Admiralty brass

The heat-transfer quaUties of titanium are characterized by the coefficient of thermal conductivity. Even though the coefficient is low, heat transfer in service approaches that of admiralty brass (thermal conductivity seven times greater) because titanium s greater strength permits thinner-walled equipment, relative absence of corrosion scale, erosion—corrosion resistance that allows higher operating velocities, and the inherently passive film. 

Phosphorized deoxidized arsenical copper (alloy 142 (23)) is used for heat exchangers and condenser tubes. Copper-arsenical leaded Muntz metal (alloy 366), Admiralty brass (alloy 443), naval brass (alloy 465), and aluminum brass (alloy 687), all find use in condensers, evaporators, ferrules, and heat exchanger and distillation tubes. The composition of these alloys is Hsted in Table 5. 

Admiralty Brass and Naval Brass are 30 and 40% zinc alloys, respectively, to which a 1% tin addition has been added. Resistance to dezincification of Cu—Zn alloys is increased by tin additions. Therefore, these alloys are important for thein corrosion resistance in condenser tube appHcations. In these, as weU as the other higher zinc compositions, it is common to use other alloying additives to enhance corrosion resistance. In particular, a small amount (0.02—0.10 wt %) of arsenic (C443), antimony (C444), or phosphoms (C445) is added to control dezincification. When any of these elements are used, the alloy is referred as being "inhibited." For good stress corrosion resistance, it is recommended that these alloys be used in the fiiUy annealed condition or in the cold worked plus stress reHef annealed condition. 

I I Admiralty brass, aluminum brass n Manganese bronze... 

Yellow brass Admiralty brass Aluminum bronze Red brass Copper Silicon bronze 70-30 cupronickel Nickel (passive)... 

Many shell-and-tube condensers use copper alloy tubes, such as admiralty brasses (those containing small concentrations of arsenic, phosphorus, or antimony are called inhibited grades), aluminum brasses, and cupronickel austenitic stainless steel and titanium are also often used. Utility surface condensers have used and continue to use these alloys routinely. Titanium is gaining wider acceptance for use in sea water and severe service environments but often is rejected based on perceived economic disadvantages. 

The relatively long service life of the duplex tubes suggested that similar tubes be used for retubing. Because of supplier delays in securing duplex tubing, however, alternative materials, including admiralty brass, were considered. 

Sampie Specifications 1 in. (2.5 cm) outer diameter, admiralty brass tubes... 

Figure 7.8 Striations on the internal surface of admiralty brass condenser tube after acid cleaning. (Magnification 15x.)...

Figure 8.6 Severe grooving by ammonia-containing condensate on an admiralty brass condenser tube. Condensate flowed down the tube sheet and collected at the tube end, cutting an annular groove. Note the perforation just outside the tube roll.

Sample Specifications 1 in. (25 mm) outer diameter, 30 ft (9 m) long, inhibited admiralty brass... 

Sample Specifications h in. (13 mm) outside diameter, admiralty brass... 

Admiralty brass (70% Cu, 29% Zn, 1% Sn, 0.05% As or Sb) and arsenical aliuninum brass (76% Cu, 22% Zn, 2% Al, 0.05% As) are resistant to dezincification in most cooling water environments. In the recent past, heat exchangers have virtually always been tubed with inhibited grades of brass. Brasses containing 15% or less zinc are almost immune to dezincification. Dezincification is common in uninhibited brasses containing more than 20% zinc. Inhibiting elements include arsenic, antimony, and phosphorus. Without inhibiting elements. 

Admiralty brass Red brass Yellow brass Naval brass Muntz metal... 

Marine, /. navy, -blau, n. navy blue, -legie-rung, /. admiralty alloy, admiralty brass, -leim, m. marine glue, -fil, n. marine oil. marinieren, v.t. marinate, pickle. 

Brasses Brasses are basically alloys of copper and zinc, containing between about 10 and 45 l o Zn, but many other additions are made and the resulting alloys are the most complicated of all the copper-base series. The singlephase (a) brasses, containing up to about 37 7o Zn in the binary alloys, may have additions of 1% Sn (Admiralty brass), 2 7o A1 (aluminium-brass), or... 

Fig. 4.11 Typical impingement attack on Admiralty brass condenser tube. Magnification x 2...

In early times 70/30 brass condenser tubes failed by dezincification and Admiralty brass (70Cu-29Zn-lSn) was brought into use. This proved little better, but some time later the addition of arsenic was found to inhibit dezincification. Failures of Admiralty brass by impingement attack became a serious problem, particularly as cooling water speeds increased with the development of the steam turbine. The introduction of alloys resistant to this type of attack was a great step forward and immediately reduced the incidences of failure. 

Fresh waters are, in general, less corrosive towards copper than is sea-water, and copper is widely and satisfactorily used for distributing cold and hot waters in domestic and industrial installations . Copper and copper alloys are used for pipes, hot-water cylinders, fire-back boilers, ball floats, ball valves, taps, fittings, heater sheaths, etc. In condensers and heat exchangers using fresh water for cooling, tubes of 70/30 brass or Admiralty brass are usually used, and corrosion is rarely a problem. 

A similar method of test was used at the International Nickel Company s Corrosion Laboratory at North Carolina. The specimen discs are mounted on insulated vertical spindles and submerged in sea-water, which is supplied continuously to the tank in which the specimens are immersed. The maximum peripheral speed of the spinning disc is about 760cms , and the characteristic pattern of attack is shown in Fig. 19.3a. Studies of variation of depth of attack with velocity indicate that at low velocities (up to about 450 cm s ) alloys such as Admiralty brass, Cu-lONi and cupro-nickel alloys containing iron maintain their protective film with a consequent small and similar depth of attack for the diflferent alloys. At higher velocities the rate increases due to breakdown of the film. 

The transport of pre-boiler corrosion debris to the boiler section includes the oxides of iron, copper, nickel, zinc, and chromium and results from the corrosion of pre-heaters and condensers, and the like. Specifically, equipment components variously fabricated from admiralty brass, aluminum brass, cupronickels, and stainless steels are most affected. 

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