What are Chemical Tankers – Types, Designs, and Regulations
A large portion of the global trade supply chain system is based on maritime transport and relies on commercial shipping for the transportation of liquid cargoes.
When we think of liquid cargoes, we first think of oil tankers, vessels carrying oil and gas-related products. Chemical tankers are another type of commercial vessel that transports liquid bulk cargoes.
As the name suggests, a chemical tanker is a commercial cargo ship designed to transport bulk liquid chemicals from one location to another. Chemicals are widely purchased, distributed, supplied, processed, and consumed for a wide range of uses, from industry to agriculture to households.
Chemical Tankers
Chemical cargoes can vary widely, but inorganic chemicals such as acids, alcohols, toluene, and benzene are the most common. Other chemical tanker cargoes include organic products for agricultural or domestic use, organic and inorganic oils, some specialty chemicals for medical purposes, biofuels, and more.
The design concept of a chemical tanker is similar to that of an oil tanker and is based on the following key considerations:
Similar to oil tankers, chemical tankers carry large quantities of liquid cargo.
Cargoes are often highly flammable, as these hazardous chemicals not only have extremely low flash points but are also highly reactive, making them highly susceptible to fire.
The high reactivity of chemical tankers poses a significant risk of hull disturbance.
Even a small leak or release of these substances into the environment can cause significant water and air pollution.
About Design and Construction
Practically speaking, chemical tankers are smaller than oil tankers, with a deadweight capacity ranging from 5,000 to 50,000 dwt.
The small size of these vessels is due to a variety of factors, including port restrictions on handling these hazardous substances, restrictions on the passage of these hazardous chemicals through sea lanes, the specialized nature of the cargo, and, of course, the lower demand for chemical transport compared to other similar traditional cargoes, such as oil and gas or bulk cargoes.
However, because the bulk liquid cargoes they transport are classified as dangerous goods, the design and construction rules, guidelines, and regulations for chemical tankers are more stringent than those for oil tankers.
Generally speaking, the hull shape of chemical tankers is similar to that of other traditional commercial vessels, such as oil tankers or bulk carriers. These ships do not require high speeds. They are primarily powered by durable diesel or diesel-electric propulsion systems, which provide sufficient power to navigate in all sea conditions while ensuring a continuous fuel supply to keep onboard systems operating smoothly.
The main distinguishing or distinctive features of chemical tankers are their internal structure, cargo holds, and the various systems used to transport these dangerous goods in bulk, which we will briefly discuss.
Regulations
One of the most important foundations for the carriage of chemicals on chemical tankers is MARPOL Annex II (the Pollution Control of Noxious Liquid Substances in Bulk), which regulates the carriage of hazardous substances by sea in any quantity.
MARPOL Annex II technically defines chemical tankers as “ships presumed to carry noxious liquid cargoes in bulk.” This definition is found in Chapter 17 of the International Bulk Chemical Code (IBC Code), which forms the core of chemical tanker design and construction.
The IBC Code is a set of rules, guidelines, specifications, and warnings covering the carriage of hazardous chemicals in bulk by sea. Therefore, all chemical tankers are, by default, governed by the IBC Code. These special requirements, or supplements, are considered to be derived from Annex II of MARPOL.
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The International Bulk Chemical Code was adopted by the Maritime Safety Committee (MSC) and the Marine Environment Safety Committee (MEPC) of the International Maritime Organization (IMO) in 1983 and 1985, respectively, and entered into force in 1986. The Code was last amended in 2004.
The IBC Code officially replaces the Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk (BCH Code), which applied to all chemical tankers built before July 1, 1986. However, these nearly four-decade-old ships are currently being phased out, and the IBC Code is the globally recognized code for all new construction and conversion projects for chemical tankers.
The BCH Code remains a Special Recommendation under the 1974 SOLAS Convention (Chapter 7), supplementing the IBC Code when needed.
In addition to MARPOL Annex II, which governs the applicability of the IBC Code, Chapter 7 of SOLAS, another core pillar of IMO guidance, also addresses the importance of the IBC and its relevance to the scope of work of chemical tankers.
In contrast, both the IBC and BCH reference MARPOL and SOLAS within their chapters, highlighting the interrelationship between the original regulations and these specialized regulations, which are detailed standards that clearly define requirements for the transport of hazardous chemicals. Any changes or amendments to IMO regulations regarding these hazardous chemicals will be reflected in these specialized regulations, and vice versa.
In addition to the IBC Code, chemical tankers must also comply with rules established by classification societies, all of which are based on these regulations.
Thus, in short, the following rules and framework generally govern the design and construction of chemical tankers:
- MARPOL Annex II
- IBC Chemical Cargo Code
- BCH (applicable to older ships and applicable under the requirements of the 1974 SOLAS Convention)
- SOLAS (Chapter VII)
- Applicable Classification Rules
Classification of Noxious Liquids and Types of Chemical Tankers Based on the IBC Code
Chemical tankers carry a wide range of chemicals, from acids to alcohols, with denatured acids, alkanes, ethers, and paraffins posing the greatest risk. A key foundation for the IBC Code is Chapter II (Regulation 6) of MARPOL Annex II, which classifies noxious liquid substances carried by sea into Classes X, Y, and Z.
These three categories are categorized by their degree of hazard and potency, with X representing the highest and Z the lowest. Furthermore, substances not falling into these categories are classified as pollutants or other substances under the relevant regulations.
In addition to the IBC Code and other fundamental regulations of MARPOL Annex II (such as Regulation 13 on the Control and Management of Hazardous Substances at Sea), the IBC Code also influences and sets the framework for the design and construction of chemical tankers.
