Paint Delamination Research Articles

Unlocking the Potential of Sebacate: Investigating Its Role in the Inhibition of Filiform Corrosion on Organic Coated Steel

The study investigated the effect of sebacate as a corrosion inhibitor for acrylic-coated steel. Specifically, it examined its impact on mitigating a frequent case of paint delamination, known as filiform corrosion (FFC), through a chosen weathering test designed to stress the degradation of the produced samples. Sebacate was demonstrated to be an efficient organic molecule for enhancing the corrosion resistance of steel. This efficacy was evaluated through electrochemical characterization based on electrochemical impedance spectroscopy measurements and potentiodynamic polarization curves, including the application of an FFC susceptibility prediction methodology based on measurements obtained in FFC-simulated electrolytes. An inhibition efficiency of 98% was measured in near-neutral saline solutions compared to conditions lacking inhibitor presence. During FFC simulation, the primary effect observed was associated with a reduction in cathodic activity evolution. Furthermore, a significant reduction in corrosion creep evolution of 35% was found. These experimental findings aligned closely with the outcomes projected by the simulated investigations.

Scanning and transmission electron microscopy examinations of composite hybrid chromate and chromate phosphate conversion coatings exposed in hot 100% relative humidity environments

Conversion coatings are sine qua non in the finishing of aluminium alloys. They may be put into service without coating of paints. However, for aesthetics in architectural applications, paint overcoat is common. Chromate phosphate coatings are relatively less toxic than chromate which gained the pride of place until recently. Thus, aluminium specimens coated with hybrid chromate/phosphate conversion coatings have been subjected to 100% relative humidity for 480 h at 313K in comparison to chromate coatings and bare aluminium. Scanning electron microscopy examination revealed that initial dried river bed morphologies on coated specimens were obliterated. The friable outer coatings collapsed into the cracks/environment leaving a relatively smooth surface after exposure. Additionally, transmission electron microscopy of sections before and after exposure revealed similar texture and morphological striations nearly parallel to each other throughout the length of the coatings to the metal/coating interface. These were not disrupted as well as the metal/coating interface which remained relatively smooth with no visible corrosion products after exposure. Thus, the coatings formed effective barrier between the substrate and the relatively harsh environment. From EDS, elemental compositions were the same albeit, spectral intensities remained relatively constant after humidity exposure regimes. The coatings are made up of either Cr, O and Al for chromate and Cr, P, O and Al for chromate/phosphate. At deliberately breached regions, the coatings prevented spread of corrosion and paint delamination over the substrates. On the other hand, bare aluminium was decorated with mounds of hydrated aluminium oxide/hydroxide after exposure as revealed in the SEM/TEM.

Investigation and modelling of edge corrosion of e‐coated galvanized steel with respect to the spatial edge orientation

AbstractThe effect of the spatial orientation of e‐coated hot dip galvanized test sheets on edge corrosion is investigated. Therefore paint delamination from corrosion sample edges at different steps in time of samples at different angles relative to the horizontal during a corrosion test is analysed. Two general relations are found: Horizontally oriented edges exhibit significantly increased coating delamination compared with vertically oriented edges. This is due to increased exposure to the electrolyte, resulting from the pinning of electrolyte droplets along the upper edge. With increasing angular displacement relative to the ground, electrolyte exposure and edge delamination decrease. The edges of the upward‐facing specimen side showed a higher delamination width compared with the downward‐facing side at the same angle. These results are supported by electrochemical impedance spectroscopy and a wetting test. Ultimately, a semi‐empirical model to numerically predict the edge delamination over time, incorporating electrochemical impedance spectroscopy and polarization curves, is presented.

