Cargo Properties and Classifications

Study Notes

Tankers transport a variety of bulk liquids
Understanding cargo properties is crucial for minimizing risks during transport
Improper handling (transfer, stowage, care) can lead to incidents harming personnel, the vessel, the environment, and the cargo itself.

Cargoes are broadly categorized into three classifications:
- Petroleum Liquids
- Chemical Liquids
- Special Liquids

Composed of crude oil and refined products
Examples include:
- Gasoline
- Fuel Oil
- Diesel Oil
- Kerosene
- Jet Fuel
- Lubricants
- Residual Fuels
- Asphalt
- Coke
Crude oil varies in properties:
- "Heavy" or "light"
- "Sweet" or "sour" (based on sulfur content)
Sweet crude has less than 0.5% sulfur, is easier to refine, and safer to transport
Sour crude has more than 0.5% sulfur, is harder to refine and is corrosive.

Substances used or obtained through chemical processes
Numerous types with varying characteristics - Categorized as organic or inorganic
Examples (organic):
- Acetone
- Vinyl Chloride
- Acetic Acid
- Styrene Monomer
- Acrylonitrile
- Aromatic Hydrocarbons (Benzene, Toluene, Xylenes)
Examples (inorganic):
- Boric Acid
- Sulfuric Acid
- Phosphoric Acid
- Caustic Soda
- Hydrochloric Acid
- Molten Sulfur
- Anhydrous Ammonium Nitrate

Crude oil is a complex mixture of hydrocarbon molecules
Hydrocarbons are compounds of hydrogen and carbon with various chain lengths
Crude quality varies, influencing refining difficulty and product yields
Crude can be differentiated based on specific gravity and sulfur content (sweet vs sour), degree of paraffin content, etc.

Light crude: low density, flows easily, higher API gravity (>20°API)
- Lower paraffin content.
Heavy crude (extra heavy): high density, flows less easily, lower API gravity (<20°API)
- Higher paraffin content.

Involves separating hydrocarbons into different groups based on boiling point ranges
Three main methods used in refining are:
- Distillation
- Cracking
- Purification

Most cargoes are categorized by flammability
Flammability relates to a liquid's ability to produce flammable vapors
Key terms for describing volatility include:
- True Vapor Pressure (TVP)
- Reid Vapor Pressure (RVP)
- Flash Point
- Fire Point
- Autoignition Temperature
Flammable ranges (lower explosive limit (LEL) and upper explosive limit (UEL)) define the vapor concentrations at which a mixture will ignite.
Vapor density is essential to assess and safely manage cargo operations

Inert gas systems prevent flammable mixtures by maintaining non-flammable tank atmospheres
Proper inerting results in low levels of oxygen, making explosions and fire impossible.

International Classifications usually categorize petroleum cargoes as volatile or nonvolatile based on flash point
- Volatile liquids have low flash points (below 140 °F)
- Nonvolatile liquids have high flash points (above 140 °F)
USCG further classifies petroleum into flammable and combustible liquids based on flashpoint. Different grades have varying flashpoints and vapor pressures.