Search Results for under-film corrosion

This article discusses the commonly encountered forms of automotive body corrosion. The corrosion forms include general or uniform corrosion, cosmetic or under-film corrosion, galvanic corrosion, crevice corrosion, poultice or under-deposit corrosion, and pitting corrosion. Corrosion-resistant sheet metals, such as electrogalvanized steel, hot dip galvanized steel, and hot dip galvannealed steel, are reviewed. The article provides information on the paint and sealant systems for corrosion control in automotive body applications.

This article reviews the types of passivity and presents tactics that employ passivity to control corrosion. Thermodynamics provides a guide to the conditions under which passivation becomes possible. A valuable guide to thermodynamics is the potential-pH diagram and the Pourbaix diagram. The article presents a potential-pH diagram for the iron-water system and an illustration of an idealized anodic polarization curve for a metal surface, which serves as a basis for describing the kinetics of passivation. It discusses five properties of passive films: thickness, composition, structure, electronic properties, and mechanical properties. The article outlines three possible processes that can form passive films: direct film formation, dissolution precipitation, and anodic oxidation of metal ions in solution. It describes the breakdown of the passive film using various models and highlighting the effect of alloy composition and structure.

This article describes the methods of wear measurements and a model of corrosive wear in mill atmospheres. It explains the polarization curves of pyrrhotite and high-carbon low-alloy steel in a quartzite slurry with examples. The surfaces of pyrrhotite in contact with mild steel or stainless steel affected by galvanic interaction are discussed. The article contains a table that lists the results of laboratory marked ball wear tests for three types of steel balls in wet grinding of magnetic taconite. It also provides information on the mechanism of electrochemical interaction and relative significance of corrosion and abrasion in wear. Galvanic interactions in multielectrode systems are reviewed. The article presents a case history on the material selection for grinding balls to minimize corrosion loss and the adverse effect on flotation.

This article provides useful information on the occurrence of corrosion in crude oil refinery units, namely, crude unit, catalytic and thermal cracking units, hydroprocessing units, amine sweetening units, and sour water units. Types and applications of corrosion inhibitors, namely, neutralizers, filming inhibitors, scavengers, microbiocides, and anti-foulants and scale inhibitors, are reviewed. The article describes the direct and indirect corrosion monitoring methods used to reduce equipment damage due to corrosion events and to assess the reliability and useful service life of process equipment.

This article focuses on the effects of microscopic organisms and the by-products they produce on the electrochemical corrosion of metals. The general characteristics of the microorganisms that facilitate their influence on the electrochemistry of corrosion are discussed. The industries most often reported as being affected by microbiological corrosion are listed, along with the organisms usually implicated in the attack. The article explains that the influence of organisms can be addressed successfully for a corrosion control program by using four types of evidence: metallurgical, microbiological, chemical, and electrochemical. It provides information on the microbiologically influenced corrosion (MIC) of irons and steels, passive alloys (austenitic stainless steels), aluminum alloys, copper alloys, and composites. The article reviews the formation of microbial biofilms and macrofouling films. It also describes the general approaches taken to prevent MIC.

This article describes the analytical methods for analyzing surfaces for corrosion and corrosion inhibition processes as well as failure analysis based on surface structure and chemical identity and composition. The principles and applications of the surface-structure analysis techniques, namely, optical microscopy, scanning electron microscopy, scanning tunneling microscopy, and atomic force microscopy, are reviewed. The article discusses the principles and applications of chemical identity and composition analysis techniques. These techniques include the energy dispersive X-ray spectroscopy, Auger electron spectroscopy, X-ray photoelectron spectroscopy, ion scattering spectroscopy, reflectance Fourier transform infrared absorption spectroscopy, Raman and surface enhanced Raman spectroscopy, and extended X-ray absorption fine structure analysis.

Rust-preventive compounds are removable coatings used for the protection of the surfaces of iron, steel, coated or galvanized products, and other alloys. This article describes the basic parts of rust-preventive compounds, namely, carrier, film former, polar materials, and specialty additives. It explains types of rust-preventive compounds, including dry films and water-based dry films. The article also discusses the methods of application of various compounds, such as petrolatum compounds and emulsion compounds. It contains tables that provide information on the characteristics, applications, and physical properties of rust-preventive materials covered by military specifications. Finally, the article describes the various considerations and parameters for selecting rust-preventive materials.

This article provides a general introduction to the kinetics of aqueous corrosion with an emphasis on electrochemical principles. It describes the thermodynamic basis for corrosion by determining the equilibrium potentials of electrochemical reactions from the Nernst equation. A corrosion process can be controlled by the electronic conductivity of passive films when the cathodic reaction occurs on the surface of the film and by activation control of corrosion. Passivation becomes thermodynamically possible when the corrosion potential exceeds the potential corresponding to the equilibrium between a metal and one of its oxides/hydroxides. The article schematically illustrates a current-potential or polarization curve for an anodic process.