Surface Acoustic Wave Nebulization–Mass Spectrometry as a New Tool to Investigate the Water Sensitivity Behavior of 20th Century Oil Paints

The sensitive surfaces of many unvarnished 20th century oil paintings are of great concern for conservators and collection keepers. They may show degradation problems such as paint delamination, dripping, and soft and sticky paint and pose challenges for cleaning due to solvent sensitivity. We report for the first time the use of an innovative ambient ionization technique, surface acoustic wave nebulization-mass spectrometry (SAWN-MS), for the identification and characterization of fatty acids, dicarboxylic species and glycerides in water-sensitive modern oil paints. The composition of 10 relevant Winsor and Newton 1964-1965 paint swatches that present different degrees of water sensitivity and two paint samples from a painting by the British artist Francis Bacon were studied. Principal component analysis was used for SAWN-MS data classification. Electrospray ionization (ESI)-MS was used as control method, specifically to compare the obtained ratios of markers of interest by the two ionization techniques. The results obtained by both ESI-MS and SAWN-MS are correlated and discussed in a broader context including the information on the oil media obtained by gas chromatography (GC-MS) and also on the inorganic materials and salts characterized using a combination of methods in previous reports on samples from the same manufacturer. SAWN-MS was found to be a suitable tool for the determination of soluble organic constituents present in the paints. The method provides an indication of the level of oxidation and hydrolysis of the paint film by monitoring specific markers such as free palmitic and stearic acids, azelaic acid, monoacylglycerols, and diacylglycerols. The data showed that a higher level of water sensitivity coupled with a high level of oxidation and hydrolysis is linked to higher dicarboxylic acid, diacyl- and triacylglyceride content and lower levels of short chain fatty acids. The data obtained by SAWN-MS provided a good correlation between the monitored species and the degree of water sensitivity.

Crack channelling mechanisms in brittle coating systems under moisture or temperature gradients

Crack channelling is predicted in a brittle coating-substrate system that is subjected to a moisture or temperature gradient in the thickness direction. Competing failure scenarios are identified, and are distinguished by the degree to which the coating-substrate interface delaminates, and whether this delamination is finite or unlimited in nature. Failure mechanism maps are constructed, and illustrate the sensitivity of the active crack channelling mechanism and associated channelling stress to the ratio of coating toughness to interfacial toughness, to the mismatch in elastic modulus and to the mismatch in coefficient of hygral or thermal expansion. The effect of the ratio of coating to substrate thickness upon the failure mechanism and channelling stress is also explored. Closed-form expressions for the steady-state delamination stress are derived, and are used to determine the transition value of moisture state that leads to unlimited delamination. Although the results are applicable to coating-substrate systems in a wide range of applications, the study focusses on the prediction of cracking in historical paintings due to indoor climate fluctuations, with the objective of helping museums developing strategies for the preservation of art objects. For this specific application, crack channelling with delamination needs to be avoided under all circumstances, as it may induce flaking of paint material. In historical paintings, the substrate thickness is typically more than ten times larger than the thickness of the paint layer; for such a system, the failure maps constructed from the numerical simulations indicate that paint delamination is absent if the delamination toughness is larger than approximately half of the mode I toughness of the paint layer. Further, the transition between crack channelling with and without delamination appears to be relatively insensitive to the mismatch in the elastic modulus of the substrate and paint layer. The failure maps developed in this work may provide a useful tool for museum conservators to identify the allowable indoor humidity and temperature fluctuations for which crack channelling with delamination is prevented in historical paintings.

Uncovering the illegible: multi-analytical approach to reveal paint stratigraphy of corroded signposts from the Auschwitz-Birkenau State Museum

