Factors Influencing Early Crack Development in Marine Cargo and Ballast Tank Coatings

Abstract Stress development in epoxy coatings applied in water ballast tanks (WBT) on ships can lead to cracking, corrosion, and failure of ship's hulls, with catastrophic consequences to the environment as well as loss of seamen at sea. Typically these cracks do not appear during application and curing of the coating but after some finite time of service. The financial well being of the ship’s owner can suffer greatly. To avoid such cracking it is critical to have a clear understanding of the underlying mechanisms and primary controlling factors behind the coating cracks. In this paper we review some of the primary contributing factors that produce the internal coating stresses that produce the cracking. These include the following: 1) Initial coating shrinkage from chemical cross-linking; 2) Thermally induced stress; 3) Increase in stress due to loss of migratory specie from free-volume within the binder polymer matrix such as solvents and binder extenders; 4) The effect of steel-structural strain; and 5) How the flexibility of the coatings change after the coatings age. The primary root causes to the early cracking phenomena of epoxy coating in the ship’s water ballast tank will then be offered along with suggestions on how to alleviate some of the problems seen.