Chapter 6

Question 1

Tanks are cleaned for
x4

Answer 1

quality control for next cargo
residue control
dry dock preparation
tank entry and inspection purposes

Question 2

Tanks may be washed with
x3

Answer 2

clean sea water
crude oil
or water/chemical mixtures

Question 3

Most tank cleaning can be successfully carried out with

Answer 3

clean sea water at ambient temperatures

Question 4

Residues that solidify may require washing

Answer 4

with heated water.
Tank cleaning heaters are fitted on most tankers for this purpose.

Question 5

Hot water washing should be carried out with a wash water temperature of
at least

Answer 5

60oC

Question 6

Tank cleaning chemicals should only be used in

Answer 6

extreme cases for removing
persistent residues or in preparation for particularly sensitive ‘next’ cargoes

Question 7

Tank cleaning is one of the most hazardous operations carried out on
tankers due to

Answer 7

vapour generation and the risk of electrostatic discharges

Question 8

Tank atmospheres may be _____ or non-_____

Answer 8

inert
inert

Question 9

ISGOTT gives operational restrictions on each of the

Answer 9

atmospheres defined

Question 10

Washing in an ________ atmosphere is preferred

Answer 10

inerted

Question 11

Tank cleaning machines may be portable or _____

Answer 11

fixed

Question 12

Portable machines are lowered into the tank on

Answer 12

flexible tank washing hoses

Question 13

The machines are driven by the pressure of the washing medium and rotate about both ____ to achieve ____ tank coverage by the ___

Answer 13

axis
full
jet

Question 14

_____ machines are located on the end of steel pipes connected to the washing main

Answer 14

Fixed

Question 15

Many _____ machines are programmable to allow the ____ to control which parts of the tank are washed

Answer 15

Fixed
user

Question 16

Efficient tank draining is required. Stripping _____ or ________ are used for this purpose

Answer 16

pumps
eductors

Question 17

Tankers over __,___ dwt that carry crude oil are required to ____ ____ ___
(COW)

Answer 17

20,000
crude oil wash

Question 18

Crude oil is drawn off from the main discharge of the cargo and directed

Answer 18

through the tank cleaning machines

Question 19

The pressure of the crude oil and its solvent effect achieve

Answer 19

a high level of tank cleanliness

Question 20

Some crude oils are not suitable for COW due to

Answer 20

their high wax content and/or viscosity or pour point

Question 21

MARPOL regulations dictate that all cargo tanks that will, or may, carry ballast plus 25% of the remaining tanks for sludge control purposes must be

Answer 21

cleaned prior to departure from the last discharge port

Question 22

COW can only be carried out with cargo tanks

Answer 22

inerted

Question 23

Fixed tank cleaning machines are required for ___

Answer 23

COW

Question 24

The ship will have a ___ Manual that details equipment and procedures to
be used

Answer 24

COW

Question 25

Advantages of COW x5

Answer 25

1. Reduced sea pollution 2. Improved cargo outturn 3. Reduced tank corrosion 4. More cargo deadweight available due to reduced residues 5. Less de-sludging time for dry dock preparation

Question 26

Disadvantages of COW x4

Answer 26

1. Higher workload during cargo discharge 2. Extended discharge time 3. Higher risk of pollution in port 4. More equipment and personnel required

Question 27

Gas freeing is required to create

Answer 27

safe tank atmospheres for cleaning or entry purposes

Question 28

Gas freeing can be carried out using portable fans, or

Answer 28

directing fresh air through the inert gas plant bowers

Question 29

Tanks can use the dilution or displacement method to change

Answer 29

tank atmospheres

Question 30

The dilution method relies on a high air input velocity to create

Answer 30

mixing

Question 31

The displacement method relies on a low air input velocity to maintain the

Answer 31

interface between the incoming air and the displaced tank atmosphere

Question 32

Full length purge pipes are some times used, especially when using

Answer 32

displacement method

Question 33

Tank atmospheres must be monitored for

Answer 33

oxygen content, hydrocarbon levels and the presence of toxic gases

Question 34

Combustible gas indicators (‘Explosimeters’) are used to measure

Answer 34

the hydrocarbon content as a percentage of the lower flammable limit

Question 35

Hydrocarbon meters measure

Answer 35

hydrocarbon contents above the LFL

Question 36

Some combustible gas indicators cannot be used in

Answer 36

oxygen deficient atmospheres

Question 37

A common type of oxygen analyser uses electrochemical detection cells which must be replaced at intervals usually...

Answer 37

12 to 18 months

Question 38

Toxic gas detectors rely on

Answer 38

an aspiration unit into which is placed a glass tube containing reactive crystals

Question 39

Toxic gas detectors rely on an aspiration unit into which is placed a glass tube containing reactive crystals * The crystals only react to

Answer 39

The specific substance being tested for

Question 40

A tank atmosphere should be tested in the following order:

Answer 40

oxygen content, ;hydrocarbon level and finally for toxic gases