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MATERIALS OF CONSTRUCTION
7.7.1. Surface finish
In industries such as the food, pharmaceutical, biochemical, and textile industries, the
surface finish of the material is as important as the choice of material, to avoid contami-
nation.
Stainless steel is widely used, and the surfaces, inside and out, are given a high finish by
abrasive blasting and mechanical polishing. This is done for the purposes of hygiene; to
prevent material adhering to the surface; and to aid cleaning and sterilisation. The surface
finishes required in food processing are discussed by Timperley (1984) and Jowitt (1980).
A good surface finish is important in textile fibre processing to prevent the fibres
snagging.

7.8. COMMONLY USED MATERIALS OF CONSTRUCTION
The general mechanical properties, corrosion resistance, and typical areas of use of some
of the materials commonly used in the construction of chemical plant are given in this
section. The values given are for a typical, representative, grade of the material or alloy.
The multitude of alloys used in chemical plant construction is known by a variety of
trade names, and code numbers designated in the various national standards. With the
exception of the stainless steels, no attempt has been made in this book to classify the
alloys discussed by using one or other of the national standards; the commonly used,
generic, names for the alloys have been used. For the full details of the properties and
compositions of the grades available in a particular class of alloy, and the designated
code numbers, reference should be made to the appropriate national code, to the various
handbooks, or to manufacturers’ literature. For the United Kingdom standards, the British
Standards Institute Catalogue should be consulted.
The US trade names and codes are given by Perry et al. (1997). A comprehensive
review of the engineering materials used for chemical and process plant can be found in
the book by Evans (1974).

7.8.1. Iron and steel

Low carbon steel (mild steel) is the most commonly used engineering material. It is cheap;
is available in a wide range of standard forms and sizes; and can be easily worked and
welded. It has good tensile strength and ductility.
The carbon steels and iron are not resistant to corrosion, except in certain specific
environments, such as concentrated sulphuric acid and the caustic alkalies. They are
suitable for use with most organic solvents, except chlorinated solvents; but traces of
corrosion products may cause discoloration.
Mild steel is susceptible to stress-corrosion cracking in certain environments.
The corrosion resistance of the low alloy steels (less than 5 per cent of alloying
elements), where the alloying elements are added to improve the mechanical strength
and not for corrosion resistance, is not significantly different from that of the plain
carbon steels.
A comprehensive reference covering the properties and application of steels, including
the stainless steels, is the book by Llewellyn (1992). The use of carbon steel in the
construction of chemical plant is discussed by Clark (1970).