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Pipe Fittings

This chapter presents various types of pipe fittings. Of all the fittings, the elbow is the one most often used. Simply put, the elbow, or ell, is used when a pipe changes direction. Elbows can turn up, down, left, right, or any angle in between. When one finds it necessary to draw a 90° elbow or calculate how much space it will occupy in a routing configuration, knowing its length becomes essential. An elbow's length is commonly referred to as the center-to-end dimension and is measured from the centerpoint of its radius to the end of either opening. Dimensional sizes of fittings are typically provided by the manufacturer of the fitting. Manufacturers issue dimensioning charts containing lengths for a particular fitting. Another elbow that may be used under certain circumstances and with permission from the customer is the 90° short-radius elbow. The 90° short-radius ell makes a much sharper turn than does the long-radius ell.

Emissions from Pipe Fittings and Gaskets

Threaded pipe fittings in the seal flush line can be significant leak sources, with readings above 1,000 ppm.4,17 Similar emission levels may be measured near the gasket region on the seal chamber face. Any leakage from these areas may drift into the emission measurement area for the mechanical seal. The mechanical seal may then be erroneously implicated as a leaker. It should be standard practice to sniff nearby hydraulic fittings and the flange gasket area if excessive VOC concentrations are detected adjacent to the mechanical seal.

Leak-tight threaded pipe fittings can be more easily attained using anaerobic paste-type sealants rather than PTFE tape. The seal chamber face must be smooth to be emission tight. Gaskets and O-rings must be free of nicks and scratches.

32.16.2 Thermoplastic Fittings Manufacturing

Thermoplastic pipe fittings may be injection-molded, fabricated, rotomolded, or thermoformed. Injection-molded fittings are generally made in sizes through 12-in. nominal diameter. Typical molded fittings are tees, 45-degree and 90-degree elbows, reducers, couplings, caps, flange adapters, stub ends, branch saddles, service saddles, and self-tapping saddle tees. Electrofusion couplings and fittings are either made by injection molding or machined from pipe stock. Electrofusion fittings and couplings are made with a coil-like integral heating element incorporated into the fitting. Joining with other fittings uses an electrical fusion device that provides electricity into the heating element, which melts the adjacent thermoplastic material and creates a fusion-welded joint.

Larger-diameter fittings exceed the capabilities of injection molding and are typically fabricated. Rotomolding is used for the manufacture of polyethylene large-diameter (up to 60 in.) and custom fittings for polyethylene corrugated drainage piping applications.

Thermoformed fittings are made by heating a section of pipe and then using a forming tool to reshape the heated area. Examples of thermoformed fittings are sweep elbows, swaged reducers, and forged stub ends. Some polyethylene corrugated pipe fittings and appurtenances are also thermoformed.

All proprietary joints shall be made in accordance with the manufacturer’s instructions. Care shall be taken to establish satisfactory jointing techniques for all water service pipework. When making joints by welding, brazing, or soldering, precautions shall be taken to avoid the risk of fire. All burrs shall be removed from the ends of pipes and any jointing materials used shall be prevented from entering the waterways. All piping and fittings shall be cleaned internally and free from particles of sand, soil, metal filings, and chips, etc.

8.19.3 Cast iron pipes

Flexible mechanical joints shall be made in accordance with the manufacturer’s instructions.

For molten lead joints, the spigot and socket shall be centered with rings of dry yarn caulked tightly into the bottom of the spigot to prevent the entry of lead into the bore of the pipe and to prevent contact of lead with the water.

Synthetic yarns that do not promote the growth of bacteria shall be used to prevent contamination of the water. The remainder of the joint space shall be filled with molten lead (taking care that no dross enters the joint), cold wire, strip, or spun lead (lead wool). The joint shall be caulked to a smooth finish with pneumatic tools or a hand hammer of mass not less than 1.5 kg. When working with spun lead, caulking tools shall be of a thickness to fill the joint space, ensuring thorough consolidation of the material to the full depth of the socket.

Lead joints shall be finished about 3 mm inside the face of the socket.

Flange joints shall be made with screwed or cast on flanges.

8.19.4 Steel pipes

Welded joints shall not be used where a protective lining would be damaged by heat, or where the pipework is employed as a primary circulation to an indirect hot water heating system.

Screwed joints in steel piping shall be made with screwed socket joints using wrought iron, steel, or malleable double crimping fitting. A thread filler shall be used. Exposed threads left after jointing shall be painted or, where installed underground, thickly coated with bituminous or other suitable corrosion preventative agent.

Flange joints shall be made with screwed or welded flanges of steel or cast iron using jointing rings and, if necessary, a suitable jointing paste. The nuts shall be carefully tightened, in opposite pairs, until the jointing ring is sufficiently compressed between the flanges for a watertight joint.

8.19.5 Unplasticized PVC pipes

8.19.5.1 Mechanical joints

Mechanical joints in unplasticized PVC piping of sizes 2 and upwards shall be made in accordance with BS4346: Part 2, by the use of push-fit integral elastomeric sealing rings which are compressed when the plain ended pipes are inserted into the adjoining sockets. The plain pipe ends shall be chamfered and the surfaces cleaned and lubricated.

The chamfered pipe end shall be inserted fully into the adjoining socket (except where provision is to be made for expansion), or as far as any locating mark put on the spigot end by the manufacturer. The sealing rings shall comply with BS2494.

8.19.5.2 Compression joints

Compression joints shall only be used with unplasticized PVC piping of size 2 and smaller. The joints shall be of the nonmanipulative type. Care shall be taken to avoid overtightening.

8.19.5.3 Solvent cement welded joints

Solvent cement welded joints in unplasticized PVC piping shall be made using solvent cement complying with BS4346: Part 3 recommended by the manufacturer of the pipe. The dimensions of the spigots and sockets shall comply with BSEN1452: Part 1–5.

Joints may also be made using integral sockets formed in the pipes and solvent cemented.

8.19.5.4 Flanged joints

Flanged joints used for connections to valves and fittings shall use full-face flanges or stub flanges, both with corrosion resistant or immune backing rings and bolting.

8.19.5.5 Polyethylene pipes

Mechanical joints shall be either plastics or metal proprietary compression fittings, for example, brass, gunmetal, or malleable iron. These shall include insert liners to support the bore of the pipe except where the manufacturer of the fitting instructs otherwise.

To ensure satisfactory jointing of the materials from which the pipe and transition elbow are made compatibility shall be established. The manufacturer’s instructions shall be carefully followed.
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