Stainless Steel Screw Cargo Oil Pump

I. Product Overview

Stainless steel screw cargo oil pumps feature high-precision screw meshing structures, using austenitic stainless steel (316/316L) or duplex stainless steel (2205) as the main material. Designed based on positive displacement transportation principles, they provide low-pulsation and high-pressure transportation solutions for loading/unloading and transfer of crude oil, heavy oil, refined oil, and chemical liquid cargo. The screw profile adopts a 5:6 asymmetric tooth design (tri-screw pump) or single-screw eccentric design with a meshing clearance ≤0.03mm, enabling stable transportation of cargo oil with viscosity 10-5000cSt under 0.5-4.0MPa pressure, with a volumetric efficiency of 92%-96%. They are suitable for marine cargo oil systems, port loading/unloading, and industrial liquid cargo transportation.

II. Core Materials and Performance Adaptation

1.316 Stainless Steel (Medium-Sulfur Cargo Oil Scenarios)

Characteristics: Contains 2-3% molybdenum, corrosion rate <0.008mm/year in crude oil with sulfur content ≤1%, tensile strength ≥520MPa, resistant to cargo oil temperatures of -40℃~150℃. The screw surface is sprayed with tungsten carbide (thickness 50-80μm), hardness reaches HRC65-70, and wear resistance to particles such as sediment and rust in cargo oil is 6 times higher than cast iron.

Applications: Transporting light refined oils such as diesel and kerosene, or medium-sulfur crude oil (API gravity >20), suitable for coastal tankers and short-distance port loading/unloading.

2.316L Stainless Steel (Low-Sulfur/High-Purity Cargo Oil)

Improved Design: Carbon content ≤0.03%, excellent intergranular corrosion resistance after welding, screw surface electrolytic polishing (Ra≤0.4μm), wear rate 35% lower than 316 stainless steel in ultra-low sulfur crude oil with sulfur content ≤0.5%, suitable for biodiesel (blend ratio ≤30%) or food-grade vegetable oil transportation.

Typical Scenarios: Marine fuel systems after IMO 2020 sulfur restrictions, palm oil loading/unloading for edible oil tankers, meeting food hygiene requirements (FDA certification).

3.Duplex Stainless Steel (2205/2507)

High-Strength Corrosion Resistance: Ferritic-austenitic duplex structure, pitting corrosion resistance index (PREN) ≥40, stress corrosion resistance 2.5 times higher than 316L in high-sulfur heavy oil with sulfur content 1-3%, tensile strength ≥620MPa, can withstand 4.0MPa high-pressure cargo oil impact, and resist acidic substances (pH≤3) from cargo oil high-temperature cracking.

Special Applications: 380cSt heavy oil loading/unloading for ocean-going tankers, sulfur-containing residue oil transport in refineries, resisting composite corrosion from asphaltenes and sulfides.

III. Technical Advantages and Application Limitations

Core Technical Advantages

1. Low-Pulsation Transportation and High-Viscosity Adaptability

The spiral meshing of tri-screw pumps forms continuous sealing chambers, with outlet pressure pulsation ≤±0.5%, suitable for precise cargo oil metering and compartment transfer. In 5000cSt heavy oil (preheated to 130℃), it still maintains 90% volumetric efficiency, with a self-priming height ≥6m, 20% better than gear pumps.

2. Long Life and Low-Noise Design

Duplex stainless steel screws undergo ion nitriding treatment, surface hardness HRC58-62, service life reaches 100,000 hours in cargo oil containing 0.2% solid impurities; operation noise ≤70dB (at 1500rpm), 15-20dB lower than gear pumps, suitable for port noise reduction requirements.

3. High Safety and Anti-Leakage Design

The pump body adopts an explosion-proof design (Ex d IIB T4 Gb), with static grounding resistance ≤1Ω. Equipped with bellows mechanical seal + PTFE lip seal double protection, cargo oil leakage ≤2 drops/hour, complying with MARPOL Annex I anti-pollution requirements and API 676 standards.

Performance Limitations

1. High-Temperature and Impurity Sensitivity Boundaries

When the cargo oil temperature of 316 stainless steel pumps >180℃, fuel carbonization causes screw wear to increase by 60%, requiring a cooling jacket (heat exchange area ≥4m²). When transporting cargo oil with particles >15μm, a double-barrel filter (accuracy ≤5μm) is required; otherwise, meshing clearance wear increases by 0.015mm monthly.

