The Importance of Dewpoint Measurement

LNG and LPG Bulk Carriers

What is LNG and LPG?
Liquefied Natural Gas (LNG) and Liquefied Petroleum Gas (LPG) are transported worldwide in bulk as cryogenic liquids or under pressure. Liquefaction makes long-distance transport practical and economical, as the liquid occupies about 600 times less volume than its gaseous form. LNG is natural gas cooled to approximately -162 °C at near-atmospheric pressure, requiring storage in cryogenic tanks onboard specialised carriers or insulated road trailers. Throughout transport, operators must maintain strict temperature control and manage boil-off gas to ensure safety and efficiency.

LPG, which comprises propane and butane, is transported either under moderate pressure or in refrigerated conditions depending on the vessel type. Storage options include pressurised tanks, semi-refrigerated vessels or fully refrigerated carriers. Given that propane boils at -42 °C and butane at -0.6 °C, these gases require precise temperature management to prevent condensation, freezing and potential safety hazards during handling and transportation.

Preparing Cargo Tanks and Why Dryness Matters
Before loading LNG or LPG, operators follow a carefully sequenced preparation process to remove moisture and establish safe loading conditions. The procedure begins with drying, which eliminates residual water to prevent ice formation during cooldown. This is followed by inerting, where oxygen is displaced with inert gas, typically nitrogen to create a stable, non-explosive environment inside the cargo tanks. The gassing-up stage then replaces the inert gas with cargo vapour, conditioning the tanks for liquefied gas loading. Finally, during cool-down, the tank temperature is gradually reduced to match the carriage temperature of the cargo, ensuring smooth and stable transfer.

Every stage of this process depends on precise moisture monitoring and accurate dewpoint measurement. Even trace levels of water can freeze at cryogenic temperatures, leading to blockages, equipment damage or safety risks. Continuous monitoring and maintenance of low moisture levels are therefore critical to protecting assets, preserving product integrity and ensuring the safety of personnel throughout loading operations.

For further information regarding how you can measure trace moisture in your LNG/LPG application, please contact us.