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Cargo sampling & manifold arrangement for liquefied gas carriers
Why Sampling ?
Cargo is normally sampled by shippers’ or receivers’ personnel, or by authorised petroleum inspectors.
The responsible officer must, however, be present when sampling is carried out to ensure that samples
are taken from correct sampling points and that this is performed in a correct and safe manner. He is
to also make a proper record of the samples taken as these may be of considerable value
subsequently. A good rule is to request samples to be taken from the liquid shore connections at the
start of loading to safeguard against possible contamination of shore transfer lines.
The following precautions are to be observed when sampling cargo liquid or vapour:-
(a) The sample container must be completely clean and compatible with the cargo to be sampled
and is to be able to withstand the extremes of temperature and pressure anticipated.
(b) Sample containers must be purged of air by pure nitrogen before use with flammable cargoes.
(c) If the sample is to be representative its container has to be purged thoroughly with cargo from
the sampling connection. Sufficient cargo must be passed through the container to cool it down to
liquid temperature. If the cargo is a mixture (which is often the case) the most volatile components
will evaporate more rapidly than the heavier fractions as the container is cooled down; this will leave
the sample with a higher concentration of the heavy fraction than present in the cargo, and it will
therefore be unrepresentative.
To counteract this, sample containers are to be turned with the vent
valve downwards during cool down, to drain off the liquid that first collects. For the same reason,
samples from the bottom of cargo tanks at the beginning of, or just after, loading may not be
representative. It is recommended that the cargo is circulated using the cargo pump, if possible,
before taking bottom samples.
(d) It is imperative that sufficient ullage or vapour space is left in the sample container to allow for
the liquid expansion that will occur when the temperature increases to ambient. Ullage is obtained by
holding the full sample container upright after disconnecting it from the sample connection and draining
some liquid by opening the bottom valve for a moment.
(e) Unless the sample container is free of cargo vapour, it should not be stored in an unventilated
(f) Gloves, goggles and protective clothing must be worn when sampling cold cargoes.
(g) If the cargo is toxic, a suitable respirator, or preferably self-contained breathing apparatus,
must be worn. If sampling in an enclosed space, a respirator is unsuitable, due to the possibility of
asphyxiation, then breathing apparatus is necessary.
(h) If electrical equipment is used when taking samples this is to be of the certified-safe type.
(a) Appropriate precautions as stated above paragraph (a), (b), (c), (f), (g) and (h) are to be observed when sampling
cargo vapour or inert gas.
(b) Plastic sample bags are sometimes used for collecting vapour samples. These must be handled
carefully, never used for liquid samples and always purged after use.
(1) The manifold area should be clear of obstructions which could interfere with the automatic release of a hard arm.
(2) Pressure gauges should be regularly checked during the discharge for manifold valve leakage.
(3) All flange connections should be fully bolted.
(4) This includes any line which is being used for, or might become pressurized during, cargo operations on both sides of the vessel.
(5) The manifold valves and lines should be clearly marked as to whether they are liquid or vapour.
(6) The manifolds fitted with drain lines and purge points should be valved & capped.
Custody Transfer Measurement (CTM) System
Records of the calibration of key cargo instrumentation, including temperature and pressure gauges
The high level alarm system
Gas analyzing equipment
Decontamination showers and an eye-wash
Gas cargo containment systems - primary barrier (the cargo tank),secondary barrier, thermal insulation and more
Discussion prior to cargo transfer in liquefied gas carrier
Safety checklist for gas carrier
Tanker Cargo Operations Logbook
Connecting Bonding Cable
Safety checklist for gas carrier
Reactivity of liquefied gas cargo and safety guideline
Procedure for loading Liquefied Gas Cargoes
Procedure for Cargo Conditioning in Liquefied Gas Carriers
Procedure for segregation of Liquefied Gas Cargoes
Procedure for Stripping Liquefied Gas Cargoes
Procedure for Changing Liquefied Gas Cargoes
Displacing Atmosphere with Inert Gas (Inerting)
Maintaining tank pressure during a laden voyage
Liquefied gas carrier safety training
Tackling fire onboard liquefied gas carrier ship
LNG spill risk during marine transportation and hazards associated
Inerting of Cargo Tanks prior loading LNG cargo
Gassing-up requirement for cargo tanks
Preparation for Cargo Transfer
Procedure for discussion prior cargo transfer
Defining various gas carrier types
Fuel flexibility of LNG ships
LNG ship spillage risk
Initial Cool Down of cargo tanks
Leaks on the Cargo System, Continuous Flow - how to prevent
LNG tank leaks and immediate action by gas carriers
Leaks from a Loading Arm due to Tidal or Current Effects
Minor or major leaks from LNG tanks
Procedures for LNG cargo discharging
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