Cast Iron Screw Fuel Oil Pumps: Performance Characteristics, Market Applications, and Marine Adaptability Analysis

I. Working Principle and Structural Design

Marine cast iron screw fuel oil pumps operate based on the positive displacement principle of screw meshing. The efficient transportation of fuel oil is achieved through the meshing motion of the driving screw and the driven screw. When the screws rotate at a speed of 1000 - 1800 rpm, the screw grooves push the fuel oil from the suction end to the discharge end. The pressure increases from 0.05 MPa at the inlet to 0.8 - 1.5 MPa at the outlet, with a flow rate ranging from 10 - 100 m³/h, meeting the fuel transportation requirements of ships of different tonnages.

Core Features of Structural Design

Screw Pair Design: A twin - screw or triple - screw structure is adopted (the lead is 3 - 5 times the diameter). The surface of the screws is quenched to a hardness of HRC30 - 35, with a wear rate of < 0.02 mm/year when transporting 1000 cSt heavy oil.

Pump Body Structure: The pump body is made of gray cast iron HT250, equipped with replaceable wear - resistant bushings (made of QT600 - 3). The double - layer explosion - proof shell design meets the ATEX Zone 0 explosion - proof requirements, and the measured explosion - proof grade reaches Ex d IIB T4.

Sealing System: A dual - protection structure of mechanical seals and fluororubber O - rings is used, with a leakage rate ≤ 2 ml/h, complying with the anti - leakage standards of IMO MEPC.307(73) Resolution.

II. Core Performance Advantages

1. Stability in Transporting High - Viscosity Fuel Oil

Viscosity Adaptability: It can stably transport fuel oils with a viscosity of 50 - 2000 cSt. When transporting 1500 cSt crude oil at 50°C, the volumetric efficiency reaches 88 - 92%, which is 10% higher than that of gear pumps.

Low Pulsation Characteristics: The outlet pressure pulsation rate is < 1%. During the fuel oil transportation of a VLCC, the pressure fluctuation is ≤ 0.03 MPa, ensuring the stability of the fuel system.

Self - Priming Performance: No priming device is required, with a self - priming height of up to 6 m. A stable oil pressure can be established within 20 seconds after startup, making it suitable for low - level operations in fuel oil tanks.

2. Wear - Resistance, Corrosion - Resistance and Explosion - Proof Design

Wear - Resistant Material: The fatigue strength of ductile iron screws reaches 380 MPa. The screw pair of an ocean - going oil tanker has been in continuous operation for 8 years without replacement.

Oil Resistance: Cast iron forms a passivation film in fuel oil, with a corrosion rate of < 0.003 mm/year, which is better than ordinary carbon steel.

Explosion - Proof Certification: The fully enclosed shell design, along with the motor and accessories, has passed explosion - proof certification, making it suitable for hazardous environments in cargo oil tank areas.

3. Cost and Maintenance Advantages

Low Initial Investment: The manufacturing cost is 25 - 40% lower than that of stainless steel screw pumps. The selling price of a DN200 cast iron screw pump is 3000 - 5000 US dollars, while that of a stainless - steel pump is 6000 - 8000 US dollars.

Easy Maintenance: With a simple structure (screws + bearings + seals), the maintenance man - hours are 30% less than those of gear pumps. An annual maintenance cost savings of 7000 US dollars can be achieved for a container ship.

Accessory Compatibility: Screws, seals and other accessories are compatible with most ship fuel systems, reducing inventory costs by 30%.

III. Application Limitations

1. Medium and Working Condition Restrictions

Taboo for Strongly Corrosive Media: It is prohibited from transporting acidic fuel oils with a pH < 5 or emulsified oils with a water content exceeding 1%.

Poor Low - Temperature Adaptability: When the viscosity of fuel oil > 2000 cSt, preheating is required. For polar routes, an electric tracing system (power 2 - 3 kW) is needed.

Restrictions in High - Speed Conditions: When the rotation speed > 2000 rpm, the noise > 80 dB, making it unsuitable for high - speed fuel oil barge operations.

2. Efficiency and Weight Shortcomings

Efficiency Decay with Viscosity Change: When the viscosity of fuel oil < 30 cSt, the efficiency decreases by 10%, and the pump type needs to be switched.

Heavy Equipment: A DN200 cast iron screw pump weighs 120 kg, which is 150% heavier than an aluminum alloy pump.

Cavitation Sensitivity: The NPSH requirement is ≥ 3.0 m. When the liquid level in the fuel oil tank is low, cavitation is likely to occur.

3. Installation and Maintenance Requirements

High Alignment Accuracy Requirement: The alignment error of the screw shaft needs to be < 0.03 mm.

Dependence on Oil Quality: The solid content of fuel oil needs to be ≤ 0.05%, and the contamination level needs to be ≤ ISO 4406 17/15/12 level.

Regular Disassembly and Maintenance: Disassembly and cleaning are required every 6000 hours to prevent sealing failure.

IV. Analysis of Marine Market Applications

1. Global Market Share

According to DNV GL 2024 data, cast iron screw fuel oil pumps account for 35% of the merchant ship fuel system market, as detailed below:

2. Regional Market Differences

Asian Market: It accounts for 52%. Oil tanker fleets in China, India and other countries widely use them due to cost and stability.

European Market: It accounts for 30%. Due to strict environmental protection requirements, stainless - steel pumps are mostly used on cruise ships (accounting for 65%).

Polar Routes: It accounts for 2%. An electric tracing system is required, increasing the transformation cost by 10%.

3. Comparison with Competing Products

4. Technological Development Trends

Application of Ceramic Coating: Coating the screw surface with a SiC ceramic layer increases wear resistance by 4 times, extending the service life to 10 years.

Lightweight Design: Adopting hollow screws combined with resin sand casting reduces the weight by 18%. The weight of a new type of DN200 pump is reduced to 100 kg.

Intelligent Monitoring: Integrated with pressure and temperature sensors, the fault warning accuracy rate can reach 94%.

V. Key Points for Selection and Maintenance

1. Key Selection Indicators

Flow Rate and Head: For a 100,000 - ton oil tanker, it is recommended that the flow rate ≥ 80 m³/h and the head ≥ 1.2 MPa.

Viscosity Adaptation: When the viscosity > 500 cSt, select a screw with a large lead. When the sulfur content > 2%, choose high - chromium cast iron material.

Explosion - Proof Certification: It needs to pass explosion - proof certifications such as ATEX and IECEx, meeting the Ex d IIB T4 requirements.

NPSH Margin: Reserve ≥ 3.5 m to avoid cavitation.

2. Best Maintenance Practices

Oil Quality Monitoring: Detect the viscosity and sulfur content of fuel oil monthly to prevent screw corrosion.

Bearing Lubrication: Apply oil - resistant lithium - base grease (NLGI grade 3) every 2000 hours.

Seal Inspection: Check the mechanical seal every voyage. Replace it immediately if the wear exceeds 0.3 mm.

Screw Wear Detection: Measure the thickness with ultrasonic technology every year. Replace the screw if the tooth surface wear exceeds 0.2 mm.