Cast Steel Diaphragm Pumps: Analysis of Material Characteristics, Application Advantages, and Adaptability to Marine Conditions

I. Classification of Marine Cast Steel Materials and Their Adaptability to Diaphragm Pumps

1.Carbon Cast Steel

Carbon cast steel is represented by typical grades such as ZG230-450 and ZG270-500, with a carbon content of 0.12%-0.6%:

Material Characteristics: Tensile strength of 450-600MPa, yield strength of 230-300MPa, good weldability and machinability, and lower cost than alloy cast steel.

Marine Applications:

Bilge Water Diaphragm Pumps: In bilge sewage with solid impurities ≤5%, the ZG270-500 pump body has a service life of 4 years.

Freshwater Booster Systems: Suitable for low-pressure (≤1.6MPa) freshwater transportation, such as drinking water booster pumps on ro-ro passenger ships, complying with LR classification society material requirements.

2.Alloy Cast Steel

Alloy cast steel enhances performance by adding elements such as Cr, Mo, and Ni, widely used in marine diaphragm pumps:

Cr-Mo Series Alloy Cast Steel: Such as ZG20CrMo, containing 1-3% chromium and 0.5-1% molybdenum:

Performance Highlights: 40% increase in high-temperature strength, strength retention rate >80% at 300°C, and outstanding hydrogen corrosion resistance.

Core Applications: Main engine fuel diaphragm pumps can withstand 3.5MPa pressure in 150°C heavy oil (viscosity 380cSt), with wear amount <0.05mm per thousand hours.

Ni-Cr Series Alloy Cast Steel: Such as ZG340-640, containing 2-4% nickel and 1-2% chromium:

Low-Temperature Characteristics: Impact energy ≥27J at -40°C, suitable for low-temperature medium transportation on polar ships.

Marine Applications: LNG carrier cryogenic diaphragm pumps show no plastic deformation during -162°C liquid nitrogen transportation, meeting BV classification society low-temperature certification.

3.Stainless Steel Cast Steel

Stainless steel cast steel is indispensable for special medium transportation due to its corrosion resistance:

Austenitic Stainless Steel Cast Steel: 304 (ZG0Cr18Ni9), 316L (ZG00Cr17Ni14Mo2):

Corrosion Resistance Index: Corrosion rate <0.01mm/year in media with pH 2-12, and 316L has 50% enhanced chloride ion corrosion resistance compared to 304.

Application Scenarios: Chemical tanker diaphragm pumps for transporting weakly corrosive chemicals, complying with IMO anti-pollution requirements.

Duplex Stainless Steel Cast Steel: 2205 (ZG0Cr22Ni5Mo3N):

Comprehensive Performance: Strength twice that of 316L, 3-5 times enhanced chloride ion stress corrosion resistance, and pitting resistance equivalent number (PREN) ≥34.

Typical Applications: Seawater desalination diaphragm pumps have a service life of 8 years in 35‰ salinity seawater, 3 times longer than ordinary stainless steel.

4.Wear-Resistant Cast Steel

Wear-resistant cast steel improves wear resistance through alloying or surface hardening:

High-Chromium Wear-Resistant Cast Steel: Containing 12-18% chromium, hardness HRC55-60:

Wear Resistance: In mud with a sand content of 15%, the wear rate is 50% lower than carbon cast steel.

Special Scenarios: Port dredging diaphragm pumps. High-chromium cast steel diaphragm pumps used by sand mining ships to transport mud have a diaphragm service life of 10,000 hours.

II. Core Technical Advantages of Marine Cast Steel Diaphragm Pumps

1.Adaptability to High-Pressure and Heavy-Duty Conditions

Pressure Breakthrough: Alloy cast steel diaphragm pumps can withstand a maximum system pressure of 10MPa, far exceeding the 2.5MPa upper limit of cast iron diaphragm pumps:

Deep-Sea Mining Vessel Diaphragm Pumps: An ocean exploration vessel uses ZG340-640 diaphragm pumps, operating stably under the pressure of 5,000-meter water depth.

High-Pressure Fuel Systems: Main engine high-pressure fuel injection diaphragm pumps can provide 8MPa pressure to ensure sufficient fuel atomization.

2.Dual Advantages of Leak-Free and Corrosion Resistance

Sealing Design: Adopts PTFE or metal composite diaphragms to achieve zero-leakage transportation of hazardous media:

Fuel Bunkering: A VLCC uses 316L stainless steel cast steel diaphragm pumps to transport crude oil, with a 10-year leakage-free record.

Chemical Transportation: Duplex stainless steel cast steel diaphragm pumps transport concentrated nitric acid (68% concentration) with a corrosion rate <0.005mm/year.

3.Adaptability to Ship Vibration Environments

Vibration Damping Performance: Cast steel damping coefficient 0.02 (5 times that of steel). Under the vibration condition of the main engine at 1800rpm:

Bearing amplitude ≤0.03mm. A scientific research ship's diaphragm pump sailed continuously for 150,000 nautical miles without structural cracks.

Fatigue Resistance Design: Ni-Cr alloy cast steel diaphragm pumps have a fatigue strength of 1100MPa, suitable for long-term continuous operation.

4.High-Viscosity Medium Transportation Efficiency

Hydrodynamic Design:

Double Diaphragm Structure: In 10,000cSt heavy oil, the volumetric efficiency reaches 88% (only 65% for centrifugal pumps).

Self-priming Capacity: Self-priming height up to 8m, suitable for open storage tank unloading without auxiliary vacuum devices.

III. Application Limitations of Marine Cast Steel Diaphragm Pumps

1.Dual Pressure of Cost and Weight

Cost Comparison: The price of 2205 duplex stainless steel cast steel diaphragm pumps is 4 times that of cast iron pumps. A luxury cruise ship replacing all pumps with cast steel diaphragm pumps increased equipment investment by 300,000 USD.

Weight Disadvantage: A DN100 cast steel diaphragm pump weighs 85kg (aluminum alloy pump 30kg), affecting the ship's center of gravity configuration, requiring additional counterweight adjustment and increasing installation costs by 25%.

2.High-Temperature and Strong Corrosion Performance Bottlenecks

Temperature Limitation: The long-term working temperature of carbon cast steel ≤300°C. A cargo ship's engine room diaphragm pump transporting 350°C heat-conducting oil showed thermal deformation after 1 year.

Corrosion Limitation: In strongly corrosive media such as hydrofluoric acid, even stainless steel cast steel requires fluorine lining treatment (cost increased by 40%). A chemical tanker thus switched to titanium alloy diaphragm pumps.

3.Processing and Maintenance Complexity

Cutting Difficulties: Cast steel work hardening index n=0.25, tool wear rate 30% higher than cast iron. A factory processing ZG20CrMo diaphragm pump bodies had a tool life only 1/2 that of processing cast iron.

Maintenance Requirements: Stainless steel cast steel diaphragm pumps require special tools for disassembly. A container ship suffered a diaphragm tear due to improper maintenance, with maintenance costs reaching 50,000 USD.

IV. Key Points for Marine Selection and Maintenance

1.Material Selection Matrix

2.Key Maintenance Actions

Pressure Test: Conduct a 1.5-fold rated pressure test annually (e.g., 4.5MPa for a rated 3MPa). A cargo ship suffered diaphragm rupture due to omitted testing.

Diaphragm Inspection: Replace PTFE diaphragms after 5,000 hours of cumulative operation. Magnetic particle inspection is required for metal diaphragms to detect cracks.

Temperature Monitoring: Activate the cooling system when the medium temperature of alloy cast steel diaphragm pumps >300°C to avoid material annealing.