Mechanical Joints
Mechanical joints include transition, compres- sion, and threaded joints. Mechanical joints shall incorporate a positive mechanical system for axial restraint in addition to any restraint pro- vided by friction. All internal grab rings shall be manufactured from corrosion-resistant steel. Polyethylene sealing rings shall be Type 1 (LDPE) compound.
Compression Joints
Compression type gaskets have been used in pressure pipe joints for years. The compression joint uses hub-and-spigot pipe and fittings (as does the lead and oakum joint). The major dif- ference is the one-piece neoprene rubber gasket. When the spigot end of the pipe or fitting is pulled
or drawn into the gasketed hub, the joint is sealed by displacement and compression of the neoprene gasket. The resulting joint is leak free, and it absorbs vibration and can be deflected up to 5° without leaking or failing. Gaskets are precision molded of durable neoprene. Note that service gaskets must be used with service weight pipe and fittings. Extra-heavy gaskets must be used with extra-heavy pipe and fittings. The stan- dard specification for rubber gaskets for joining cast-iron soil pipe and fittings is ASTM C564. Neoprene will not support combustion and gas- ket materials can be safely used up to 212°F. Maximum deflection should not exceed ½ in. per foot of pipe. This would allow 5 in. of deflection for a 10-ft piece of pipe and 2½ in. for 5 ft of pipe. For more than 5° of deflection, fittings should be used.
Lead and Oakum Joints (Caulked Joints)
Hub-and-spigot cast-iron soil pipe and fitting joints can be made with oakum fiber and mol- ten lead, which provides a leak-free, strong, flexible, and root-proof joint. The waterproofing characteristics of oakum fiber have long been recognized by the plumbing trades, and when molten lead is poured over the oakum in a cast- iron soil pipe joint, it completely seals and locks the joint. This is because the hot lead fills a groove in the bell end of the pipe or fitting, firmly anchoring the lead in place after cooling. To make a caulked joint, the spigot end of a pipe or fit- ting is placed inside the hub of another pipe or fitting. Oakum is placed around the spigot in the hub using a yarning tool and then the oa- kum is packed to the proper depth using a packing tool. Molten lead is then poured into the joint making sure the lead is brought up near the top of the hub. After the lead has cooled sufficiently, it is caulked with a caulking tool to form a solid lead insert. The result is a locktight soil pipe joint with excellent flexural character- istics. If horizontal joints are to be made, a joint runner must be used to retain the molten lead. Customary safety precautions should be taken when handling molten lead.
Shielded Hubless Coupling
The shielded coupling for hubless cast-iron soil pipe and fittings is a plumbing concept that pro- vides a more compact arrangement without
sacrificing the quality and performance of cast iron. The hubless coupling system typically uses a one-piece neoprene gasket, a shield of stain- less steel retaining clamps. The hubless coupling is manufactured in accordance with CISPI 310 and ASTM C1277. The great advantage of the system is that it permits joints to be made in limited-access areas. The 300 series stainless steel, which is always used with hubless cou- plings, was selected because of its superior corrosion resistance. It is resistant to oxidation, warping and deformation, offers rigidity under tension with substantial tension strength, and yet provides sufficient flexibility. The shield is corrugated in order to grip the gasket sleeve and give maximum compression distribution to the joint. The stainless steel worm gear clamps compress the neoprene gasket to seal the joint. The neoprene gasket absorbs shock and vibra- tion and completely eliminates galvanic action between the cast iron and the stainless steel shield. Neoprene will not support combus- tion and can be safely used up to 212°F. The neoprene sleeve is completely protected by a nonflammable stainless steel shield, and as a result a fire rating is not required. Joint deflec- tion using a shielded hubless coupling has a maximum limit of up to 5°. Maximum deflection should not exceed ½ in. per foot of pipe. This would allow 5 in. of deflection for a 10-ft piece of pipe. For more than 5° of deflection, fittings should be used.