Based on the hazard index of these hazardous substances, the IBC Code classifies chemical tankers into three categories:
Category 1: Ships carrying hazardous substances that pose the greatest risk and cause the greatest harm.
Category 2: Ships carrying substances that pose a significant risk and have an adverse effect on the environment.
Category 3: Ships carrying substances that are less hazardous but require containment.
Of note here is Chapter 17 of the IBC Code, which clearly lists the substances permitted to be transported by all classified chemical tankers and specifies specific data, such as determining the ship category (1, 2, or 3) based on the cargo type (X, Y, or Z). Other important details include tank type, required dimensions, required materials, fire protection measures, etc.
For example, alkyl phosphate ester mixtures are considered highly hazardous substances and are therefore classified as Category X (column 1) and must be transported using Category 1 (column 3) vessels. Similarly, non-trace alkanes are considered low-hazard substances (Category Z) and must be transported using Category 3 vessels.
However, substance categories do not necessarily correspond to the intended vessel type. For example, acetonitrile, although a Category Z substance, must be transported using Category 2 vessels, not Category 3 vessels.
Characteristics of Chemical Tankers
In practice, the design parameters for chemical tankers are specified in multiple sections and regulations of the IBC Code. Without going into detail, we will first review some key characteristics of these vessels:
Hull Structure: All modern chemical tankers utilize a double hull design, complying with the regulatory requirements of the International Convention for the Safety of Life at Sea (SOLAS) and the International Convention for the Safety of Life at Sea (MAPROL) (as well as special requirements such as IBC and BCH). Cargo (like in oil tankers) is stored solely in the center tank, while the double-bottom wing tanks are used for other utilities, such as fresh water and ballast water.
Chemical tankers are reinforced both longitudinally and transversely to withstand various external and internal loads, as well as dynamic loads that can vary over time due to the irregular movement of the high-density liquid chemical cargo.
Another key feature of these ships is the lack of stiffeners in the hold areas, which facilitates cleanliness and reduces the accumulation of chemical waste. Instead, transverse stiffeners are added to the deck area to compensate.
Compartment Division and Compartment Segregation: Because these ships carry high-risk cargoes, regulations require them to be divided into additional sub-compartments to improve their resilience and reduce the environmental damage caused by leaks.
Furthermore, the greater compartment division of chemical tankers helps reduce risks such as liquid cargo leaks, which can pose additional risks, including fires caused by sudden movement and friction of cargo within the holds, as well as high transient pressure loads on primary structural members.
Even the smallest chemical tankers have at least two compartments, while this is only true for oil tankers exceeding 150 meters in length. Stability Guidelines: Stability is crucial for these ships, as poor stability can lead to serious problems such as overheating, fires caused by excessive cargo movement, and spills. Even under adverse conditions, the regulations allow the ship to heel a maximum of 25 to 30 degrees.
Cargo, Tanks, and General Provisions: This is one of the most critical aspects of a chemical tanker. Chapters II and III of the IBC Code primarily address the stowage and arrangement of cargo, internal arrangements, and the design of holds or spaces within these vessels.
Chemical Tanker Deck
The design and location of tanks must consider the potential hazards of the cargo, how to minimize its impact on the ship’s stability and maintenance, and how to properly clean and maintain them after unloading operations. Cargo hold openings are one of the most critical aspects of a material tanker.
These holds must be spacious enough to allow for safer access to work below (such as cleaning and maintenance) while also serving as vents to release hazardous gases that accumulate from chemicals. However, in some cases, such as in high-pressure areas like the bottom floor, these openings are kept to a minimum to limit overall durability losses.
For practical purposes, cargo holds are typically filled to capacity, but some headroom is left to allow for ventilation and prevent overpressurization.
Chemical tanker tanks come in four main types: (a) self-contained tanks, (b) modular tanks, (c) gravity tanks, and (d) pressure tanks. The use of these types depends on the gravity of the cargo being stored. However, self-contained tanks are best suited for transporting highly hazardous chemicals with low flash points because they do not transfer heat to the cargo.
Cargo Maintenance and Storage: The IBC Code emphasizes four key aspects of transporting this type of dangerous goods: a) moisture protection; b) cushioning and insulation; c) drying and temperature control; and d) ventilation.
The essence of moisture protection is the continuous supply of inert gas to the cargo and its associated piping to reduce the risk of explosion due to low oxygen levels. The inert gas is supplied by a constant-power pump system.
Insulation is crucial. Chemical tanker cargo holds utilize durable, multi-layer insulation certified by recognized organizations. A wide variety of insulation materials are available, including polyurethane foam, mineral wool, and perlite.
Chemical tanker temperatures are primarily controlled by heating or cooling coils, depending on the cargo’s needs. These vessels’ heating and cooling systems are strictly regulated and require regular maintenance to ensure optimal performance. Finally, ventilation is a crucial aspect of transporting dangerous goods. Chapter 8 of the IBC Code discusses ventilation for different types of chemicals.
Materials: The IBC Code does not specify the construction materials for chemical tankers, which primarily comply with class standards. Construction materials are primarily mild steel and stainless steel. Vessels designed to transport a single type of chemical are simpler to build, while vessels designed to transport multiple chemicals are more complex.
The choice of cargo tank material depends on the type of chemical being transported. For example, austenitic stainless steel is more corrosion-resistant and therefore suitable for highly reactive chemicals. Other types of steel, such as molybdenum-free steel, are more suitable for transporting less corrosive chemicals. In chemical tankers, there is a fundamental balance between the strength and reactivity of the chemicals.
