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LGTCO/LGTF exit exam questions and answers — Set 10 — Liquefied Gas Tanker Cargo Operations

Set 10 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 10 — 30 LGTCO/LGTF exit exam questions with answers

1. What is the atmospheric boiling point of propane?

  • A. -88.6 °C
  • B. -20 °C
  • C. -48 °C
  • D. -42.3 °C
Answer: D — -42.3 °C
Propane boils at about -42 °C at atmospheric pressure, so fully refrigerated LPG carriers keep it at around -42 °C. Ethane boils at -88.6 °C, and the other values do not match common LPG components.

2. Airlock doors should be self-closing, with no hook or other device by which they could be held open. The minimum distance between the two doors should be at least ____.

  • A. 0.5 metres
  • B. 1.5 metres
  • C. 1.0 metre
  • D. 2.0 metres
Answer: B — 1.5 metres
The IGC Code requires an airlock to have two self-closing, substantially gastight steel doors spaced at least 1.5 m apart, with no hold-back hooks. This prevents both doors being open at once and stops gas getting from a hazardous area into a safe space.

3. Which of the following applies to Type C independent tanks?

  • A. Both a primary barrier and a full secondary barrier are required
  • B. No secondary barrier is required
  • C. A partial secondary barrier in the form of a drip tray is required
  • D. A secondary barrier is required only when carrying LNG
Answer: B — No secondary barrier is required
Type C tanks are pressure vessels designed to the IGC Code with conservative stress levels, so the probability of crack propagation is very low. For this reason the IGC Code requires no secondary barrier for Type C tanks.

4. Can cargo be loaded if the MSDS for the cargo is not supplied by the shipper or terminal?

  • A. Yes, the MSDS can be obtained after sailing
  • B. No, loading should not start until the cargo information (MSDS) is provided
  • C. Yes, it does not make any difference
  • D. Yes, provided the Chief Officer has carried the cargo before
Answer: B — No, loading should not start until the cargo information (MSDS) is provided
The IGC Code (Chapter 18) requires cargo information, including physical and chemical properties, hazards and emergency procedures, to be on board before loading. Without the MSDS the crew cannot plan safe handling, PPE or emergency response, so the cargo should not be loaded.

5. During inerting prior to aerating, where is the methane content monitored with gas meters?

  • A. At the liquid line sampling point of each cargo tank
  • B. At the spray line sampling point of each cargo tank
  • C. At each cargo tank's vapour dome sampling point
  • D. At the manual level gauging sampling point
Answer: C — At each cargo tank's vapour dome sampling point
While inert gas displaces cargo vapour, the hydrocarbon content of the outgoing gas is measured at the vapour dome sampling points of each tank. Inerting continues until the readings are low enough that air can be introduced without passing through the flammable range.

6. What is the agreement between the LNG supplier and the buyer called?

  • A. Free On Board (FOB)
  • B. Delivery Ex-Ship (DES)
  • C. Gas Supply Agreement (GSA)
  • D. Sale and Purchase Agreement (SPA)
Answer: D — Sale and Purchase Agreement (SPA)
In the LNG chain the long-term contract between the LNG seller (supplier) and the buyer is the Sale and Purchase Agreement. FOB and DES describe delivery terms within such a contract, while the Gas Sale Agreement is between the buyer and end users.

7. On board an LNG carrier, which equipment is used to produce vapour from shore-supplied LNG when purging (gassing up) the cargo tanks?

  • A. Vacuum pumps
  • B. Heater
  • C. Purging pumps
  • D. Vaporiser
Answer: D — Vaporiser
For gassing up, LNG supplied from shore is passed through the ship's LNG vaporiser to produce methane vapour. The vapour is fed into the tanks to displace the inert gas, which goes ashore or to the vent mast until the tanks contain only cargo vapour.

8. Which two types of insulation systems are used on Moss spherical tanks?

  • A. CS1 and NO 88 systems
  • B. Membrane and GT systems
  • C. Mark III insulation and Technigaz systems
  • D. Panel insulation system and spiral-generated insulation system
Answer: D — Panel insulation system and spiral-generated insulation system
Moss spheres are insulated externally either with prefabricated polyurethane or polystyrene panels or with the spiral-generated system, where foam is applied to the sphere as it rotates. CS1, NO 96 and Mark III are membrane containment systems, not Moss insulation.

9. What is the secondary membrane of the Technigaz Mark III membrane cargo tank made of?

  • A. 1.2 mm Invar steel and 2 layers of glass cloth
  • B. 1.2 mm nickel steel and 2 layers of glass cloth
  • C. 0.7 mm aluminium foil and 2 layers of glass cloth
  • D. 0.7 mm coated steel and 2 layers of glass cloth
Answer: C — 0.7 mm aluminium foil and 2 layers of glass cloth
In the Mark III system the primary barrier is 1.2 mm corrugated stainless steel. The secondary barrier is Triplex, a thin aluminium foil about 0.7 mm thick bonded between two layers of glass cloth, built into the reinforced polyurethane foam insulation panels.