Mechanically Formed Tee Fittings for Copper Tube
Mechanically formed tee fittings shall be formed in a continuous operation consisting of drilling a pilot hole and drawing out the tube surface to form a tee having a height of not less than three times the thickness of the branch tube wall so as to comply with the American Welding Society’s lap joint weld. The device shall be fully adjust- able to ensure proper tolerance and complete uniformity of the joint. (See Figure 2-17.)
The branch tube shall be notched to con- form to the inner curve of the run tube and have two dimple/depth stops pressed into the branch tube, one ¼ in. (6.4 mm) atop the other so as to serve as a visual point of inspection. The bottom dimple is to ensure that penetration of the branch tube into the tee is of sufficient depth for brazing and that the branch tube does not obstruct the flow in the main line tube. Dimple/
depth stops shall be in line with the run of the tube.
Mechanically formed tee fittings shall be brazed in accordance with the Copper Develop- ment Association’s Copper Tube Handbook using BCuP series filler metal.
Note: Soft soldered joints will not be permit- ted. Mechanically formed tee fittings shall conform to ASTM F 2014-00, ANSI B 31.9, Build-
ing Services Piping, and ASME Code for Pressure Piping, ANSI B 31.5c.
Mechanical Joining of Copper Pipe
The tubing should be severed with a tube cutter or fine-toothed steel saw and all burrs are to be removed both inside and out. The seal located inside the fitting should be checked; the seal is made of EPDM material. While being turned slightly, the fitting should be slid and pressed onto the pipe until properly seated. The inser- tion depth should be marked. The appropriate clamping jaw should be set into the pressing tool and pushed in until the jaw locks in place. The clamping jaw should be opened and placed at a right angle on the fitting; and the insertion depth should be verified. The pressing procedure should be started upon completion of the press- ing cycle. The clamping jaw should be opened; the joint is completed.
Figure 2-17 Copper Pipe Mechanical T-Joint Source: Courtesy of T-Drill.
Brazing
“Brazing” is defined as a process where the filler metals (alloys) melt at a temperature greater than 840°F and the base metals (tube and fittings) are not melted. Most commonly used brazing filler metals melt at temperatures around 1150 to 1550°F.
Soldering
“Soldering” is defined as a process wherein the filler metal (solder) melts at a temperature of less than 840°F and the base metals (tube and fit- tings) are not melted. Most commonly used leak-free solders melt at ranges around 350 to 600°F. Lead-free solders must contain less than 0.2% lead (Pb) in order to be classified as no lead.
Making up soldered joints Soldered joints should be installed in accordance with the re- quirements, steps, and procedures outlined in ASTM B828, Standard Practice for Making Cap-
illary Joints by Soldering of Copper and Copper Alloy Tube and Fittings and the procedures found
in the Copper Tube Handbook of the Copper De- velopment Association.
Fluxes used for the soldering of copper and copper alloys should be those meeting the re- quirements of ASTM B813, Standard Specification
for Liquid and Paste Fluxes for Soldering Applica- tions of Copper and Copper Alloy Tube.
The tubing should be severed with a tube cutter and all burrs should be removed. The out- side of the tubing and the inside fitting should be cleaned to bright metal with a medium-grade emery cloth or sandpaper. The flux must be evenly applied with a brush to the outside tub- ing and inside fitting. The fitting should be slipped on the tubing and twisted to distribute the flux. The joint should be soldered immedi- ately, before moisture collects in the flux. (This could cause corrosion later on.) It should be heated evenly with the specified solder then filled with solder, and the excess should be wiped off.
Joining Plastic Pipe
Schedule 80 plastic pipe can be threaded. Sched- ule 40 must be solvent welded. The pipe and socket must be cleaned, burrs must be removed, and solvent should be applied to both. The pipe must be assembled quickly and twisted one-
quarter turn to spread the solvent. The joint usually sets within two minutes.
Assembling Flanged Joints
The face of the flange should be cleaned with a solvent-soaked rag to remove any rust-preven- tive grease. Any dirt should be cleaned from the gasket. The pipe and the flanges should be aligned to eliminate any strain on the coupling. The gasket should be coated with graphite and oil or some other recommended lubricant, in- serted, and then bolted. Thread lubricant should be applied to the bolts. The bolts should be evenly tightened with a wrench. The nuts should be hand tightened. When tightening the bolts, care should be exercised that they are diametrically opposed; adjacent bolts should never be tight- ened.
