Skip to content
DG Exit Exam
Home CHEMCO sets
Answer Key

CHEMCO exit exam questions and answers — Set 20 — Advanced Training for Chemical Tanker Cargo Operations

Set 20 of the Advanced Training for Chemical Tanker Cargo Operations (CHEMCO) exit exam bank — 30 of 663 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.

These are the bank's original groupings. Practising deals the whole bank out again every time you reshuffle, so a practice “Set 3” is a different 30 questions each time — the set numbers below are the source file's, and are only used here so the key stays navigable. Options are listed in their original order with fixed letters; when you practise, those move too.

Bank last rebuilt .

Practise these CHEMCO questions CHEMCO mock exit exam, 30 marks CHEMCO exit exam sets and syllabus

30 of 30 shown · Set 20

Nothing in this set matches that. Try a shorter word, or search the whole key.

Set 20 — 30 CHEMCO exit exam questions with answers

1. Why are zinc and aluminium unsuitable materials for tanks and fittings in caustic soda (sodium hydroxide) service?

  • A. Strong alkalis attack these metals and generate flammable hydrogen gas
  • B. They catalyse polymerisation of caustic soda
  • C. They become electrostatically charged by the cargo
  • D. They absorb the cargo and change its concentration
Answer: A — Strong alkalis attack these metals and generate flammable hydrogen gas
Sodium hydroxide solution reacts with amphoteric metals such as zinc and aluminium, dissolving them and releasing hydrogen. This damages zinc silicate coatings and fittings and can create a flammable atmosphere, so stainless steel, mild steel or a suitable coating is used instead.

2. Concentrated sulphuric acid can be carried in mild steel tanks, but dilution with water is dangerous because:

  • A. Diluted acid attacks mild steel rapidly and releases hydrogen, besides the heat generated on mixing
  • B. Diluted acid becomes flammable
  • C. Diluted acid polymerises and solidifies in the lines
  • D. Diluted acid stops conducting electricity, causing static build-up
Answer: A — Diluted acid attacks mild steel rapidly and releases hydrogen, besides the heat generated on mixing
Concentrated sulphuric acid forms a protective iron sulphate layer on mild steel, but when water is added the diluted acid becomes highly corrosive to steel, producing hydrogen gas. Mixing is also strongly exothermic, so water must be kept out of tanks and lines.

3. Aqueous ammonia should not be handled with fittings made of which material?

  • A. Copper and copper alloys such as brass
  • B. Stainless steel
  • C. Mild steel
  • D. Polytetrafluoroethylene (PTFE) gaskets
Answer: A — Copper and copper alloys such as brass
Ammonia solutions attack copper, brass and zinc-containing alloys, causing corrosion and cargo contamination. Cargo-handling equipment for ammonia solutions is therefore made of steel or stainless steel, and the material compatibility tables of the cargo information must be checked.

4. Nitric acid must be kept well segregated from organic cargoes such as alcohols, oils and solvents mainly because it is:

  • A. A strong oxidising agent that can react violently or ignite organic materials
  • B. A polymerising cargo that needs an inhibitor
  • C. Heavier-than-air flammable vapour
  • D. Water-reactive, releasing hydrogen
Answer: A — A strong oxidising agent that can react violently or ignite organic materials
Concentrated nitric acid is a powerful oxidiser. In contact with organic substances it can cause vigorous exothermic reactions, toxic nitrous fumes and fire, so compatibility charts list it as incompatible with most organic cargo groups and spills must not be absorbed with sawdust or rags.

5. A cargo tank has a total capacity of 1,000 m3 and may be filled to 98% at the highest temperature expected on passage, 50°C. The cargo density is 0.900 t/m3 at the loading temperature of 20°C and 0.876 t/m3 at 50°C. What is the maximum volume that may be loaded at 20°C?

