Petroleum and petroleum-derived fuel oils collectively account for approximately 20% of all pump applications globally. They range from ultra-light volatile products such as liquefied petroleum gas and gasoline through to heavy residual fuel oil and cold crude oil — a viscosity span of more than six orders of magnitude. Each product class presents a distinct set of challenges around vapour pressure, flammability, viscosity and material compatibility.
Product Classification
- Light ends / LPG: Propane, butane, light naphtha — vapour pressure above atmospheric at ambient temperature; must be kept pressurised; flash point below –20 °C
- Motor spirit (gasoline): Kinematic viscosity 0.5–0.7 cSt at 15 °C; flash point –43 °C; high vapour pressure creates NPSH challenges
- Kerosene / Jet fuel: Viscosity 1.5–2.5 cSt; flash point 38–60 °C; moderate vapour pressure
- Gas oil / Diesel: Viscosity 2–6 cSt at 40 °C; flash point 55–70 °C; the standard reference fuel for many pump acceptance tests
- Heavy fuel oil (HFO / bunker fuel): Viscosity 50–700 cSt at 50 °C; must be heated to 80–130 °C for pumping; pour point above 30 °C
- Crude oil: Viscosity 1 cSt (light condensate) to 100,000 cSt (cold heavy crude) — the widest range of any single commodity
Key Physical Properties
- API gravity / density: Ranges from 70 °API (light condensate, 0.70 g/cm³)
- Pour point: Temperature below which the oil will not flow — critical for cold-start design; heavy crudes may require heat tracing
- Flash point: Temperature at which vapour ignites — determines ATEX zone classification and pump seal requirements
- Viscosity index (VI): Measures how rapidly viscosity changes with temperature — high VI oils are preferred for wide-temperature-range systems
- Wax content: Waxy crudes gel on cooling, blocking suction lines and making pump restart difficult after a shutdown
Pumping Challenges
- NPSH and vapour lock: Volatile light products have high vapour pressure — suction conditions must be carefully controlled to avoid cavitation and vapour lock in the pump
- Viscosity variation with temperature: Heavy oils change viscosity by a factor of 10 or more across the operating temperature range — pump power draw and head can vary dramatically
- Fire and explosion risk: Flash point below 60 °C classifies the product as flammable — all electrical equipment must be ATEX-rated; shaft seals must prevent leakage to atmosphere
- Wax deposition: Cooling below the pour point causes wax to crystallise on pump internals — requires heat tracing or insulation on all cold-climate installations
- Emulsification: Water contamination in crude oil creates stable emulsions that alter viscosity unpredictably
Pump Type Selection
- Light products (gasoline, kerosene, diesel): Centrifugal pump — sealless (magnetic drive or canned motor) for volatile and flammable products to eliminate shaft seal leakage
- Medium fuel oils: Centrifugal — apply viscosity correction factors above 50 cSt
- Heavy fuel oil and bitumen: Screw pump or progressive cavity — self-priming, handles viscosities up to 1,000,000 cSt; steam-jacketed for cold-start
- Crude oil transfer: Centrifugal for light crude; screw or twin-screw for heavy or waxy crude
- LPG and condensate: Centrifugal or screw — sealed against vapour pressure; cryogenic design for LNG
Materials of Construction
- Carbon steel: Standard for most petroleum service — compatible with hydrocarbon fluids, cost-effective
- Stainless steel 316: For refined products where carbon contamination must be avoided; for mildly acidic crude streams
- Duplex stainless: Where sour crude (H₂S) or high Cl⁻ brine is co-produced with the petroleum
- Shaft seals: Single mechanical seal for most fuel oils; double seal with barrier fluid for volatile and hazardous products; sealless design for highest-hazard service
- Gaskets and O-rings: Viton (FKM) for most petroleum products; PTFE for aromatic solvents
Applications
- Crude oil gathering, pipeline transfer and offshore loading
- Refinery in-plant transfer of process streams at all stages
- Fuel terminal loading arms and tanker loading
- Marine fuel oil transfer and bunkering
- Power station heavy fuel oil unloading and forwarding to burners
- Aviation fuel dispensing at airports
- Retail forecourt fuel dispensing