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Coatings Cracking in Water Ballast Tanks: A Different Look

Mechanisms of corrosion and cathodic delamination resulting from the cracking of paint in a water ballast tank environment and what may be expected in the corrosive environment. This will be based on the concept of a thermodynamic barrier existing at the coating/steel interface.

Product Number: 51317--9088-SG
ISBN: 9088 2017 CP
Author: Carl Reed
Publication Date: 2017
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The cracking and subsequent corrosion in water ballast tanks has long been a problem for the maritime industry. The potential damage to ships’ hulls from this type of corrosion can be devastating and catastrophic. Consequently there has been much study into the root causes of coatings cracking over the years. These studies have primarily centered on the mechanical considerations of crack initiation and propagation. It has generally been agreed that cracking is due to stress in the film caused by film shrinkage loss of low molecular weight components strain within in the steel substrate and impact from environmental forces such as thermal expansion/contraction and hygroscopical volume changes.One facet of the cracking problem which has not been studied to any great degree is what happens after the crack has formed and corrosion commences. Worth considering is the extent corrosion and cathodic delamination progresses under the film at the crack point. Although corrosion is inevitable at the crack point limiting its progress can provide valuable savings in the repair of any corrosion damage.This study will look at the mechanisms of corrosion and cathodic delamination resulting from the cracking of paint in a water ballast tank environment and what may be expected in the corrosive environment. This will be based on the concept of a thermodynamic barrier existing at the coating/steel interface resulting from Lewis acid-base interactions between polymer and substrate.Although cracking is a cohesive failure and delamination is an adhesive failure it has not escape the authors’ notice that the very mechanism that may inhibit the progress of corrosion in an after the fact cracking situation may also contribute to preventing the cracking in the first place. A recent study on internal stresses and mechanical properties of paint films indicates that adhesion is probably the most important parameter. Adhesion however is not a fundamental property of the coating/substrate interface rather it is the consequence of the interaction between the polymer and the substrate. It is these interactions which must be understood to provide answers to the cracking issue. Examined in this monograph as well will be how these interactions the same Lewis acid-base interactions described previously in combination with shrinkage mitigating factors may be able to be used to prevent cracking and delamination of a coating in a water ballast tank.

Key words: water ballast tanks, cracking, corrosion, cathodic delamination, Lewis acid-base interaction

 

The cracking and subsequent corrosion in water ballast tanks has long been a problem for the maritime industry. The potential damage to ships’ hulls from this type of corrosion can be devastating and catastrophic. Consequently there has been much study into the root causes of coatings cracking over the years. These studies have primarily centered on the mechanical considerations of crack initiation and propagation. It has generally been agreed that cracking is due to stress in the film caused by film shrinkage loss of low molecular weight components strain within in the steel substrate and impact from environmental forces such as thermal expansion/contraction and hygroscopical volume changes.One facet of the cracking problem which has not been studied to any great degree is what happens after the crack has formed and corrosion commences. Worth considering is the extent corrosion and cathodic delamination progresses under the film at the crack point. Although corrosion is inevitable at the crack point limiting its progress can provide valuable savings in the repair of any corrosion damage.This study will look at the mechanisms of corrosion and cathodic delamination resulting from the cracking of paint in a water ballast tank environment and what may be expected in the corrosive environment. This will be based on the concept of a thermodynamic barrier existing at the coating/steel interface resulting from Lewis acid-base interactions between polymer and substrate.Although cracking is a cohesive failure and delamination is an adhesive failure it has not escape the authors’ notice that the very mechanism that may inhibit the progress of corrosion in an after the fact cracking situation may also contribute to preventing the cracking in the first place. A recent study on internal stresses and mechanical properties of paint films indicates that adhesion is probably the most important parameter. Adhesion however is not a fundamental property of the coating/substrate interface rather it is the consequence of the interaction between the polymer and the substrate. It is these interactions which must be understood to provide answers to the cracking issue. Examined in this monograph as well will be how these interactions the same Lewis acid-base interactions described previously in combination with shrinkage mitigating factors may be able to be used to prevent cracking and delamination of a coating in a water ballast tank.

Key words: water ballast tanks, cracking, corrosion, cathodic delamination, Lewis acid-base interaction

 

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