APC Article Reprints

Coating selection for small tankers is a strategic choice
Tanker Shipping & Trade


Chemical and product tanker owners are faced with the daily challenge of maximizing their profitability while being able to carrying high end cargoes. In the past they would need to specify stainless steel tanks to ensure high product purity; now there is the option of specifying MarineLine® coatings at ‘one third of the cost.’

MarineLine is based around a unique polymer technology that provides an impermeable barrier to protect cargo tanks from chemical attack and keep the steel intact. However, the key benefit is the coating’s ability to resist cargo absorption. Hundreds of chemical and product tankers currently trade with this coating installed.

When properly applied and cured, MarineLine creates an extremely smooth, hard and slick surface. This cargo resistance is created by the highly cross-linked polymer structure of the coating. A polymer is used in the formulation to create a barrier.     

MarineLine Coating application

Heat curing a MarineLine coating in a cargo tank at a Turkish shipyard

Because the coating is impermeable, it limits the possibility of cross cargo contamination and maintains product purity from port to port. It also supports efficient tank cleaning and therefore fast vessel turnaround times.

Cleaning chemicals can destroy zinc coatings when cleaning from a dyed petrol, gas oil or vegetable oil to methanol or mono ethylene glycol (MEG). Tank cleaning is also a time and energy intensive process.

Epoxy coatings have very high absorption properties, especially with a cargo such as methanol, and have high restrictions for cleaning and cargo loading. In addition there are strict cargo restrictions on the carriage of edible oils and other sensitive chemicals.

While stainless steel tanks have carried sensitive cargoes for years, there are considerable costs associated with their use. This starts with the cost of construction and continues through maintenance, passivation and cleaning.

Passivation of tanks is expensive and dangerous; however, is necessary at various points throughout a cargo tank’s lifecycle. In addition, stainless steel has inherent problems with chloride attack, making cleaning the tanks a costly business as fresh water or treated seawater is required.

In 2008 independent testing laboratory, Marinspec Associates (MA), investigated the absorption and retention of chemical cargoes in organic cargo tank coatings prior to the carriage of vegetable oil cargoes.

In 2009, MA then compared the transmission characteristics of MarineLine® 784 against a typical zinc silicate coating, a typical epoxy phenolic coating and stainless steel. The following surfaces were evaluated:

  • mild steel coated with an industry standard ethyl zinc silicate coating
  • mild steel coated with an industry standard epoxy phenolic coating
  • mild steel coated with MarineLine® 784 coating
  • stainless steel, grade 304

MA investigated the cargo absorption (and retention) characteristics of each of the five surfaces under the same operational conditions, with a view to comparing the contamination threat that each surface posed after exposure to styrene monomer and ethylene Dicholoride, to subsequently load ambient-temperature and high melting point vegetable oils. The objective was to compare MarineLine coatings against stainless steel and inorganic coatings under the international industry rules for the carriage of edible oils in ship's cargo tanks.

The conclusion was clear: MarineLine out-performed the phenolic epoxy and matched the performance of stainless steel and inorganic coating in ensuring edible oil purity when tested respectively with styrene monomer and EDC as immediate last cargoes.

This paper is an edited version of a longer paper presented during March at the Tanker Shipping & Trade Asia conference by Douglas Robinson, president, Asia division, Advanced Polymer Coatings