Naval Steel Research Articles

Validación de la soldabilidad mediante alambre tubular con núcleo de fundente “FCAW” para aceros navales deteriorados (FLUX CORED ARC WELDING)

Repairs and changes of steel plates in the structure of the vessels where it is possible to find steels with a high degree of deterioration need reliable welded joints in naval steel of the type ASTM A–131 Gr. A new to old. Due to the fact that the variables associated to the weldability of the materials to be repaired are not known, it is necessary to make a study on the weldability of steel ASTM A131 Gr A, in full penetration seams or junctures, under the various parameters involved in the welding process, to determine the influence of the corroding residues that affect the application of welding compounds through the analysis of the metallurgical reactions of liquid condition in order to select the contributing materials with the alloy elements that are able to prevent these phenomena and to recommend the best practices for the electric arc welding process with tubular electrode with FCAW flux core.

Experimental investigations on the growth of small fatigue cracks in naval steel

ABSTRACTThe concept of damage tolerance is now largely employed to evaluate the fatigue life of structures. However, part of this fatigue relies on the initiation and growth of small cracks. The fatigue behaviour of a naval structural steel (S355NL) was investigated. In order to characterize the behaviour of short and long cracks, tests were performed under constant amplitude loading for several load ratios between –1.0 and 0.5. A major part of fatigue life is constituted by short crack initiation and propagation.

The Influence of electrochemical surface modifications on naval steel corrosion

The corrosion behaviour of naval steels is characterized by cyclic voltammetric profiles, open-circuit potential decays and polarization curves in 0.5 M sodium nitrate and in 0.6 M sodium chloride at 20 °C. Naval steel surfaces can be modified by the application of periodic symmetric and/or asymmetric potential routines in strong alkaline solutions. These perturbations produce the formation of protective or non-protective surface oxides, which can be characterized by scanning electron microscopy and cyclic voltammetry. Corrosion parameters of the new surface oxides are evaluated by polarization curves after long-time exposures in electrolytes containing sodium chloride and sodium nitrate.

Application of a polythiophene derivative as anticorrosive additive for paints

This work compares the resistance against marine corrosion of several paints before and after being modified by adding a conducting polymer derived from polythiophene. The selected paints, which were applied to the naval steel St F111, are primers specially indicated for protection in marine environments. The physical properties of both the unmodified and the modified paints were characterized using viscosity measurements, FTIR and thermal analyses, and mechanical properties evaluations. Results show that the addition of a low concentration (0.2%, w/w) of poly(3-decylthiophene-2,5-diyl)-regioregular greatly improve the performance of the epoxy-based resin. Thus, laboratory immersion tests in NaCl solution showed irregular surface and composition degradations of the film without conducting polymer, after 3 days, while the polymeric film with the conducting polymer did not suffer any change until 30 days. The effects of the degradation on the coating surfaces were analysed using both optical and scanning electron microscopy (SEM).

Waterborne Paints Anticorrosive Behaviour on Steels

Organic coatings, mainly paints, are one of the most important methods for protecting steel against corrosion. Both their low cost and easy applicability are between the reasons for selecting them as a method for protecting approximately 90% of the structures exposed to atmosphere. In this work, anticorrosive properties of an acrylic waterborne paint applied to a naval steel have been evaluated in NaCl at 3.5% solutions by means of electrochemicals techniques, such as Linear Polarisation and Electrochemical Impedance Spectroscopy.

Application of EIS and SEM to evaluate the influence of pigment shape and content in ZRP formulations on the corrosion prevention of naval steel

The effects of pigment volume concentration and morphology of zinc particles employed in the formulation of zinc rich paints (ZRP) suitable for the corrosion protection of naval steel in sea water, have been investigated using electrochemical impedance spectroscopy combined with open circuit potential measurements and SEM micrograph analysis. Different ZRP samples were tested during exposure to artificial sea water for up to 70 days. The characteristics and properties of the naval steel/ZRP coating/sea water systems were determined from an impedance transfer function model which involves the reactions occurring at the metal/ZRP and ZRP/solution interfaces as well as diffusion processes through the active ZRP coating. Information concerning the influence of concentration and shape of the zinc pigment on the corrosion protective behaviour of ZRP coatings and on the exposure time dependence of the system parameters allowed to interprete the form in which the galvanic action and the barrier effect diminish progressively. The degree of rusting of the steel substrates as well as the blistering resistance of the formulated ZRP have been also evaluated according to conventional ASTM standards.

