Corrosion surface deterioration

Corrosion Surface deterioration or destmction due to metal loss caused by chemical or electrochemical reactions... 

Free mineral acidity H2SO4, HCl, and other acids, expressed as CaCOj. Causes rapid corrosion and deterioration of surfaces. 

Common packaging materials are a potential source of aggressive substance s, and careful selection is recommended to avoid surface deterioration. Where paper is in contact with aluminium, the chloride content should be below 0-05 7o, sulphate content below 0-25 7o, copper content below 0-01% and the pH of aqueous extracts in the range pH 5-5-7-5, in order to avoid corrosion in damp conditions. Papers and felts used in building applications should also conform to this specification as a minimum requirement and be of the highest quality, since metallic copper found in materials of inferior origin can result in severe local galvanic attack of aluminium. 

Failure may be mechanical, due to wear, abrasion and erosion, britle fracture, surface deterioration, cyclic loading, embrittlement, thermal or pressure shock, or fatigue. Failure may also be chemical, in essence due to corrosion. 

Fretting corrosion occurs where there is friction, generally caused by vibrations, between two metal surfaces. The debris formed by fretting corrosion accelerates the initial damage done by contact welding. Vibrations cause contact welds to break with subsequent surface deterioration. Debris formed acts to accelerate this form of corrosion by serving as an abrasive. Fretting corrosion is especially prevalent in areas where motion between surfaces is not foreseen. 

Water has proved to be the most harmful environment for bonded joints. Problems arise because water is universally found, and the polar groups which confer adhesive properties make the adhesives inherently hydrophilic the substrates or substrate surfaces themselves may also be hydrophilic. Experience has demonstrated that the main processes involved in the deterioration of joints subjected to the influence of moisture are (a) absorption of water by the adhesive (b) adsorption of water at the interface through displacement of adhesive (c) corrosion or deterioration of the substrate surface. 

In combined corrosion by solntions that contain simultaneously chlorides and sulfates, the surface deterioration and loss of strength are greater in mixes made with blended cements that contain blast furnace slag or silica fume, than in those made with plain Portland or Portland-fly ash cemenL However, the corrosion of steel reinforcement is lower in the former cements (Al-Amoudi, 1993). 

Mathematical models of biofibns systems, which are layers of usually nonresistant microorganisms such as bacteria that attach to a surface, are critical to the medical and technical industries. Biofibn systems can cause infections in humans and corrosion and deterioration in technical systems. Biomathematics can be used to model biofilms systems to help understand and prevent their formation. 

Carbon and low-alloy steels are probably the most commonly used materials for pipes handling water, petroleum products, and some chemicals. Reference 1 provides a summaiy of the different specifications used for pipelines. Steel tends to corrode by both pitting and uniform surface deterioration [2]. Steel must usually be protected from corrosion both on the inside from the material being carried and on the outside from corrosion by the atmosphere, soil, or water that surrounds the pipe. External corrosion protection is provided by material selection, selective backfill, barrier coatings, stray current control, and cathodic protection. Internal corrosion protection can be provided by inhibitors, coatings, design process control, and materials selection. 

The contamination of tower surfaces with aggressive chemicals can lead to enhanced corrosion and deterioration of protective coatings. Although the methods of detection and deteimination of surface contamination are not standardized, several test methods [7] are accepted by the industry. Surface contamination analysis kits are available [8] to measure pH, chlorides (detection limit 40 ppm) and soluble ferrous ions (detection limit approximately 3 ppm). In most cases, these detection limits are sufficient to establish aggressivity of the operating enviroiunent and surface cleanliness before painting. 

The sulfuric acid attacks exposed concrete and unprotected surfaces of iron, steel, and copper, resulting in corrosion and deterioration of the exposed vulnerable materials. Electrical and instrumentation systems are particularly vulnerable to low levels of hydrogen sulfide gas. H2S readily attacks copper contacts to form copper sulfide, a poor conductor of electricity. This can cause equipment failure or poor reliability of control systems. 

Galvanic corrosion can occur in a polycrystaUine alloys, such as pearMc steels, due to differences in microstmctural phases. This leads to galvanic-phase coupling or galvanic microceUs between ferrite (a-Fe) and cementite FesC) since each phase has different electrode potentials and atomic stmcture. Therefore, distinct localized anodic and cathodic microstmctural areas develop due to microstmctural inhomogeneities, which act as micro-electrochemical cells in the presence of a corrosive medium (electrolyte). This is an electrochemical action known as galvanic corrosion, which is mainly a metallic surface deterioration. 

First of all, corrosion is basically an electrochemical process that involves ionic interactions leading to metal dissolution or surface deterioration. Thus, the theory of corrosion requires thorough understanding of the electrochemical events... 

Erosion-corrosion is the acceleration or increase in rate of deterioration or attack on a metal because of relative movement between a corrosive fluid and the metal surface (see Figure 2.18). This movement is quite rapid, and mechanical wear effects or abrasion are involved. Metal is removed from the surface as dissolved ions, or it forms sohd corrosion products that are mechanically swept from the metal surface. Sometimes movement of the environment decreases corrosion, particularly when localized attack occurs under stagnant conditions, but this is not erosion-corrosion because deterioration is not increased. Erosion-corrosion is characterized by grooves, gullies, waves, rounded holes, and valleys. 

A type of corrosion attack (deterioration) uniformly distributed over metal surface. (2) Corrosion that proceeds at approximately the same rate over a metal surface. Also called general corrosion. General corrosion is characterized by a chemical or electrochemical reaction that occurs uniformly over the exposed surface. Anodic and cathodic sites shift constantly so that corrosion spreads over the entire metal surface. Identifying general corrosion is usually simple, but determining its cause is often difficult. Chemical dissolution by acids, bases or chelants frequently results in general corrosion. 

Provided normal piecantions are taken when filling the tank, few contaminants should be introduced at this stage. The possible exception is water, which is always likely to be present in small proportions in pumped petrol. The main cause of fuel contamination is corrosion or deterioration of the inner surfaces of the tank itself, or the redistribution of foreign matter already in the tank. 

Erosion is the deterioration of a surface by the abrasive action of solid particles in a liquid or gas, gas bubbles in a liquid, liquid droplets in a gas or due to (local) high-flow velocities. This type of attack is often accompanied by corrosion (erosion-corrosion). The most significant effect of a joint action of erosion and corrosion is the constant removal of protective films from a metal s surface. This can also be caused by liquid movement at high velocities, and will be particularly prone to occur if the solution contains solid particles that have an abrasive action. 

Siace dimer acids, monomer acids, and trimer acids are unsaturated, they are susceptible to oxidative and thermal attack, and under certain conditions they are slightly corrosive to metals. Special precautions are necessary, therefore, to prevent product color development and equipment deterioration. Type 304 stainless steel is recommended for storage tanks for dimer acids. Eor heating coils and for agitators 316 stainless steel is preferred (heating coils with about 4s m (50 ft ) of heat transfer surface ia the form of a 5.1 cm schedule-10 U-bend scroU are recommended for a 37. 9-m (10,000-gal) tank. Dimer acid storage tanks should have an iaert gas blanket. 

Biological Corrosion The metabohc activity of microorganisms can either directly or indirectly cause deterioration of a metal by corrosion processes. Such activity can (1) produce a corrosive environment, (2) create electrolytic-concentration cells on the metal surface, (3) alter the resistance of surface films, (4) have an influence on the rate of anodic or cathodic reaction, and (5) alter the environment composition. 

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