Prolonged delays for vessels carrying Australian coal to China
Dr Martin Jonas, Director of Science UK and Dr Penelope Cooke, Managing Scientist have joined with the UK P&I Club for an article about the hazards faced and necessary precautions to be taken by vessels delayed with Australian coal at Chinese ports.
There are reports that vessels carrying Australian coal are still facing significant delays while they wait for authorisation to discharge in Chinese ports. Coal is listed as a hazardous cargo within Group B of the IMSBC Code and so vessels must follow the detailed requirements relating to gas monitoring, ventilation and pH monitoring of the bilges.
The recommended precautions are:
Gas monitoring (self-heating/methane emission hazards)
Coal shipments may self-heat and may (also) emit methane, as a result the levels of oxygen, carbon monoxide and flammable gasses (methane) must be monitored via the gas port. During lengthy delays gas monitoring should be conducted frequently and the results recorded and reported.
During a long delay, slow oxygen depletion is likely in unventilated cargo spaces for all coal cargoes. The most common type of gas meter employed on ships uses catalytic sensors to detect flammable gases (methane). This type of sensor does not function correctly in holds with depleted oxygen, and this may give rise to spurious high methane readings. Methane readings in holds with less than about 10% oxygen should be conducted with a gas meter equipped with an infrared sensor for flammable gas, or using a “splitter”-type attachment that augments the oxygen levels in the gas supply to the sensor.
pH monitoring (corrosion hazard)
The water draining out of some coals can be highly acidic and may cause corrosion to uncoated metal surfaces including tanktops, sounding pipes and/or bilge systems. To monitor potential corrosion damage to the vessel, the IMSBC Code requires all vessels carrying coal to be equipped to measure and record the pH value of cargo space bilge samples.
Regular bilge testing must be systematically carried out during the voyage and during any waiting periods or delays. If the pH monitoring indicates that a corrosion risk exists, the bilges should be frequently pumped out during the voyage to avoid possible accumulation of acids on tanktops and in the bilge system.
Based on past cases, the pH values may be acidic from the outset, or may decrease from neutral to acidic over time. In this event, expert advice should be obtained. If there is a concern about potential corrosion, a thorough inspection of the metal surfaces which have been in contact with the coal cargo or bilge water should be carried out after discharge.
A further consideration for vessels at anchorage is that depending on the distance from shore, they may not be permitted to the pump the bilges. However, reported cases of significant corrosion are relatively rare, and at this stage it is not known if there is an increased risk of corrosion for the vessels currently waiting off China with Australian coal.
The full article can be read here.
For those wanting more information about bulk cargoes, the comprehensive practical guide written by Dr Martin Jonas, Brookes Bell’s Director of Science UK and Brookes Bell’s (now retired) Master Mariner Charles Bliault, for the North of England P&I Association may be of interest.
The practical reference work covers; Safety, rules and regulations, Operations and maintenance, Identification, care and carriage, Understanding the hazards, Cargo specific information, The voyage and a Guide to basic records.