Study of the pigment type effect on the corrosion behaviour of epoxy painted steel/ sea water systems

The effect of different kind of pigments on the corrosion resistance properties of an epoxy paint has been investigated using electrochemical impedance spectroscopy and open circuit potential measurements. Painted naval steel samples were studied during the exposure to artificial sea water. The epoxy paint coatings were prepared employing red lead, zinc, red iron oxide or titanium dioxide as pigment with 0.8 of PVC/CPVC ratio. From the EIS and corrosion potential data analyis was found that the anticorrosive protection given by an anticorrosive (pigmented with red lead) and a top coat (pigmented with red iron oxide) epoxy painting scheme was both more lasting and more effective. This was attributed to the fact that both the effective adhesion provided by the chemical bonding between the steel surface and the epoxy paint groups and the constant high barrier effect afforded by this type of top coat were a perfect complement for the high corrosion inhibitive capacity of the red lead pigment.

Study of the pigment type effect on the corrosion behaviour of epoxy painted steel/sea water systems

The effect of different kind of pigments on the corrosion resistance properties of an epoxy paint has been investigated using electrochemical impedance spectroscopy and open circuit potential measurements. Painted naval steel samples were studied during the exposure to artificial sea water. The epoxy paint coatings were prepared employing red lead, zinc, red iron oxide or titanium dioxide as pigment with 0.8 of PVC/CPVC ratio. From the EIS and corrosion potential data analyis was found that the anticorrosive protection given by an anticorrosive (pigmented with red lead) and a top coat (pigmented with red iron oxide) epoxy painting scheme was both more lasting and more effective. This was attributed to the fact that both the effective adhesion provided by the chemical bonding between the steel surface and the epoxy paint groups and the constant high barrier effect afforded by this type of top coat were a perfect complement for the high corrosion inhibitive capacity of the red lead pigment.

The characterization of protective properties for some naval steel/polimeric coating/3% NaCl solution systems by EIS and visual assessment

Electrochemical impedance measurements have been made in 3% NaCl solution on coated naval steel with alkyd, epoxies, chlorinated rubber and acrylic conventional paints as well as with epoxy-polyamide, ethyl-silicate or alkyd zinc rich paints. Electrochemical impedance measurements have made it possible to monitor the uptake of the surrounding aqueous electrolyte into the paint and simultaneously to determine the extent of paint breakdown. Based on corrosion potential and impedance measurements, together with the visual assessment using both the ASTM Standards 610/85 and 714/87, the different paints have been ranked in terms of the effectiveness of their anticorrosive properties in a chloride containing solution. A comparison of visual assessment, corrosion potential and impedance measurements data indicates that the electrochemical impedance technique is a powerful tool for the study of the coated steel behaviour exposed to aggressive aqueous media.

The corrosion protection of steel in sea water using zinc-rich alkyd paints. An assessment of the pigment-content effect by EIS

The effect of pigment volume concentration ( c v,p) on the corrosion resistance properties of zinc-rich paints (ZRP) has been investigated using electrochemical impedance spectroscopy (EIS) combined with cathodic protective potential measurements. Painted naval steel samples were studied during the exposure to artificial sea water for up to 45 days. ZRP coatings were prepared employing zinc pigment content in the 77–88% concentration range. Results show clearly that samples prepared with c v,p values >86% deteriorated more rapidly than panels painted using a relatively lower pigment content. The corrosion behaviour of painted steel samples was found to be practically independent of c v,p within the 78–86% range. The cathodic protection effect in action during 45 days' immersion time arises because these alkyd resin paint coatings behave like a porous active surface layer. Under aggressive conditions similar to those afforded by the artificial sea water, zinc-rich alkyd coatings containing c v,p values within the 78–86% range seem to provide longer corrosion protection to steel substrates than other types of ZRP commonly used.

