficult and archaic as this sounds, it is amazing that caulked joints made essentially the same way as described in that document were used in the water and sewer industries as late as the 1950s. The first major improvement in pipe and fitting joints was the introduction of the Mechanical Joint in 1927. This joint was standardized by the cast iron pipe industry in 1946 using the design of the "Double-X" joint developed by AMERICAN. It is still used today, particularly for fittings. The standardized Mechanical Joint is specified in ANSI/AWWA C111/A21.11. Although a quantum leap beyond the earlier caulked joint, the Mechanical Joint is considered to be labor intensive and ergonomically unfriendly in today’s fast moving construction projects. After the Mechanical Joint came the Roll-On Joint. It was a bell-and-spigot joint and was sealed with a rubber O-ring gasket. It was less labor intensive than the Mechanical Joint but very sensitive to installation technique. The O-Ring gasket was designed to roll between the surfaces of the socket and the spigot as the joint was assembled. However, field conditions such as improper placement of the gasket or moisture on the joint surfaces could cause the gasket to slide instead of rolling, which resulted in improper seating. A better, more foolproof joint was still needed. The push-on joint, also specified in ANSI/AWWA C111/A21.11, proved to be the answer for pipe and fitting joints. AMERICAN patented the Fastite ® joint in 1961, and since that time, it has come to be the joint of choice among pipe and fittings sold by AMERICAN. The Fastite ® joint is rated for up to 350 psi working pressure in all sizes, 4-inch through 64-inch, depending on the pressure rating of the pipe. The Fastite ® gasket can be supplied in several different polymers, as required for various types of services. It is the ultimate for simple joint assembly. Today, the speed of a pipe job is not controlled by the assembly of pipe and fitting joints, but by excavation and preparation of the trench. The final pipe and fitting joint development, which is still evolving today, is the restrained joint. As construction methods improved and rights-of-way became more crowded, it became very evident in the 1960s that restrained joints would be of great importance to designers and installers of water and wastewater pipelines. Restrained joints were needed in all pipe sizes, and the need was particularly critical in larger pipe to eliminate large and expensive thrust blocks. The earliest restrained joint was the MJ Retainer Gland, which was used with Mechanical Joint pipe and fittings. Although widely used at one time, it always had several limitations. The joint was rigid after assembly, which did not allow for ground movement in service. Also, it was not available in sizes greater than 24-inch. Finally, even more than the Mechanical Joint, it was labor intensive. The first large diameter restrained joint developed at AMERICAN was the Lok-Fast ® joint. Like all restrained joints produced today at AMERICAN, the Lok-Fast ® joint used the Fastite ® gasket as its sealing element. This joint consisted of a Fastite ® socket cast in a bell with a Mechanical Joint type flange. The entering spigot was equipped with a mating gland mounted behind a welded-on ring. The restraining elements were ANSI/AWWA C115/A21.15 Tee Head bolts that joined the bell flange and spigot gland. This was a tough, well-designed system. It had the advantages of reasonable deflection and good pressure ratings. However, it too was labor intensive to install and was very expensive to manufacture. Today, AMERICAN manufactures three types of restrained joint systems, depending on size. The first of these is the Lok-Ring ® joint, developed to overcome the problems of the Lok-Fast ® . It is produced in sizes 42-inch through 64-inch and is rated for 250 psi operating pressure. It provides reasonable joint deflection, and is extremely simple to assemble. Restraint is provided by an alloy steel lok-ring that is shipped already mounted on the spigot behind a welded-on alloy steel ring. When the joint is assembled, the lok-ring is assembled into a locking groove in the socket. For pipe and fitting sizes smaller than 42 inches in diameter, AMERICAN produces two restrained joint systems. The first is the Flex-Ring ® joint, and there are actually two styles of Flex-Ring ® joints. For 4-inch through 12-inch sizes, restraint is provided by a loose ductile iron ring that is inserted into the Flex-Ring ® socket behind a welded-on ring on the spigot after the joint is assembled. This joint provides 5 degrees deflection in all sizes and is rated for 350 psi operating pressure. The Flex-Ring ® joint for 14"-36" sizes provides restraint using ductile iron locking segments mounted on a rubber backing ring that is placed in a specially designed socket before assembly. When the joint is assembled, the rubber backing ring positions the locking segments behind a restraining weld bead on the spigot. Deflection for this joint varies from 4 degrees in the 14-inch size to 2 degrees in the 36-inch diameter. Pressure ratings are 350 psi working pressure in 14-inch through 24-inch sizes and 250 psi working pressure in the 30-inch and 36-inch sizes. The most simple restrained joint at AMERICAN is the Fast-Grip ® joint. Restraint is provided by high-strength, stainless-steel, wedge-shaped elements molded into the Fast Grip ® gasket that are activated and grip the spigot firmly when the joint is assembled. This joint is produced in sizes 4-inch through 24-inch and is now rated for 350 psi working pressure in 4-inch through 10-inch sizes and 250 psi working pressure in 12-inch through 24-inch. The Fast-Grip ® is the ultimate restrained joint system available at AMERICAN today. Only one joint component, the Fast-Grip ® gasket, is required to provide a bottle-tight seal and reliable joint restraint. Total reliability, ease of installation, and reasonable costs are all attributes required for pipe and fitting joints today. The Fastite ® joint and the restrained joints now provided by AMERICAN meet those requirements. Although the caulked joint was sold for more than 170 years, it is doubtful in today’s innovative environment that current product lines will have that much longevity. So research and new product development are always ongoing processes at AMERICAN.
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Ben Helton, Technical Director, AMERICAN Cast Iron Pipe Company |
© 1998 American Cast Iron Pipe Co.