Carbon steel corrosion seawater

A practical illustration of the application of more negative (cathodic) potential to carbon steel in seawater to reduce the corrosion rate is provided in Figure 1.69. The figure shows that the more cathodic the applied potential, the lower is the corrosion rate. In the figure rp is the maximum acceptable (or allowed) corrosion rate with a corrosion current density of ip and protection potential of Ep. For this particular case the protection potential range is —800 to —900 mV. The corrosion rate iv may be written as 75... 

Uniform corrosion usually occurs in fairly aggressive environments that attack the whole surface. Examples include carbon steel in seawater or acids, or aluminum alloys in strong alkali. The rate of metal loss is usually rather high, but, because it is distributed over the whole surface, the performance can usually be predicted, and managed with corrosion allowances, in most situations. Thus, sheet steel piling is often used in seawater without any corrosion protection, the corrosion rate of around 0.1 mm/yr, coupled with the relatively thick steel sections, giving an acceptable life. 

Carbon steels corrode in aerated seawater conditions. Their corrosion rate decreases with time as protective barrier films are formed on the carbon steel surfaces. These protective films may be a rust layer, calcareous deposits, or biofouling. The corrosion rate of carbon steels increases in high velocity seawater because the protective barrier layer is either not allowed to form or is stripped away under the flow conditions. Also, the available oxygen at the metal surface is increased in flowing seawater, which promotes a higher carbon steel corrosion rate. 

T able 9.13 shows the corrosion rate of carbon steel in seawater under conditions [30]. 

Since the formation nature and breakdown of protective surface films depends on both material and environmental parameters such influences on erosion corrosion will be discussed together. Particular attention will be paid to the copper/seawater and carbon steel/water (steam) systems. 

For the following pairs of alloys that are coupled in seawater, predict the possibility of corrosion and if corrosion is possible, note which alloy will corrode (a) Al/Mg (b) Zn/low carbon steel (c) brass/Monel (d) titanium/304 stainless steel and (e) cast iron/315 stainless steel. Clearly state any assumptions you make about compositions of alloys. 

Seawater-based utility systems for condenser and process cooling systems in power plants exhibit serious corrosion, erosion and fouling problems. Equipment made from carbon steel and even stainless steel shows sign of degradation from galvanic effect, corrosion, erosion and microbiological induced corrosion (MIC). Corrosion... 

The EHD method with a RDE has been applied to the characterisation of porous layers of corrosion products formed on carbon steel [110], for the characterisation of salt films formed on copper [90, 111, 112] and iron [113], and for biofilms developed in natural seawater [114]. Corrosion inhibition films formed by an organic surfactant acting on the surface of pure iron have been characterised in this way, too [115]. An effect of a... 

The four important areas of application of carbon steels are (i) atmospheric corrosion (ii) corrosion in fresh water (iii) corrosion in seawater and (iv) corrosion in soils. The atmospheric corrosion of steel is caused by major environmental factors such as (i) time of wetness as defined by ISO 9223-1992 (ii) sulfur dioxide in the atmosphere due to the combustion of fossil fuels and (iii) chloride carried by the wind from sea. The equations for corrosion rates of carbon steel by multiple regression analysis have been obtained.1... 

The corrosion rate of carbon steel increases with increase in velocity until a critical velocity is reached. This behavior is different from that of the carbon steel in fresh water where the corrosion rate decreases beyond a critical velocity due to the formation of a passive him. In seawater passive films are not formed because of the presence of high concentrations of chloride. The erosion corrosion occurs after critical velocity 20 m/s is reached. The maximum corrosion rate of 1,0/mm/yr is reached at velocities up to 4 m/s. 

Galvanic corrosion rates (mils) of some couples after 16 yr exposure to seawater and fresh water are given in Table 7.23. In the cae of carbon steel/aluminum the data show that in fresh water carbon steel corrodes to a greater extent than aluminum which provides further evidence for polarity reversal of the steel/Al couple in fresh water. 

Materials such as metals, alloys, steels and plastics form the theme of the fourth chapter. The behavior and use of cast irons, low alloy carbon steels and their application in atmospheric corrosion, fresh waters, seawater and soils are presented. This is followed by a discussion of stainless steels, martensitic steels and duplex steels and their behavior in various media. Aluminum and its alloys and their corrosion behavior in acids, fresh water, seawater, outdoor atmospheres and soils, copper and its alloys and their corrosion resistance in various media, nickel and its alloys and their corrosion behavior in various industrial environments, titanium and its alloys and their performance in various chemical environments, cobalt alloys and their applications, corrosion behavior of lead and its alloys, magnesium and its alloys together with their corrosion behavior, zinc and its alloys, along with their corrosion behavior, zirconium, its alloys and their corrosion behavior, tin and tin plate with their applications in atmospheric corrosion are discussed. The final part of the chapter concerns refractories and ceramics and polymeric materials and their application in various corrosive media. 

