51313-02577-Case Studies on Failures for Waterborne Coatings in Shipbuilding Sagging

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Product Number: 51313-02577-SG

ISBN: 02577 2013 CP

Author: Jineok Kim

Publication Date: 2013

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Water borne coatings have been applied to non-immersed areas such as accommodations and engine rooms of vessels in order to reduce the VOC(Volatile Organic Compounds) emission and improve worker’s health and safety. It is expected that the use of the water borne coatings leads to not only decline of the amount of the VOC emission but also reduction of the workload because it can be build up to controlled WFT(Wet Film thickness) referred to the coating specifications by spraying to 1 coat while the solvent borne alkyd coatings which were used before need to apply 2 coats to reach the controlled WFT. Especially the touch-to-dry time of the water borne coatings is about 4 times as short as than that of alkyd coatings.
However it occurred to sagging failures immediately after spraying in the pre-erection ship block in which it did not appear before when the solvent borne alkyd coatings were used although there were not conditions which induce the sagging failures such as high coating thickness and humidity. These failures cause additional workload and costs because surface pretreatment and spraying have to be carried out after removing the coating area in which failures occurred.
In this research we performed visual inspections between airing and airtight conditions as well as measuring the alkalinity changes during curing a viscosity with stomer type viscometer and the drying time with mechanical recorders. Also the failure mechanism the relations between viscosity and sagging and the effect of rusting on alkalinity changes during curing are examined.