Two distinct groups of brasses used for marine service are distinguished by their metallurgical structure: 1) Alpha brasses, which have a single-phase structure and contain up to about 37% zinc; and 2) Alpha-beta (duplex) brasses, which have two phases - the second phase, beta, starts to form above about 37.5% zinc. Al, Sn, Mn additions give a range of ‘high tensile strength’ alpha-beta brasses. Aluminum brass (an alpha brass used for tube and pipe) contains As to prevent dezincification. Tin is used in naval brass (alpha beta brass) and slows dezincification in heat exchanger tube plates. High tensile brass (can be called manganese bronze) needs cathodic protection to avoid dezincification. Uses include medium duty propellers, shafts, deck fittings. Alloys with about 3% Mn and similar amounts of aluminum and nickel have good service as medium duty propellers.
Brasses can give good service in seawater but require consideration of two types of corrosion. 1) Dezincification can be controlled by alloying or cathodic protection. 2) Ammonia stress corrosion cracking can be prevented by stress relieving, or by cathodic protection when submerged.
UR30™ in Aquaculture Operations
The Mitsubishi-Shindoh Co., Ltd., has developed a proprietary copper-zinc brass alloy, called UR30™, specifically designed for aquaculture operations. The alloy, which is composed of 64% copper, 35.1% zinc, 0.6% tin, and 0.3% nickel, resists mechanical abrasion when formed into wires and fabricated into chain link, woven or other types of flexible mesh. To date, in over 10 years of aquaculture experience, chain link mesh fabricated by this brass alloy has not suffered from dezincification, stress corrosion cracking, or erosion corrosion.
Tungum: UNS C69100/ CZ127 (CW700R)
Tungum® is a well-known tube product and has been successfully used in marine environments, particularly hydraulic control and instrumentation lines. It has high resistance to dezincification and performed extremely well in seawater and marine atmospheres.
Red Brass/Gunmetals
Gunmetals are tin bronze castings that have been widely used in shipbuilding and marine engineering.
References
- Introduction to Brasses (Part I), An overview of the large and industrially important family of alloys based on copper and zinc. The article is especially recommended to designers, engineers and others who specify materials for manufactured products. A brief history of brasses is included for those interested in learning about these interesting alloys. Links are provided to sources on The Copper Page and other websites where more detailed information can be obtained. .
- Introduction to Brasses (Part II), This section provides explanations about duplex, free cutting and high strength brasses as well as alloying agents and European designations .