4.1 INTRODUCTION

Awide spectrum of corrosion problems are encountered in industry as a result of combination of materials, environments and service conditions. Corrosion may not have a deleterious effect on a material immediately but it affects the strength, mechanical operations, physical appearance and it may lead to serious operational problems. Corrosion may manifest itself as a cosmetic problem only, but it can be very serious if deterioration of critical components is involved. Serious corrosion problems, such as the pitting of condenser tubes in heat exchangers, degradation of electronic components in aircrafts and corrosion fatigue of propellers can lead to catastrophicfailures. Whencatastrophicfailuresoccur, the cost in terms of lives, equipment, and time is very high. While evaluating the long range performance of materials, it is essential for an engineer to consider the effects of corrosion along with other characteristics, such as strength and formability. In order to be able to select suitable materials, it is important for an engineer to understand the nature of corrosion, types of corrosion and methods of prevention of different types of corrosion. The mechanism of corrosion has already been discussed at length in Chapter 3, and so is not repeated here.

Environment plays a very important part in corrosion. The severity of corrosion varies considerably from one place to another. For instance, the rate of corrosion of steel will not be the same in Dhahran and Riyadh, ^[1]because the former has a sea-coastal (marine) environment and the later, a typical desert environment. Generally, the variation in...