Vessel protective coating characterization by laser-induced plasma spectroscopy for quality control purposes M.P. Mateo, V. Piñon, G. Nicolas ⁎ Universidad de A Coruña, Laboratorio de Aplicaciones Industriales del Láser, Campus de Esteiro, Ferrol (A Coruña), 15403 Spain abstract article info Available online 15 January 2012 Keywords: Laser-induced plasma spectroscopy (LIPS) Paints Marine coatings Process control Protective coatings are the first line of defense of vessels against the corrosive marine environment. For this reason, painting process and maintenance tasks derived are critical in the protection of the metallic structure of a ship. In particular, an adequate film thickness is necessary for a coating system to fulfil the requirements and provide good anti-corrosion protection. In this sense, both under thickness and over application can cause failures. In this work, laser-induced plasma spectroscopy (LIPS) is proposed for the characterization of the composition and thickness of the protective coatings used in the naval sector, in order to overcome some of the limitations of thickness gauges using ultrasound, commonly used. Compositional characterization together with thick- ness measurements of painting layers has simultaneously been obtained by LIPS and tested for quality control purposes. The results demonstrate the potential of this technique to perform the on-line chemical and thickness charac- terization of applied painting layers in order to improve the control of the process and to avoid coating defects. © 2012 Elsevier B.V. All rights reserved. 1. Introduction The steel structure of a vessel is prone to corrosion throughout its service life. Due allowance should be made at the new building stage and by periodic maintenance, to provide effective corrosion protection that contributes to the continued structural integrity of the vessel. Painting process is one of the main steps both in the manufacturing and in the periodic maintenance of a vessel because protective coatings are the first line of defense against the corrosive marine environment [1]. For esthetic or functional reasons coating systems are made up of a group of coats which thickness, type and number will depend on the vessel area to treat. An adequate film thickness is necessary for a coating system to fulfil the requirements and to provide good anti-corrosion protection or to achieve the expected anti-fouling lifetime, etc. [1]. Under thickness will result in premature failure. However, over applica- tion can also cause problems, such as solvent entrapment and subse- quent loss of adhesion, cracking of the paint (including mud-cracking) or splitting of primer coats. Therefore, an adequate system for the con- trol of each coating thickness is essential. Nowadays, thickness gauges using ultrasound are used to measure the thickness of each layer just applied while it is still wet (WFT). Next, the thickness of the layer once dry is calculated using formulas provided by the paint supplier. Finally, the thickness of the layers altogether (DFT) is measured and the result is compared with the painting diagram. However, this thick- ness measurement procedure presents several drawbacks such as the dry film thickness of each layer that is not directly measured but only estimated, thin films (of less than 25 μm) cannot be measured accurate- ly over blasted surfaces using commercially available paint thickness gauges, and measurements of DFT at edges and corners are not accurate due to the measurement techniques used by these gauges. Laser-induced plasma spectroscopy (LIPS) also known as laser- induced breakdown spectroscopy (LIBS) is an analytical technique based on emission spectroscopy [2–6]. LIPS is a relatively novel tech- nique that can be applied, among others, to the characterization of in- terfaces in layered materials in air at atmospheric pressure [7–13]. To perform depth analysis by LIPS, a laser is fired repetitively over a single position of the sample surface, in such a way that depth-related spec- tra can be obtained by monitoring laser-induced plasma emission from each laser shot [14–21]. Afterwards, a plot of emission intensities at specific wavelengths against pulse number yields the depth pro- files. If the ablation rate is known, then the number of pulses can be substituted by depth scale [22,23]. In this work, LIPS technique is evaluated for the characterization of the composition and thickness of protective coatings used in naval sector, as an alternative to conventional paint thickness gauges. Layers thickness below micrometers can be characterized with this technique, while the spatial resolution, that is, the analyzed diameter, can be adjusted according to analysis requirements, overcoming the drawbacks of conventional methods. In this work, LIPS technique will allow determining elemental composition of the coating layers, and will provide painting-layers thickness measurements from the Surface & Coatings Technology 211 (2012) 89–92 ⁎ Corresponding author. Tel.: + 34 981337400x3411; fax: + 34 981337410. E-mail address: gines@udc.es (G. Nicolas). 0257-8972/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2012.01.018 Contents lists available at SciVerse ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat