LPG, LNG, cryogenic gas couplings

LPG, LNG, cryogenic gas couplings – general information

Couplings and fittings for liquefied gas hoses and loading/unloading installations: LPG (propane-butane), LNG (natural gas), cryogenic gases (low temperature when liquefied) such as carbon dioxide, nitrogen, argon, oxygen. Basically, the couplings can be divided into two groups: LPG couplings, which are made of carbon steel and brass, for application at temperatures close to ambient and the other group – LNG and cryogenic gases couplings working at very low temperatures down to -196°C (liquid-nitrogen temperature at atmospheric pressure). Therefore the cryogenic couplings are made of stainless steel and brass with high fracture toughness . The couplings for liquid gases often have tapered threads and code features i.e. appropriate slots and pins on the coupler and on the adapter of the coupling. It prevents connecting the coupler of the particular medium e.g. oxygen with the adapter of another medium e.g. nitrogen. There are also the cryogenic couplings compliant with EIGA (European Industrial Gases Association) in this group.

Types of gases

LPG (Liquefied Petroleum Gas)

Propane – butane is a mixture of two hydrocarbons: propane (C3H8) and butane (C4H10). At atmospheric pressure it is naturally gaseous, but when stored in pressurised cylinders it is a fluid. It condenses at a low pressure of a few bar, at room temperature. It is widely used as a heating fuel and as an engine fuel (autogas) for vehicles, mostly cars.

Natural Gas

Natural gas is extracted from underground reservoirs. Its main component (90%) is methane (CH4), and smaller amounts of ethane, propane and butane. Natural gas is one of the main raw materials used to generate energy and manufacture chemicals. Natural gas is converted into liquefied natural gas (LNG), or compressed under high pressure (CNG) to be stored and transported.

LNG (Liquefied Natural Gas)

LNG is liquefied natural gas cooled to about – 162°C (the boiling point of methane). As it is liquefied, natural gas reduces its volume by 630 times. LNG that is kept at a low temperature in a cryogenic tank can be transported at a low pressure, close to the atmospheric pressure, by special ships – LNG carriers and road or rail tankers. LNG can be used to power large heavy-duty vehicles, for example, public transport buses. These vehicles have insulated cryogenic tanks with working pressures up to 10 bar.

CNG (Compressed Natural Gas)

CNG is natural gas compressed to about 200 ÷ 250 bar at room temperature, used to power vehicles e.g., buses. It must be stored in high-pressure steel or composite tanks. For CNG hoses and fittings, see HIGH PRESSURE section.

Cryogases

Cryogases are technical gases ( industrial gases) such as CO2, N2, Ar, O2. Once they are cooled to a certain temperature, technical gases are
in a liquid state under atmospheric pressure.

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