Page 162 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

2 THE PROPERTIES OF MATERIALS

There are many materials that you, as a plumber, will deal with in your working
life. Each one will have different characteristics, such as weight, melting point,
density and strength. It is important that we know and understand the materials
we work with to ensure that the correct material is used for a given application.
Here, we will investigate some of the many different materials we use, together
with their working properties and their uses.

Relative density of solids, liquids and gases
Relative density is the ratio of the density of a substance to the density of
a standard substance under specific conditions. For liquids and solids, the
standard substance is usually distilled water at 4°C. For gases, the standard
is usually air at the same temperature and pressure as the substance being
measured.

When we talk about a material’s relative density, we are basically comparing
the mass of that material against water or air (see Table 3.5). In both cases the
water and air have a relative density (or specific gravity) of 1.

 Table 3.5 Relative densities of common substances used in the plumbing industry

INDUSTRY TIP Solids
Substance Relative density Mass/m 3
Another phrase for relative Water (1 m 3 of water has a mass 1 1000 kg
density is ‘specific gravity’ and of 1000 kg at 4°C)
this usually refers to gases. Copper 9 9000 kg
Steel 7.48–8.0 (depending on the grade) 7480–8000 kg
Lead (milled) 11.34 11,340 kg
 Table 3.6 Gases’ specific Lead (cast) 11.30 11,300 kg
gravity
Brass 8.4 8400
Gas uPVC 1.35 1350 kg
Gas Specific Polypropylene 0.91 910 kg
gravity
Air 1 Principal applications of solid materials
Natural 0.7 Lighter
gas than air The solid materials used in the plumbing industry can be classified into three
Propane 1.5 Heavier distinct groups:
than air
1 those made from metals
Butane 2.0 Heavier 2 those made from plastics
than air
3 those made from ceramics and fireclays.
Hydrogen 0.069 Lighter
than air
Metals
Metals are one of the main materials used in the plumbing industry. They can be
found in the form of pipes, tubes and fittings, and in the manufacture of boilers,
radiators and other heating appliances, as well as sundry items such as solder,
screws and nails.

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