Page 309 - Chemical engineering design

CHAPTER 7

Materials of Construction

7.1. INTRODUCTION

This chapter covers the selection of materials of construction for process equipment and
piping.
Many factors have to be considered when selecting engineering materials, but for
chemical process plant the overriding consideration is usually the ability to resist corrosion.
The process designer will be responsible for recommending materials that will be suitable
for the process conditions. He must also consider the requirements of the mechanical
design engineer; the material selected must have sufficient strength and be easily worked.
The most economical material that satisfies both process and mechanical requirements
should be selected; this will be the material that gives the lowest cost over the working
life of the plant, allowing for maintenance and replacement. Other factors, such as product
contamination and process safety, must also be considered. The mechanical properties that
are important in the selection of materials are discussed briefly in this chapter. Several
books have been published on the properties of materials, and the metal-working processes
used in equipment fabrication, and a selection suitable for further study is given in the
list of references at the end of this chapter. The mechanical design of process equipment
is discussed in Chapter 13.
A detailed discussion of the theoretical aspects of corrosion is not given in this chapter,
as this subject is covered comprehensively in several books: Revie (2002), Fontana (1986),
Dillon (1986) and Schweitzer (1989).
Corrosion and corrosion prevention are also the subject of one of the design guides
published by the Design Council, Ross (1977).

7.2. MATERIAL PROPERTIES
The most important characteristics to be considered when selecting a material of
construction are:

1. Mechanical properties
(a) Strength tensile strength
(b) Stiffness elastic modulus (Young’s modulus)
(c) Toughness fracture resistance
(d) Hardness wear resistance
(e) Fatigue resistance
(f) Creep resistance
2. The effect of high and low temperatures on the mechanical properties

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