Liquefied Gas Carrier

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Pre-arrival check items by a gas carrier before a terminal alongside

The daily operation of a liquefied gas carrier involved potential hazards. It should be noted that cargo pipes, valves and connections and any point of leakage at the gas cargo may be intensely cold. Contact may cause severe cold burns.

Pressure should be carefully reduced and liquid cargo drained from any point of the cargo transfer system, including discharge lines, before any opening up or disconnecting is begun.

Some cargoes such as ammonia have a very pungent, suffocating odour and very small quantities may cause eye irritation and disorientation together with chemical burns. Seafarers should take this into account when moving about the vessel, and especially when climbing ladders and gangways. The means of access to the vessel should be such that it can be closely supervised and is sited as far away from the manifold area as possible. Crew members should be aware of the location of eye wash equipment and safety showers.

Everyone involved in liquefied natural gas trans- portation takes safety very seriously. There are many lives and a great deal of money at stake. Government and industry work together to make sure these ships are designed, maintained, and manned with safety in mind; industry maintains them with oversight by periodic government inspection, and government sets the standards for crew training.

The popular perception of liquefied natural gas is that it is inherently dangerous. While it possesses a set of hazards that need to be managed, when look- ing at the actual incidents involving liquefied natural gas, there are very few that put the surrounding area and public in danger. The rigorous attention to detail, coupled with the constantly emerging tech- nology, should continue to give LNG one of the bet- ter safety records for a hazardous material.

Within 5 days of the ship’s estimated time of berthing, the following checks and tests shall be carried out, and the results recorded. These records are to be made available to the gas terminal upon request.

(1) Deck water spray line

(2) Water curtain

(3) Gas free condition of hold space

(4) Alarm function of fixed gas detection equipment

(5) Cargo gauging system and alarm set points.

(6) Emergency Shutdown System (ESD), all the relevant system shall be tested prior to arrival port and time needed to shut should be confirmed around 25 up to 30 seconds.

(7) Operation of cargo system remote control valves and their position indicating systems.

(8) Confirm Cargo transfer emergency stops fully operational and date of last test.

(9) Confirm tank high level and pressure alarms operational.

(10) Confirm that remotely operated manifold valves have been operated through a complete open/closed cycle, functioning and advise valve type(ball, gate, etc)and actual closing time. The corresponding records shall be produced by the master on the ship arrival at berth. Any defects or deficiencies must be reported to the terminal as an addendum to the Pre-Arrival information notice

(11) Deep well cargo pump and booster pump mechanical seals are free of oil leaks.

What is Custody Transfer Measurement (CTM) System on board gas carrier?

(1) The CTM is a system which allows the quantity of cargo on board at any time to be accurately calculated and therefore provide a means by which the amount of cargo that is transferred either internally or between the ships and shore to be accurately quantified. Such a system can be used on LNG carriers because the cargo is always same whereas on other type of vessels such as oil or LPG, large differences can occur between the cargoes carried on each voyage.

(2) There are two primary types of measuring system used currently on LNG carriers:

i) Based on capacitance measuring system
ii) Based on radar gauging system

(3) The verification and accuracy check of custody transfer measurement system is conducted at each dry dock.

Records of the calibration of key cargo instrumentation, including temperature and pressure gauges

(1) There should be records of the regular checking and calibration of instrumentation, particularly cargo tank temperature and pressure gauges and reliquefaction plant instruments.

(2) Calibration should be carried out preferably at intervals not exceeding 30 months.

(3) Calibration of instrumentation is often difficult whilst the vessel is in service and it is usually carried out during repair periods. However, comparisons between local and remote thermometer readings and cross checking with cargo vapour pressure (from tables) provide a practical cross-reference, particularly for high purity cargoes such as Polymer Grade Propylene.

Related Information:

  1. General precautions and instructions for gas carrier

  2. Cargo machinery room safety precautions

  3. Toxicity and associated health hazards in liquefied gas carrier

  4. Liquefied gas cargo handling equipment

Cargo Information - physical and chemical properties necessary for the safe containment of the cargo

Liquefied gas carrier safety training

Procedures for LNG cargo loading

Procedures for LNG cargo discharging

Rollover effect of LNG cargo and countermeasures

Boil-off & Vaporized Gas (BVG) Management System for LNG cargo

Liquefied gases - How to remove all cargo liquid from tanks

External links :

  1. International maritime organization

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