There are about 360 LNG carriers around the world. Also known as LNG ships, this type of vessel is specifically designed to handle the unique properties of liquefied natural gas (LNG) during its transportation. Given the nature of LNG, it cannot be shipped on regular vessels. Instead, it needs to go on an advanced LNG ship which can ensure that during its transit, the LNG is kept at either:
- Pressures much greater than atmospheric pressures, or
- Very low temperatures (around -162°C), or
- A combination of both.
Due to the nature of LNG, it needs to be transported under high pressures or very low temperatures, or sometimes both, to keep it in its liquid state. LNG carriers are designed to handle these specific conditions.
What is LNG?
The earth has large quantities of natural gas, however it has to be transported from gas fields to the areas where it’s needed. To ship natural gas safely and efficiently, it must first be converted into liquefied natural gas (LNG) in a process called liquefication. When you cool natural gas to extremely low temperatures (around -162°C), it transforms from a gas to a liquid state and reduces to 1/600th of its original volume. Once condensed into a liquid, LNG can be safely stored and efficiently shipped, using specially designed LNG vessels, to meet the energy needs of communities located far away from the gas source.
What is an LNG vessel?
An LNG vessel (also known as an LNG tanker, carrier, or ship) is specially designed to transport LNG in large quantities. Typically, they are around 300 metres long, 43 metres wide, and have a draft of about 12 metres.
LNG vessels stand out from other bulk cargo carriers due to their unique features (e.g. heavy insulation and temperature-controlled tanks) which allow them to keep the gas in a liquid state. They usually have a turbine-powered propulsion system that uses boil-off-gas (BOG) from LNG, boiled liquid fuels like oil, or a combination of both. By using natural gas as their fuel for propulsion, LNG carriers produce fewer greenhouse gas emissions than traditional ships.
What are the different types of LNG ships?
LNG ships can be categorised in a number of different ways:
1. Based on pressurisation
LNG ships can be classified as:
- Fully pressurised
- Semi-pressurised and refrigerated
- Fully refrigerated.
2. Based on the hazard level of the material being transported
LNG carriers can be categorised as:
- Type 1G - designed to carry the most hazardous cargo
- Type 2G and 2PG - designed to carry cargo with a lesser degree of hazard
- Type 3G - designed to carry the least hazardous cargo.
3. Based on their type of cargo tanks
The International Maritime Organization (IMO) classification of LNG vessels is the most common way to distinguish between different gas carriers. It classifies them into two main categories and then further divides these into sub-types as follows:
- Independent tanks - where the tank is not a part of the ship’s hull and so is not crucial to hull strength
- Type A – operates at pressure less than 700 mbar and has a full secondary barrier to hold leaks for at least 15 days
- Type B - spherical Moss-tanks or prismatic IHI SPB tank that operates at a pressure less than 700 mbar and has a partial secondary barrier
- Type C – able to operate at pressures above 2,000 mbar and does not have a secondary barrier. Sensors in the hold space detect leaks by monitoring changes in gas composition.
- Integral tanks – where the tank forms a structural part of the ship's hull. Membrane tanks are a type of integral tank and can be sub-categorised into:
- TGZ Mark III (or GTT Mark III) – designed by Technigaz, the tank has several layers, including a primary stainless steel barrier, primary insulation, a triplex membrane secondary barrier, secondary insulation, and the hull structure
- GT 96 (or GTT 96) – this tank from Gaztransport uses an invariable nickel-iron alloy called Invar for its primary and secondary membranes. It also has insulation based on plywood boxes with perlite, flushed with nitrogen gas.
How much LNG can a ship carry?
LNG carriers come in various different sizes, from small-scale to large-scale carriers. The amount of LNG a ship can carry will depend on that specific vessel’s size and capacity:
- Small-scale carriers have an approximate cargo capacity of 1,000m³ (35,300 ft³) to 40,000m³ (1.4 million ft³)
- Medium-scale carriers have an approximate cargo capacity of 40,000m³ (1.4 million ft³) to 80,000m³ (2.8 million ft³)
- Large-scale carriers (also known as Q-max or Q-flex ships) have an approximate cargo capacity of 120,000m³ (4.2 million ft³) to over 260,000m³ (9.2 million ft³).
It is worth noting, however, that the above figures are only estimates. The actual cargo capacity of an LNG ship will depend on its specific:
Furthermore, it is expected that we will see vessels with much larger capacities in the coming years as LNG carrier technology continues to advance.
How do LNG ships work?
LNG ships have a number of specialised features which enable them to transport liquefied natural gas (LNG) safely and efficiently. These include:
- A double hulled structure
The ship’s hull is made from materials which can withstand a wide range of temperatures. Furthermore, the space between the inner and outer hull reduces heat transfer and protects cargo tanks in the case of an emergency.
- Insulated tanks
Four or five large tanks hold the LNG. Usually made of aluminium or 9% nickel steel, they are each several layers thick in order to prevent leaks and maintain the cold temperature necessary to keep the gas in its liquid form.
- A gas combustion unit (GCU) in the propulsion system
Several different propulsion systems are used in LNG carriers, but they all feature a GCU. This avoids pressure build-up in the cargo tanks by allowing for the disposal of excess boil-off gas (BOG).
LNG vessel charter rates
In 2022, Clarksons Securities analyst Frode Mørkedal wrote, “LNG carriers are shooting for the stars. Spot earnings have reached dizzying heights.” At that point average voyage rates for the most efficient LNG carriers were at $313,000 per day while tri-fuel, diesel engine (TFDE) carrier rates were assessed at $276,700 per day. These high charter rates reflect LNG’s important role in the green transition.
As the world’s most comprehensive and widely recognised gas brokerage service, Clarksons’ expert teams are able to advise and guide clients on both short and long-term chartering. Spanning three continents and covering most time zones, our gas broker specialist teams work seamlessly to provide the highest level of client support with LNG vessel chartering.