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Hydrates: Hydrocarbons


  • ASME B31.8 defines ‘petroleum’ as: ‘crude oil, condensate, natural gasoline, natural gas liquids, liquefied petroleum gas, and liquid petroleum products.’.
  • Petroleum is a range of compounds of hydrogen and carbon.
    • Hence, petroleum is known as a ‘hydrocarbon’.

Oil and Gas

  • Oil and natural gas are made of hydrocarbon molecules.
  • These hydrocarbons range from light gases (e.g., methane), to liquids (e.g., crude oil), to heavy, gummy near-solids.
  • The differences in hydrocarbons are due to varying proportions of hydrogen and carbon making up the hydrocarbon molecule:
    • natural gas is the simplest hydrocarbon (it is mainly methane, CH4).

Examples of liquid hydrocarbons

Liquid hydrocarbons have more complex structures:

Oil and gas

  • Crude oil and natural gas are made up of a variety of ‘hydrocarbons’.
  • These hydrocarbons are called:
    • paraffins (e.g., methane, CH4);
    • aphthenes (e.g., cyclohexane, C6H12); and,
    • aromatics (e.g., benzene, C6H6).
  • Crude oil is usually a liquid at ambient temperatures.
  • Natural gas is usually a gas at ambient temperatures.

Oil barrel pouring oil

Wax and hydrates

  • A drop in temperature can create solids in crude oil and natural gas:
    • wax’ (solid paraffin) can form in crude oil;
    • hydrates’ (a mix of water and methane, in ice form) can form in natural gas.


  • These solids can cause problems in pipelines:
    • increases pumping requirements;
    • can block the pipeline; and,
    • lowers pipeline efficiency.
  • Reduced throughput means reduced revenue for the pipeline company.
Hydrates being removed from a gas pipeline.
Hydrates being removed from a gas pipeline.
This class will now focus on hydrate formation. See our bitesize class on ‘Wax’ if you want a quick introduction to this solid.


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About PHL

PHL is an engineering consultancy company, based in the UK. We offer consultancy in pipeline engineering, and present training courses and education programmes in pipeline engineering and management. We specialise in pipeline integrity consultancy (including defect assessment, risk management, and failure analysis), and in pipeline engineering training (onshore pipeline engineering, and pipeline integrity engineering). We also offer a wide range of coaching and mentoring services to staff on all levels.

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