Much of the work of installing a piping or plumbing system involves making leakproof, reliable connections, and most piping requires mechanical support against
gravity and other forces (such as
wind loads and
earthquakes) which might disrupt an installation. Depending on the connection technology and application, basic skills may be sufficient, or specialized skills and
professional licensure may be legally required.
Fasteners and supports Fasteners join, or affix, two or more objects. Although they are usually used to attach pipe and fittings to mechanical supports in buildings, they do not connect the pipes. Fasteners commonly used with piping are a stud bolt with nuts (usually fully threaded, with two heavy, hexagonal nuts); a machine bolt and nut; or a
powder-actuated tool (PAT) fastener (usually a
nail or
threaded stud, driven into concrete or masonry).
Threaded pipe A
threaded pipe has a
screw thread at one or both ends for assembly. Steel pipe is often joined with threaded connections; tapered threads are cut into the end of the pipe, and sealant is applied in the form of
thread-sealing compound or
thread seal tape (also known as
PTFE or Teflon tape) and the pipe is screwed into a threaded fitting with a
pipe wrench. Threaded steel pipe is widely used in buildings to convey
natural gas or
propane fuel and is also a popular choice in
fire sprinkler systems due to its resistance to mechanical damage and high heat (including the threaded joints). Threaded steel pipe may still be used in high-security or exposed locations because it is more resistant to vandalism, more difficult to remove, and its scrap value is much lower than copper or brass. A
galvanized coating of metallic
zinc was often used to protect steel water pipes from
corrosion, but this protective coating eventually would dissolve away, exposing the iron to deterioration. Pipes used to convey fuel gas are often made of "black iron", which has been chemically treated to reduce corrosion, but this treatment does not resist erosion from flowing water. Despite its ruggedness, steel pipe is no longer preferred for conveying drinking water because corrosion can eventually cause leakage (especially at threaded joints), deposits on internal surfaces will eventually restrict flow, and corrosion will shed black or
rusty residues into the flowing water. These disadvantages are less problematic for fire sprinkler installations because standing water in the steel pipes does not flow, except during occasional tests or activation by a fire. Introducing oxygen dissolved in freshwater supplies will cause some corrosion, but this soon stops without any source of additional water-borne oxygen. In older installations, the threaded
brass pipe was similarly used and was considered superior to steel for drinking water because it was more resistant to
corrosion and shed much fewer residues into the flowing water. Assembling threaded pipe is labor-intensive, and requires skill and planning to allow lengths of pipe to be screwed together in sequence. Most threaded-pipe systems require strategically located pipe-union fittings in final assembly. The threaded pipe is heavy and requires adequate attachment to support its weight. To ensure a comprehensive pressure test, it is crucial to explicitly request a 3.1 certificate in accordance with EN HFF 10204:2004. This certificate attests that the 'metallic products' meet the stipulated order requirements and provides detailed test results. Typically, each fitting is associated with a unique heat number, which corresponds to the information documented in the 3.1 certificate datasheet.
Solvent welding A solvent is applied to
PVC,
CPVC,
ABS or other plastic piping to partially dissolve and fuse the adjacent surfaces of piping and fitting. Solvent welding is usually used with a sleeve-type joint to connect pipe and fittings made of the same (or compatible) material. Unlike metal welding, solvent welding is relatively easy to perform (although care is needed to make reliable joints). Solvents typically used for plastics are usually
toxic and may be
carcinogenic and
flammable, requiring adequate ventilation.
Soldering To make a
solder connection, a chemical
flux is applied to the inner sleeve of a joint and the pipe is inserted. The joint is then heated, typically by using a
propane or
MAPP gas torch, although electrically heated soldering tools are sometimes used. Once the fitting and pipe have reached sufficient temperature, solder is applied to the heated joint, and the molten solder is drawn into the joint by
capillary action as the flux vaporizes. "Sweating" is a term sometimes used to describe the soldering of pipe joints. Where many connections must be made in a short period (such as plumbing of a new building), soldering is quicker and less expensive joinery than compression or flare fittings. A degree of skill is needed to make several reliable soldered joints quickly. If flux residue is thoroughly cleaned, soldering can produce a long-lasting connection at a low cost. However, using an open flame for heating joints can present fire and health hazards to building occupants and requires adequate ventilation.
