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LGTCO/LGTF exit exam questions and answers — Set 6 — Liquefied Gas Tanker Cargo Operations

Set 6 of the Liquefied Gas Tanker Cargo Operations (LGTCO/LGTF) exit exam bank — 30 of 599 questions, with the correct option marked and a one-line explanation for every one. Read it end to end, jump to a single set, or search it — then sit the same bank as a timed paper. The real DG Shipping exit exam is 30 marks with 15 to pass.

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Set 6 — 30 LGTCO/LGTF exit exam questions with answers

1. Your vessel has completed loading and is ready for gauging. Which of the following should you ensure?

  • A. All cargo systems on the ship are closed and the shore connections isolated or disconnected
  • B. All personnel are on board and ready at their departure stations
  • C. The custody transfer system is closed and isolated in the presence of shore representatives
  • D. Cargo system valves are lined up to fill the largest tank to allow topping-up
Answer: A — All cargo systems on the ship are closed and the shore connections isolated or disconnected
Custody transfer gauging must be done with the cargo system static. All ship cargo valves are closed and the shore connections isolated or disconnected so that no liquid or vapour can move between ship and shore while levels, temperatures and pressures are recorded.

2. With a pneumatic ship/shore link, what happens when the ship moves off the jetty beyond its safe working limits?

  • A. The air hose breaks
  • B. The air pressure in the link drops
  • C. Alarms sound and the ESD is activated
  • D. All of the above
Answer: D — All of the above
In a pneumatic ship/shore ESD link the air hose is designed to part if the ship drifts beyond the safe envelope. The resulting loss of air pressure trips the system, sounding alarms and activating the emergency shutdown of cargo transfer.

3. The heat used in the process of evaporation is called ____.

  • A. Latent heat
  • B. Sensible heat
  • C. Potential heat
  • D. Specific heat
Answer: A — Latent heat
Latent heat is the heat absorbed or released during a change of state without any change in temperature. During evaporation the liquid absorbs latent heat of vaporization, which is how boil-off cools a liquefied gas cargo.

4. Pressure measured above a perfect vacuum is called ____ pressure.

  • A. Absolute
  • B. Atmospheric
  • C. Gauge
  • D. Differential
Answer: A — Absolute
Absolute pressure is measured from a perfect vacuum, or zero pressure. Gauge pressure is measured relative to the local atmospheric pressure, so absolute pressure equals gauge pressure plus atmospheric pressure.

5. What is the typical expansion ratio of high-expansion foam?

  • A. Up to about 1000:1
  • B. 5:1 to 12:1
  • C. 1:1 to 3:1
  • D. Above 5000:1
Answer: A — Up to about 1000:1
Foam is classed by expansion ratio. Low-expansion foam is up to about 12:1, medium-expansion foam is in the tens to around two hundred, and high-expansion foam reaches up to about 1000:1, which allows it to fill enclosed spaces such as engine rooms quickly.

6. The function of a cargo tank pressure relief valve is to ____.

  • A. Release excessive pressure from the tank
  • B. Measure the liquid level in the tank
  • C. Supply inert gas to the tank
  • D. Prevent liquid entering the vapour header
Answer: A — Release excessive pressure from the tank
IGC Code Chapter 8 requires each cargo tank to have pressure relief valves set at or below the MARVS. When tank vapour pressure rises above the set point, the valve lifts and vents vapour to the vent mast, protecting the tank from overpressure.

7. What medium is used for the initial pressurization of insulation spaces?

  • A. Nitrogen
  • B. Oxygen
  • C. Methane gas
  • D. Dry air
Answer: A — Nitrogen
Insulation and inter-barrier spaces of membrane LNG tanks are filled and pressurized with dry nitrogen, which is inert and has a very low dew point. This prevents a flammable atmosphere and condensation or ice in the insulation, and allows leaks to be detected.

8. What happens in an air dryer plant when the seawater flow to the refrigerant condenser is insufficient?

  • A. The air is not cooled enough at the outlet
  • B. The air is over-cooled at the outlet
  • C. The moisture in the air freezes at the outlet
  • D. The air outlet temperature is not affected at all
Answer: A — The air is not cooled enough at the outlet
With insufficient cooling water the refrigerant condenser pressure rises and the refrigerating capacity falls. The process air is then not cooled enough, less moisture condenses out, and the dew point of the dried air rises.

9. What is required to enable BOG to be burned in the event of a reliquefaction plant shutdown on an LNG carrier?

  • A. Gas Combustion Unit (GCU)
  • B. Steam dump plant
  • C. Degasification plant
  • D. Steam boiler
Answer: A — Gas Combustion Unit (GCU)
On ships with reliquefaction plants and diesel propulsion, a Gas Combustion Unit is fitted to dispose of excess boil-off gas safely when the reliquefaction plant is stopped or the engines cannot consume it, keeping tank pressure within limits without venting.