Object discoveries from the Auschwitz-Birkenau State Museum (PMA-B) in Poland challenge the efforts to preserve paint on corroded steel supports. The objects have been exposed to outdoor weathering conditions and then buried for about 65 years. This caused severe damage, such as corrosion and paint delamination. The fragile condition of such cultural heritage objects makes their preservation difficult and comprehensive studies for paint conservation are lacking. Additionally, a thorough investigation of used materials is needed to put objects produced by forced labour in historical context. In this study, we analysed signposts from the Auschwitz-Birkenau State Museum (Poland) collection to gain information about used materials, the object’s genesis as well as damage phenomenology. Literature research suggests that the signposts may be produced within the former German NAZI concentration and extermination camp. Inorganic constituents were identified using elemental analysis, such as X-ray fluorescence (XRF) and scanning electron microscopy coupled to an energy dispersive X-ray spectrometer (SEM–EDS). Organic matter was analysed utilizing vibrational spectroscopic instrumentation Fourier transform infrared spectroscopy (FTIR). Our results include the use of synthetic organic pigments (SOPs) and binders, which were newly emerged paint materials at that time. The study highlights the need for conservators to have detailed understanding of composite materials and demonstrates the need for further investigation concerning painted steel objects.

Synchrotron Deep-UV Photoluminescence Imaging for the Submicrometer Analysis of Chemically Altered Zinc White Oil Paints.

Zinc oxide (ZnO) is a II-VI semiconductor that has been used for the last 150 years as an artists' pigment under the name of zinc white. Oil paints containing zinc white are known to be prone to the formation of zinc carboxylates, which can cause protrusions and mechanical failure. In this article, it is demonstrated how a multispectral synchrotron-based deep-UV photoluminescence microimaging technique can be used to show the distribution of zinc soaps on the submicrometer scale and how this information is used to further the understanding of zinc white degradation processes in oil paint. The technique is based on the luminescence of zinc soaps in the near-UV (∼3.65 eV) upon excitation in the deep-UV (4.51 eV), involving transitions that are argued to subsequently involve ligand-to-metal and metal-to-ligand charge transfer with intermediate structural reconfiguration. Because the primary emission peak lies at a higher energy than the band gap of ZnO (3.3 eV), the signal can easily be isolated from the pigment's very intense band gap and trap state emission by employing a multispectral acquisition approach. Moreover, analysis at such short wavelengths, in combination with a UV-transparent optical setup, allows for lateral resolution on the order of 200 nm to be obtained. The unprecedented capabilities of the microimaging technique are illustrated by showing its application to the study of a historical cross section from an early 20th century painting by Piet Mondrian. Revealing the submicrometer distribution of crystalline zinc soaps in this cross section provides new insights that suggest that microfissures, the starting points of paint delamination, are the result of an overall expansion of a heavily saponified zinc white layer.

In situ Investigations of Near Phase Boundary Water Diffusion of Ageing Adhesive Bonds by Scanning Kelvin Probe

Many industries nowadays rely on the adhesive bonding technology for their success, most notably aerospace, automotive, construction, and the electronics industry. One of the main advantages of the adhesives is the ability to bond dissimilar materials and the more efficient load transfer in comparison to other joining methods. Several industrial applications request the adhesive joint to withstand loads under different environmental conditions such as high moisture, and extreme temperatures. Thus, predicting the lifetime of adhesively bonded joints under moist environments is crucial to support tailoring the properties for the respective application demand. Relevant effects of water in adhesively bonded components may be strength degradation and introduction of stresses. Knowing the behaviour of the water in adhesive joints may contribute to directing the design of bonded components, lead to greater confidence and increase the use of adhesives in the industry. A significant cause of joint weakening is the effect of water in the interface between adhesive and substrates. There is evidence that the transport kinetics of water in the adhesive bulk do not correspond to the kinetics in the adhesive joint, studies show that water can be absorbed much faster by the interface than by the bulk. [1, 2] The study of the kinetics of water absorption in the interface is a particular challenge, and is also gravimetrically hardly detectable. A powerful and established method which can detect directly the corrosion induced delamination of polymer coatings is the scanning Kelvin probe (SKP). [3] In the present work the SKP is used to study the water uptake of adhesive bonds. To determine the water uptake processes of an adhesive joint by means of SKP, an adhesive is applied to a metal surface, and as second substrate a very thin non-conductive barrier layer is used. Several scanning Kelvin probe experiments are carried out, under different environmental conditions, to define which are the most suitable adhesives, substrates and barrier layers to investigate the water diffusion in situ and near the interface of an adhesive joint. The potential difference distribution is measured time-dependent in order to obtain information about the water absorption kinetics. The tests are accompanied by analytical and electrochemical methods, e.g., dynamic vapour sorption and electrochemical impedance spectroscopy. [1] Zanni-Deffarges, M. P.; Shanahan, M.E.R. (1995): Diffusion of water into an epoxy adhesive. Comparison between bulk behaviour and adhesive joints. In International Journal of Adhesion and Adhesives 15 (3), pp. 137–142. DOI: 10.1016/0143-7496(95)91624-F. [2] Wapner, K.; Grundmeier, G. (2004): Spatially resolved measurements of the diffusion of water in a model adhesive/silicon lap joint using FTIR-transmission-microscopy. In International Journal of Adhesion and Adhesives 24 (3), pp. 193–200. DOI: 10.1016/j.ijadhadh.2003.09.008. [3] Hausbrand, R.; Stratmann, M.; Rohwerder, M. (2009): Corrosion of zinc–magnesium coatings. Mechanism of paint delamination. In Corrosion Science 51 (9), pp. 2107–2114. DOI: 10.1016/j.corsci.2009.05.042.

