Copper alloys marine applications

Copper alloys in wrought or cast form are used for other purposes in ships and other marine installations, such as for propellers bearings, valves and pumps. One widespread application of aluminium-brass is its use for heating coils in tankers carrying crude oil or petroleum products. Some corrosion problems encountered in this and other applications on board ship have been described by Gilbert and Jenner . 

Much attention continues to be devoted to the corrosion behaviour of copper alloys in an increasing range of marine applications ... 

Three broad classes of aluminium alloys will be considered here the heat-treatable high-strength aluminium-copper 2000 series and aluminium-zinc-magnesium 7000 series alloys and the non-heat-treatable lower strength aluminium-magnesium 5000 series alloys which are used extensively in marine applications. 

Pure nickel was first isolated in 1751. Like cobalt, nickel was used to color glass, though nickel compounds turn glass and other substances green rather than blue. Because nickel is resistant to corrosion, it is often combined with other metals to form alloys that resist oxidation. A process known as electroplating uses nickel to coat the surface of metals that are vulnerable to corrosion, like iron or steel. Stainless steel is an example of a product made from nickel almost half the nickel that is mined each year is used to manufacture it. Also composed of chromium, stainless steel is extremely resistant to corrosion. Another nickel alloy is monel, which is made with copper. Monel is hard and resistant to corrosion, making it ideal for commercial marine applications such as the manufacture of boat propellers. The heating parts in toasters and electric ovens are made from an alloy called nichrome, which is another metal, made from chromium and nickel. 

B. Todd. Materials selection for high reliability copper alloy sea water system. Copper Development Association, www.copper.org/application/marine/seawater corrosion.html. 

While ordinary carbon or alloy steel is used most commonly for reinforcement or prestressing of concrete, stainless steels have been used in construction of piers with special service requirements [/] or in critical areas on other structures [2]. Other materials such as reinforced pktstics and nickel-copper alloy 400 have been used also to a limited extent or have been proposed for use as reinforcement for concrete in piers and docks. Stainless steel clad carbon steel is a relatively new development and its use for reinforcement of marine structures currently is being evaluated. Epoxy-coated carbon steel reinforcement also has been used successfully in many marine applications, but some failures have occurred. 

The copper-nickel alloys are referred to as cupronickels and have nickel as the principal alloying ingredient. Of all the copper alloys, the cupronickels are the most resistant to stress corrosion cracking in ammonia and ammon-ical environments. These alloys do not find many applications to resist atmospheric corrosion because of their cost. They would be most suitable for marine atmospheres. 

Table 9.36 gives some widely known applications of copper alloys in marine service. 

Immersion tests in seawater at many places, some of which have exceeded 10 years, as well as more than 50 years of experience with marine applications of aluminium demonstrate that casting alloys without copper of the 40000 series A-S7G (42100), A-SIOG (43100) the 50000 series A-G3T (51100), A-G6 (51300), as well as wrought alloys of the 5000 and 6000 series have an excellent resistance to corrosion in the marine environment and seawater. 

Applications Ion implantation is widely employed to improve the life of tools. Thus press tools, dies and gear cutters can be treated to increase their durability by three times or more. Nitrogen-implanted tungsten carbide drawing dies for copper and iron wire can be improved up to fivefold. By implanting chromium, aluminium or silicon a considerable increase in the corrosion resistance of steel can be obtained. Implantation of chromium into aircraft bearing alloys has improved their durability in marine environments . 

Tin—Nickel, Alloy deposits having 65% tin have been commercially plated since about 1951 (135). The 65% tin alloy exhibits good resistance to chemical attack, staining, and atmospheric corrosion, especially when plated copper or bronze undercoats are used. This alloy has a low coefficient of friction. Deposits are solderable, hard (650—710 HV 5Q), act as etch resists, and find use in printed circuit boards, watch parts, and as a substitute for chromium in some applications. The rose-pink color of 65% tin is attractive. In marine exposure, tin—nickel is about equal to nickel—chromium deposits, but has been found to be superior in some industrial exposure sites. Chromium topcoats increase the protection further. Tin—nickel deposits are brittle and difficult to strip from steel. Temperature of deposits should be kept below 300°C. 

As with copper, the aluminum bronzes find many architectural applications. A special aluminum bronze alloy designated C-61500 has been specifically developed for architectural use. It is reported to have a film resistance 20 times that of copper C-11000. These are suitable for marine atmospheres. 

Materials with the alloy base material nickel-copper show minimum corrosion in seawater at a composition of 67% nickel and 33% copper. Materials with this base material composition are used in many marine engineering applications. The most important of these materials are listed in Table 61. 

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