Copper Screw Pumps: Analysis of Material Characteristics, Application Advantages, and Adaptability to Marine Conditions

I. Classification of Marine Copper Materials and Their Adaptability to Screw Pumps

1. Tin Bronze (Cu-Sn Alloy)

Material Characteristics: With a tin content of 3 - 14%, often added with elements such as zinc and phosphorus, it has a tensile strength of 300 - 700MPa, a corrosion rate of < 0.01mm/year in seawater, and a friction coefficient of 0.1 - 0.3 (one - third of that of cast iron).

Marine Applications:

Seawater Desalination Pump Screws: In 2,000 - ton - per - day seawater desalination plants, QSn6 - 6 - 3 tin bronze screws have a service life of 5 years (while cast iron screws only last 2 years).

Ship Bilge Pumps: In seawater containing sediment (solid content ≤ 5%), the wear rate is 40% lower than that of cast iron.

Classification Society Certification: Complies with DNV GL's corrosion resistance requirements for seawater system materials (Norsok M - 630 standard).

2. Aluminum Bronze (Cu - Al Alloy)

Alloy System: With an aluminum content of 5 - 12% (such as QAl9 - 4), it has a tensile strength of 600 - 1000MPa, a strength retention rate of > 80% at 300℃, and better cavitation resistance than stainless steel.

Core Applications:

Main Engine Lubricating Oil Pumps: In 150℃ lubricating oil (viscosity 150cSt), the wear amount of QAl10 - 3 - 1.5 aluminum bronze screws is < 0.05mm per thousand hours.

Ballast Water Systems: It has 1.5 times the chloride ion stress corrosion resistance of 316L stainless steel, suitable for tropical sea areas (water temperature > 30℃).

3.Brass (Cu - Zn Alloy)

Typical Grades: H62, H68 (zinc content 20 - 40%), with a thermal conductivity of 109W/(m·K) (three times that of cast iron), suitable for low - pressure (≤1.6MPa) non - corrosive media.

Marine Applications:

Drinking Water Systems: H68 brass screw pumps meet the IMO drinking water standards (ISO 21483), with a lead content < 0.2%.

Auxiliary Fuel Pumps: In fuel with a viscosity of 320cSt, the volumetric efficiency reaches 85% (while centrifugal pumps are only 60%).

4.Beryllium Bronze (Cu - Be Alloy)

Performance Highlights: With a beryllium content of 1.6 - 2.0%, after heat treatment, the hardness reaches HRC38 - 44, the impact toughness is twice that of tin bronze, and the fatigue strength is 1100MPa.

Special Scenarios:

Hydraulic Pumps for Deep - Sea Exploration Vessels: Under the pressure of 5,000 - meter water depth, BeCu2 beryllium bronze screws do not undergo plastic deformation.

LNG Carrier Cryogenic Pumps: During the transportation of liquid nitrogen at - 162℃, the impact energy ≥ 40J (while ordinary copper alloys < 20J).

II. Advantages of Marine Copper Screw Pumps in Marine Conditions

1.Breakthrough in Seawater Corrosion Resistance

Corrosion Protection Mechanisms:

Tin bronze forms a basic copper chloride protective film on its surface, with a corrosion current density < 1μA/cm² in a 3.5% sodium chloride solution.

Aluminum bronze generates a dense Al₂O₃ oxide film, with a pitting potential > + 0.8V (vs SCE) in seawater containing 2000ppm chloride ions.

Actual Ship Data: A 100,000 - ton oil tanker using QSn7 - 0.2 tin bronze screw pumps showed a wall thickness reduction of < 0.1mm after 5 years of seawater transportation.

2.Efficiency Advantages in Transporting High - Viscosity Media

Screw Design Features:

The three - head screw structure (lead ratio 1:2.5) results in a flow pulsation of < 3% when the fuel viscosity is 1000cSt.

The thermal conductivity of copper alloys makes the pump body temperature 15 - 20℃ lower than that of cast iron, preventing high - viscosity media from overheating and deforming.

Energy Consumption Comparison: When transporting 380cSt heavy oil, copper screw pumps are 12% more energy - efficient than cast iron pumps (measured data from a container ship).

3.Adaptability to Ship Vibration Environments

Vibration Damping Performance: The damping coefficient of copper alloys is 0.02 (five times that of steel). Under the vibration condition of the main engine at 1800rpm, the bearing amplitude ≤ 0.03mm.

Maintenance - Free Design: Self - lubrication reduces the demand for bearing lubrication. A copper screw pump on a research vessel achieved 8000 hours of trouble - free operation.

III. Application Limitations of Marine Copper Screw Pumps

1.Dual Pressure of Cost and Weight

Cost Comparison: The price of QAl9 - 4 aluminum bronze screw pumps is 2.8 times that of cast iron pumps. The procurement cost of copper pumps for an entire bulk carrier increased by 150,000 US dollars.

Weight Disadvantage: A DN100 copper screw pump weighs 75kg (while an aluminum alloy pump weighs 32kg), affecting the ship's center of gravity configuration and requiring additional counterweight adjustment.

2.Insufficient Compatibility with Special Media

Ammonia Corrosion Risk: In the ammonia refrigeration systems of refrigerated ships, brass is prone to stress corrosion when in contact with liquid ammonia, and it is necessary to switch to titanium alloys (cost increases by 3 times).

Limitations in Strong Acidic Media: In acidic ballast water (treated by electrolysis) with a pH < 2, the pitting rate of copper screws > 0.1mm/year, and fluorine lining treatment is required (cost increases by 40%).

3.High - Temperature and High - Pressure Performance Bottlenecks

Temperature Limit: When tin bronze operates at temperatures above 120℃ for a long time, the diffusion of tin elements leads to a 15% decrease in strength.

Pressure Limit: The rated pressure of copper screw pumps ≤ 4.0MPa, unable to meet the requirements of deep - sea mining ships (working pressure 10MPa).

IV. Key Points for Marine Material Selection