Paint Delamination Inspection for Light Buoys by Infrared Thermography with Distance Heating

Paint Delamination Inspection for Light Buoys by Infrared Thermography with Distance Heating

Electrophoretic painting on AZ31 Mg alloy pretreated in cerium conversion coating solutions prepared in ethanol-water mixtures

Electrophoretic painting (E-paint) was prepared on AZ31 Mg alloy samples pretreated in cerium conversion coating (CeCC) solutions with various ratios of ethanol and water mixture and its characteristics, adhesion and corrosion resistance were investigated. It was found that CeCC formed on AZ31 Mg alloy in a CeCC solution without ethanol was partly cracked structure and mainly consisted of Mg(OH)2/MgO, which exhibited weak adhesion with E-painting layer after water immersion test, and low corrosion resistance, as indicated by rapid formation of blisters and paint delamination during salt spray test. The addition of ethanol promoted the growth of a fine nano-crystalline CeO2 layer over the entire substrate surface. The E-paint on AZ31 pretreated in the CeCC solutions with addition of ethanol showed also improved corrosion resistance, as represented by the delayed time for paint delamination and blister formation. The E-paint layers on the CeCC layers formed in solutions containing 50–80 vol% ethanol showed stronger adhesion and better corrosion resistance than those formed on the samples treated in a non-ethanol containing CeCC solution.

Role of steel and zinc coating thickness in cut edge corrosion of coil coated materials in atmospheric weathering conditions; Part 2: Field data and model

Abstract Paint delamination from cut edges of model coil coated hot dip galvanized materials exposed at a marine test site for 5 years increased with steel thickness and decreased with zinc coating thickness. It was larger in sheltered locations than for openly exposed cut edges whereas red rust protection was more efficient on sheltered edges due to higher electric conductivity of deposits. The rate of paint delamination increased or decreased in time depending on the relative amount of zinc ions available for formation of the protective film on steel controlled by the initial steel substrate and zinc coating thicknesses.

Role of steel and zinc coating thickness in cut edge corrosion of coil coated materials in atmospheric weathering conditions; Part 1: Laboratory study

Abstract Cathode surface area and its ability to reduce oxygen controlled the rate of zinc dissolution and paint delamination from cut edges of hot dip galvanised steel sheets. Zinc corrosion products deposited on steel in atmospheric exposure conditions inhibited oxygen reduction decreasing galvanic current and zinc dissolution and paint delamination. The opposite effect was observed for iron corrosion products. The initial steel substrate and zinc coating thicknesses affected the availability of zinc ions for formation of the protective film.

