C H A P T E R 1

Introduction

Mankind first began using copper domestically some 6,000 to 10,000 years ago. Copper trinkets that date to the 9th millennium BC have been found in Iran. Copper is soft; however, when smelted with tin, it forms bronze, a harder, stronger metal. The period of widespread use of bronze is termed the Bronze Age, which began in northern Europe about 1500 BC. The fact that we are discovering copper and copper alloy implements that are thou- sands of years old, and in good condition, testifies to the metals excellent corrosion resistance.

Bronze enabled the manufacture of weapons, tools, vessels, vases, and so on. The Romans were the first to use bronze for building ties in construc- tion. Brass is an alloy of copper and zinc, which is less strong than bronze but widely used by the ancient Greeks and Romans for personal ornamen- tation and decorative metalwork. Many brass artifacts from this era are in good condition, again showing the metals excellent resistance to corrosion.

During the Middle Ages, bronze was used for bells and cannon. The decorative use of copper on buildings also came to be appreciated. Fig- ure 1.1 shows the copper clad roofs on the towers of the medieval cathedral in Bamberg, Germany.

The industrial revolution brought about big changes, with increased production, lower levels of impurities, and a wider range of alloys. At this time, the high electrical conductivity of copper and its use for both wires and lightning conductors were demonstrated. This period also saw the invention of the brass stamping press, which made brass forgings cheap and plentiful. Copper sheathing was also being used on wooden-hulled ships, particularly by the Royal Navy, to prevent attack of the timbers by marine borers. The cladding also reduced marine fouling, enabling higher water speeds.

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2 THE CORROSION OF COPPER AND ITS ALLOYS

FIGURE 1.1 Copper cladding on the towers of Barnberg Cathedral, Germany. (See color section.)

The latter half of the 19th century heralded the commercial production of electricity using copper wire for generators and transmission lines. A century later, the electronics era made extensive use of copper for printed circuit boards. Figure 1.2 shows copper wire being used in a modern, high- efficiency electric motor.

Copper has also been shown to be essential for human health, and the World Health Organization recommends a daily intake of 1-3 mg of copper to maintain health.

Copper is ever present in the modern world, for instance, as an elec- trical conductor in domestic appliances and electronics and as a vehicle for carrying our drinking water. Copper and its alloys are widely used for piping, pumps, and valves handling fresh water, seawater, and brines, and they are also used in heating systems. Copper alloys have also found nu- merous applications in industry, where corrosion resistance is important for handling more aggressive fluids.

Their high thermal conductivity and corrosion resistance means that copper alloys are widely used for heat exchanger tubes in power stations,

Introduction 3

FIGURE 1.2 Copper wires being used in the construction of a modern, high-efficiency electric motor. (Photograph courtesy of CDA.) (See color section.)

desalination plants, oil and gas production, and so on. Corrosion resistance and the pleasing appearance of copper and its alloys mean that they are popular for fittings inside and outside buildings as well as for decoration.

The foregoing demonstrates the combination of properties that makes copper and its alloys so widely used today. The aim of this book is to draw together the large body of information on the corrosion of copper and its alloys into a single volume in a form that is useful to engineers who are trying to select the most suitable alloy for a specific application.

The next chapter classifies the commonly used copper alloys by group and discusses the merits and properties of each group. The corrosion resis- tance of copper and its alloys is dependent on the film that forms when they are first exposed to the service environment. Chapter 3 describes the current

4 THE CORROSION OF COPPER AND ITS ALLOYS

thinking about the composition and nature of the films on the commonly used alloys, what is needed to make them protective, and what can cause the formation of less protective films.

Chapters 4 to 14 describe different types of corrosion and how these can affect copper and its alloys. In particular, each chapter ends with a section on how to avoid that form of corrosion, both in new plants and in service. Chapters 15 to 17 deal with the specific environments of under- ground corrosion, atmospheric corrosion, and corrosion in waters. These chapters discuss the factors that affect corrosion and the types of corrosion that may occur, referring readers back to Chapters 4 to 14. The final chapter discusses corrosion issues associated with the three most common methods of joining copper alloys: soldering, brazing, and welding.

In addition, there are two appendixes. Appendix A summarizes the compositions of the commonly used alloys by group. Alloys are mostly referred to by their UNS numbers,' but national standards have been used for alloys for which no UNS number exists. Appendix B reviews the differ- ent test methods used to determine erosion corrosion resistance and assists the reader in comparing results from the wide variety of methods reported in the literature.

If this document is read from beginning to end, a certain amount of repetition is noticeable. This is because most readers will want to dip into sections relevant to their current problem and will not wish to keep following references to other chapters. Where the point at issue requires more lengthy discussion, references to other chapters are unavoidable.

Reference

1. Metals and Alloys in the UniJed Numbering System (Warrendale, PA: SAE International and West Conshohocken, PA: ASTM International, 2004).

Front MatterTable of Contents1. IntroductionReference

AppendicesIndexColor Plates