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Wet cargo operations > Chapter 3 > Flashcards

Chapter 3 Flashcards

1
Q

What happens if the tanks are not vented when cargo is loaded

A

over pressurisation will occur

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2
Q

When discharging the cargo volume being discharged must be replaced by what

A

an equivalent volume of atmosphere to prevent under pressurisation

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3
Q

Cargo tanks will be tested to what psi

A

3.4 / 0.245 bar

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4
Q

A pressure not exceeding minus what is allowed on the vacuum side

A

-0.07 bar
-1 psi

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5
Q

How many factors affect the design of venting systems and what are they

A

4
-loading rate
-maximum vapour flow velocity
-gas evolution
-obstructions to flow

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6
Q

How does loading rate for tanks affect venting systems

A

The higher the liquid flow rate (loading), the faster the vapour must be removed from the tank

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7
Q

What is the maximum vapour flow velocity

A

Typically 40 metres per second is used

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8
Q

What may happen to the volume of vapour flowing out of the tank

A

It may be greater than the volume of oil flowing into the tanks due to evaporation from the oil

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9
Q

What factor is required by SOLAS to allow for vapour generation

A

1.25 times the maximum loading rate

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10
Q

What obstructions to flow are used

A

Flame screen, pipeline friction, bends and valves in pipes

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11
Q

What does a P/V valve consist of

A

A weighted pressure disk and a weighted vacuum disk

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12
Q

In a p/v valve the weight of the disk is calculated so that what

A

They lift at a pre-set pressure

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13
Q

If the tans pressure exceed the lift pressure what will a p/v valve do

A

The weight will be lifted allowing pressure to be relieved to the outside atmosphere

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14
Q

If the tanks is subject to under pressurisation the vacuum created acts in the upper surface of the vacuum disk meaning the p/v valve will do what

A

The vacuum disk will lift allowing air into the tank

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15
Q

Where is a flame screen fitted

A

on the vacuum

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16
Q

Pressure vacuums operate at what measurement of water column

A

1400 mm
and at a vacuum of -250mm

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17
Q

What is cargo tank design pressure tested at

A

2,500 mmWG or 0.245 bars

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18
Q

SOLAS requires these P/V valves:

A

-be fitted at least 2m above the deck to disperse flammable vapours.

(SOLAS II/2 Regulation 6.6.2.1)
-be at least 5m horizontally from the nearest air intakes and openings to enclosed spaces containing a source of ignition and from deck machinery and equipment which may constitute an ignition hazard. Anchor windlass and chain locker openings constitute an ignition hazard.
(SOLAS II/2 Regulation 6.6.2.2)
These P/V valves are often incorporated into High Velocity Vent Valves.

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19
Q

What does HVVV stand for

A

High velocity vent valve

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20
Q

Why to fit a HVVV:

A

-A hydrocarbon mixture within the flammable range will have an open-air flame speed of 3 metres per second.

-If the flame is confined within a pipe the flame path is constricted and speed may exceed the sound’s speed.

-The resultant pressure wave could be catastrophic.

-If the exit velocity of the gas can be maintained above 3 m/sec then flame cannot travel back down the pipe.

-HVVV ensures the exit velocity is at least 30 m/sec thereby giving a factor of safety.

-For this reason, a flame screen is not required in the HVVV.

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21
Q

-HVVV ensures the exit velocity is at least __ m/sec thereby giving a factor of safety.

A

30

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22
Q

What is the exit velocity required by SOLAS

A

at least 30m/s

23
Q

Where do SOLAS require HVVV to be

A

at least 2m above deck level

24
Q

What is different about a PV breaker compared to a PV valve

A

They operate of higher pressure settings

25
Q

PV breakers are usually filled with what?

A

Liquid

26
Q

When do pV breaker open

A

during an abnormal increase in pressure on cargo tanks when loading rate exceed the max rate capacity, resulting in pressure inside the tanks

27
Q

Where are PV breaker fitted

A

inert gas deck main line

28
Q

When do PV valves operate

A

1- Cargo is to be discharged at the maximum rated capacity of the pumps and suddenly the inert gas blower fails, creating a negative pressure of more than -630 mmAq.

2-During loading operations where tanks are to be filled at maximum capacity by the cargo and all outlets are left shut and/or the mast riser fails, creating a positive pressure of more than 1890 mmAq.

29
Q

Why are mast riser generally carried on crude oil tankers

A

As they carry homogenous cargo and their cargo tanks have the same venting pipeline

30
Q

Max height of mast risers is

A

6m

31
Q

What will monitoring equipment provide

A

an alarm facility which is activated by the detection of over pressure or or under pressure conditions within a tanks

32
Q

What does VOC stand for

A

Volatile Organic Compound

33
Q

Marpoll annex 5 regulations against VOC

A

Air pollution from vessels:
-Engine exhaust
-VOCs
Damaging Ozone layer

Cargoes emitting VOCs:
Crude oil,
Gasoline,
Volatile cargoes,
Benzene

VOC manual (certified by the administration/classification society)

34
Q

What does VEC stand for

A

Vapour Emission Control

35
Q

Terminals who wish to set up VEC can do what

A

can require tankers to send all the vapours they would normally vent to the atmosphere back to the shore based MVEC which would process the vapours in an environmentally safe manner.

36
Q

What are the four hazards involved with VEC operations

A

Misconnection of vapour recovery lines

Over and under pressurisation

Cargo tank overfill

static elec

Fire and explosion

37
Q

On a tanker fitted with bottom lines, the discharge line from the cargo pump to the main deck is called the

A

Riser

38
Q

A conventional tanker fitted with bottom lines will also have

A

A pumproom

39
Q

Bottom line systems in which each line serves a group of tanks and is connected to its own pump is called

A

Direct line

40
Q

Tankers load and discharge cargo through the

A

Manifold

41
Q

When large tankers load and discharge the shore connection is called what?

A

Chiksan

42
Q

A tanker fitted with bottom lines is discharging cargo. Identify the lines used for discharging

A

Bottom line, riser, deck line, manifold

43
Q

A tanker fitted with bottom lines is loading cargo. Identify the lines used for loading

A

Manifold, drop line, bottom line

44
Q

As tankers become larger what is constructed in the cargo tanks to reduce the Free Surface Effect?

A

Longitudinal bulkheads

45
Q

On a tanker fitted with bottom lines the line connecting the manifold to the bottom lines is called

A

drop line

46
Q

Which publication contains a pro-forma checklist which is commonly used for ship/shore safety meetings?

A

ISGOTT

47
Q

Typical maximum pressure in a fully pressurised LPG carrier?

A

18 bar

48
Q

Fully refrigerated cargo tanks on LPG ships have the following characteristics

A

Large size, prismatic shape, low pressure

49
Q

Which convention requires tankers carrying oil to have slop tanks?

A

MARPOL

50
Q

Chemical and some product tankers don’t have bottom lines. In such vessels each tank has

A

Submerged cargo pump and loading line

51
Q

Final stripping of clean products from a tank with a submersible pump uses what source of energy to ‘push’ the cargo up the stripping line?

A

General service compressed air

52
Q

On a double hull tanker with bottom lines the ballast pipelines are located in

A

The ballast tanks

53
Q

When stripping with submersible cargo pumps on oil tankers, what is used to push the stripped liquid?

A

Compressed air

Wet cargo operations (9 decks)

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