  • A. About 954 m3
  • B. 980 m3
  • C. About 1,007 m3
  • D. About 931 m3
Answer: A — About 954 m3
The maximum volume at 50°C is 0.98 × 1,000 = 980 m3, a mass of 980 × 0.876 = 858.5 t. At 20°C this mass occupies 858.5 / 0.900 = 953.9 m3, so about 954 m3 may be loaded to leave room for thermal expansion.

6. A cargo tank holds 2,500 m3 of cargo at standard temperature (15°C) with a density at 15°C of 0.8500 t/m3. Using the usual air buoyancy deduction of 0.0011, what is the weight of cargo in air?

  • A. 2,122.25 t
  • B. 2,125.00 t
  • C. 2,127.75 t
  • D. 2,941.18 t
Answer: A — 2,122.25 t
Weight in air is the standard volume multiplied by the density in vacuum minus 0.0011: 2,500 × (0.8500 − 0.0011) = 2,500 × 0.8489 = 2,122.25 t. Multiplying by the vacuum density alone gives the mass in vacuum, which is slightly greater.

7. The gross observed volume in a cargo tank is 1,200 m3 at 30°C and the volume correction factor for that temperature is 0.9850. What is the volume at standard temperature?

  • A. 1,182 m3
  • B. 1,218 m3
  • C. 1,200 m3
  • D. 1,170 m3
Answer: A — 1,182 m3
Volume at standard temperature equals the observed volume multiplied by the volume correction factor: 1,200 × 0.9850 = 1,182 m3. The factor is less than 1 because the cargo is warmer than 15°C and has expanded.

8. A shipper nominates 1,500 t of a chemical with a density of 1.250 t/m3 at the loading temperature. What volume will this cargo occupy in the tank?

  • A. 1,200 m3
  • B. 1,875 m3
  • C. 1,250 m3
  • D. 1,500 m3
Answer: A — 1,200 m3
Volume equals mass divided by density: 1,500 / 1.250 = 1,200 m3. For high-density cargoes the tank may be well below its normal filling limit while still carrying its maximum permitted mass, so both volume and mass must be checked.

9. 1,000 m3 of cargo is loaded at 20°C. Its coefficient of cubical expansion is 0.0010 per °C and it will be heated to 40°C on passage. Approximately what volume will it occupy when heated?

  • A. 1,020 m3
  • B. 1,002 m3
  • C. 1,200 m3
  • D. 980 m3
Answer: A — 1,020 m3
Expanded volume = original volume × (1 + coefficient × temperature rise) = 1,000 × (1 + 0.0010 × 20) = 1,020 m3. This is why the ullage left at loading must allow for the temperature the cargo will reach during heating.

10. A rectangular slack cargo tank is 20 m long and 10 m wide and contains a liquid of density 1.0 t/m3. The ship's displacement is 10,000 t. What is the virtual loss of GM due to free surface?

  • A. About 0.17 m
  • B. About 0.02 m
  • C. About 0.67 m
  • D. About 1.67 m
Answer: A — About 0.17 m
Free surface moment = density × l × b³ / 12 = 1.0 × 20 × 1,000 / 12 = 1,666.7 t·m. The loss of GM is this moment divided by displacement: 1,666.7 / 10,000 = 0.167 m, about 0.17 m.

11. Under MARPOL Annex I regulation 27, which applies to oil tankers of 5,000 dwt and above including product/chemical tankers certified for oil, what minimum initial metacentric height, corrected for free surface, is required in port?

  • A. 0.15 m
  • B. 0.05 m
  • C. 0.30 m
  • D. 0.50 m
Answer: A — 0.15 m
Regulation 27 requires that in port the initial metacentric height GMo, corrected for free surface measured at 0° heel, shall be not less than 0.15 m, and that the IS Code criteria be met at sea in every loading condition, including intermediate stages of liquid transfer.