10. In a Moss-type LNG cargo tank, what is the annular (hold) space filled with to avoid fire risk?

  • A. Inert gas
  • B. Moist air
  • C. Oxygen
  • D. Dry air
Answer: A — Inert gas
The hold space around a Moss spherical tank is filled with dry inert gas so that any cargo leak cannot form a flammable mixture. Being dry, it also prevents condensation and ice on the cold tank insulation, and gas detection monitors it for leaks.

11. In an LNG Sale and Purchase Agreement, who is responsible for transportation of the LNG by sea?

  • A. Either the buyer or the seller, as agreed in the contract
  • B. The seller, always
  • C. The buyer, always
  • D. Members of SIGTTO only
Answer: A — Either the buyer or the seller, as agreed in the contract
Responsibility for shipping depends on the delivery terms agreed in the SPA. Under FOB the buyer arranges the ship, while under DES or CIF the seller does, so transportation can fall to either party.

12. The pipeline connecting the vapour spaces of the shore tank and the ship during cargo transfer is called the ____.

  • A. Vapour return line
  • B. Vapour escape line
  • C. Liquid crossover line
  • D. Stripping line
Answer: A — Vapour return line
During loading, vapour displaced from the ship's tanks is sent back to the shore tank through the vapour return line, and during discharge the flow is reversed. This balances pressures and avoids venting cargo vapour to atmosphere.

13. The sum of gauge pressure and one atmosphere gives the ____ pressure.

  • A. Absolute
  • B. Atmospheric
  • C. Gauge
  • D. Vacuum
Answer: A — Absolute
Gauge pressure is measured relative to atmospheric pressure. Adding the atmospheric pressure, about 1.013 bar, to the gauge reading gives the absolute pressure measured from a perfect vacuum, which is used in gas law calculations.

14. The main purpose of zero gas is calibration of the ____ reading of gas detectors.

  • A. Zero
  • B. Span
  • C. Alarm set-point
  • D. Full-scale
Answer: A — Zero
Zero gas, normally nitrogen or clean air free of the target gas, is used to set the instrument's zero point. A span gas of known concentration is then used to adjust the upper reading, completing the calibration.

15. The temperature at which a liquid starts boiling is called the ____.

  • A. Boiling temperature
  • B. Critical temperature
  • C. Absolute temperature
  • D. Freezing temperature
Answer: A — Boiling temperature
The boiling temperature is the temperature at which the saturated vapour pressure of a liquid equals the surrounding pressure, so vapour forms throughout the liquid. For liquefied gases it is quoted at atmospheric pressure, such as -162°C for methane.

16. Latent heat is termed latent heat of vaporization in the case of ____.

  • A. Boiling
  • B. Melting
  • C. Freezing
  • D. Sublimation
Answer: A — Boiling
Latent heat of vaporization is the heat absorbed when a liquid changes into vapour at constant temperature, as in boiling. Melting and freezing involve latent heat of fusion, while sublimation involves latent heat of sublimation.

17. ____ refers to the strongest concentration of petroleum vapour in air that will burn.

  • A. Upper explosive limit
  • B. Lower explosive limit
  • C. Stronger explosive limit
  • D. Maximum explosive limit
Answer: A — Upper explosive limit
The upper explosive (flammable) limit is the maximum concentration of hydrocarbon vapour in air that can be ignited. Above it the mixture is too rich to burn; below the lower explosive limit it is too lean.

18. ____ is a process in which a liquid changes into a vapour or gas.

  • A. Boiling
  • B. Freezing
  • C. Condensation
  • D. Melting
Answer: A — Boiling
Boiling is the change of state from liquid to vapour that occurs throughout the liquid when its vapour pressure equals the surrounding pressure. Condensation is the reverse process, while freezing and melting involve the solid state.

19. A gas at a temperature ____ its critical temperature is called a vapour.

  • A. Below
  • B. Above
  • C. Exactly at
  • D. Far above
Answer: A — Below
Above the critical temperature a gas cannot be liquefied by pressure alone. Below the critical temperature it is called a vapour because it can be condensed by compression, which is the basis of carrying liquefied gases under pressure or refrigeration.

20. LNG carriers are designed and constructed to meet the standards of which code?

  • A. International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code)
  • B. International Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk (IBC Code)
  • C. International Code of Safety for Ships using Gases or other Low-flashpoint Fuels (IGF Code)
  • D. Rules of classification societies only
Answer: A — International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code)
Ships carrying liquefied gases in bulk, including LNG carriers, must comply with the IGC Code, made mandatory under SOLAS Chapter VII. The IBC Code covers chemicals and the IGF Code covers ships using gas as fuel.