As mentioned above, the environment has a significant effect on whether or not galvanic corrosion will be a problem. For example, carbon steel will corrode rapidly if equal or larger areas of Monel 400 are coupled with it in seawater. Conversely, carbon steel is compatible with Monel 400 in concentrated caustic solutions. Even freshwater can be sufficiently different from seawater couples incompatible in seawater work well in freshwater. For example, copper-steel and aluminum-steet couples are satisfactory for handling... 

The effect of fluid velocity on the corrosion of several commercial materials in seawater is shown in Fig. 7.31 (Ref 51). Three generalized types of materials are indicated by the corrosion behavior. The copper-base alloys, cast iron, and carbon steels tend to progressively increase in corrosion rate with increasing velocity. This is consistent with the schematic representation shown in Fig. 4.10, where the limiting current density for diffusion control of the cathodic reaction increases with... 

Composition of carbon steel and low-alloy steel is of little significance for corrosion in soils, as is the case for corrosion in seawater and other waters. 

E. Malard, D. Kervadec, O. Gil, Y. Lefevre, S.Malard. Interactions between steels and sulphide-producing bacteria—Corrosion of carbon steels and low-alloy steels in natural seawater. Electrochimica Acta,No. ... 

J. Duana, S. Wua, X. Zhanga, G. Huangb, M. Due, B. Houa. Corrosion of carbon steel influenced by anaerobic biofihn in natural seawater. Electrochimica Acta, Vol. 54, pp. 22-28, 2008. 

Seawater is generally considered as an aggressive environment, and carbon steel as a mechanically resistant material but not very resistant to corrosion on the other hand, stainless steel is considered as a corrosion-resistant but expensive material. Then, in order to design a seawater reservoir, one might think of a carbon steel reservoir plated with stainless steel as an intermediate solution, of intermediate cost, but able to exploit, on one hand, the corrosion resistance of stainless steel and, on the other, the mechanical strength of carbon steel. Quite likely, according to the most widespread opinion, a nonexpert designer would put the stainless steel in contact with seawater. 

The reservoir of carbon steel plated with stainless steel, with the latter in contact with seawater, would be quite probably the most rapidly perforated. Indeed, the localized corrosion on stainless steel, once it reaches the carbon steel, would allow the galvanic coupling between the cathodic high surface area of stainless steel and the anodic small surface area of carbon steel, exposed through the holes in the stainless steel layer, with consequent rapid perforation. 

FIGURE 12.13 Morphology of corrosion in seawater for (1) carbon steel, (2) austenitic stainless steel, and (3-5) their combinations, (a) To be avoided, (b) Preferable. 

An amoimt up to 5% chromium (0.08% C) was reported to decrease weight losses in seawater at the Panama Canal [53] at the end of one year. A sharp increase in rates was observed between 2 and 4 years after 16 years, the chromium steels lost 22-45% more weight than did 0.24% C steel. Depth of pitting was less for the chromium steels after one year, but comparable to pit depth in carbon steel after 16 years. Hence, for long exposures to seawater, low-chronaium steels apparently offer no advantage over carbon steel. By comparison, however, low-alloy chromium steels (<5% Cr) have improved resistance to corrosion fatigue in oil-well brines free of hydrogen sulfide. 

The protection potentials for seawater are described in Section 2.4. In pipelines and harbor installations, there is no limiting negative potential f/ for uncoated carbon steel or for steel provided with thick coatings over 1 mm, with yield points up to 800 N mm". With dynamically highly loaded structures, the protection potential ranges in Table 16-2 should be adhered to as in the regulations [1-3] because of the risk of hydrogen-induced stress corrosion (see Section 2.3.4). 

A 690 High-strength low-alloy steel H-piles and sheet piling Ni, Cu, Si Structural-quality H-pills and sheet piling Corrosion resistance two to three times greater than that of carbon steel in the splash zone of marine marine structures Dock walls, sea walls Bulkheads, excavations and similar structures exposed to seawater... 

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