Uniform corrosion effective

Corrosion effect of forming Elongation X gauge length Standard hydropress specimen test True stress-strain curve Uniformity of characteristics... 

In addition to impurities, other factors such as fluid flow and heat transfer often exert an important influence in practice. Fluid flow accentuates the effects of impurities by increasing their rate of transport to the corroding surface and may in some cases hinder the formation of (or even remove) protective films, e.g. nickel in HF. In conditions of heat transfer the rate of corrosion is more likely to be governed by the effective temperature of the metal surface than by that of the solution. When the metal is hotter than the acidic solution corrosion is likely to be greater than that experienced by a similar combination under isothermal conditions. The increase in corrosion that may arise through the heat transfer effect can be particularly serious with any metal or alloy that owes its corrosion resistance to passivity, since it appears that passivity breaks down rather suddenly above a critical temperature, which, however, in turn depends on the composition and concentration of the acid. If the breakdown of passivity is only partial, pitting may develop or corrosion may become localised at hot spots if, however, passivity fails completely, more or less uniform corrosion is likely to occur. 

There is no good substitute for an internal inspection. Assuming the hazardous chemical residues can be easily removed, the internal inspection is easily accomplished and relatively inexpensive. Internal inspections are essential to determine possible weakening of the vessel or any conditions that may develop into unwanted leaks, because very few vessels experience uniform corrosion. Typically, internal inspections are established with frequencies between semi-annually and once every ten years. The exact frequency is best determined by the corrosive nature of the chemical being processed or stored, including the effect of trace components and the past history of this equipment. 

Very often the long experience with chemicals operating as corrosion inhibitors, e. g. in the oil field, gas or petroleum industry, is taken as an example for the successful use of corrosion inhibitors for many decades. This undoubtedly is true and the overwhelming majority of literature on corrosion inhibitors deals with the effects of inhibitors on uniform corrosion, e. g. of steel in acidic or neutral solutions, where they can be classified into [2] a) adsorption inhibitors, acting specifically on the anodic or on the cathodic partial reaction of the corrosion process or on both reactions (mixed inhibitor), b) JUm-forming inhibitors, blocking the surface more or less completely, and c) passivators, favouring the passivation reaction of the steel (e. g. hydroxyl ions). 

Generally, under conditions of uniform corrosion, the effect on pH of the anodic and cathodic partial reactions cancel each other. In contrast, under conditions of localized corrosion, the anodic and cathodic partial reactions are locally separated and a pH difference builds up between anodic and cathodic sites. 

The formation of thick biofilms could in principle be beneficial if a compact film would uniformly cover a metal, preventing access of oxygen to the surface. However, biofilms usually do not form uniformly over a metal surface but usually in patches. Therefore they stimulate the formation of corrosion cells between covered and non-covered areas. The phenomenon is further enhanced if anaerobic conditions prevail at the metal surface in the areas covered by the biofUm, creating conditions for the development of anaerobic bacteria such as SRB that inhibit passivation. The following two examples illustrate the corrosive effect of microorganisms. 

In-situ testing is also performed in the field to determine the effectiveness of a water treatment system, the performance of difference alloys, and the effects of var5dng operating parameters such as flow rate and temperature. Uniform corrosion rates, t5fpes of corrosion, and pitting tendencies are identified with in-situ testing. 

The duration of the test can have a significant effect on the test data. Most materials wiU corrode most rapidly in the early stages of exposure to an enviromnent—before oxide films are developed that may inhibit the corrosion rate by limiting the diffusion rate of reacting species to and from the metallic surface. Thus, tests of 24-h duration extrapolated to 30-day or f-year behavior may be extremely conservative. Where time allows, multiple test durations may be evaluated to determine the actual effect of exposure time on uniform corrosion. 

The anions also play a very important role in the corrosion process. If they react with metal ions, produced during the anodic corrosion reaction, 2md form an insoluble salt precipitate on the metsd surface, this layer could act as an effective barrier against corrosion. This is the case of corrosion of lead sheathing for power and communications cables in a soU solution that contains sulfate ions (S04 ). The most corrosive anion for metals is the chloride ion (Cl"), which is usually naturally present in soils and sands of the marine-coastal regions, or it may be present as a result of external sources such as de-icing salts applied to roadways. Its attack is localized and more dangerous than the uniform corrosion, because the formed pits could perforate the metal surface. The chloride ion concentration in corrosive soil electrol3 tes (moisture) varies as soil conditions alternate between wet and dry. 

The chassis and undervehicle is most susceptible to mechanical damage because of its proximity to external road conditions [24] (Fig. 4). Usual corrosion mechanisms apply such as those due to the effect of stone impingement and crevice and uniform corrosion. Coatings failure can enhance deterioration as can poultice built up in entrapment areas. 

Corrosion inhibitors for steels are being continuously developed because of the ubiquitous use of steel in construction and its somewhat limited corrosion resistance, especially in the presence of water. A great number of papers are on the effect of corrosion inhibitors, and the overwhelming majority deals with the effect of inhibitors on uniform corrosion. Due to environmental restrictions on common inorganic inhibitors (Freedman, 1986), several studies suggest derivatives of some amino acids as corrosion inhibitors. A survey of a number of different organic compounds commonly used as uniform corrosion inhibitors showed that most compounds hardly affect the pitting corrosion of stainless steel however, one of... 

What effect wiii uniform corrosion have on serviceability ... 

For more on macro-fouUng and its effects on corrosion see, for example, [9] and [1] also especially [10], In their paper, Pabaj and Venkatacahri rank Mandapam first in corrosivity (0.244 mmpy) and third in hiofouHng. They are also reporting that in their study mild steels exposed to natural seawater for quarterly, semi-annual and annual periods have undergone uniform corrosion. 

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