21. What is the IGC Code definition of a liquefied gas?

  • A. A product with a saturated vapour pressure of 1.76 bar absolute at 37.8°C
  • B. A product with a vapour pressure exceeding 2.8 bar absolute at 37.8°C
  • C. A product with a saturated vapour pressure of 2.8 bar absolute at 38.7°C
  • D. A product with a saturated vapour pressure of 1.77 bar absolute at 38.7°C
Answer: B — A product with a vapour pressure exceeding 2.8 bar absolute at 37.8°C
The IGC Code defines liquefied gases as liquids with a vapour pressure exceeding 2.8 bar absolute at a temperature of 37.8°C, together with certain other products listed in Chapter 19 of the Code.

22. Which type of cargo tank is completely self-supporting and neither forms part of the ship's hull nor contributes to hull strength?

  • A. Independent tank
  • B. Membrane tank
  • C. Semi-membrane tank
  • D. None of the above
Answer: A — Independent tank
The IGC Code defines independent tanks, of Type A, Type B or Type C, as self-supporting tanks that do not form part of the hull structure and are not essential to hull strength. Membrane tanks rely on the adjacent hull structure for support.

23. Which type of gas carrier, based on the hazardous nature of the cargo, requires the maximum preventive measures?

  • A. Type 1G
  • B. Type 2G
  • C. Type 2PG
  • D. Type 3G
Answer: A — Type 1G
The IGC Code assigns Type 1G ships to products with the greatest hazards, such as chlorine, requiring maximum preventive measures against cargo escape, including the greatest cargo tank distances from the shell. Types 2G/2PG and 3G need progressively lower measures.

24. The carriage of LNG in bulk requires which statutory certificate?

  • A. Pollution Prevention Certificate for Gas Carriers
  • B. International Certificate of Fitness for the Carriage of Liquefied Gases in Bulk
  • C. IGC and IBC Code Certificate
  • D. LNG Trading Certificate
Answer: B — International Certificate of Fitness for the Carriage of Liquefied Gases in Bulk
Under the IGC Code, a gas carrier that has been surveyed and found to comply is issued the International Certificate of Fitness for the Carriage of Liquefied Gases in Bulk, which lists the products it may carry.

25. How can a gas be liquefied?

  • A. By mixing it with gases of higher density
  • B. By the application of pressure or by cooling
  • C. By fusion in a closed chamber
  • D. By evaporation in a closed chamber
Answer: B — By the application of pressure or by cooling
A gas is liquefied by raising its pressure, lowering its temperature, or both, provided it is below its critical temperature. Gas carriers therefore carry cargo fully pressurised, semi-refrigerated or fully refrigerated.

26. Why is natural gas liquefied for sea transportation?

  • A. The ship can choose the form of natural gas
  • B. Sea transport of natural gas as vapour is banned
  • C. LNG has a higher calorific value than natural gas, which increases revenue
  • D. Liquefaction makes transport more economical
Answer: D — Liquefaction makes transport more economical
Cooling natural gas to about -162°C reduces its volume by roughly 600 times, allowing a large energy quantity to be carried in a ship of practical size. This makes sea transport economical; the calorific value of the methane itself does not change.

27. According to Gay-Lussac's (pressure) law, with P = pressure and T = absolute temperature at constant volume:

  • A. Pressure = Constant - Temperature
  • B. Pressure = Constant + Temperature
  • C. Pressure = Constant x Temperature
  • D. Pressure = Constant / Temperature
Answer: C — Pressure = Constant x Temperature
Gay-Lussac's law states that for a fixed mass of gas at constant volume, pressure is directly proportional to absolute temperature, so P/T = constant, or P = constant x T. Heating a closed cargo tank therefore raises its pressure.

28. According to Charles's law, with V = volume and T = absolute temperature at constant pressure:

  • A. Volume = Constant x Temperature
  • B. Volume = Constant - Temperature
  • C. Volume = Constant + Temperature
  • D. Volume = Constant / Temperature
Answer: A — Volume = Constant x Temperature
Charles's law states that for a fixed mass of gas at constant pressure, volume is directly proportional to absolute temperature, so V/T = constant, or V = constant x T.

29. LNG vapour can explode when mixed with air within the flammable range of approximately:

  • A. 25 to 30 percent
  • B. 5 to 15 percent
  • C. 40 to 50 percent
  • D. 6 to 18 percent
Answer: B — 5 to 15 percent
Methane, the main constituent of LNG vapour, has a lower flammable limit of about 5% and an upper flammable limit of about 15% by volume in air. Mixtures within this range can ignite or explode if an ignition source is present.

30. Which of the following are characteristics of LNG?

  • A. LNG is odourless
  • B. LNG is non-toxic
  • C. LNG is colourless
  • D. All of the above
Answer: D — All of the above
LNG is mainly methane, which is colourless, odourless and non-toxic. Its principal hazards are flammability, asphyxiation by oxygen displacement and cryogenic burns or brittle fracture of steel from its very low temperature of about -162°C.

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