Welding The
welding of metals differs from soldering and brazing in that the joint is made without adding a lower-melting-point material (e.g. solder); instead, the pipe or tubing material is partially melted, and the fitting and piping are directly fused. This generally requires piping and fitting to be the same (or compatible) material. Skill is required to melt the joint sufficiently to ensure good fusion while not deforming or damaging the joined pieces. Properly welded joints are considered reliable and durable. Pipe welding is often performed by specially licensed workers whose skills are retested periodically. For critical applications, every joint is tested with
nondestructive methods. Because of the skills required, welded pipe joints are usually restricted to high-performance applications such as
shipbuilding, and in
chemical and
nuclear reactors. Adequate
ventilation is essential to remove
metal fumes from welding operations, and
personal protective equipment must be worn. Because the high temperatures during welding can often generate intense
ultraviolet light, dark goggles or full face shields must be used to protect the eyes. Precautions must also be taken to avoid fires caused by stray sparks and hot welding debris.
Compression fittings Compression fittings (sometimes called "lock-bush fittings") consist of a tapered, concave conical seat; a hollow, barrel-shaped compression ring (sometimes called a ferrule); and a compression nut which is threaded onto the body of the fitting and tightened to make a leakproof connection. They are typically brass or plastic, but stainless steel or other materials may be used. Although compression connections are less durable than soldered (aka sweated) connections, they are easy to install with simple tools. However, they take longer to install than soldered joints and sometimes require re-tightening to stop slow leaks which may develop over time. Because of this possible leakage, they are generally restricted to accessible locations (such as under a kitchen or bathroom sink) and are prohibited in concealed locations such as the interiors of walls.
Push-to-pull compression fittings Push-to-pull fittings are easily removed compression fitting that allows pipes to be connected with minimal tools. These fittings are similar to regular compression fittings but use an
O-ring for sealing and a grip ring to hold the pipe. The main advantage is that it can easily be removed and re-used, it is easy to assemble, and the joints are still rotatable even after assembly. The pipe end should be square, so it sits against the stop in the fittings and does not create turbulence, and needs to be a clean cut to avoid damaging the O-ring during insertion.
Flare fittings Flared connectors should not be confused with compression connectors, which are generally not interchangeable. Lacking a compression ring, they use a
tapered conical shaped connection instead. A specialized flaring tool is used to enlarge tubing into a 45º tapered bell shape matching the projecting shape of the flare fitting. Although a
gasket,
packing, or
O-ring may be installed between the flanges to prevent leakage, it is sometimes possible to use only a special grease or nothing at all (if the mating surfaces are sufficiently precisely formed). Although flange fittings are bulky, they perform well in demanding applications such as large
water supply networks and
hydroelectric systems. Flanges are rated at 150, 300, 400, 600, 900, 1500, and 2500
psi; or 10, 15, 25, 40, 64, 100, and 150
bars of pressure. Various types of flanges are available, depending on construction. Flanges used in piping (orifice, threaded, slip-on, blind,
weld neck, socket weld, lap-joint, and reducing) are available with a variety of facings, such as raised, flat, and ring-joint. Flange connections tend to be expensive because they require the precision forming of metal. Factory-installed flanges must meet carefully measured dimensional specifications, and pipe segments cut to length on-site require skilled precision welding to attach flanges under more-difficult field conditions.
Mechanical fittings Manufacturers such as
Victaulic and
Grinnell produce sleeve-clamp fittings, which replace many flange connections. They attach to the end of a pipe segment via circumferential grooves pressed (or cut) around the end of the pipe to be joined. They are widely used on larger steel pipes and can also be used with other materials. The chief advantage of these connectors is that they can be installed after cutting the pipe to length in the field. This can save time and considerable expense compared to flange connections, which must be factory- or field-welded to pipe segments. However, mechanically fastened joints are sensitive to
residual and thickness stresses caused by dissimilar metals and temperature changes. A grooved fitting, also known as a grooved coupling, has four elements: grooved pipe, gasket, coupling housing, and nuts and bolts. The groove is made by cold-forming (or machining) a groove at the end of a pipe. A gasket encompassed by coupling housing is wrapped around the two pipe ends, with the coupling engaging the groove; the bolts and nuts are tightened with a
socket or
impact wrench. The installed coupling housing encases the gasket and engages the grooves around the pipe to create a leakproof seal in a self-restrained pipe joint. There are two types of grooved coupling; a flexible coupling allows a limited amount of angular movement, and a rigid coupling does not allow movement and may be used where joint immobility is required (similar to a flange or welded joint).
