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October 26, 2018
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 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 to each other. 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).
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, 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 threaded 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 a popular choice in fire sprinkler systems due to its resistance to mechanical damage and high heat. Threaded steel pipe may still be used in high-security locations, because it is more resistant to vandalism, more difficult to remove, and its scrap value is lower than copper or brass.
in older installations, threaded brass pipe was similarly used, and was considered superior to steel for drinking water, because it was more resistant to corrosion.
Assembling threaded steel pipe takes skill and planning to allow lengths of pipe to be screwed together in sequence. Most threaded-pipe systems require the use of strategically located pipe-union fittings in final assembly. Threaded steel pipe is heavy, and requires adequate attachment to support surfaces. Despite its thick walls steel pipe is no longer preferred for conveying drinking water, because corrosion can cause leakage especially at threaded joints, and deposits on internal surfaces will eventually restrict flow.
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.
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 using a propane or MAPP gas torch, 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 of time (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 a number of reliable soldered joints quickly. If flux residue is thoroughly cleaned, soldering can produce a long-lasting connection at low cost. However, the use of an open flame for heating joints can present fire and health hazards to building occupants, and requires adequate ventilation.
Brazing is a thermal joining process in which two pieces of base metal are joined by a molten brazing filler metal which is drawn between them by capillary action. The process can be used to join most metals and alloys commonly used in engineering. A brazing filler metal has a high melting temperature, which is nevertheless lower than the melting point of the metals being joined. Brazing can join pipes, rods, and metal pieces which fit tightly against each other without large gaps; it can even join tungsten carbide, ceramics, and similar non-metallic materials.
Well-brazed joints are as strong as their parent-metal pieces and can withstand demanding service. With smooth, neat fillets, they have good electrical conductivity.
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 that the piping and fitting are the same (or compatible) material. Skill is required to melt the joint sufficiently to ensure good fusion, while not deforming or damaging the pieces being joined.
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 starting fires caused by stray sparks and hot welding debris.