10. What are the two main constituents of LPG cargo?

  • A. Propane and butane
  • B. Propane and cetane
  • C. Butane and cetane
  • D. Natural gas and NGL
Answer: A — Propane and butane
Liquefied petroleum gas consists mainly of propane and butane, carried separately or as mixtures. Cetane is a heavy diesel-range hydrocarbon, and natural gas is mainly methane carried as LNG.

11. On board an LNG carrier during loading, what should you do before topping off the first cargo tank?

  • A. Request shore to increase the loading rate
  • B. Increase the onboard HD compressor flow output
  • C. Shut the vapour manifold
  • D. Request shore to reduce the loading rate
Answer: D — Request shore to reduce the loading rate
Before topping off, the loading rate is reduced as agreed in the pre-loading ship/shore meeting so the tank filling valves can be closed smoothly. This avoids overfilling the tank above the permitted filling limit, and also avoids surge pressure and sudden closure of valves.

12. The main purpose of ____ gas is the calibration of gas detectors.

  • A. Span
  • B. Argon
  • C. Butane
  • D. Ammonia
Answer: A — Span
Span gas is a certified calibration gas of known concentration used to adjust the reading of a gas detector at a reference point. It is used together with zero gas, usually nitrogen or clean air, to make sure the instrument gives accurate readings.

13. On an LNG carrier with a steam turbine plant, which of the following machinery is used for power generation?

  • A. A forcing vaporiser
  • B. A diesel generator
  • C. A degasification unit
  • D. A reliquefaction plant
Answer: B — A diesel generator
Steam turbine LNG carriers generate electricity with steam turbo-generators and at least one diesel generator, used in port, at standby and for emergency start. Vaporisers and reliquefaction plants are cargo-handling equipment, not power generators.

14. What is the agreement between the LNG buyer and end users such as a utility company called?

  • A. Delivery Ex-Ship (DES)
  • B. Sale and Purchase Agreement (SPA)
  • C. Gas Sale Agreement (GSA)
  • D. Free On Board (FOB)
Answer: C — Gas Sale Agreement (GSA)
After regasification the LNG buyer sells the gas on to end users such as power utilities under a Gas Sale Agreement. The Sale and Purchase Agreement covers the earlier supplier-buyer transaction, while FOB and DES are delivery terms.

15. In the case of melting, the latent heat is termed the latent heat of ____.

  • A. Vaporisation
  • B. Fusion
  • C. Ignition
  • D. Sublimation
Answer: B — Fusion
Latent heat of fusion is the heat needed to change a solid into a liquid at constant temperature. Latent heat of vaporisation applies to liquid changing into vapour, which is the process that matters for boil-off in gas tankers.

16. The pressure exerted by the atmosphere at sea level is called ____ pressure.

  • A. Absolute
  • B. Gauge
  • C. Atmospheric
  • D. Vapour
Answer: C — Atmospheric
Atmospheric pressure is the pressure of the air above sea level, about 1.013 bar. Gauge pressure is measured above atmospheric, and absolute pressure equals gauge pressure plus atmospheric pressure.

17. After the liquid is discharged from a cargo tank, a small quantity remains which is difficult to pump out. This small quantity of liquid is called the:

  • A. Liquid trap
  • B. Heel
  • C. Mole
  • D. Ullage
Answer: B — Heel
The heel is the liquid left in the tank after discharge. On LNG carriers a heel is often kept deliberately to keep the tanks cold during the ballast voyage, so they do not need full cool-down before the next loading.

18. ____ is the standard atmospheric pressure, equivalent to 760 mm or 29.92 inches of mercury.

  • A. 912.5 millibars / 13.2 psi
  • B. 1013.25 millibars / 14.7 psi
  • C. 1212.5 millibars / 17.6 psi
  • D. 1113.25 millibars / 16.1 psi
Answer: B — 1013.25 millibars / 14.7 psi
Standard atmospheric pressure is 1013.25 mbar (hPa), which equals 760 mmHg, 29.92 inHg or about 14.7 psi. It is the reference pressure for atmospheric boiling points of liquefied gases.

19. When the temperature of a liquefied gas rises, the ____ increases and the density of the liquid decreases.

  • A. Saturated vapour pressure
  • B. Saturated vapour density
  • C. Unsaturated vapour pressure
  • D. Liquid viscosity
Answer: A — Saturated vapour pressure
The saturated vapour pressure of a liquefied gas rises with temperature, while the liquid expands so its density falls. This is why tank pressure rises with heat ingress and why filling limits leave space for thermal expansion.

20. When the pressure ____, there is a rise in the boiling temperature.

  • A. Increases
  • B. Decreases
  • C. Remains steady
  • D. Drops below atmospheric
Answer: A — Increases
Boiling point depends on pressure. Raising the pressure above the liquid raises the boiling temperature, which is why pressurised tanks can carry LPG at ambient temperature, while lowering the pressure lowers the boiling point.

