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Protection of intermittently wetted steel structures by means of coating systems

Abbas, Sa'ad (2017). Protection of intermittently wetted steel structures by means of coating systems. Bachelor of Engineering Co-op (4th Year Project) Thesis, Charles Darwin University.

Document type: Thesis
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Author Abbas, Sa'ad
Title Protection of intermittently wetted steel structures by means of coating systems
Institution Charles Darwin University
Publication Date 2017
Thesis Type Bachelor of Engineering Co-op (4th Year Project)
Supervisor Wolff, R.
Kannoorpatti, Krishnan
0905 - Civil Engineering
Abstract The use of steel in marine environments has been invaluable to the construction industry, steel structures in marine environments are subject to severe corrosive effects compared to urban areas.

All coatings rely on a physical bond to the substrate. As with any physical bond this can be compromised with sufficient impact, in the context of marine environment a very real example is when boats and vehicles dock alongside. Such impact can chip off the coating and corrosion will rapidly propagate. Corrosion effectively destroys the structural integrity of a structure if allowed to spread, with rust taking up approximately 6 times to volume of steel with none of the structural integrity.

Hot dipped galvanising (HDG) is the process of submersing a steel substrate in a molten zinc bath, once dried the zinc is anodic to the steel and will corrode sacrificially to the steel. HDG will form a passive layer of oxide to prevent further exposure to the atmosphere. Such a coating has proven very beneficial in the past however does come with a higher initial cost. This is associated with the high costs involved in maintaining a molten zinc bath (requiring temperatures of 450°C sometimes 24/7) as well as ongoing maintenance of the zinc itself as levels deplete from usage/contamination.

Painting systems are more versatile when it comes to application as no molten baths are needed. However, it is critical to ensure the coating is applied to recommended specifications, this will certainly govern the performance of the coating system, in the case of fundamental structural element a premature service life can result in millions in repair; further highlighting the importance of correct preparation and application.

Any chosen coating system is rarely chosen on performance alone, in all projects the entire timeline must be considered. HDG is a very suitable coating system when maintenance is to be avoided due to access issues etc. However, it may not prove practical for projects with smaller life cycles, these factors and more shall be considered in the project scope. The importance of preparing for the correct coating system can save a project from significant cost overruns in the future.
Keyword corrosion
tidal zone
chloride attack
surface preparation
costing systems
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Created: Wed, 13 Sep 2017, 09:18:57 CST by Jessie Ng