This chapter contains sample problems with worked solutions pertaining to the application of corrosion inhibitors. Correct answers require an understanding of potentiodynamic polarization scan (PDS) curves, the determination of corrosion current and inhibitor efficiency, and the development of a test plan to evaluate the long-term corrosion protection of a potential inhibitor.

Corrosion involves chemical reactions in equilibrium that that are understood through principles of thermodynamics. In practice, the rate at which corrosion reactions occur is the most important consideration. This chapter deals with corrosion kinetics, which allows engineers to to understand rates of corrosion. The discussion covers two kinetic processes, namely electrode reactions at the cathode and anode and conduction of ions in the electrolyte. The chapter also provides information on passivation and its effect on polarization diagrams.

This chapter covers the engineering aspects of corrosion inhibitors and their effect on corrosion reactions. It explains how different metallic salts and heterocyclic compounds influence chemical reactions on metal surfaces exposed to corrosive media or environments. It describes how to evaluate inhibition efficiency through weight loss measurements, linear polarization resistance tests, electrochemical impedance spectroscopy, electrochemical noise monitoring, and surface analysis. It demonstrates the use of potentiodynamic polarization curves, Tafel extrapolations, equivalent circuit models, and various methods for characterizing corrosion damage and protective surface films. It also discusses typical applications, industry trends, and the emerging role of high-throughput experimentation, quantitative modeling, and machine learning in the development of cleaner and more effective corrosion inhibitors.

This chapter lays the groundwork for understanding electrode kinetics associated with corrosion. It presents a simple but useful theory relating kinetics to the polarization behavior of half-cell reactions. The theory is based on the observation that electrode potentials vary as a function of current density or charge transfer in a given area. The chapter explains how to measure and plot electrode potentials and currents and how to interpret the resulting polarization curves. It also discusses the effects of concentration gradients, explaining how they cause diffusion and, in some cases, produce changes in electrode potential.

This chapter develops a corrosion model that accounts for solution potentials and the effects of coupling between cathodic and anodic reactions. It begins by examining potential differences at various points (in the solution) along a path from the anode to the cathode area. It then presents a simple model of a galvanically coupled electrode, in which the metal is represented as an array of anode and cathode reaction surfaces. The chapter goes on to develop the related theory of mixed electrodes, showing how it can be used to predict corrosion rates based on measured potentials and current densities, polarization characteristics, and physical variables such as anode-to-cathode area ratios and fluid velocity. It also discusses the effect of corrosion inhibitors, galvanic coupling, and external currents, making extensive use of polarization curves.

This chapter discusses the principles and procedures of electrochemical measurements used to investigate corrosion behaviors. It begins by presenting a diagram of a basic potentiostatic circuit, which consists of a working electrode and an auxiliary or counter electrode suspended in an electrolytic solution. It describes how corrosion potentials and current densities are measured and explains how to deal with various sources of error. It also explains how electrochemical impedance measurements are used and describes the underlying theory and procedures in some detail.

This appendix is a compilation of terms and definitions related to corrosion.

Corrosion testing and monitoring are powerful tools in the fight to control corrosion. This chapter provides a general overview of three major categories of corrosion tests, namely laboratory tests, pilot-plant tests, and field tests. It begins with brief sections describing the purposes of corrosion tests, the logical steps in a test program, and the preparation and cleaning of test specimens. The focus then moves on to discuss the types and applications of these test categories and the associated evaluation procedures. Excluding electrochemical tests which are addressed separately in this chapter, the other laboratory tests covered under this category are simulated atmosphere tests, salt-spray tests, and immersion tests. Only corrosion testing in the atmosphere is discussed in the section on field tests. Corrosion monitoring techniques are finally considered, covering the characteristics of corrosion monitoring techniques, the factors to be considered in selecting a corrosion-monitoring method, and the strategies in corrosion monitoring.

This chapter discusses the principles of corrosion of metals in aqueous environments. The thermodynamics of aqueous corrosion is the subject of the first half of this chapter, which addresses concepts such as corrosion reactions and free-energy change, the relationship between free energy and electrochemical potential, the effect of ionic concentration on electrode potential, and the corrosion behavior of a metal based on its potential-pH diagram. The corrosion (potential-pH) behavior of iron, gold, copper, zinc, aluminum, and titanium are described. Understanding the kinetics of corrosion and the factors that control the rates of corrosion reactions requires examination of the concepts of polarization behavior and identification of the various forms of polarization in an electrochemical cell. These concepts, addressed in the remaining of this chapter, include anodic and cathodic reactions, the mixed-potential theory, and the exchange currents.

This chapter addresses in-service monitoring and corrosion testing of weldments. Three categories of corrosion monitoring are discussed: direct testing of coupons, electrochemical techniques, and nondestructive testing techniques. The majority of the test methods for evaluating corrosion of weldments are used to assess intergranular corrosion of stainless steels and high-nickel alloys. Other applicable tests evaluate pitting and crevice corrosion, stress-corrosion cracking, and microbiologically influenced corrosion. Each of these test methods is reviewed in this chapter.

This chapter is a compilation of terms and definitions related to corrosion in the petrochemical industry.

This chapter examines methods of internal corrosion prediction for multiphase pipelines and details methodologies to perform internal corrosion direct assessment for natural gas pipelines. Further, real-time monitoring techniques for assessing actual corrosion at critical locations are discussed.

This chapter discusses the particular corrosion problems encountered and the methods of control used in petroleum production and the storage and transportation of oil and gas up to the refinery. It begins by describing those aspects of corrosion that tend to be unique to corrosion as encountered in applications involving oil and gas exploration and production. This is followed by a section reviewing the methods of corrosion control, namely the proper selection of materials, protective coatings, cathodic protection systems, use of inhibitors, use of nonmetallic materials, and control of the environment. The chapter ends with a discussion on the problems encountered and protective measures that are based on the state-of-the-art as practiced daily by corrosion and petroleum engineers and production personnel.

This chapter provides a detailed account of cathodic protection. It begins by discussing the fundamentals of cathodic protection followed by a description of the various types of cathodic protection. It then describes the origins, types, and alleged failures of cathodic protection criteria. This is followed by a section providing information on anode materials that are used for cathodic protection applications. General guidelines for designing the cathodic protection systems are also listed. Finally, the chapter presents various examples on cathodic protection of steel structures. The examples are selected to familiarize the design engineer with the steps to follow in selecting a specific corrosion-control method.