Wikipedia about elbow pipes
An elbow is a pipe fitting installed between two lengths of pipe or tubing to allow a change of direction, usually a 90° or 45° angle, though 22.5° elbows are also made. The ends may be machined for butt welding, threaded (usually female), or socketed, etc.
When the two ends differ in size, the fitting is called a reducing elbow or reducer elbow.
Elbows are categorized based on various design features as below:
Long Radius (LR) Elbows ? radius is 1.5 times the pipe diameter
Short Radius (SR) Elbows ? radius is 1.0 times the pipe diameter
90 Degree Elbow ? where change in direction required is 90°
60 Degree Elbow ? where change in direction required is 60°
45 Degree Elbow ? where change in direction required is 45°
A 90 degree elbow is also called a "90 bend" or "90 ell".
It is a fitting which is bent in such a way to produce 90 degree change in the direction of flow in the pipe. It is used to change the direction in piping and is also sometimes called a "quarter bend".
A 90 degree elbow attaches readily to plastic, copper, cast iron, steel and lead.
It can also attach to rubber with stainless steel clamps.
It is available in many materials like silicone, rubber compounds, galvanized steel, etc.
The main application of an elbow (90 degree) is to connect hoses to valves, water pressure pumps, and deck drains.
These elbows can be made from tough nylon material or NPT thread.Źródło: https://en.wikipedia.org/wiki/Piping_and_plumbing_fitting
Plumbing and its standards
Much of the plumbing work in populated areas is regulated by government or quasi-government agencies due to the direct impact on the public's health, safety, and welfare.
Plumbing installation and repair work on residences and other buildings generally must be done according to plumbing and building codes to protect the inhabitants of the buildings and to ensure safe, quality construction to future buyers.
If permits are required for work, plumbing contractors typically secure them from the authorities on behalf of home or building owners.
In the United Kingdom the professional body is the Chartered Institute of Plumbing and Heating Engineering (educational charity status) and it is true that the trade still remains virtually ungoverned; there are no systems in place to monitor or control the activities of unqualified plumbers or those home owners who choose to undertake installation and maintenance works themselves, despite the health and safety issues which arise from such works when they are undertaken incorrectly; see Health Aspects of Plumbing (HAP) published jointly by the World Health Organization (WHO) and the World Plumbing Council (WPC).
WPC has subsequently appointed a representative to the World Health Organization to take forward various projects related to Health Aspects of Plumbing.Źródło: https://en.wikipedia.org/wiki/Plumbing
Water systems - materials
Water systems of ancient times relied on gravity for the supply of water, using pipes or channels usually made of clay, lead, bamboo, wood, or stone.
Hollowed wooden logs wrapped in steel banding were used for plumbing pipes, particularly water mains.
Logs were used for water distribution in England close to 500 years ago.
US cities began using hollowed logs in the late 1700s through the 1800s.8 Today, most plumbing supply pipe is made out of steel, copper, and plastic; most waste (also known as "soil")11 out of steel, copper, plastic, and cast iron.11
The straight sections of plumbing systems are called "pipes" or "tubes".
A pipe is typically formed via casting or welding, whereas a tube is made through extrusion.
Pipe normally has thicker walls and may be threaded or welded, while tubing is thinner-walled and requires special joining techniques such as brazing, compression fitting, crimping, or for plastics, solvent welding.
These joining techniques are discussed in more detail in the piping and plumbing fittings article.Źródło: https://en.wikipedia.org/wiki/Plumbing#Materials