Joining Ductile Or Cast-Iron Pipe - Part 2

This article is in continuation to Joining Ductile Or Cast-Iron Pipe - Part 1. Please go through part 1 before reading this.

Mechanical Screw-Gland-Type Joint

This type of mechanical joint for cast-iron pipe makes use of a coarse-threaded screw gland drawn up by means of a spanner wrench to compress a standard rubber or composition packing gasket. The joint allows from 2 to 7 angular deflection, as well as expansion or contraction without danger of leaks. A lead ring, inserted in the bell ahead of the gasket, seals off the contents of the line from the gasket. The ring also provides an electric circuit through the joint for thawing out frozen underground mains and service lines by the electrical method. The screw-gland joint is used in piping which conveys water, gas, oil, and other fluids at considerable pressure. The gaskets and lead rings are interchangeable with those used in equivalent lines of mechanical joints of the bolted-gland type. A full line of fittings is available for use with screw-gland pipe.

Ball-and-Socket Joints

Ball-and-socket mechanical joint for cast-iron pipe

For river crossings, submarine lines, or other places where great flexibility is necessary, ductile cast-iron pipe can be obtained with ball-and-socket joints of the mechanical-gland types, as shown in above figure. Provision is made for longitudinal expansion and contraction, and a positive stop against disengagement of the joint is a feature of the design. As much as 15 angular deflection can be accommodated without leakage. This pipe is heavy enough to remain underwater where laid without requiring river clamps or anchorage devices. The pipe may be pulled across streams with a cable, since the joints are positively locked against separating, or it may be laid directly from a barge, bridge, or pontoons, without the services of a diver. The mechanical ball-and-socket joint is suitable for use with water, sewage, air, gas, oil, and other fluids at considerable pressure. Either bell-and-spigot or mechanical (gland-type) fittings can be used with this line of pipe, although the integral ball present on the spigot end of some designs has to be cut off before the pipe can be inserted in a regular bell.

Universal Pipe Joints

Universal cast-iron pipe joint

This type of cast-iron pipe joint (shown in figure) has a machined taper seat which obviates the need for caulking or for a compression gasket. The joint is pulled up snugly with two bolts, after which the nuts are backed off slightly, thus enabling the lock washers to give enough to avoid overstressing the socket or lugs. Pipe is made in 12- to 20-ft (3.5- to 6-m) lengths to the usual pressure classes and can be bought as Type III under Federal Specification WW-P-421. Universal-joint fittings are available for use with the pipe. This type of joint is used to some extent in pipe diameters of NPS 4 (DN 100) to NPS 24 (DN 600) for underground water supply systems; but it is not considered suitable for gas service, and it does not permit much angular displacement or expansive movement.

Compression-Sleeve Coupling

Compression sleeve (Dresser) coupling for plain-end cast-iron or steel pipe

The type of joint shown in figure is used with plain-end pipe of either cast iron or steel. It is widely known under the trade names of Dresser coupling and Dayton coupling. Compression sleeve couplings are used extensively for air, gas, oil, water, and other services above- or underground. With a joint of this type, it is necessary to anchor or brace solidly at dead ends or turns to prevent the line from pulling apart. Compression couplings and fittings with screwed packing glands are available for use with small-size cast-iron or steel pipe. In welded transmission lines for oil or gas where any significant change in temperature is expected, a certain percentage of the joints may be made up with compression couplings instead of welding in order to allow for expansion.

Grooved Segmented-Ring Coupling

Victualic coupling for grooved-end cast-iron or steel pipe

The type of split coupling shown in Fig. A2.34 is used with either ductile cast-iron or steel pipe that has grooves near the ends which enable the coupling to grip the pipe, in order to prevent disengagement of the joint. The couplings are manufactured in a minimum of two segments for small pipe sizes and several segments for large pipe sizes. Grooved-end fittings are available for use with the couplings. With proper choice of gasket material, the joint is suitable for use above- or underground with nearly any fluid or gas. The joint’s advantages are its:

● Ability to absorb minor angular and axial deflections

● Ability to increase gasket sealing force with increased system pressure. Refer to AWWA C.606, Standard for Grooved and Shouldered Joints.

● Simplicity for rapid erection or dismantling for systems requiring frequent disassembly.

The coupling is also available in a style where grooving of the pipe ends is not required. Joint separation is prevented by the use of hardened steel inserts (teeth) which grab the mating pipe ends.

 

Flanged Joints

Screwed-on cast-iron flange

High-hub cast-iron flanges with bitumastic to protect the exposed threads

Flanged ductile or cast-iron pipe is used aboveground for low and intermediate pressures in water-pumping stations, gas works, power and industrial plants, oil refineries, booster stations for water, and gas and oil transmission lines. Cast iron flanges usually are faced and drilled according to ASME B16.1. For flanged joints in a ductile iron pipe, refer to ASME B16.42, ANSI/AWWA C110/A21.10, C111/ A21.11, C115/A21.15, and C153/A21.53. Cast-iron pipe is made both with integrally cast flanges and with threaded companion flanges for screwing onto the pipe (as shown in above figures). In the latter case, the outside diameter of the pipe conforms to iron pipe size (IPS) dimensions to allow for the threads provided. It is available in sizes NPS 3 (DN 50) through NPS 24 (DN 600) and in length to 18 ft (5.5 m). For lengths less than 3 ft (1 m), in sizes NPS 3 (DN 50) through NPS 12 (DN 300), the flanges may be cast integrally with the pipe, rather than screwed on the pipe, at the manufacturer’s option. Standard dimensions of flanged joints for silver brazing are shown in below given table.

Standard Dimensions of Class 125 Flanged Joints for Silver Brazing with Centrifugally Cast Pipe