Critical Constraints Responsible to Solar Glass Mirror Degradation

Abstract The degradation of solar glass mirrors is analyzed as a function of various constraints such as temperature, humidity, rain and solar irradiation. In order to understand the degradation mechanisms, two kinds of tests have been performed: simple tests to identify the effect of each constraint and complex tests to highlight the effects of synergy and to reproduce the natural ageing. The study of the paints coat degradation evidences that UV exposure is one of the most aggressive constraints for paint binder. But results show also a strong effect of liquid water on paint degradation and particularly on pigments loss and blistering phenomenon. Whereas temperature in dry environment is not a very degrading factor for coats, presence of liquid water is a strong accelerating constraint at high temperature. Agreement between outdoor ageing and indoor ageing with a new procedure involving UV, temperature and rain also shows that liquid water is the critical constraint responsible to edge corrosion of silver layer and paint delamination. This work shows also that relation between paint degradation and corrosion of silver layer is not obvious. Homogeneous corrosion by pitting was observed without any deep chemical deterioration of the paint coat system.

Coil-coated Zn–Mg and Zn–Al–Mg: Effect of climatic parameters on the corrosion at cut edges

We studied the effect of temperature, wet/dry cycling, pH, and the type and concentration of the corrosion activator on cut edge corrosion of painted Zn–15Mg and Zn–1.5Al–1.5Mg coated steel. In most accelerated tests, paint delamination and red rust formation were reduced compared to hot dip galvanised steel (HDG), and Zn–15Mg outperformed Zn–1.5Al–1.5Mg; however, Zn–1.5Al–1.5Mg showed better results when exposed outdoors. The alloyed materials were particularly resistant when HDG was prone to elevated corrosion, i.e. under permanent wetness, at higher temperatures, with high chloride loadings and in the presence of sulphate. Oxygen reduction on steel cut edges was inhibited by the alloying elements.

ZnMg and ZnMgAl alloys for improved corrosion protection of steel: Some new aspects

The performance of ZnMg and ZnMgAl coatings for corrosion protection of steel crucially depends on a number of factors. One is the degree of alloying. For instance, under standard testing conditions very promising inherent resistance against paint delamination even without conversion treatment was reported for highly Mg-alloyed zinc coatings. However, it will be shown in this work that under certain conditions very fast delamination may occur. For the much lower alloyed ZnMgAl coatings that are at the main focus of current research, as well as for lower alloyed ZnMg microstructural aspects of their corrosion performance will be discussed in more detail.

Behavior of two eco-compatible duplex systems used in the construction industry against corrosion

Two types of coated steels are currently competing in the construction industry: the hot-dip galvanized steel (HDGS) and the 55%Al–Zn alloy coated steel (HDZAS). Both systems are typically coated by a chromate-based conversion film, which is dangerous for human health and environment. Furthermore, for aesthetics purposes and/or to prolong their expected or planned service life, they are painted designing each paint system as a function of the service conditions to which they will be subject to. The present work reports on a comparative study of two duplex systems: steel/metal coating/organic coating. In both cases, the chromate-based pretreatment was replaced by another one that features γ-mercaptopropyltrimethoxysilane (MTMO) as an active element. The organic coating used was a water-based polyurethane. Behavior of this paint against corrosion was assessed by exposing the samples in salt spray or humidity chambers, and monitoring its evolution by electrochemical impedance spectroscopy, visual observation, scanning electron microscopy and energy dispersive X-ray analysis. The results revealed that: MTMO was suitable for promoting adhesion both in HDGS and HDZAS; in humidity chamber, both duplex systems provided good protection; the presence of corrosion products of the base steel and paint blistering was detected in the HDGS/paint system seventy-two days after exposure; however, 150 days after that, none of these effects were observed in the HDZAS/paint system; differences in behavior were significant in Salt spray chamber: speed of paint delamination from the mark done and the bulk of corrosion products generated was much higher in HDGS/paint system than in HDZAS/paint.