This article provides a description of the classification, industrial applications, microstructures, physical, chemical, corrosion, and mechanical properties of zirconium and its alloys. It discusses the formation of oxide films and the effects of water, temperature, and pH on zirconium. The delayed hydride cracking of zirconium is also described. The article provides information on the resistance of zirconium to various types of corrosion, including pitting corrosion, crevice corrosion, intergranular corrosion, galvanic corrosion, microbiologically induced corrosion, erosion-corrosion, and fretting corrosion. The article explains the effects of tin content in zirconium and effects of fabrication on corrosion. Corrosion control measures for all types of corrosion are also highlighted. The article concludes with information on the safety precautions associated with handling of zirconium.

This article tabulates the chemical composition of iron-base, titanium-base, and cobalt-base alloys and illustrates the microstructures of these materials. It discusses the surface morphology and chemistry of oxide-film-covered alloys and provides insights into the interaction. The article illustrates the interfacial structure of a biomaterial surface contacting with the biological environment. It describes the corrosion behavior of stainless steel, cobalt-base alloy, and titanium alloys. The electrochemical methods used for studying metallic biomaterials corrosion are also discussed. The article concludes with information on the biological consequences of in vivo corrosion and biocompatibility.

This article focuses on the different parameters that influence the pitting corrosion of passive metals. The parameters are environment, metal composition, potential, temperature, surface condition, alloy composition, stochastic nature of the processes, and inhibitors. In addition, the article provides a detailed discussion on the various stages of pitting. These include passive film breakdown, metastable pitting, pit growth, and pit stifling or death.

Tribocorrosion is the subject dealing with complex, synergistic effects of chemical and mechanical conditions that cause wear. This article begins with a discussion on oxidative wear and corrosive wear, as well as quantitative measurements of corrosion, mechanical wear, and wear-corrosion effects. It illustrates the mechanism of corrosive-abrasive wear and discusses the factors affecting two-body wear. These factors include particle shape, size, density, and hardness; slurry velocity; slurry particle angle of attack; solids concentration in the slurry; hydrodynamic factors; corrosion products and the mass transfer of oxygen. The article describes slurry particle impingement tests and grinding tribocorrosion tests, as well as the factors to be considered for mitigating corrosive wear, such as materials selection, surface treatments, and environment modifications.

Corrosive wear is defined as surface damage caused by wear in a corrosive environment, involving combined attacks from wear and corrosion. This article begins with a discussion on several typical forms of corrosive wear encountered in industry, followed by a discussion on mechanisms for corrosive wear. Next, the article explains testing methods and characterization of corrosive wear. Various factors that influence corrosive wear are then covered. The article concludes with general guidelines for material selection against corrosive wear.

This article discusses the materials of construction found in pharmaceutical production facilities. The materials discussed are different stainless steels, nickel and nickel-base alloys, titanium, zirconium, impervious graphite, fluoropolymers, and glass-lined steel. The article describes the three primary causes of failure in the manufacture of pharmaceuticals: embedded iron, failures of glass linings, and corrosion under thermal insulation.

This article provides information on the municipal wastewater system components such as piping, pump stations, headworks, clarifiers, aeration structures, digesters, biosolids dewatering equipment, and sludge stabilization. It explains the major corrosion damage mechanisms to which those component parts of the system are exposed. It presents useful guidelines for selecting and using protective coatings in municipal sewerage collection systems and water reclamation facilities in wastewater treatment plants. The article includes annotated flow diagrams of a wastewater collection system, wastewater treatment plants, and spreadsheets listing the most widely used generic coating systems by structure and substrate material. It concludes with a section on quality watchouts when selecting or using protective coatings in municipal wastewater systems.

Corrosion fatigue refers to the phenomenon of cracking in materials under the combined actions of fatigue loading and a corrosive environment. This article focuses on the various mechanisms of corrosion fatigue, namely, hydrogen-assisted cracking, anodic dissolution, and surface energy reduction. It discusses the variables affecting corrosion fatigue. The effect of fatigue load frequency, environment, grain size, stress ratio, waveform, and temperature fatigue crack growth are also discussed.

This article focuses on the various coatings used on Department of Defense (DoD) systems. These include electroplated coatings; conversion coatings; supplemental oils, waxes, and lubricants; organic paint coatings; and other finishes such as vacuum deposits, mechanical plating, thermal spray coatings, and hot-dip coatings. The article also lists the test requirements and time to failure of the coatings.

This article discusses the general properties of ocean water and their effects on corrosion. It describes the major and minor features of the ocean water on corrosion, including the effects of variability, pollutants, and fouling organisms. Effects of water flow velocity on marine corrosion are also reviewed.

This article provides a summary of the concepts discussed in the articles under the Section “Fundamentals of Corrosion” in ASM Handbook, Volume 13A: Corrosion: Fundamentals, Testing, and Protection. In this section, the thermodynamic aspects of corrosion are descried first followed by a group of articles discussing the fundamentals of aqueous corrosion kinetics. The fundamentals of gaseous corrosion are addressed next. The fundamental electrochemical reactions of corrosion and their uses are finally described.