Marine Engineering Study Materials

Most early chemical tankers were slightly modified product tankers, in which the main variation was coating of the cargo tanks. Although many of the products shipped could be carried quite safely in uncoated mild steel tanks, the need to maintain product quality, to minimize the potential for discoloration, and to facilitate tank cleaning between cargoes led to tank surfaces being coated with an impervious material.

As the shipment of bulk chemicals developed, different countries involved with the trade developed regulations to minimize the risk to the ship, its crew and the environment, and applied them to their own ships and ships trading to their ports. These regulations were not an the same, and it was extremely difficult for a ship and its crew to comply with them all.

To establish an international standard for the safe design, construction and equipment of chemical tankers, IMO developed the Bulk Chemical Codes. It was a major step forward. A ship that complies with the IMO Codes is issued with a Certificate of Fitness that is recognized internationally, and enables the ship to trade worldwide carrying the cargoes for which it is approved. The cargoes now carried in these ships range from petrochemicals used as feedstock for plastics or synthetic rubbers and fibers, industrial acids and alkalis, alcohols and solvents, highly refined lubricating oils and lubricating oil additives, to detergents, animal and vegetable oils, and edible products such as fruit juices or wine.

Furthermore, certain refined petroleum products that were previously considered to be oils are now classified as chemicals under IMO marine pollution or toxicity regulations, and must only be carried by chemical tankers. In addition to MARPOL 73/78 there are two IMO Codes applicable to chemical tankers:

• Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk (the BCH Code). This was first adopted by IMO in 1971 as voluntary guidelines providing advice to the industry and to authorities. Under the subsequent provisions of MARPOL Annex II , chemical tankers constructed before 1 July 1986 and engaged in international trade must comply with this Code.

• International Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk (the IBC Code). This was adopted by IMO in 1983. Under the provisions of SOLAS Chapter VII and MARPOL Annex II all chemical tankers constructed on or after 1 July 1986 must comply with the provisions of this Code.

Both Codes have been amended several times since their adoption, in order to keep them up to best practice in the industry. The IBC Code also contains the current requirements for safe handling of cargoes, and should be available on board for reference regardless of the age of the ship. The relevant Code or Codes applying to a particular ship must be carried on board. The IMO Codes are intended to produce a uniform set of regulations, allowing a ship to be issued with a Certificate of Fitness indicating compliance with the relevant Code. The certificate is accepted by the nations to which the ship may trade as an assurance of the ship’s constructional safety, in a similar way to the international acceptance of Safety Equipment, Safety Construction, Load Line and other certificates issued to signify compliance with IMO standards. As with other certificates, the Codes require periodic re-inspection of the ship during its lifetime to maintain validity. The implementation of these international regulations is through the approval by national administrations of a Procedures and Arrangements (P&A) Manual, individually developed for each ship.

MAIN REQUIREMENTS OF THE IMO CODES

The IMO Codes address the safety of everyone involved and protection of the environment by ensuring that the ship will remain afloat after an assumed extent of damage, thereby minimizing potential pollution and the uncontrolled release of cargo that could follow if a ship sank. They set detailed requirements for specific aspects of the ship: materials of construction; the separation of cargo, accommodation and machinery spaces; segregation of different types of cargoes; controls and instrumentation for cargo handling equipment; control of conditions within cargo spaces and venting from them; piping and pumping arrangements; electrical installations; fire fighting and extinguishing systems; and personal protective equipment. The IMO Codes then list cargoes, identifying the hazards each presents during carriage by sea. Cargoes which are assessed as presenting a safety or pollution hazard to such an extent as to warrant protection are required to be carried in designated ship types providing the appropriate degree of protection.

Three ship types are prescribed, with the most hazardous cargoes receiving the most protection through further requirements applied to individual cargo tanks. Chemicals in bulk are classed into three types:

1. Type 1‘ ship is a chemical tanker intended to transport Chapter 17 of the IBC Code products with very severe environmental and safety hazards which require maximum preventive measures to preclude an escape of such cargo.

2. Type 2‘ ship is a chemical tanker intended to transport Chapter 17 of the IBC Code products with appreciably severe environmental and safety hazards which require significant preventive measures to preclude an escape of such cargo.

3. Type 3‘ ship is a chemical tanker intended to transport Chapter 17 of the IBC Code products with sufficiently severe environmental and safety hazards which require a moderate degree of containment to increase survival capability in a damaged condition.

In addition, tank construction type for containment, venting requirements, gauging equipment, vapour detection, compatible fire protection medium, heating requirements, inhibition requirements, density limitations of the product in relation to the cargo tank, and pumping requirements are important considerations. Most of this information is set out in the IBC or BCH Code. In addition, the vessels also need to take into account the information contained in safety data sheets, applicable load-line zones encountered during the voyage, changes in sea/harbour water densities, bunker quantities and disposition, the loading sequence of each grade, final quantities/ullages, charterers‘ options on cargo lift requirements, segregation requirements, valve line-up and the line-up and sequence of concurrent ballast operations.