Marine Valves
Sep 11, 2024
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The piping systems of ships include fuel pipes, steam pipes, circulating water pipes, cooling water pipes, and various water pumps. Valves are indispensable components in a ship's piping system. Valves can connect or cut off the flow of pipeline media, change the direction, pressure, and rate of flow, and protect pipelines while maintaining the normal operation of equipment. The selection of valve materials is crucial and requires considering many factors: safety and reliability, process reliability, ease of operation, installation, maintenance, and economic efficiency. The appropriate selection of copper alloys for valves plays an important role in ensuring the reliability of marine valves. Copper alloys offer excellent seawater corrosion resistance, machining characteristics, high strength, and good resistance to bacteria, making them widely used in marine valves and components.
The unique working environment of ships makes marine valves distinct from ordinary valves, forming an independent system. The differences between marine valves and ordinary valves are evident in appearance, weight, materials, and other factors. Although the working principles of marine valves are the same as ordinary valves, their quality requirements are often higher due to the different operating environments. Marine valves must meet the specific demands of the marine environment. For military ships, in particular, the valves must exhibit corrosion resistance, impact resistance, vibration resistance, and good reliability. Valves for civilian ships must comply with the international standard ISO 9002, while valves for military ships need to meet various military standards. Military ship valves must often undergo multiple tests, including hydraulic, air tightness, fatigue life, functional, vibration, and torque tests. Valves for civilian ships require quality certificates from classification societies of various countries, whereas valves for military ships require certification from the defense department’s quality assurance committee. Due to limited space on ships, stricter requirements are imposed on the weight and size of the valves. Additionally, marine valves have good reliability requirements, and maintenance must be simple and time-saving. If marine valves do not meet quality standards, it can affect the ship's navigation rate, increase maintenance costs and time, and on military ships, potentially delay missions and endanger the lives of personnel.
Since the founding of the People's Republic of China, China’s marine valve technology has significantly improved. On one hand, by digesting and absorbing Soviet marine valve technology, relevant supporting facilities and standards have been formulated; on the other hand, independent research has been conducted on marine valve-related technologies. Since 1965, after China issued the first batch of national standards for marine valves in 2000, several generations of effort have resulted in nearly complete valve specifications and marine valve standards, which have essentially met the needs of China's shipbuilding industry. Each ship requires thousands of different valves, including gate valves, stop valves, butterfly valves, ball valves, check valves, safety valves, flow control valves, and sea valves. Marine valve materials mainly include cast iron, alloy steel, copper alloy, aluminum alloy, titanium alloy, and stainless steel, while applicable media include fresh water, seawater, air, steam, fuel oil, and lubricating oil. The maximum operating pressure can reach 600MPa, with a maximum operating temperature of 650°C for the body, 1200°C for the refractory lining, a minimum operating temperature of -196°C, and a maximum nominal diameter of 5350 mm. The performance of the valve directly impacts both the system and overall performance of the ship.
Copper alloys have excellent electrical conductivity, thermal conductivity, antimagnetic properties, corrosion resistance, and antibacterial properties, along with good mechanical properties such as processing, forming, cutting, and sealing. Additionally, copper alloys used in marine valves offer economic and practical advantages, making them widely used in marine valves and components. The following highlights several characteristics of copper alloys suitable for use in valves.
Corrosion resistance: Copper and its alloys have excellent corrosion resistance and are suitable for atmospheric, freshwater, and seawater environments. Copper alloys effectively resist seawater corrosion due to copper’s high thermodynamic stability and the formation of a cuprous oxide protective film on the surface. Corrosion products deposit on the film, further protecting the alloy. Brass has good corrosion resistance in the atmosphere and freshwater but is prone to dezincification and stress cracking in seawater. Bronze includes tin bronze and aluminum bronze. Tin bronze has extremely high corrosion resistance in the atmosphere, seawater, and low-concentration alkaline solutions, making it widely used in the shipping industry and marine valves. Aluminum bronze surpasses tin bronze and brass in strength, hardness, wear resistance, and corrosion resistance, but its cutting and welding performance is poor. QA19-2 and QA19-4 alloys significantly improve strength, wear resistance, and corrosion resistance by adding elements like Fe, Mn, and Ni, making them suitable for manufacturing high-strength, wear-resistant parts such as valve gears, sleeves, nuts, and worms.
Wear resistance: Copper alloys offer good wear resistance, plasticity, and processing performance.
Antibacterial properties: Microbial corrosion is a significant cause of corrosion in seawater pipe systems. The primary corrosive microorganisms include sulfate-reducing bacteria, slime-producing bacteria, acid-producing bacteria, and ammonia-producing bacteria. Copper alloys prevent the growth and attachment of marine organisms, increase hull smoothness, and reduce maintenance costs. A cuprous oxide corrosion film forms on the surface of copper alloys, which is toxic to organisms and acts as an anti-fouling layer. The most effective way to control microbial corrosion in ship seawater pipe systems is by regularly adding bactericides, corrosion inhibitors, and slime strippers.
Good processing and forming performance: Copper alloys have excellent machining properties. When alloyed with different elements, their performance and strength can be significantly improved. Additionally, copper alloy processing is a mature technology with low production costs and high manufacturing quality.
Economical applicability: After alloying, the structure of copper changes, significantly improving its material properties and strength. This results in copper alloys of various grades that effectively meet the material requirements of marine valves. Additionally, the processing technology of copper alloys is mature, offering low production costs and high manufacturing quality.
Corrosion resistance: Copper and its alloys have excellent corrosion resistance and are suitable for atmospheric, freshwater, and seawater environments. Copper alloys effectively resist seawater corrosion due to copper’s high thermodynamic stability and the formation of a cuprous oxide protective film on the surface. Corrosion products deposit on the film, further protecting the alloy. Brass has good corrosion resistance in the atmosphere and freshwater but is prone to dezincification and stress cracking in seawater. Bronze includes tin bronze and aluminum bronze. Tin bronze has extremely high corrosion resistance in the atmosphere, seawater, and low-concentration alkaline solutions, making it widely used in the shipping industry and marine valves. Aluminum bronze surpasses tin bronze and brass in strength, hardness, wear resistance, and corrosion resistance, but its cutting and welding performance is poor. QA19-2 and QA19-4 alloys significantly improve strength, wear resistance, and corrosion resistance by adding elements like Fe, Mn, and Ni, making them suitable for manufacturing high-strength, wear-resistant parts such as valve gears, sleeves, nuts, and worms.
Wear resistance: Copper alloys offer good wear resistance, plasticity, and processing performance.
Antibacterial properties: Microbial corrosion is a significant cause of corrosion in seawater pipe systems. The primary corrosive microorganisms include sulfate-reducing bacteria, slime-producing bacteria, acid-producing bacteria, and ammonia-producing bacteria. Copper alloys prevent the growth and attachment of marine organisms, increase hull smoothness, and reduce maintenance costs. A cuprous oxide corrosion film forms on the surface of copper alloys, which is toxic to organisms and acts as an anti-fouling layer. The most effective way to control microbial corrosion in ship seawater pipe systems is by regularly adding bactericides, corrosion inhibitors, and slime strippers.
Good processing and forming performance: Copper alloys have excellent machining properties. When alloyed with different elements, their performance and strength can be significantly improved. Additionally, copper alloy processing is a mature technology with low production costs and high manufacturing quality.
Economical applicability: After alloying, the structure of copper changes, significantly improving its material properties and strength. This results in copper alloys of various grades that effectively meet the material requirements of marine valves. Additionally, the processing technology of copper alloys is mature, offering low production costs and high manufacturing quality.