21. A gas or vapour cannot be liquefied by pressure alone above a particular temperature. This temperature is called the:

  • A. Critical temperature
  • B. Adiabatic expansion
  • C. Absolute temperature
  • D. Boiling temperature
Answer: A — Critical temperature
Above its critical temperature a gas cannot be liquefied however much pressure is applied. Methane's critical temperature is about -82 °C, which is why LNG must be carried fully refrigerated and not pressurised at ambient temperature.

22. The heat that changes the state of a substance without changing its temperature is called:

  • A. Sensible heat
  • B. Latent heat
  • C. Potential heat
  • D. Specific heat
Answer: B — Latent heat
Latent heat is absorbed or released during a change of state, such as boiling or condensing, while the temperature stays constant. In gas tankers, heat ingress supplies latent heat of vaporisation, which produces boil-off gas.

23. The heat that increases the temperature of a substance without changing its state is called:

  • A. Sensible heat
  • B. Latent heat
  • C. Potential heat
  • D. Heat of fusion
Answer: A — Sensible heat
Sensible heat changes the temperature of a substance and can be measured with a thermometer, with no change of state. Latent heat, including heat of fusion, changes the state at constant temperature.

24. What is the boiling point of methane at standard atmospheric pressure?

  • A. -260 °F / -162 °C
  • B. -360 °F / -218 °C
  • C. -159 °F / -106 °C
  • D. -44 °F / -42 °C
Answer: A — -260 °F / -162 °C
Methane, the main component of LNG, boils at about -161.5 °C (-259 °F) at atmospheric pressure. LNG is therefore carried fully refrigerated at about -162 °C in insulated tanks close to atmospheric pressure. -42 °C is the boiling point of propane.

25. The temperature of a gas or vapour ____ when it is compressed.

  • A. Increases
  • B. Decreases
  • C. Remains constant
  • D. Falls to ambient
Answer: A — Increases
Compressing a gas does work on it and raises its temperature, as in adiabatic compression. This is why cargo compressors on gas tankers have high discharge temperatures and why reliquefaction plants use condensers to remove the heat.

26. In liquefied gas tanker operations, what does the term 'cargo containment system' refer to?

  • A. Methods of cargo heating
  • B. Procedures for cargo transfer
  • C. Design and construction of the cargo tanks, including barriers and insulation
  • D. Emergency response plans
Answer: C — Design and construction of the cargo tanks, including barriers and insulation
The IGC Code defines the cargo containment system as the arrangement for containing cargo, including the primary and secondary barriers, insulation, interbarrier spaces and adjacent structure. Examples include independent Type A, B and C tanks and membrane tanks.

27. What is the primary function of the inert gas system on a liquefied gas tanker?

  • A. Cargo heating
  • B. Preventing flammable atmospheres and explosions in cargo tanks and spaces
  • C. Increasing cargo transfer speed
  • D. Reducing cargo vapour pressure
Answer: B — Preventing flammable atmospheres and explosions in cargo tanks and spaces
Inert gas, usually nitrogen or flue gas with low oxygen content, is used to inert cargo tanks, hold spaces and interbarrier spaces so that the oxygen concentration stays below the level needed for combustion. This prevents flammable mixtures during gas-freeing, gassing-up and normal operation.

28. Which gas is commonly transported as a cryogenic liquid on liquefied gas tankers?

  • A. Methane
  • B. Propane
  • C. Butane
  • D. Ammonia
Answer: A — Methane
Methane (LNG) boils at about -162 °C and cannot be liquefied by pressure at ambient temperature because its critical temperature is about -82 °C. It must be carried at cryogenic temperature. Propane, butane and ammonia can be carried pressurised or semi/fully refrigerated at much milder temperatures.

29. In liquefied gas tanker operations, what does the term 'boil-off gas' refer to?

  • A. Cargo vapour generated by heat ingress into the tanks, mainly during the voyage
  • B. Emergency fire control gas
  • C. Inert gas used for purging
  • D. Gas generated by the cargo compressors
Answer: A — Cargo vapour generated by heat ingress into the tanks, mainly during the voyage
Boil-off gas is cargo vapour produced as heat leaks through the insulation and vaporises some of the refrigerated cargo. On LNG carriers it is burnt as fuel, reliquefied or burnt in a gas combustion unit to control tank pressure.

30. Which liquefied gas tanker cargo operation involves transferring cargo from one ship to another?

  • A. Loading
  • B. Discharging
  • C. Ship-to-ship transfer
  • D. Tank purging
Answer: C — Ship-to-ship transfer
Ship-to-ship transfer moves cargo directly between two vessels alongside each other, at anchor or under way. It is carried out following the ship-to-ship transfer guides (OCIMF/SIGTTO/CDI) and the STS operations plan required by MARPOL.

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