Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Corrosion rate changes with time

Corrosion rate is a function of time of wetness, considered as the time during which corrosion occurs, but in general it should not be a linear function because corrosion rate changes with time. There are different factors influencing, for example, the protective properties of the corrosion products, the increase or decrease of the acceleration caused by contaminants, increase or decrease of the thickness and conductivity of the electrolyte layer,... [Pg.65]

The acceleration rate caused by the addition of a salt spray under natural conditions causes a higher acceleration of corrosion rate at Havana. For copper, the difference does not appreciably change with time but it does for steel. A more aggressive action of chloride ions is observed in the case of steel. [Pg.81]

An important measurement is the corrosion potential, Ecor. This is the open circuit potential, whose value can change with time. ECOT is a mixed potential, since the anodic and cathodic reactions are different. The partial anodic or cathodic current that flows at this potential is called the corrosion current, 7cor, and is directly related to the rate constant of the electrode reaction. [Pg.356]

The corrosion potential, ECOrr, adopted by the system will be dictated by the relative kinetics of the anodic material degradation process and the cathodic reduction kinetics of the oxidant. While ECOrr yields no quantitative information on the rate of the overall corrosion process, its value, and how it changes with time, is a good qualitative indication of the balance in corrosion kinetics and their evolution with time. Thus a knowledge of ECOrr and its comparison to ther-... [Pg.207]

Pmnps wear and the curve will change with time. In addition, friction factors will generally increase with time because of corrosion and deposits. For these reasons, puirqrs are usually oversized and thus will initially deliver larger flow rates than required. A control valve installed on the discharge side of the pump will bring the pump to the desired operating point on the curve. [Pg.261]

Measurements of the rates of surface reactions on insulator surfaces, such as dissolution, adsorption, and surface diffusion, are possible (Chapter 12). For example, proton adsorption on an oxide surface can be studied using the tip to reduce proton and induce a pH increase near the surface (22). Then, by following the tip current with time, information about proton desorption kinetics is obtained. Studies of corrosion reactions are also possible. Indeed, work has been reported where a tip-generated species has initiated localized corrosion and then SECM feedback imaging has been used to study it (28). In these types of studies, the tip is used both to perturb a surface and then to follow changes with time. [Pg.11]

The corrosion current can be influenced by the formation of a layer of corrosion products at the surface and change with time. In most cases, the corrosion rate... [Pg.69]

It should also be noted that corrosion rates vary with the weather conditions. Corrosion rates increase in warm conditions. Re. istivity will decrease as the concrete gets wet, also allowing corrosion rates to increase. For a full picture of corrosion conditions, measurements. hould be taken at regular intervals throughout the year so that seasonal changes can be identified. Alternatively readings can be taken at the same time each year, preferably under comparable weather conditions, so that re. ults are comparable. [Pg.81]

Reinhart (1976) has reported on the use of zinc alloys and zinc wire ropes that were exposed in the Pacific Ocean at depths of 720-2070 m for periods varying from 123 to 1064 days. The zinc alloy composition was 99.9% zinc, 0.9% lead, and 0.1% iron. The wire ropes were galvanized steel cables of various types. The data obtained from the study are given in Tables 3.23 and 3.24. From the data shown in Table 3.23, the corrosion rate of zinc in Pacific Ocean seawater is seen to decrease with the duration of exposure, except for zinc at the 2400 ft depth, at which the corrosion rate increased with increasing time of exposure. Also, the corrosion of zinc was greater at depth than at the surface. In addition, the report indicated that the corrosion of zinc was not uniformly influenced by changes in the concentration of oxygen in seawater between the limits of 0.4-5.75 mL/L. [Pg.326]

Sometimes, changes with time of the rate of corrosion call for a procedure with mass loss measurements at several intervals. Figure 4.15 shows the schedule for a planned interval test with four identical samples. Samples 1 to 3 are used to determine the evolution with time of the rate of corrosion. This provides information about a number of parameters, including the role of surface films formed during corrosion. On the other hand, a comparison of the corrosion rate of samples 1 and 4 reveals possible changes in the corrosivity of the solution during the test. [Pg.138]

Here, JC represents the electrolyte conductivity in the corrosion pit, L(t) is the depth of the pit that changes with time, and A0 corresponds to the potential difference between the pit base and the pit opening. For relatively deep corrosion pits, the potential drop in the electrolyte outside the pit is negligible compared to that within the pit because of the much larger cross section for current flow. In this case, A

potential difference between anode and cathode. According to Faraday s law, the growth rate of the pit is proportional to the anodic current density ... [Pg.324]

In all these examples, the biofilm is able to substantially change the chemistry of the electrolyte at the metal-water interface. Thus, the corrosion rate may depend more on the details of the electrolyte chemistry at the interface under the biofilm than it does on the bulk environment chemistry. The fact that biofilms tend to be spatially heterogeneous allows them to support sharp chemical gradients both parallel and perpendicular to the metal surface. This is one of the reasons why corrosion tends to become more localized in the presence of microorganisms. On top of this is the tendency for films of microbes to develop and change with time. This can produce corrosion rates, which also vary with time emd are thus hard to predict. [Pg.510]

If the oxide film or scale cracks or is porous, that is, if the corrosive gas can continue to penetrate readily and react with the base metal in a catastrophic manner, no protection will be afforded and attack will proceed at a rate determined essentially by the availability of the corrosive gas. In this case, the rate will not sensibly change with time, and, as is apparent from Fig. 15.12, the weight change or depth of penetration from oxidation is a straight line or linear function of time and may be expressed as... [Pg.678]

In the real world corrosion rates always change with time, for instance some forms of localized corrosion such as microbiologically influenced corrosion can accelerate rapidly and grow exponentially once initiated, and therefore it is important to identify the specific time periods of maximum corrosion rates and the effects of corrosion inhibitors. For this reason instantaneous techniques are important for continuous measirrement of the prevailing corrosion rates for... [Pg.46]

The situation may also occur where a dense oxide film is formed on the surface, as is shown in Fig. 2.2(c). Such dense films are formed in the case of corrosion-resistant materials such as Cr and Ni and some valve metals. In this case the kinetics may be controlled by the movement of ions or electrons through the film (Sehmuki, 2002), or the dissolution rate of the film at the film-electrolyte interface, as depicted in Fig. 2.2(c). Since the film thickness, film composition and thereby film formation and dissolution can change with time (Yu and Scully, 1997), it is difficult to predict the rate of corrosion in this case. More importantly, the difference between active and passive dissolution rates, i.e. corrosion loss, is due to the presence of the film, be it porous or compact... [Pg.23]


See other pages where Corrosion rate changes with time is mentioned: [Pg.689]    [Pg.618]    [Pg.722]    [Pg.119]    [Pg.146]    [Pg.2440]    [Pg.27]    [Pg.46]    [Pg.54]    [Pg.2195]    [Pg.2703]    [Pg.532]    [Pg.9]    [Pg.56]    [Pg.61]    [Pg.2680]    [Pg.372]    [Pg.372]    [Pg.2444]    [Pg.96]    [Pg.299]    [Pg.189]    [Pg.382]    [Pg.406]    [Pg.497]    [Pg.501]    [Pg.829]    [Pg.354]    [Pg.71]    [Pg.55]    [Pg.409]   
See also in sourсe #XX -- [ Pg.7 , Pg.9 , Pg.19 ]

See also in sourсe #XX -- [ Pg.7 , Pg.9 , Pg.19 ]




SEARCH



Change rates

Rate with Time

© 2024 chempedia.info