12. Under the 2014 amendments to MARPOL Annex I and the IBC Code, chemical tankers constructed on or after 1 January 2016 must be fitted with:

  • A. A stability instrument capable of verifying compliance with intact and damage stability requirements
  • B. A ballast water treatment system with cargo tank monitoring
  • C. A fixed cargo vapour recovery plant
  • D. A hull stress monitoring system with strain gauges on deck
Answer: A — A stability instrument capable of verifying compliance with intact and damage stability requirements
Resolutions MSC.369(93) and MEPC.248(66) require oil and chemical tankers to carry a stability instrument able to verify intact and damage stability, applying to new ships from 1 January 2016 and to existing ships by their first renewal survey after that date, and not later than 1 January 2021.

13. When a high-density cargo such as concentrated sulphuric acid is to be carried in a tank designed for a lower cargo density, what is the correct approach?

  • A. Fill the tank only partially so the cargo mass stays within the design limit, checking any sloshing restrictions
  • B. Fill the tank to 98% as with any other cargo
  • C. Dilute the cargo with water to reduce its density
  • D. Carry the cargo only in deck tanks
Answer: A — Fill the tank only partially so the cargo mass stays within the design limit, checking any sloshing restrictions
Tank structure is designed for a maximum cargo density at full filling. A heavier cargo must be loaded to a reduced level so its weight does not overstress the tank, and the approved loading manual's limits on partial filling and sloshing must be observed.

14. How do the permissible shear force and bending moment limits for harbour conditions normally compare with the seagoing limits shown in the loading manual?

  • A. Harbour limits are higher, because wave-induced loads are not present in port
  • B. Harbour limits are lower, because the ship is moored
  • C. Both are always identical
  • D. Harbour limits apply only when ballasting
Answer: A — Harbour limits are higher, because wave-induced loads are not present in port
Seagoing limits allow for additional wave bending and shear loads, so the permissible still-water values in port are generally higher. The ship must, however, be within seagoing limits before departure and at every intermediate stage of a loading or discharge sequence planned for sea.

15. Loading heavy cargo in the end tanks while the midship tanks are left empty will tend to make the ship:

  • A. Hog
  • B. Sag
  • C. List to port
  • D. Trim by the head only
Answer: A — Hog
Concentrating weight at the ends while buoyancy remains greatest amidships causes the hull to bend with the middle higher than the ends, which is hogging. The loading computer is used to keep bending moments and shear forces within limits at every stage.

16. Why must the loading sequence of a chemical tanker be checked on the loading computer for intermediate stages and not only for the final condition?

  • A. Stress, stability and trim limits can be exceeded at an intermediate stage even when the final condition is acceptable
  • B. The loading computer can only calculate intermediate stages
  • C. The final condition never affects stresses
  • D. It is required only for ships carrying Category X cargoes
Answer: A — Stress, stability and trim limits can be exceeded at an intermediate stage even when the final condition is acceptable
Parcel tankers load and discharge many tanks in sequence, often with slack tanks and ballast changes. Shear forces, bending moments, free surface and GM can pass through critical values during the operation, so each stage must be verified before it is carried out.

17. According to the IBC Code, a ship type 3 chemical tanker is intended to carry products with:

  • A. Sufficiently severe environmental and safety hazards to require a moderate degree of containment to increase survival capability
  • B. The most severe hazards requiring maximum preventive measures
  • C. No safety hazards at all
  • D. Only liquefied gases under pressure
Answer: A — Sufficiently severe environmental and safety hazards to require a moderate degree of containment to increase survival capability
IBC Code 2.1.2 defines ship type 3 for products with sufficiently severe hazards to require a moderate degree of containment in the damaged condition. Ship type 1 is for the most severe hazards and ship type 2 for products requiring significant preventive measures.

18. Duplex stainless steel is increasingly used for chemical tanker cargo tanks because it:

  • A. Combines austenitic and ferritic structures, giving higher strength and better resistance to chloride stress corrosion
  • B. Does not need any cleaning between cargoes
  • C. Is immune to attack by all acids
  • D. Is cheaper and lighter than mild steel
Answer: A — Combines austenitic and ferritic structures, giving higher strength and better resistance to chloride stress corrosion
Duplex grades such as 2205 have a mixed austenitic-ferritic microstructure. They offer higher strength than 316L, allowing thinner plating, and better resistance to pitting and chloride stress corrosion cracking, but they are still attacked by some cargoes and need correct cleaning.

