Types of Chemical Tankers
The trainees should have a general knowledge about the important stages in the development of Chemical tankers and bulk chemical shipping. This is a brief view of the manner in which Chemical tankers and the bulk chemical shipping have evolved over the years.
The important stages in the development of bulk chemical shipping are:
- sea transport of chemicals started with the chemical industries rapid growth in the years after World War II
- at first chemicals were transported in bottles or drums on dry cargo ships; larger quantities were shipped in bulk in the deep tanks on these ships
- as the world’s demand for chemicals increased, the need for a new type of seagoing ship became evident
- the first chemical tankers were converted war-built American oil tankers (T2 tankers)
- conversion work usually included adding bulkheads to provide more and smaller tanks extending the line system – installing additional cargo pumps
- the first conversion of this type was done in 1948 on the R.E. Wilson, of 9073 tons gross tonnage
- in addition to these converted, relatively big chemical carriers, smaller tankers specially designed and constructed for the carriage of “acids” – e.g. sulphuric acid, were built during the early 1950s, the cargo tanks of which were made of special alloy steel, strengthened for cargo densities up to 2.0 kg/1
- in order to carry chemicals of high purity and sensitive to contamination, coating techniques were developed for cargo tanks of mild steel
- the first real chemical tanker specially designed for the carriage of liquid chemicals in bulk was the Norwegian M/T Lind, delivered in 1960; this was the first tanker equipped with stainless-steel cargo tanks
- a modern chemical tanker has a large number of cargo tanks and is designed for carriage of a wide variety of cargoes
- the cargo-tank section on these modern ships is normally divided into some stainless steel tanks and some coated mild-steel tanks, each of which is normally equipped with deepwell pumps and a separate piping system
Chemical tankers are required to transport a wide range of different cargoes, and many tankers are designed to carry a large number of segregated products simultaneously. The operation of chemical tankers differs from any other bulk liquid transportation operations, on a single voyage a large number of cargoes with different properties, characteristics and inherent hazards may be carried. Moreover, in port several products may be handled simultaneously at one berth, typically including different operations such as discharge and loading as well as tank cleaning. Even the less sophisticated chemical tankers are more complex to operate than oil tankers.
Transportation of bulk chemicals by sea not only requires specialist ships and equipment, but also specialist crew training, in both theoretical and practical aspect for those involved, in order to understand the characteristics of the various chemicals and be aware of the potential hazards involved in handling them. A particularly important aspect of this requirement is the provision of a data sheet, or cargo information form, giving details specific to a substance, which is required to be held on board whenever that substance is carried by the ship.
A modern chemical tanker is primarily designed to carry some of the several hundred hazardous products now covered by the IMO Bulk Chemical Codes.
The following general types of chemical carriers have developed since the trade began:
Sophisticated parcel chemical tankers Typically up to 40,000 tonnes deadweight with multiple small cargo tanks – up to 54 – each with an individual pump and a dedicated pipeline, to carry small parcels of high grade chemicals. These ships have a significant proportion of the cargo tanks made with stainless steel, allowing maximum flexibility to carry cargoes that need their quality safeguarded. The list of the important stages in the development of bulk chemical shipping is given in Part D 2, figure no.
Product / chemical tankers Of similar size to parcel tankers but with fewer cargo tanks, mostly of coated steel rather than stainless, and less sophisticated pump and line arrangements. Such ships carry the less difficult chemicals, and also trade extensively with clean oil products.
Specialised chemical carriers Small to medium sized ships, often on dedicated trades and usually carrying a single cargo such as an acid, molten sulphur, molten phosphorus, methanol, fruit juice, palm oil and wine. Cargo tanks are coated or stainless steel according to the trade.