2. Viscosity and Speed Matching Limitations

When transporting low-viscosity cargo oil with viscosity <15cSt (such as gasoline), the speed should be controlled ≥2500rpm to reduce internal leakage; when viscosity >3000cSt (unpreheated), pump efficiency decreases by 35%, requiring pre-installed electric heating (power configured as 2.5kW/100L/h flow).

3. Cost and Installation Requirements

Duplex stainless steel pumps cost 10-12 times more than cast iron pumps, with a 70% increase in weight (e.g., DN100 pump weighs about 48kg), requiring a rigid foundation (levelness ≤0.05mm/m). Large-flow models (≥500m³/h) need an inlet flow stabilizer to prevent cavitation (NPSHa≥4m).

IV. Typical Application Scenarios

1. Marine Cargo Oil Loading/Unloading Systems

Ocean-Going Tanker Crude Oil Transportation: Duplex stainless steel tri-screw pump transports high-sulfur crude oil (sulfur content 2.5%) for 300,000 DWT VLCCs, configured with steam tracing jackets (120℃), achieving large-flow loading/unloading of 1500m³/h under 2.0MPa pressure to meet port rapid turnover needs.

Product Tanker Compartment Transfer: 316L stainless steel single-screw pump is used for compartment transportation of gasoline and diesel, with electrolytically polished screw surface to avoid cargo oil cross-contamination, cooperating with the Oil Management System (OMS) for precise transfer.

2. Ports and Oil Storage Facilities

Onshore Cargo Oil Loading/Unloading Arm Systems: 316 stainless steel twin-screw pump connects tankers to storage tanks, transporting sulfur-containing crude oil (API gravity 15-20), equipped with Emergency Shutdown Valves (ESD) to close the system within 10 seconds in emergencies, complying with OCIMF safety codes.

Bunker Fuel Loading Systems: 316L stainless steel pumps load low-sulfur bunker fuel (sulfur content ≤0.5%) for ported ships, with a flow rate of 200-500m³/h and pressure of 0.6-1.0MPa, adapting to IMO 2020 sulfur restriction requirements.

3. Industrial Liquid Cargo Transportation

Corrosive Media for Chemical Tankers: Duplex stainless steel pumps transport chemicals such as phenol and styrene, using perfluororubber seals (FFKM), heat-resistant up to 220℃, resisting cargo oil chemical corrosion, complying with IBC Code requirements for bulk liquid chemical tankers.

Refinery Heavy Oil Transportation: 316 stainless steel tri-screw pump transports residue oil (viscosity 2000cSt) for atmospheric-vacuum units, pressure 1.8MPa, cooperating with online viscometers to adjust preheating temperature in real-time, ensuring continuous unit operation.

V. Usage and Maintenance Specifications

1. Cargo Oil Pretreatment Requirements

High-viscosity heavy oil must be preheated to viscosity ≤800cSt (corresponding temperature 120-140℃), using steam coils or electric heating (power density ≤3W/cm²). When cargo oil sulfur content >1.5%, add anti-corrosion additives (dosage 0.2-0.5%) to inhibit stainless steel pitting.

2. Operation Monitoring Key Points

Real-Time Parameters: Monitor inlet and outlet pressure (fluctuation ≤±3%), bearing temperature (temperature rise ≤40℃), cargo oil temperature, equipped with pressure transmitters (accuracy 0.2 class) and vibration sensors (accuracy 0.01mm/s), and automatically shut down in case of abnormalities (such as vibration value >0.08mm/s).

Regular Maintenance: Inspect screw meshing clearance every 3000 hours (allowable wear ≤0.02mm), replace mechanical seals every 8000 hours (replace in advance when leakage >5 drops/hour), and flush the pump cavity with fresh water (pressure 0.4MPa) after cargo oil tank cleaning.

3. Safety and Compliance Requirements

Marine pumps must pass CCS/DNV classification society certification, providing sulfur corrosion test reports for stainless steel materials (ASTM G35 standard, no pitting after 96-hour immersion). Industrial pumps must comply with API 676 standards, with an explosion-proof rating not lower than Ex d IIB T4, and static grounding resistance ≤4Ω.

Cargo oil systems should have dual protection: low-pressure alarm value ≤0.3MPa, high-pressure cut-off value ≥4.2MPa. Install magnetic filters at the pump inlet and safety valves at the outlet (opening pressure 1.1 times working pressure).