19. After a stainless steel tank surface has been contaminated with iron particles or damaged, which treatment restores its corrosion resistance?

  • A. Pickling and passivation, usually with a nitric acid based solution
  • B. Painting with zinc silicate
  • C. Washing with hot seawater
  • D. Applying a cathodic protection anode
Answer: A — Pickling and passivation, usually with a nitric acid based solution
Pickling removes contamination and the damaged surface layer, and passivation with an oxidising acid solution rebuilds the protective chromium oxide film. Without this treatment rust spots and pitting can develop and contaminate sensitive cargoes.

20. Before a newly coated epoxy cargo tank can carry cargo, what must be ensured?

  • A. The coating has fully cured according to the manufacturer's time and temperature requirements
  • B. The tank has been filled with seawater for one week
  • C. The coating has been covered with a layer of oil
  • D. The coating is at least one year old
Answer: A — The coating has fully cured according to the manufacturer's time and temperature requirements
Epoxy and phenolic epoxy coatings achieve their chemical resistance only after full curing, which depends on time and temperature, sometimes with post-curing by heating. Loading cargo too early can soften or damage the coating and contaminate the cargo.

21. Under SOLAS chapter II-2, cargo pump rooms of tankers must be fitted with a system for continuous monitoring of hydrocarbon gas concentration, with an alarm set at not higher than:

  • A. 10% of the lower flammable limit
  • B. 50% of the lower flammable limit
  • C. 100% of the lower flammable limit
  • D. 1% by volume of oxygen
Answer: A — 10% of the lower flammable limit
SOLAS II-2/4.5.10 requires sampling points or detector heads in suitable locations in cargo pump rooms so that leakages are promptly detected, with continuous audible and visual alarms in the pump room, engine control room, cargo control room and navigation bridge at not higher than 10% LFL.

22. For cargo pumps in a pump room driven by shafts passing through the pump room bulkhead, SOLAS requires:

  • A. Temperature sensing devices for the bulkhead shaft glands, bearings and pump casings
  • B. A fixed water spray system on each pump
  • C. Pumps to be stopped every two hours for inspection
  • D. A vapour return line from each pump
Answer: A — Temperature sensing devices for the bulkhead shaft glands, bearings and pump casings
SOLAS II-2/4.5.10.1 requires temperature sensing devices on bulkhead shaft glands, bearings and pump casings, with continuous audible and visual alarm in the cargo control room or pump control station, since overheating of these parts is a known ignition source in pump rooms.

23. Which monitoring arrangement is required by SOLAS in the cargo pump room bilges of a tanker?

  • A. Bilge level monitoring devices with appropriately located alarms
  • B. An oxygen analyser in each bilge well
  • C. A sounding pipe only
  • D. A fixed CO2 nozzle in each bilge
Answer: A — Bilge level monitoring devices with appropriately located alarms
SOLAS II-2/4.5.10.1 requires bilge level monitoring devices with alarms in cargo pump rooms so that a leakage of cargo or water collecting in the bilges is detected early and can be dealt with before it becomes a fire or toxic hazard.

24. For the same liquid, how does the closed-cup flash point normally compare with the open-cup flash point?

  • A. The closed-cup value is lower
  • B. The closed-cup value is higher
  • C. They are always the same
  • D. Closed-cup values are used only for solids
Answer: A — The closed-cup value is lower
In the closed-cup test vapour is retained above the liquid, so a flammable mixture forms at a lower temperature than in the open cup, where vapour disperses. Closed-cup flash points are used for ship classification purposes because they are lower and therefore conservative.

25. A solution with a pH of 3 compared with a solution of pH 5 has a hydrogen ion concentration that is:

  • A. 100 times greater
  • B. 2 times greater
  • C. 20 times greater
  • D. 100 times smaller
Answer: A — 100 times greater
The pH scale is logarithmic: each unit decrease means a tenfold increase in hydrogen ion concentration. A difference of two units therefore means 10 × 10 = 100 times more hydrogen ions, so the pH 3 solution is much more strongly acidic.

