Page 171 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 3 Scientific principles

Preventing corrosion

Corrosion is one of the most destructive processes to plumbing and heating
systems, but there are methods we can employ to prevent and protect from
corrosion:

l Galvanisation is one method of protecting steel from rusting by coating with
a thin layer of zinc. Galvanising is a process by which the steel is dipped in a
bath of molten zinc.
l Greasing and oiling are some commonly used methods to prevent rusting.
The grease and oil prevent water and moisture penetration. KEY TERM
l Chrome plating and anodising prevent corrosion of metal by coating the Anodising: coating one
metal, creating a barrier between it and the corrosive environment. metal with another by
l Wet central heating systems can be protected from corrosion by the use of electrolysis to form a
corrosion inhibitors mixed with the system water. protective barrier against
corrosion.
l Plastics can be protected from the effects of UV light by painting.
l Sacrificial anodes (magnesium rods) placed inside hot water storage cylinders
protect the cylinder from electrolytic corrosion.
l Metals can be coated with enamel for protection. Enamel consists of a thin
layer of glass heated to a high temperature which then fuses on to the
surface of the metal.
The properties of liquids

The plumbing industry is primarily concerned with liquids in one form or
another, with water being the most common fluid we deal with. Liquids you may
come across in your working life include:
l water
l refrigerants
l glycols and anti-freeze
l fuel oils
l lubricants.

Here, we will investigate these liquids and their uses within the building services
industry.

Water
Water is the most abundant compound on earth. It covers seven-tenths of the
Earth’s surface and is the key to life on Earth. Water has many uses, including  Table 3.10 The energy of sensible
and latent heat of water from
hot and cold water supplies and wet central heating systems. Yet, what do we 0°C of water to 100°C of steam
actually know about water?
Boiling point of
The properties of water Pressure the water
bar kPa °C kJ/kg
l Water is a colourless, odourless and tasteless liquid: any taste it does 0 0 100.00 419.06
have comes from the minerals that may be dissolved in it, and this can often
explain why water tastes different in different parts of the country. 1 100.0 120.42 505.6
l Water can exist in all three states of matter: liquid (water), solid (ice) 2 200.0 133.69 562.2
and gas (steam). 3 300.0 143.75 605.3

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