ISSUE 12 // AUGUST 2024 BRITANNIA LOSS PREVENTION TANKER SHIPS ARE DESIGNED TO TRANSPORT VARIOUS TYPES OF PRODUCTS AND CHEMICALS, AND THEIR ONBOARD TANKS REQUIRE SPECIALISED COATINGS TO ACCOMMODATE A WIDE RANGE OF CARGO TYPES. ESSENTIAL GUIDE TO TANKER SHIP COATINGS A reliable and effective tank coating prevents water and corrosive agents from coming into direct contact with the metal surfaces, reducing the likelihood of structural damage and preventing cargo contamination during transportation. Therefore, it is essential to understand the significance of tank coatings and how they can impact claims and risk management. OUR PARTNER FOR THIS ISSUE With over 70 marine surveyors and consultants worldwide, Van Ameyde Marine is one of the largest single service providers for the marine industry. Van Ameyde Marine This article outlines the primary types of tank coatings, their basic properties and their limitations. TYPES OF COATING SEVERAL TYPES OF CARGO TANK COATINGS ARE AVAILABLE, EACH WITH THEIR OWN PROPERTIES AND ADVANTAGES FOR VARIOUS PRODUCT TYPES. STAINLESS STEEL Stainless steel is technically not a coating. However, it is a common tank lining found on the majority of chemical tankers. Commonly used alloys in the tanker industry include: 316 and Duplex stainless steel. The 316L or LN-graded alloys are predominantly used where the surfaces in between cargo tanks are made of solid stainless steel and the surfaces between cargo tanks and adjacent ballast tanks or void spaces are cladded. “Cladded” implies a three-millimeter stainless steel layer has been applied to the construction steel of the vessel. One distinctive property of stainless steel is the presence of a chromium-oxide layer, often known as the “passive layer”. This ultra-thin layer, measuring about three-nanometers in thickness, serves as a protective barrier between the stainless steel and the product carried in the tank. This passive layer may deteriorate over time when exposed to specific cargoes. Nevertheless, stainless steel has the natural capability to regenerate this passive layer when it interacts with oxygen. The integrity of the chromium-oxide layer is commonly referred to as “passivity”. To facilitate the complete restoration of the chromium-oxide layer in stainless steel, it is recommended that stainless steel cargo tanks are exposed to air for a duration of 24 to 72 hours after tank cleaning. However, this may not always be achievable due to quick turnarounds where discharging, tank cleaning and loading are carried out consecutively. Following the repeated carriage of potentially aggressive cargoes, such as acids, the chromium-oxide layer may not be fully restored. This can be attributed to to the presence of contaminants, primarily consisting of free iron molecules originating from the stainless steel. To facilitate the steel to regenerate it’s protective passive layer, a process known as “passivation” is conducted. During this process, a solution of nitric acid or citric acid is circulated in the cargo tanks via the tank cleaning equipment. The acid effectively removes the free iron impurities. Subsequently, the tanks undergo thorough washing and are left exposed to air (oxygen) for some 72 hours. During this time, the chromium within the stainless steel alloy reacts with the oxygen to form the passive layer to its full extent. Ship crews can carry out passivation, but extreme caution and careful handling should be exercised. Additionally, another process cal