The use of electrochemical impedance measurements to assess the performance of organic coating systems on naval steel

Electrochemical impedance and corrosion potential measurements were carried out on naval steel coated with various organic paints systems whilst immersed in 3% NaCl solution. These techniques have been used to determine the mechanisms involved in the corrosion process as well as to assess the protective power of paint systems commonly used in marine environments. The paint systems studied consisted of a zinc-rich ethyl silicate primer (ZRP) with a chlorinated rubber or epoxy poly(amide) topcoat, in different thicknesses. Prior to immersion the painted specimens were subjected to thickness and adhesion measurements. After immersion, impedance measurements were carried out periodically as well as the standard tests according to ASTM D-610/68 and ASTM D-714/87. The latter were undertaken in order to assess the degree of rusting and blistering of the painted steel surfaces, respectively, in an attempt to correlate the visual observations with the electrochemical data. Complex plane plots of the resistive and reactive components of impedance, obtained over the frequency range from 65 KHz to 1 mHz were analyzed in accordance with resistive-capacitive equivalent electrical circuit models assumed to describe the painted metal/solution interfaces. The experimental results suggest that both the type and the thickness of the topcoat paints could be of paramount importance in controlling the rate of action of the zinc-rich primer and hence allowing an extension of its useful life. At the same time, the cathodic protection increases the tendency of cathodic reactions occurring at the coated steel interface and consequently increases the likelihood of delamination and blistering of the coating near a defect.

Effect of plasticizer on the physicochemical properties of vinyl coatings submerged in artificial seawater

AbstractThe effect that type and content of plasticizer has on several physicochemical properties of vinyl varnishes was studied.A vinyl resin (VAGD) plasticized with di‐isodecyl phthalate (DIDP) or tricresyl phosphate (TP) in 2:1, 4:1, 6:1 and 10:1 resin:plasticizer ratios was employed. Naval steel plates were coated with the different formulations and submerged in artificial seawater.The coefficients of diffusion, solubility and permeability to water were calculated, measuring the impedance vector evolution during the first 15 min of immersion. Corrosion potential measurements as well as the ionic resistance (Rm) and dielectric capacitance (Cm) were carried out for 40 days.The results obtained make it possible to infer that, independently of the type of plasticizer employed in the formulation, the increase of the resin:plasticizer ratio produces a decrease of water permeability. This effect is associated with more positive corrosion potentials, higher ionic resistances and lower dielectric capacitances. Besides, for equal resin:plasticizer ratios, the samples plasticized with DIDP showed, in general, lower permeability than those plasticized with TP.Finally, the high barrier effect corresponding to samples with 6:1 and 10:1 resin:plasticizer ratios is very important since decreasing solvent content also decreases solvent retention in the film and consequently its adverse effects on the protective properties of the coating.

Effects of Rolling Direction and Tensile Stress on the Corrosion of a Naval Carbon Steel in Natural Marine Environments: I. Natural sea water

AbstractThe effect of rolling direction and tensile stress on the corrosion morphology of a naval carbon steel was investigated in continuous immersion tests for a period of about three years in natural sea water in Genoa Harbour. In order to avoid the effects of macrofouling, the specimens were immersed in tanks containing carefully filtered sea water, periodically renewed, and controlled by monitoring the hydrological parameters, oxygen content and temperature.The experiments were performed on specimens cut both parallel and perpendicular to the rolling direction of the plate, and some specimens were subjected to differing degrees of elongation. The corrosion rate was initially high and decreased to reach stable values between the second and third years of exposure. The rolling direction has a greater effect on the behaviour of the transverse surfaces than on the rolling surfaces. In particular, the transverse surfaces which were parallel to the rolling direction underwent considerable localised corrosi...

Marine Corrosion of Mild Steel in a Thermically Altered Natural Environment

Summary The corrosion behaviour of a naval mild steel has been studied in the natural environment in a part of the Port of Genoa, where the water temperature is evelated by a hot effluent from a generating station.