Making Up Threaded Pipe
Male and female threads should be cleaned with a wire brush. Pipe dope should be applied only to the male thread. (If dope is applied to female thread, it will enter the system). The pipe and coupling should be aligned and hand tightened and then finished by turning with a wrench. A few imperfect threads should be left exposed. Sections of the assembled piping should be blown out with compressed air before being placed in the system.
Thread Cutting
The pipe should be cut with a pipe cutter. It should be clamped in a vise and the pipe stock and die engaged with short jerks; when the cut- ter catches, it should then be pulled slowly with a steady movement using both hands. Enough cutting oil should be used during the cutting process to keep the die cool and the edges clean. The die should be backed off frequently to free the cutters, and the follower should be watched when reversing the dies against the jumping threads, cross-threading, or the stripping of threads. Leaky threaded joints are usually caused by faulty or improper lubricants.
Welding
Basic welding processes include electric arc, oxyacetylene, and gas shielded. Commercial welding fittings are available with ends designed
for butt welding or for socket-joint welding. The type of joint used depends on the type of liquid, the pressure in the system, the pipe size and material, and the applicable codes. The butt joint is frequently used with a liner (backing ring). See Figures 2-18 and 2-19.
Electric arc welding Electric arc welding is used for standard, extra-heavy, or double extra-heavy commercial steel pipe. ASTM A-53 grades of low- carbon steel butt-welded pipe are the most weldable.
Oxyacetylene welding In this welding process, the flame develops a temperature to 6300°F (3482.2°C), completely melting commercial met- als to form a bond. The use of rod increases strength and adds extra metal to the seam. This process is used with many metals (iron, steel, stainless steel, cast iron, copper, brass, alumi- num, bronze and other alloys) and can be used to join dissimilar metals. When cut on site, the pipe ends must be beveled for welding; this can be accomplished with an oxyacetylene torch. Gas-shielded arcs This process keeps the at- mosphere from the molten puddle and is good for nonferrous metals since flux is not required, producing an extremely clean joint. There are two types of gas-shielded arc: tungsten inert gas (TIG) and metallic inert gas (MIG). Gas-shielded arcs are used for aluminum, magnesium, low- alloy steel, carbon steel, stainless steel, copper nickel, titanium, and others.
Joining Glass Pipe
The joints are either bead to bead or bead to plain end. The bead-to-bead coupling is used for joining factory-beaded or field-beaded end pipe and fittings. The bead-to-plain-end coupling is used to join a pipe section or fitting that has a beaded end to a pipe section that has been field cut to length and is not beaded.
Bending Pipe and Tubing
Pipe bending (cold or hot method) is usually done with a hydraulic pipe bender. The radius of the bend should be large enough to free the surface of cracks or buckles (see ANSI B31.1). Some bends are specifically designed to be creased or corrugated. Corrugated bends are more flexible than conventional types and may have smaller radii. Straight sections of pipe are sometimes corrugated to provide flexibility. Copper tube is usually bent with a spring tube bender, grooved wheel and bar, bending press, or machine. Sharp bends are usually made by filling the pipe with sand or other material to prevent flattening or collapsing. Bending pipe or tubing is easier and more economical than installing fittings. Bends reduce the number of joints (which could leak) and also minimize friction loss through the pipe.
Electrofusion Joining
Electrofusion is a heat fusion joining process wherein a heat source is an integral part of the fitting. Where electric current is applied, heat is produced, melting and joining its components. Fusion occurs when the joint cools below the melting temperature of the material. The appli- cable standard is ASTM F-1290-98 9,
Electrofusion Joining Polyolefin Pipe and Fittings. Figure 2-18 Typical Welding Fittings
Both PP and PVDF are not generally suit- able for threaded joints, these materials simply do not take a satisfactory thread. It is noted that thermal fusion is generally considered the best joining method.