26. Sodium hydroxide has a molar mass of 40 g/mol. What mass of sodium hydroxide is contained in 1 litre of a 1 molar (1 mol/L) solution?

  • A. 40 g
  • B. 1 g
  • C. 20 g
  • D. 400 g
Answer: A — 40 g
Molarity is the number of moles of solute per litre of solution. One litre of 1 mol/L sodium hydroxide therefore contains one mole, which is 40 g, the sum of the atomic masses of sodium (23), oxygen (16) and hydrogen (1).

27. What happens to the boiling point of a liquid cargo when the pressure above it is reduced?

  • A. It falls, so the liquid boils at a lower temperature
  • B. It rises
  • C. It does not change
  • D. It becomes equal to the flash point
Answer: A — It falls, so the liquid boils at a lower temperature
A liquid boils when its vapour pressure equals the surrounding pressure. Lowering the pressure, for example by drawing a vacuum in a tank or on a pump suction, lowers the boiling temperature, which is why volatile cargoes can flash off and cause cavitation at pump suctions.

28. When preparing a stowage plan for a parcel chemical tanker, which check must be made for every nominated product before allocating it to a tank?

  • A. That the product is listed on the ship's Certificate of Fitness and the allocated tank meets its ship type, tank coating and equipment requirements
  • B. That the product has the same flash point as the previous cargo
  • C. That the product is lighter than water
  • D. That the shipper has supplied a bill of lading in advance
Answer: A — That the product is listed on the ship's Certificate of Fitness and the allocated tank meets its ship type, tank coating and equipment requirements
A product may be carried only if it is named on the list of products attached to the Certificate of Fitness, and only in tanks meeting the chapter 17 requirements for ship type, tank type, venting, gauging and environmental control, with coating or steel compatibility confirmed.

29. In planning tank allocation, which combination should be avoided?

  • A. A heat-sensitive cargo in a tank sharing a bulkhead with a cargo that will be heated
  • B. Two compatible solvents in tanks separated by a cofferdam
  • C. A heated cargo in a tank with heating coils
  • D. A cargo that needs nitrogen padding in a tank connected to the nitrogen system
Answer: A — A heat-sensitive cargo in a tank sharing a bulkhead with a cargo that will be heated
Heat passing through a common bulkhead can raise the temperature of a heat-sensitive or self-reactive product beyond its safe limit, or damage its quality. The cargo plan must consider adjacent temperatures as well as chemical compatibility and segregation.

30. Before loading a heated cargo, why are the heating coils of the tank pressure-tested?

  • A. To ensure there are no leaks that could let cargo into the heating system or heating medium into the cargo
  • B. To calibrate the tank temperature sensors
  • C. To verify the setting of the P/V valve
  • D. To remove air from the cargo lines
Answer: A — To ensure there are no leaks that could let cargo into the heating system or heating medium into the cargo
A leaking coil can contaminate the cargo with water or thermal oil, or allow cargo to enter the heating system and condensate return, creating fire, toxicity or contamination hazards elsewhere on board. Coils are therefore tested and blanked if not to be used.

Printing this? Use your browser's Print (Ctrl/⌘ + P) — the buttons, the search box and the site chrome drop out and the questions run on as plain text, so a set fits a few pages. Filter to one set first if you only want that set on paper.

Practise these CHEMCO questions as a timed paper All 663 CHEMCO questions and answers CHEMCO exit exam sets and syllabus All 24 STCW exit exam courses

Send this CHEMCO answer key to your batch

Send on WhatsApp

More free tools for seafarers

Mariners DigestBrief for seafarers, Tue–SatSIRE PRO: Ship InspectionTanker inspection prepRightShip ProRISQ 3.2 dry-cargo inspection prepCOLREGS ReaderRules of the road, read aloud