Cast Iron Gear Cargo Oil Pumps: Performance Characteristics, Market Applications, and Marine Adaptability Analysis

I. Working Principle and Structural Design

Marine cast iron gear cargo oil pumps operate based on the positive displacement principle of gear meshing, achieving efficient transportation of cargo oil through the meshing motion of the driving gear and the driven gear. When the gears rotate at a speed of 800 - 1500 rpm, the grooves between the teeth carry the cargo oil from the suction end to the discharge end. The pressure increases from 0.05 MPa at the inlet to 0.6 - 1.2 MPa at the outlet, with a flow rate ranging from 10 - 100 m³/h, meeting the cargo oil loading and unloading requirements of oil tankers and cargo ships of different tonnages.

Core Features of Structural Design

Gear Pair Design: Involute spur gears (module 4 - 6mm) or helical gears are adopted. The tooth surfaces are carburized and quenched to a hardness of HRC35 - 40, with a wear rate of < 0.03 mm/year when transporting sulfur - containing crude oil.

Pump Body Structure: The pump body is made of gray cast iron HT300, equipped with replaceable wear - resistant bushings (made of high - chromium cast iron). 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 double - lip mechanical seals and fluororubber O - rings is used, with a leakage rate ≤ 3 ml/h, complying with the anti - leakage standards of IMO MEPC.307(73) Resolution.

II. Core Performance Advantages

1. High - Viscosity Cargo Oil Transportation Capacity

Viscosity Adaptability: It can stably transport cargo oils with a viscosity of 50 - 2000 cSt. When transporting 1500 cSt heavy crude oil at 50°C, the volumetric efficiency reaches 82 - 88%, which is 15% higher than that of centrifugal pumps.

Pressure Stability: The outlet pressure pulsation rate is < 2%. During the cargo oil loading and unloading of a VLCC, the pressure fluctuation is ≤ 0.05 MPa, ensuring the stability of the loading and unloading 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 30 seconds after startup, making it suitable for low - level operations in cargo oil tank

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

Sulfur - Resistance: Gears made of ductile iron QT700 - 2 have a corrosion rate of < 0.01 mm/year in crude oil with a sulfur content ≤ 2%.

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.

Impact Resistance: It can withstand water hammer impacts during cargo oil loading and unloading (pressure fluctuations ≤ 1.5 times the rated pressure). For example, an oil tanker can still operate normally in harsh sea conditions.

3. Cost and Maintenance Advantages

Low Initial Investment: The manufacturing cost is 35 - 50% lower than that of stainless steel gear pumps. The selling price of a DN200 cast iron cargo oil pump is between 3000 - 5000 US dollars, while that of a stainless - steel pump is as high as 6000 - 9000 US dollars.

Easy Maintenance: With a simple structure (gears + bearings + seals), the maintenance man - hours are 40% less than those of screw pumps. An oil tanker can save 8000 US dollars in annual maintenance costs.

Accessory Compatibility: Gears, seals and other accessories are compatible with most oil tanker cargo oil systems, reducing inventory costs by 35%.

III. Application Limitations

1. Medium and Working Condition Restrictions

Taboo for Strongly Corrosive Media: It is prohibited from transporting acidic cargo oils with a pH < 4 or emulsified oils with a water content exceeding 1%. For example, improper use on a chemical tanker led to gear pitting.

Poor Low - Temperature Adaptability: When the viscosity of cargo oil > 2000 cSt, preheating is required. For polar routes, an electric tracing system (power 3 - 5 kW) is needed. An LNG ship once experienced startup jams due to lack of preheating.

Restrictions in High - Speed Conditions: When the rotation speed > 1800 rpm, the noise > 85 dB, making it unsuitable for high - speed cargo oil barge operations.

2. Efficiency and Weight Shortcomings

Efficiency Decay with Viscosity Change: When the viscosity of cargo oil < 30 cSt, the efficiency decreases by 12%. A product oil tanker once had to switch pump types when transporting diesel.

Heavy Equipment: A DN200 cast iron pump weighs 150 kg, which is 180% heavier than an aluminum alloy pump. A luxury oil tanker required a special base design due to the overweight.

Cavitation Sensitivity: The NPSH requirement is ≥ 3.5 m. When the liquid level in the cargo oil tank is low, cavitation is likely to occur, resulting in increased gear wear on an oil tanker.

3. Installation and Maintenance Requirements

Explosion - Proof Zone Installation Specifications: Strict compliance with ATEX certification installation requirements is necessary, with the explosion - proof gap of the junction box ≤ 0.1 mm. Improper installation on a ship once led to explosion - proof failure.

Dependence on Oil Quality: The solid content of cargo oil needs to be ≤ 0.1%. Abnormal gear wear occurred on a bulk carrier due to excessive impurities in the cargo oil.

Regular Explosion - Proof Detection: Explosion - proof performance testing should be carried out every 12 months. Failure to test on a ship once posed a risk of spark leakage.

IV. Analysis of Marine Market Applications

1. Global Market Share

According to DNV GL 2024 data, cast iron gear cargo oil pumps account for 45% of the merchant ship cargo oil system market, as detailed below: 

2. Regional Market Differences

Asian Market: It accounts for 60%. Oil tanker fleets in China, India and other countries widely use them due to cost and reliability. For example, 35 out of 50 oil tankers of a Chinese shipping company use cast iron cargo oil pumps.

European Market: It accounts for 30%. Due to strict environmental protection requirements, they are only used on ordinary oil tankers. Stainless - steel pumps are mostly used on chemical tankers (accounting for 70%).

Polar Routes: It accounts for 5%. An electric tracing system is required, increasing the transformation cost of a Russian Arctic oil tanker by 15%.

3. Comparison with Competing Products

4. Technological Development Trends

Application of Tungsten Carbide Coating: Coating the gear surface with a WC coating increases wear resistance by 5 times, extending the pump body life of a pilot VLCC to 10 years.

Lightweight Design: Hollow gears combined with resin sand casting reduce the weight by 20%. A new type of DN200 pump has been reduced to 120 kg.

Intelligent Explosion - Proof Monitoring: Integrated spark detection and temperature sensors enable a shipping company to achieve an explosion - proof fault warning rate of 95% through real - time monitoring.

V. Key Points for Selection and Maintenance

1. Key Selection Indicators

Flow Rate and Head: Select according to the volume of the cargo oil tank. For a 100,000 - ton oil tanker, it is recommended that the flow rate ≥ 80 m³/h and the head ≥ 1.0 MPa.

Medium Compatibility: When the sulfur content > 2%, select high - chromium cast iron gears. When the water content > 0.5%, configure a dehydration pretreatment system.

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

NPSH Margin: Reserve ≥ 4.0 m to avoid cavitation. Insufficient NPSH once reduced the loading and unloading efficiency of an oil tanker by 30%.

2. Best Maintenance Practices

Explosion - Proof Seal Inspection: Detect the wear of mechanical seals every voyage. Replace immediately if the lip wear exceeds 0.3 mm. Seal failure once led to cargo oil leakage on a ship.

Gear Oil Quality Monitoring: Detect the viscosity and sulfur content of cargo oil monthly. Excessive sulfide in cargo oil once caused gear corrosion on an oil tanker.

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

Explosion - Proof Performance Test: Conduct an explosion - proof shell strength test at 1.5 times the rated pressure every year. Failure to test once led to shell cracks on a ship.