The Feasibility of Flash Thermography for the Examination and Conservation of Works of Art

This study investigates the feasibility of flash thermography for the examination and conservation of works of art: paintings, works on paper and sculpture. Thermography is a non-destructive technique for the identification of subsurface defects in materials. It is based on the propagation of surface-deposited heat through into the material. Differences in propagation between defect and defectfree areas result in a difference in the surface temperature of the material. The surface temperature is mapped over time by imaging with a mid-infrared digital camera. A xenon arc lamp is used to provide the initial source of radiation, and signal processing is typically applied to the collected data to reduce noise and to enhance key signal characteristics. This technique offers the possibility of investigating the structure of paintings and paper, particularly in cases where other non-destructive examination techniques do not provide sufficient information, for example subsurface delamination and layer structure. The results indicate that thermography is a good technique for detection of paint delamination and the degree of adhesion between layers, particularly in canvas paintings. It also successfully detected wood grain in situations where X-rays did not, although it was not effective for detecting voids or defects in wood.

Case study: the treatment of six reverse paintings on glass from William Nicholson’s Loggia with Figures and Architectural Fragment

Paint delamination is a typical concern associated with reverse paintings on glass. The experimental painting techniques of William Nicholson, however, provide a novel variety of treatment obstacles which have prompted two recent investigations into the condition and consolidation of three murals on glass: Loggia with Figures, Architectural Fragment and Beach Scene. Now property of the National Trust, the murals are destined to be re‐installed in a new location. Further to this end, six of the 54 panels that comprise the murals were transported to the Hamilton Kerr Institute for examination and treatment. Presented in this paper is an account of the consolidation tests and treatment carried out on the six panels from two of the murals, Loggia with Figures and Architectural Fragment, in pursuit of a treatment programme. Résumé «Etude de cas : traitement des six peintures sous verre de William Nicholson: Loggia avec figures et Fragment d’architecture» Le clivage de la peinture est un exemple typique des préoccupations liées à la peinture sous verre. Néanmoins, les techniques picturales expérimentales de William Nicholson apportent une variété originale d’obstacles aux traitements et ont suscité deux récentes études sur la condition et la consolidation de trois peintures sous verre: Loggia avec figures, Fragment d’architecture, Scène de plage. Devenues propriétés de la National Trust, les peintures murales sont destinées à être ré‐installées dans un nouvel emplacement. A cette fin, six des 54 panneaux que comprennent les peintures murales ont été transportés à l’Institut Hamilton Kerr pour examen et traitement. Un compte‐rendu des tests de consolidation et des traitements effectués sur les six panneaux des deux peintures murales, Loggia avec figures et Fragment d’architecture, en vue d’un programme de restauration est présenté dans cet article. Zusammenfassung „Fallstudie: Die Behandlung von sechs Hinterglasmalereien von William Nicholsons Loggia with Figures und Architectural fragment” Die Ablösung der Malschichten ist ein häufiges Problem bei Hinterglasmalereien. Die experimentelle Malweise William Nicholsons wirft jedoch ein Vielzahl von neuartigen Behandlungsschwierigkeiten auf, die kürzlich Anlass zu zwei Studien zum Erhaltungszustand und der Konsolidierung von drei Wandgemälden auf Glas gegeben hat: Loggia with Figures (Loggia mit Figuren), Architectural Fragment (Architekturfragment) und Beach Scene (Strand Szene). Die sich jetzt im Besitz des National Trust (gemeinnützige Organisation, die Objekte aus dem Bereich der Denkmalpflege und des Naturschutzes in England, Wales und Nordirland betreut), befindlichen Wandgemälde sind zur Installation an einem neuen Ort vorgesehen. Zu diesem Zweck wurden sechs der 54 Glasplatten, die die Wandgemälde ausmachen, zur wissenschaftlichen Untersuchung und restauratorisch‐konservatorischen Behandlung ins Hamilton Kerr Institut transportiert. In diesem Artikel findet sich eine Beschreibung der Tests zur Festigung der Malschichten und der anschließenden Behandlung von insgesamt sechs Platten aus den Wandgemälden Loggia with Figures und Architectural fragment, die auf der Suche nach einer adäquaten Behandlungsstrategie durchgeführt wurden. Resumen “Estudio: Tratamiento de seis pinturas invertidas sobre vidrio de Loggia with Figures and Architectural Fragment de William Nicholson” En las pinturas invertidas sobre vidrio, la delaminación de la pintura es una preocupación típica. Sin embargo, las técnicas experimentales de William Nicholson, presentan una nueva variedad de dificultades en el tratamiento que han conducido a dos investigaciones recientes sobre el estado de conservación y la consolidación de tres murales en vidrio: Loggia with Figures, Architectural Fragment and Beach Scene. Actualmente son propiedad del National Trust y los murales están destinados a ser re‐instalados en una nueva ubicación. Con este fin, seis de los 54 paneles que componen el mural, fueron transportados al Hamilton Kerr Institute para su examen y tratamiento. En este artículo se presenta un informe de las pruebas de consolidación y los tratamientos que se llevaron a cabo en los seis paneles de los dos murales, Loggia with Figures and Architectural Fragment, con el fin de encontrar un programa de tratamiento.