Pressed or crimped fittings Crimped or pressed connections to use special fittings permanently attached to tubing with a powered crimper. The fittings, manufactured with a pre-installed sealant or
O-ring, slide over the tubing to be connected. High pressure is used to deform the fitting and compress the sealant against the inner tubing, creating a leakproof seal. The advantages of this method are durability, speed, neatness, and safety. The connection can be made even when the tubing is wet. Crimped fittings are suitable for drinking water pipes and other hot-and-cold systems (including central heating). They are more expensive than sweated fittings. Press fittings with either V and M profile (or contour) in stainless steel, carbon steel, and copper are trendy in Europe, and several manufacturers such as Viega, Geberit, Swiss Fittings, and ISOTUBI, distribute proprietary systems of press fittings. Compared to other connection types, press fittings have the advantages of installation speed and safety. Pressing a stainless steel fitting can be completed within five seconds with the correct equipment. Primary pressing of fittings to pipes or other fittings is performed using electrically powered press equipment, but mechanically driven press equipment is also available. Swiss Fittings is legally protected the German Brand "Pressfittings aus Edelstahl" in the USA. Press fittings of some major brands carry a plastic slip around the sleeves on each end of the fitting which falls off when the fitting has been compressed. This allows for a simple identification whether a press fitting has securely been installed. Press fittings with appropriate and region-specific certification may be used for gas lines. Stainless steel and carbon steel press fittings can withstand up to 16 bars of pressure. A disadvantage of press fittings is the dead space between the pipe and the fitting, which can possibly rule out use for beverage and food applications.
Leaded hub fittings Cast iron piping was traditionally made with one "spigot" end (plain, which was cut to length as needed) and one "socket" or "hub" end (cup-shaped). The larger-diameter hub was also called a "bell" because of its shape. In use, the spigot of one segment was placed into the socket of the preceding one, and a ring of
oakum was forced down into the joint with a
caulking iron. Then the remainder of the space in the hub was filled up. Ideally, this would be done by pouring molten
lead, allowing it to set, and hammering it tightly with a caulking tool. If this was not possible due to position or some other constraint, the joint could be filled with
lead wool or rope, which was forcibly compacted one layer at a time. This labor-intensive technique was durable if appropriately done but required time, skill, and patience for each joint to be made up. Quicker and lower-cost methods, such as rubber sleeve joints, have replaced mainly leaded hub connections of cast-iron piping in most new installations, but the older technology may still be used for some repairs. but today they are rarely joined with traditional lead joints. The rubber sleeves are typically secured with stainless steel
worm drive clamping bands, which compress the rubber to make a tight seal around the pipes and fittings. These pipe clamps are similar to
hose clamps, but are heavier-duty and ideally are made completely of stainless steel (including the screw) to provide maximum service life. Optionally, the entire rubber sleeve may be jacketed with thin sheet metal, to provide extra stiffness, durability, and resistance to accidental penetration by a misplaced nail or screw. Although the fittings are not cheap, they are reasonably durable (the rubber is typically
neoprene or flexible
PVC). An alternative design also allows the selective use of belled fittings made entirely of flexible rubber, including more-complex shapes such as wyes or tee-wyes. They are secured to cast iron pipe segments by use of stainless steel worm drive clamps. Because these fittings are not as stiff as traditional cast-iron fittings, the heavy pipe segments may need better anchoring and support to prevent unwanted movement. The lighter rubber fittings may not muffle sound as well as the heavy cast-iron fittings. An advantage of flexible rubber fittings is that they can accommodate small misalignments and can be flexed slightly for installation in tight locations. A flexible fitting may be preferred to connect a shower or heavy tub to the drainage system without transmitting slight movements or stresses, which could eventually cause cracking. Flexible fittings may also be used to reduce the transmission of vibration into the DWV system. If necessary, clamped joints can be disassembled later, and the fittings and pipe may be reconfigured. However, it is often not customary to re-use the clamps and rubber sleeves, which their previous installation may deform and may not seal well after rearranging. Clamped fittings may occasionally need to be disassembled to provide access for "
snaking" or "rodding-out" with a unique tool to clear blockage or clogs. This is also an indication that a clean-out fitting could be installed to provide easier future access. == See also ==