Microstructural studies of interfacial deformation in painted thermoplastic polyolefins (TPOs)

The interfacial structure and deformation between chlorinated polyolefin (CPO) adhesion promoter and automotive TPO substrates have been characterized with optical, scanning electron, and transmission electron microscopy techniques. The diffusion of rubber phase into the CPO layer was observed and an interphase thickness around 200 nm was obtained from TEM imaging. In some cases, a coherent failure of the adhesion promoter during the paint delamination was observed, which could be explained by the strong interphase formed due to the interfacial diffusion. It was found that baking at 120°C could significantly enhance the swelling of the rubber phase underneath the polypropylene-rich skin layer and the diffusion of the rubber phase into this layer. With decreasing molecular weight of PP homopolymer, the apparent interfacial strength measured by tensile cracking test increased, which was ascribed to the enhanced interfacial diffusion at low molecular weight. The deformation of materials near the interface during the paint delamination process was found to be more extensive in samples with higher interfacial adhesion.

Study of the corrosion behaviour of phosphatized and painted industrial water heaters

A technology for producing industrial water heaters exists, where the internal protective layer is an organic coating. This technology was largely adopted in the last decades and different methodologies for surface preparation or coating application were proposed and used; as an example bare steel is coated by an epoxy powder resin layer obtained by spray technique after a phosphatization treatment in an iron phosphate bath. However, when defects and organic coating discontinuities are present, the main water heater failure occurs by the detachment of large coating areas. This phenomenon is due to a fast paint delamination caused by a cathodic disbonding induced by the magnesium anode. In order to obtain a better coating adhesion, also under the typical water heater working conditions, a proper preparation of surface steel must be chosen. The aim of this work is the evaluation of different types of surface preparation, including degreasing, sand blasting and the use of iron or zinc phosphate conversion coatings. The samples prepared were coated using epoxy powder resins following the same application procedure. Adhesion was evaluated using classical methods like the pull-off test and the cathodic disbonding test. In addition, electrochemical impedance measurements were carried out on defect free samples and on others having an artificial defect. Coating delamination was studied by following the evolution with time of the electrical parameters measured from the equivalent electrical circuit. Both electrochemical tests and cathodic delamination tests showed that zinc phosphate treatments, and in particular phosphatization baths containing manganese greatly improve the metal–paint adhesion under the very stressing condition typical of the water heaters, whereas chromium passivation of iron phosphates had a very limited action. Electrochemical impedance measurements were shown to be very helpful in evaluating coatings performances, and in particular coating adhesion.